letslearn3gin10days_kamalvij

W i res and Waves S o l u t i ons

EXPLOIT THE EVOLUTION

Let’s take out 10 days and learn the essential concepts about 3G technology.

Written by Kamal Vij

Let’s Learn

3G in 10 Days

So Much to Learn...

So Little Time

http://thegordonschools.typepad.co.uk/asu/

http://thegordonschools.typepad.co.uk/asu/

Let’s Learn 3G in 10 Days

written by

Kamal Vij

FOREWORD

The success story of GSM has generated a lot of motivation for businessmen, edu-cational institutes, private consultants, legacy telecom operators, mobile operators,equipment vendors and many more to master the fundamentals of 3G. It has been13 years since the publication of the first 3G specification. It is no secret that 3G(UMTS along with HSPA) has established itself as a successful and commerciallyprofitable mobile standard.

Telecom professionals keep on trying to search for the latest updates on the emergingtechnologies. There are a lot of white papers, blogs, posters, and e-books availableon the Internet which help them in the learning but their busy schedule hardlyallows them to spend even a single hour per day to learn the updates of technology.

This was my motivation to write this book. In this book, the emphasis is on keepingthe language simple and focus on the essential concepts only. This book is not aboutradio planning or RF optimization. Its sole purpose is to introduce the readers tothe 3G technology.

To get the maximum benefit out of this 10 days crash course with me, I recommendyou to follow the following plan:

DAY 1 History and Standardization: On the first day of reading, we will havean ultra quick look at the history and very brief preview of the future. Thismodule or chapter will give us an overview about the legacy systems and theirmigratory path to 3G and beyond. An the same time, we will also learn about3GPP releases and their features.

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DAY 2 Network Elements and Functionalities: The second day is plannedfor learning about the network elements, interfaces, and to have a look at thecombined network architecture of 2G & 3G network.

DAY 3 WCDMA Air Interface: On the third day, we will focus on the radiotechnology used in 3G system. In the third chapter, the principles of spreadingand code multiplexing are explained. We will also see the series of physicallayer procedures that take place at layer 1 of UE and Node B.

DAY 4 Logical, Transport & Physical Channels: On the fourth day, somemore physical layer aspects will be discussed when we will learn about thechannels of UMTS. In this module, we will focus on the UMTS channels only.For HSDPA & HSUPA, separate modules are planned.

DAY 5 Radio Resource Management: The fifth day of our reading should fo-cus on the RRM module, which discusses several features that work in parallelto optimize the radio resource utilization.

DAY 6 Protocols & Interfaces: On the sixth day, topic of discussion will bethe protocols of UMTS. Along with radio protocols, we will also learn aboutthe control plane & user plane protocols on various UTRAN interfaces.

DAY 7 HSDPA: Release 5 onwards, the downlink speeds can be pushed beyond2 Mbps. The seventh day is reserved for understanding the basics of HSDPA.

DAY 8 HSUPA: The project HSPA is completed only when both Uplink andDownlink are High Speed. The eighth module of this book will discuss howHSUPA differs from the conventional UMTS uplink.

DAY 9 Signalling: Towards the end of our journey, Module 9 is planned to dis-cuss a few signalling scenarios. Here, we will discuss how a CS AMR calland a PS data session gets established on UMTS & HSPA. Mobility relatedsignalling will also be illustrated, which plays an important role in service con-tinuity and improves call success ratio.

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DAY 10 Self Test: On the last day, I request all the readers to put themselves toa self-evaluation and evaluate whether they have learnt something from thisbook. 5 to 8 questions/exercises from each module are planned.

Please visit www.3gin10days.com to watch some video lessons related to these topicsand to download the e-book.

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ABOUT THE AUTHOR

Kamal Vij received a B.Engg. degree in Electronics & Com-munication from Kuvempu University, India in 2001. In 2005,he received a M.Sc. degree in Communication Technologyfrom University of Bremen, Germany. While pursuing hisM.Sc., he took special interest in semiconductor simulationand worked as a research assistant in the power electronicsdepartment of University of Bremen. In 2006, he started hiscareer as a trainer for telecommunication. Since then, he hasbeen delivering trainings on WCDMA, HSPA & LTE RadioAccess Network technologies across the world.

Kamal Vij is now a technical trainer and private consultant.He has keen interest in emerging technologies and following the market trends. Hisskills are signalling, parameter optimization, radio planning and optimization. Moreabout him can be found at http://www.wiresandwaves.net and he can be reachedat: [email protected].

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ACKNOWLEDGEMENTS

I, Kamal Vij, the author of this book, would like to thank 3GPP for being sokind and allowing me to use their graphics, tables and text pieces in this book.I also want to express my thankful regards to my friends working in the telecomsector who have helped me in writing this book by giving me tips and ideas. Mybiggest teachers are those telecom professionals whom I met while delivering theclassroom training. The discussions I had with them have enhanced my knowledgeand motivated me to work more passionately. I cannot mention all the names herebut a few colleagues and friends this group are Andreas Annen, Ashok Joshi, AndreyYaroshenko, Ilya Andreev, Jeetendra Ghare, Karl Hofmann, Kapil Bhutani, MichaelOestreicher, Silviu Mihailescu, Jan Berglund, Ronald Fabian, Ravindra Mawale,Saikat Nandi.

I also want to show my appreciation towards the authors of the following threebooks. These books have been an excellent source of information for me. The Ideasfor many sections of this book were inspired from these books.

• H.Holma and A. Toskala, ‘WCDMA for UMTS’ , 5th Edition, JohnWiley & Sons.• H.Holma and A. Toskala, ‘HSDPA/HSUPA for UMTS’ , 1st Edi-tion, John Wiley & Sons.• Chris Johnson, ‘Radio Access Networks For UMTS; PrinciplesAnd Practice’ , John Wiley & Sons.

I would like to thank ‘Zorba Publishers Pvt. Ltd.’ (www.zorbapublishers.com)

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for meticulously proof reading this book and removing hundreds of typographic andgrammatical errors.

Above all, I want to thank my family, who supported and encouraged me in spiteof all the time it took me away from them. It was a long and difficult journeyfor them. I apologize to all those who have been with me during my journey as atelecom trainer and whose names I have failed to mention.

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DISCLAIMER

The information contained in ‘Let’s Learn 3G in 10 Days’ is for general informationpurposes only. The author has tried to simplify the explanation, and in that processfew complicated equations and rules have been dropped while maintaining the overallcorrectness to the best of his knowledge. Every effort is made to keep the informationaccurate. However, the author takes no responsibility for any damage caused by theinformation obtained by this book.

Every care has been taken to mention the references and sources wherever needed.This process has taken several months because references were added after the bookwas written. Afterwards, it is a time-consuming and laborious task to recall all thesources. The author has tried his best but at few places, he might have forgotten tomention the source/reference due to human limitation. Author asks for forgivenessif he has failed to declare the references in any part of the book.

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CONTENTS

Preface 2

Preface 5

Acknowledgements 6

1 History and Standardization 2

1.1 Mobile Telecom Market . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.1 0G Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2.2 1G Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2.3 2G Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.2.4 3G Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.3 3GPP and 3GPP2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.3.1 3rd Generation Partnership Project (3GPP) . . . . . . . . . . 14

1.3.2 3rd Generation Partnership Project 2 (3GPP2) . . . . . . . . 15

1.3.3 WiMAX as IMT-2000 System . . . . . . . . . . . . . . . . . . 17

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1.4 WCDMA FDD - Releases . . . . . . . . . . . . . . . . . . . . . . . . 18

1.5 WCDMA FDD - Releases and Features . . . . . . . . . . . . . . . . . 19

2 Network Elements and Functionalities 25

2.1 Architecture of the GSM Network . . . . . . . . . . . . . . . . . . . . 26

2.1.1 The Mobile Station MS . . . . . . . . . . . . . . . . . . . . . . 27

2.1.2 Base Station Subsystem BSS . . . . . . . . . . . . . . . . . . . 27

2.1.3 Switching Subsystem . . . . . . . . . . . . . . . . . . . . . . . 28

2.2 Improvements of GSM Standard . . . . . . . . . . . . . . . . . . . . 32

2.2.1 CAMEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.3 GPRS Network Architecture . . . . . . . . . . . . . . . . . . . . . . . 35

2.3.1 GPRS Mobile Terminals . . . . . . . . . . . . . . . . . . . . . 36

2.3.2 GPRS Base Station Subsystem . . . . . . . . . . . . . . . . . 37

2.3.3 New Elements in the Core Network . . . . . . . . . . . . . . . 38

2.3.4 Other Changes . . . . . . . . . . . . . . . . . . . . . . . . . . 40

2.3.5 GPRS Roaming Scenario . . . . . . . . . . . . . . . . . . . . . 41

2.4 Migration to 3G Network Architecture . . . . . . . . . . . . . . . . . 42

2.5 UTRAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

2.5.1 Node B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

2.5.2 RNC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.6 Logical roles of RNC: S-RNC and D-RNC . . . . . . . . . . . . . . . 47

2.7 Release 4 Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . 50

2.7.1 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

2.7.2 New Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . 53


2.8.1 IP Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

2.8.2 IP Multimedia Subsystem (IMS) . . . . . . . . . . . . . . . . 55


2.9.1 IMS for IP-CAN or IMS phase 2 . . . . . . . . . . . . . . . . 57

2.10 Rel-7 & Rel-8 Modifications . . . . . . . . . . . . . . . . . . . . . . . 58

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3 WCDMA Air Interface 62

3.1 Duplex Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

3.2 Multiple Access Technologies . . . . . . . . . . . . . . . . . . . . . . . 63

3.2.1 Frequency Division Multiple Access . . . . . . . . . . . . . . . 64

3.2.2 Time Division Multiple Access . . . . . . . . . . . . . . . . . . 65

3.2.3 Code Division Multiple Access . . . . . . . . . . . . . . . . . . 65

3.2.4 Orthogonal Frequency Division Multiple Access . . . . . . . . 65

3.3 UMTS operating Bands and Spectrum . . . . . . . . . . . . . . . . . 65

3.4 Timing in WCDMA . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

3.5 Spreading Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

3.6 Codes in UMTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

3.6.1 Channelization Code . . . . . . . . . . . . . . . . . . . . . . . 73

3.6.2 Scrambling Code . . . . . . . . . . . . . . . . . . . . . . . . . 74

3.6.3 Summary of Scrambling Codes . . . . . . . . . . . . . . . . . 78

3.6.4 Summary of Codes in UMTS . . . . . . . . . . . . . . . . . . 78

3.7 Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

4 Logical, Transport & Physical Channels 82

4.1 Chronology: First 3G and then 3.5G . . . . . . . . . . . . . . . . . . 83

4.2 Logical Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

4.2.1 Logical Channels for Control Plane Information . . . . . . . . 84

4.2.2 Logical Channels for User Plane Information . . . . . . . . . 85

4.3 Transport Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

4.3.1 Common Transport Channels . . . . . . . . . . . . . . . . . . 87

4.3.2 Dedicated transport channels . . . . . . . . . . . . . . . . . . 88

4.4 Physical Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

4.4.1 UL Common Channel . . . . . . . . . . . . . . . . . . . . . . 91

4.4.2 DL common Channel . . . . . . . . . . . . . . . . . . . . . . . 94

4.4.3 UL Dedicated Channels . . . . . . . . . . . . . . . . . . . . . 105

4.4.4 DL Dedicated Channels . . . . . . . . . . . . . . . . . . . . . 106

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4.4.5 Summary of DCH Channels . . . . . . . . . . . . . . . . . . . 108

4.5 Cell Search Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 109

4.6 HSDPA Channels in Short . . . . . . . . . . . . . . . . . . . . . . . . 111

4.7 HSUPA Channels in Short . . . . . . . . . . . . . . . . . . . . . . . . 113

5 Radio Resource Management 117

5.1 Inputs for RRM Functionality . . . . . . . . . . . . . . . . . . . . . . 119

5.1.1 RNC Parameter Database . . . . . . . . . . . . . . . . . . . . 120

5.1.2 Node B Measurements . . . . . . . . . . . . . . . . . . . . . . 121

5.1.3 UE Measurements . . . . . . . . . . . . . . . . . . . . . . . . 123

5.1.4 Internal RNC Measurements . . . . . . . . . . . . . . . . . . . 125

5.2 Load Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

5.2.1 Uplink Load Estimation . . . . . . . . . . . . . . . . . . . . . 126

5.2.2 Downlink Load Estimation . . . . . . . . . . . . . . . . . . . . 128

5.3 Radio Resource Management Strategies . . . . . . . . . . . . . . . . . 129

5.4 Admission Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

5.5 Code Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

5.5.1 Code Tree Optimization . . . . . . . . . . . . . . . . . . . . . 134

5.6 Packet Scheduler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

5.6.1 RRC States . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

5.6.2 RRC States Transitions . . . . . . . . . . . . . . . . . . . . . 141

5.7 Power Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

5.7.1 Open Loop Power Control . . . . . . . . . . . . . . . . . . . . 145

5.7.2 Inner Loop Power Control . . . . . . . . . . . . . . . . . . . . 146

5.7.3 Outer Loop Power Control . . . . . . . . . . . . . . . . . . . . 152

5.8 Handover Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

5.8.1 Active, Monitored and Detected cells . . . . . . . . . . . . . . 156

5.8.2 Soft/Softer Handover . . . . . . . . . . . . . . . . . . . . . . . 157

5.8.3 ISHO and IFHO Triggering . . . . . . . . . . . . . . . . . . . 162

5.8.4 Inter-Frequency Measurements . . . . . . . . . . . . . . . . . . 163

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5.8.5 Inter-System Measurements . . . . . . . . . . . . . . . . . . . 164

5.8.6 Compressed Mode . . . . . . . . . . . . . . . . . . . . . . . . 165

5.8.7 Inter System HO Signalling . . . . . . . . . . . . . . . . . . . 166

6 Protocols & Interfaces 171

6.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

6.1.1 Horizontal Layers . . . . . . . . . . . . . . . . . . . . . . . . . 173

6.1.2 Vertical Planes . . . . . . . . . . . . . . . . . . . . . . . . . . 173

6.2 QoS and Bearer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

6.2.1 UMTS QoS Classes . . . . . . . . . . . . . . . . . . . . . . . . 177

6.3 Access Stratum and Non-Access Stratum . . . . . . . . . . . . . . . . 178

6.4 Radio Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

6.4.1 Control Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

6.4.2 User Plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181

6.4.3 RRC-layer Functions . . . . . . . . . . . . . . . . . . . . . . . 182

6.4.4 RLC-layer Functions . . . . . . . . . . . . . . . . . . . . . . . 183

6.4.5 MAC-layer Functions . . . . . . . . . . . . . . . . . . . . . . . 185

6.4.6 PDCP-layer Functions . . . . . . . . . . . . . . . . . . . . . . 186

6.5 Iu-CS Interface Protocols . . . . . . . . . . . . . . . . . . . . . . . . . 187

6.5.1 Control Plane - Iu-CS . . . . . . . . . . . . . . . . . . . . . . 187

6.5.2 User Plane - Iu-CS . . . . . . . . . . . . . . . . . . . . . . . . 187

6.5.3 RANAP Functions . . . . . . . . . . . . . . . . . . . . . . . . 189

6.6 Iu-PS Interface Protocols . . . . . . . . . . . . . . . . . . . . . . . . . 190

6.6.1 Control Plane - Iu-PS . . . . . . . . . . . . . . . . . . . . . . 190

6.6.2 User Plane - Iu-PS . . . . . . . . . . . . . . . . . . . . . . . . 190

6.7 Iub Interface Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . 192

6.7.1 Control Plane - Iub CP . . . . . . . . . . . . . . . . . . . . . . 192

6.7.2 User Plane - Iub UP . . . . . . . . . . . . . . . . . . . . . . . 193

6.7.3 NBAP Functions . . . . . . . . . . . . . . . . . . . . . . . . . 193

6.8 Iur Interface Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . 195

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6.8.1 Control Plane - Iur CP . . . . . . . . . . . . . . . . . . . . . . 195

6.8.2 User Plane - Iur UP . . . . . . . . . . . . . . . . . . . . . . . 195

6.8.3 RNSAP functions . . . . . . . . . . . . . . . . . . . . . . . . . 195

6.9 Non-Access Stratum Protocols . . . . . . . . . . . . . . . . . . . . . . 198

7 High Speed Downlink Packet Access 204

7.1 Why HSDPA? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

7.2 HSDPA Standardization, 3GPP Releases and Evolution . . . . . . . . 205

7.2.1 Release 99 & Rel-4 . . . . . . . . . . . . . . . . . . . . . . . . 206

7.2.2 Release 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206

7.2.3 Release 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

7.2.4 Release 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

7.2.5 Release 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207

7.3 HSDPA Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

7.3.1 HSDPA Operation: Between UE and RNC . . . . . . . . . . . 208

7.3.2 HSDPA Operation: Between Node B and RNC . . . . . . . . 209

7.4 What’s new in HSDPA? . . . . . . . . . . . . . . . . . . . . . . . . . 211

7.4.1 Adaptive Modulation & Coding . . . . . . . . . . . . . . . . . 211

7.4.2 Shorter and Fixed TTI . . . . . . . . . . . . . . . . . . . . . . 211

7.4.3 Node B-based Packet Scheduling . . . . . . . . . . . . . . . . 212

7.4.4 Multi-code Operation . . . . . . . . . . . . . . . . . . . . . . . 213

7.4.5 L1 H-ARQ Retransmission . . . . . . . . . . . . . . . . . . . . 217

7.4.6 MAC-hs Protocol in Node B and UE . . . . . . . . . . . . . . 218

7.4.7 Serving Cell Change Instead of Soft HO . . . . . . . . . . . . 219

7.5 HSDPA Protocol Architecture . . . . . . . . . . . . . . . . . . . . . . 221

7.5.1 MAC-hs entity - UE Side . . . . . . . . . . . . . . . . . . . . . 221

7.5.2 MAC-hs entity - UTRAN Side . . . . . . . . . . . . . . . . . . 224

7.6 Channels and Physical Layer . . . . . . . . . . . . . . . . . . . . . . . 226

7.6.1 HS-DPCCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

7.6.2 HS-SCCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

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7.6.3 HS-PDSCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231

7.6.4 Associated DCH . . . . . . . . . . . . . . . . . . . . . . . . . 233

7.6.5 Fractional-DPCH . . . . . . . . . . . . . . . . . . . . . . . . . 234

7.7 Timing of HSDPA Channels . . . . . . . . . . . . . . . . . . . . . . . 235

7.8 HSDPA UE Categories . . . . . . . . . . . . . . . . . . . . . . . . . . 236

7.9 HSDPA Peak Bitrate Calculation . . . . . . . . . . . . . . . . . . . . 237

7.10 Serving HS-DSCH Cell Change . . . . . . . . . . . . . . . . . . . . . 239

7.11 Summary: HSDPA Operation in Short . . . . . . . . . . . . . . . . . 241

8 High Speed Uplink Packet Access 245

8.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

8.2 Comparison with HSDPA . . . . . . . . . . . . . . . . . . . . . . . . 247

8.2.1 Commonalities with HSDPA . . . . . . . . . . . . . . . . . . . 247

8.2.2 Differences from HSDPA . . . . . . . . . . . . . . . . . . . . . 248

8.3 HSUPA User Plane Protocols . . . . . . . . . . . . . . . . . . . . . . 248

8.4 HSUPA Configuration Options . . . . . . . . . . . . . . . . . . . . . . 250

8.5 E-DCH UE Categories and Bit Rates . . . . . . . . . . . . . . . . . . 251

8.6 Starting of HSUPA Operation . . . . . . . . . . . . . . . . . . . . . . 253

8.7 HSUPA Protocol Architecture . . . . . . . . . . . . . . . . . . . . . . 254

8.8 Channels and Physical Layer . . . . . . . . . . . . . . . . . . . . . . . 260

8.8.1 E-DPDCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261

8.8.2 E-DPCCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

8.8.3 E-AGCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264

8.8.4 E-RGCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266

8.8.5 E-HICH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270

8.8.6 F-DPCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

8.9 Summary: Serving and Non-serving RLS . . . . . . . . . . . . . . . . 273

8.10 E-TFC Selection Procedure . . . . . . . . . . . . . . . . . . . . . . . 276

8.10.1 Step 1: UE sends Scheduling Requests to Node B . . . . . . . 276

8.10.2 Step 2: Serving Grant Value . . . . . . . . . . . . . . . . . . . 277

15

8.10.3 Step 3: Find Power Offset . . . . . . . . . . . . . . . . . . . . 278

8.10.4 Step 4: “Reference E-TFCI & Power Offset” Curve . . . . . . 278

8.10.5 Step 5: Calculate E-TFCI Allowed by Grant Value . . . . . . 278

8.10.6 Step 6: Calculate TB Size . . . . . . . . . . . . . . . . . . . . 278

8.10.7 Step 7: Select Channelization Code & L1 Parameters . . . . . 279

8.10.8 Step 8: UL Transmission on E-DCH . . . . . . . . . . . . . . 280

8.10.9 Step 9: Feedback from Node B on E-HICH . . . . . . . . . . 281

8.10.10Step 10: Feedback from Node B on E-RGCH . . . . . . . . . . 282

8.11 Summary: HSUPA Operation in Short . . . . . . . . . . . . . . . . . 283

8.12 UL Channelization Codes . . . . . . . . . . . . . . . . . . . . . . . . 288

8.13 DL Channelization Codes . . . . . . . . . . . . . . . . . . . . . . . . 291

8.13.1 R99 DL Channels . . . . . . . . . . . . . . . . . . . . . . . . . 291

8.13.2 HSDPA-related DL Channels . . . . . . . . . . . . . . . . . . 292

8.13.3 HSUPA Related DL Channels . . . . . . . . . . . . . . . . . . 292

9 Signalling 295

9.1 Building Blocks of 3G Signalling . . . . . . . . . . . . . . . . . . . . . 296

9.1.1 RRC Connection . . . . . . . . . . . . . . . . . . . . . . . . . 296

9.1.2 Radio Access Bearer (RAB) . . . . . . . . . . . . . . . . . . . 298

9.1.3 Radio Bearer . . . . . . . . . . . . . . . . . . . . . . . . . . . 298

9.1.4 Radio Link . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299

9.1.5 Non-Access Stratum (NAS) Signalling Connection . . . . . . . 301

9.2 RRC Connection Establishment . . . . . . . . . . . . . . . . . . . . . 302

9.2.1 RRC Connection on Dedicated Channels - DCH . . . . . . . . 302

9.2.2 RRC Connection on Common Channels - FACH/RACH . . . 304

9.3 Mobile Originated Voice Call Establishment . . . . . . . . . . . . . . 306

9.4 Mobile Terminated Voice Call Establishment . . . . . . . . . . . . . . 310

9.5 PS Data Session Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 314

9.6 Soft Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

9.7 Inter-RNC Handover with Iur Interface . . . . . . . . . . . . . . . . . 323

16

1

9.8 Inter-RNC Handover without Iur Interface . . . . . . . . . . . . . . . 326

9.9 CS Inter-System Handover (3G to 2G) . . . . . . . . . . . . . . . . . 329

9.10 PS Inter-System Handover (3G to 2G) . . . . . . . . . . . . . . . . . 335

9.11 HSDPA Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338

9.11.1 Serving HS-DSCH Cell Change . . . . . . . . . . . . . . . . . 338

9.11.2 HS-DSCH Channel Type Switch . . . . . . . . . . . . . . . . . 342

9.11.3 HS-DSCH IFHO and ISHO . . . . . . . . . . . . . . . . . . . 343

9.12 HSUPA Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

9.12.1 E-DCH Soft Handover . . . . . . . . . . . . . . . . . . . . . . 345

9.12.2 E-DCH Serving Cell Change . . . . . . . . . . . . . . . . . . . 345

9.12.3 E-DCH Channel Type Switch . . . . . . . . . . . . . . . . . . 345

9.12.4 E-DCH IFHO and ISHO . . . . . . . . . . . . . . . . . . . . . 347

10 Self Test 351

10.1 Module 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

10.2 Module 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354

10.3 Module 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

10.4 Module 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360

10.5 Module 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

10.6 Module 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367

10.7 Module 7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369

10.8 Module 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372

10.9 Module 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376

CHAPTER

1

HISTORY AND STANDARDIZATION

We have come a long way. GSM made it possible to leave the office and yet

answer the phone calls, 3G did the same for the e-mails, and SMS still creates

wonders despite its tiny size.

If you have decided to read this book, you are definitely involved with the mobilecommunication industry and it is quite possible that at least once someone has askedyou “What is 3G ?”. Especially after hearing the words iPhone 3G & 3GS, evennon-technical people have started wondering what exactly is 3G. In this chapter, wewill try to find the answer to this question and have a look at the evolutionary pathtaken by 3G.

1.1 Mobile Telecom Market

Source:Informa Telecoms & Mediahttp://www.4gamericas.org/

The statistics from the 4th Quarter 20121 show that 90% of the mobile subscriptionsin the world are using GSM, UMTS & HSPA Systems. Figure 1.1 is taken from

1Source: Informa Telecoms & Media & http://www.4gamericas.org/

2

1.2. HISTORY 3

www.4gamericas.com, which contains a lot of interesting details about the presenttelecom market. Among all the cellular systems, GSM has been the most successfultechnology and due to affordable handsets and the importance of voice service, itwill continue to remain the leading technology for the coming years as well.

When UMTS was developed as the 3G system, the 3G-2G interworking was plannedso that the investments of GSM could be reused and 3G cost of ownership could bereduced. Even today, 2G provides a coverage safety belt to 3G. When subscribersrun into 3G coverage holes, then they can use the 2G systems. Similarly, whenthe 2G load increases, 3G can provide some load-sharing possibility for the smoothoperation of 2G cell.

Figure 1.1: Mobile market in Q4 2012; source: Informa Telecoms & Media

1.2 History

Nowadays, the word mobile phone is a synonym of cellular phones. In some coun-tries2, the mobile phones are called handy. But there was a time when mobile phoneswere neither handy nor cellular. Those commercial mobile systems can be called as0G or Single Cell Systems.

2e.g., in Germany

4 CHAPTER 1. HISTORY AND STANDARDIZATION

1.2.1 0G Systems

0G Systems are called so because they were the predecessors of the first generation(1G) modern cellular communication systems. They were planned to serve a verylarge geographical area using a very high base station. Due to this huge distance,mobile was required to transmit at a very high transmit power, and it needed a bulkybattery to make it possible. Therefore, the tranmitters/receivers of these phoneswere typically mounted on the top of vehicles and the handset was fitted close tothe driver’s seat. Because of the huge cost of equipment and service operation, thiscould be used only by very few groups of people, e.g., celebrities, politicians andconstruction managers.

For operators: These systems were not a profitable technology because each fre-quency could be used only once in a very large geographical area.

For Users: Cost of service and user equipment was so high that the common mandid not feel the need of using this service.

Both of the points listed above stopped the growth of 0G systems and these remainedas low-subscriber system.

1.2.2 1G Systems

First-generation mobile systems were a big revolution. In 1G systems, for the firsttime, we divided the coverage areas into cells and hence started the history of themodern cellular mobile communication system. 1G systems could also be calledas analog3 mobile phone systems because they used analog transmission for speechservices.

In 1979, the first cellular system in the world became operational by Nippon Tele-phone and Telegraph (NTT) in Tokyo, Japan. Two years later, the cellular epochreached Europe. The two most popular analogue systems were Nordic Mobile Tele-phones (NMT) and Total Access Communication Systems (TACS). In 1981, theNMT-450 system was commercialized by NMT in Scandinavia. The system oper-ated in the 450 MHz and 900 MHz band with a total bandwidth of 10 MHz.

Advanced Mobile Phone System (AMPS) was an analog mobile phone system stan-dard developed by Bell Labs, and officially introduced in the Americas in 1983.TACS, launched in the United Kingdom in 1982, operated at 900 MHz with a bandof 25 MHz for each path and a channel bandwidth of 25 KHz. Other than NMT

3Analog: Amplitude Modulation, Frequency Modulation, Phase Modulation

1.2. HISTORY 5

and TACS, some other analogue systems were also introduced in the 1980s acrossEurope. For example, in Germany, the C-450 cellular system, operating at 450 MHzand 900 MHz (later) was deployed in September in 1985.

All of these systems offered handover and roaming capabilities but the cellular net-works were unable to inter-operate between countries. This was one of the inevitabledisadvantages of the first-generation mobile networks. Other than being just the lo-cal & region-specific systems, these systems also had some other disadvantages:

Security: Analog speech was transmitted without any encryption.

Quality: Transmission errors were not so easy to correct because it was very difficultto reconstruct exactly the same analog signal.

Capacity: Analog speech cannot be compressed. Therefore, 1G radio transmissionrequires a lot of bandwidth. This causes network congestion for the operatorand expensive operation for the subscriber.

With the introduction of 1G phones, the mobile market showed some growth andthe number of subscribers reached 20 million by 1990. But still, to own a mobilephone was a luxury and only a few people could afford it.

1.2.3 2G Systems

Just like 1G, every region had its own local 2G standards as well. For example, inthe USA, 1G AMPS was upgraded to digital AMPS (D-AMPS), in the USA itself, aCDMA based IS-95 2G network was launched. Japan developed its own 2G systemcalled Personal Digital Cellular (PDC). PDC is a TDMA-based technology that isdeployed only in Japan. Among all 2G systems, one system that made the largestimpact on our lives is Global System for Mobile communication (GSM). The second-generation (2G) mobile systems were introduced in the early 1990s. Low bit ratedata services were supported as well as the traditional speech service.

Development of GSM in Europe

But in Europe, there was a growing demand of a common standard which shouldwork in the major part of Europe. To fulfil this need, in 1982 a group was formed,which is knows as Groupe Speciale Mobile (GSM)4. This group was formed by

4This was the original name of GSM. Later it was changed to Global System of Mobile Com-munications


the Confederation of European Posts and Telecommunications (CEPT) to design apan-European mobile technology. In coming years, the European Commission andEuropean Union heads of states endorsed the GSM project. The GSM project wasstarted as a European initiative but soon the non-European operators also startedendorsing it. In fact, the GSM has been more successful than the most optimisticforecast ever made for it. For example, the number of GSM subscribers reachedthe 1 Million mark in 1994, 10 million in 1995, 50 million in 1996 and in 1998 thenumber reached 100 million mark. In 1998, there were more than 100 countrieswhich were using GSM. A more detailed description of the events can be found athttp://www.gsma.com/aboutus/history/.

On technical aspects also, the second-generation mobile systems were a big enhance-ment which fulfilled many shortcomings of 1G analog systems. One remarkableaspect of 2G systems is that they all utilize digital5 modulation.

In a digital system, the analog speech signal passes through an analog-to-digitalconverter and the digitized signal is fed to the modulator. When compared to thefirst-generation systems, 2G systems are able to achieve:

• higher spectrum efficiency due to modern speech codecs

• (encrypted) secure radio transmission

• better quality by using an error-correction scheme (channel coding)

• better data services

• more advanced roaming

Three 2G Standards of USA

In the United States, there were three lines of development in the second-generationdigital cellular systems.

1. The first digital system, introduced in 1991, was the IS-54 (North AmericaTDMA Digital Cellular) of which a new version supporting additional services(IS-136) was introduced in 1996.

2. Meanwhile, IS-95 (cdmaOne) was deployed in 1993. In many regions of theworld, it is called 2G CDMA.

5 Digital: Amplitude Shift Keying, Frequency Shift Keying, Phase Shift Keying

1.2. HISTORY 7

Figure 1.2: Commercially deployed Mobile Communication Systems of the 3GPPFamily

3. The US Federal Communications Commission (FCC) also auctioned a newblock of spectrum in the 1900 MHz band (PCS), allowing GSM1900 to enterthe US market.

In Japan, the Personal Digital Cellular (PDC) system, originally known as JDC(Japanese Digital Cellular) was initially defined in 1990. Commercial service wasstarted by NTT in 1993 in the 800 MHz band and in 1994 in the 1.5 GHz band.

GSM and its Evolution

GSM has emerged as a single, unified 2G standard operating in more than 200 coun-tries. This enabled seamless services throughout Europe by means of internationalroaming. The earliest GSM system operated in the 900 MHz frequency band. Later,GSM specifications for 1800 & 1900 MHz bands were released. During developmentover more than 20 years, the GSM technology has been continuously improved tooffer better services in the market. New technologies have been developed basedon the original GSM system, leading to some more advanced systems known as 2.5


Generation (2.5G) systems.

HSCSD, GPRS and EDGE are all based on the original GSM system.

High Speed Circuit Switched Data (HSCSD)

HSCSD is the first enhancement of the GSM air interface. The new features includedin HSCSD are illustrated in figure 1.3, These 2 features are:

1. The new channel coding used in HSCSD yields 14.4 kbps user data per timeslot.

2. For high bit rates, several time slots could be bundled and allocated to thesame user.

HSCSD bundles GSM time slots to give a theoretical maximum data rate of 57.6kbit/s (bundling 4 X 14.4 kbit/s full rate time slots). HSCSD provides both sym-metric and asymmetric services and it is relatively easy to deploy. However, HSCSDis not easy to price competitively since each time slot is effectively a GSM channel.

Figure 1.3: HSCSD compared with GSM

1.2. HISTORY 9

General Packet Radio Service

Following HSCSD, GPRS is the next step of the evolution of the GSM air inter-face. Other than bundling timeslots, 4 new channel coding schemes are proposed.GPRS provides always-on packet-switched services with bandwidth only being usedwhen needed. Therefore, GPRS enables GSM with Internet access at high spectrumefficiency by sharing time slots between different users. Theoretically, GPRS cansupport data rate up to 160 kbit/s (current commercial GPRS provides 40 kbit/s).Deploying GPRS is not as simple as HSCSD because the core network needs to beupgraded as well.

General Packet Radio Service (GPRS) provides packet data radio access for GSMmobile phones. On a general level, GPRS connections use the resources only for ashort period of time when sending or receiving data:

• In a circuit-switched system, the line is occupied even when no data is trans-ferred.

• In a packet-switched system, the resources are released so they can be used byother subscribers.

GPRS is, therefore, well adapted to the bursty nature of data applications. GPRShas minimal effects on the handling of circuit switched calls but the inter-operabilityof existing circuit switched functionalities needs to be taken into account.

An investment in the GPRS infrastructure is an investment in future services. GPRSpaves the way and is already part of the third generation (3G) network infrastruc-ture. Migration to 3G comprises deployment of the new WCDMA radio interfaceserved by the GSM and GPRS core networks. Many of the 3G services are basedon IP, and the GPRS Core network is the key step of introducing the IP serviceplatform into the present GSM networks.

When migrating to 3G services, preserving the Core Network investments is a toppriority. Introducing UMTS will complement the GSM network, not replace it.

Enhanced Data Rates for GSM Evolution

Enhanced Data rates for GSM Evolution (EDGE) boosts GSM/GPRS network ca-pacity and data rates to meet the demands of wireless multimedia applications andmass market deployment. EDGE uses the GSM radio structure but with a newmodulation scheme, 8-PSK, instead of GMSK, thereby increasing by three timesthe GSM throughput using the same bandwidth. A quick summary of EDGE tech-nology can be found in figure 1.5.


Figure 1.4: GPRS improvements for higher bit rates

With the new modulation, EDGE increases the radio interface data throughput, asper 3GPP standardization, three-fold compared to today’s GSM and boosts bothcircuit switched and packet switched services. The maximum standardized data rateper timeslot will triple, and the peak throughput, with eight time slots in the radiointerface, can be up to 473 kbit/s. Since it is fully based on GSM, introducing EDGEto the existing network requires relatively small changes to the network hardwareand software. EDGE does not entail any new network elements6. The operatorsneed not make any changes to the network structure or invest in new regulatorylicenses.

EDGE, in combination with GPRS, will deliver single user data rates of up to 384kbit/s.

EDGE or E-GPRS supports higher data rates compared to basic GPRS, using sev-eral Modulation and Coding Schemes (MCSs) varying from 8.8 kbit/s to 59.2 kbit/sin the radio interface. Nine different MCS schemes are designed for EGPRS. Whenan RLC data block is sent, the information is encoded using one of the MCSs to resist

6Compared to GPRS network architecture, the EDGE network does not need any additionalnetwork element.

1.2. HISTORY 11

Figure 1.5: Summary of EDGE Technology

8-PSK GMSKModulation 8-PSK, 3 bit/sym GMSK, 1 bit/symSymbol rate 270.833 ksps 270.833 kspsPayload/burst 346 bits 116 bitsGross rate/time slot 69.6 kbit/s 23.2 kbit/s

Table 1.1: Comparison of 8-PSK and GMSK modulation schemes

channel degradation and modulated before transmission over the radio interface.

Since the resources are limited, the higher the level of protection for information,the less information is sent. The protection that best fits the channel condition ischosen for a maximum throughput. The GMSK modulation provides a robust modefor wide area coverage while 8PSK provides higher data rates.

1.2.4 3G Systems

The idea of next generation mobile network was first conceived by ITU and wascalled IMT-2000. IMT-2000 is the result of collaboration of many entities, insidethe ITU (ITU-R and ITU-T), and outside the ITU (3GPP, 3GPP2, UWCC and so


MCS Modulation Code Rate User Rate

MCS-1

GMSK

0.53 8.8 kbpsMCS-2 0.66 11.2 kbpsMCS-3 0.80 14.8 kbpsMCS-4 1.0 17.6 kbps

MCS-5

8-PSK

0.37 22.4 kbpsMCS-6 0.49 29.6 kbpsMCS-7 0.76 44.8 kbpsMCS-8 0.92 54.4 kbpsMCS-9 1.0 59.2 kbps

Table 1.2: Peak data rates for E-GPRS Modulation and Coding Schemes

on).

As shown in figure 1.6, the vision of ITU for its next generation system was some-thing like this.

Quoted word-by-word,Source: http://www.itu.int/osg/spu/imt-2000/technology.html

IMT-2000 offers the capability of providing value-added services and applica-

tions on the basis of a single standard. The system envisages a platform for

distributing converged fixed, mobile, voice, data, Internet and multimedia ser-

vices. One of its key visions is to provide seamless global roaming, enabling

users to move across borders while using the same number and handset. IMT-

2000 also aims to provide seamless delivery of services, over a number of media

(satellite, fixed, etc). It is expected that IMT-2000 will provide higher trans-

mission rates: a minimum speed of 2 Mbit/s for stationary or walking users,

and 348 kbit/s in a moving vehicle. Second-generation systems only provide

speeds ranging from 9.6 kbit/s to 28.8 kbit/s.

When ITU defined the requirements of its next generation mobile system, severalstandards development organizations started working on finding solutions to fulfillthose requirements in the easiest and most cost-effective manner. A few well knownorganizations in this race were European Telecommunications Standards Institute(ETSI), Telecommunications Technology Association, Korea, Association of RadioIndustries and Businesses, Japan etc.

As a part of the roadmap, July 1998 was accepted as the deadline for submission ofproposals for IMT-2000 by the regional standardization development organizations.

1.3. 3GPP AND 3GPP2 13

Third-generation (3G) systems promise faster communications services, includingvoice, fax and Internet, anytime and anywhere with seamless global roaming. ITU’sInternational Telecommunication Union IMT-2000 global standard for 3G has openedthe way to enabling innovative applications and services (e.g. multimedia entertain-ment, infotainment and location-based services, among others).

Figure 1.6: ITU’s vision of IMT-2000

The terrestrial radio transmission technologies proposed to ITU in July 1998 in-cluded a number of different Wideband CDMA (WCDMA) based radio access tech-nologies, which can be grouped into two types.

Synchronous: These type of proposals requires synchronized base stations.These proposals were built on the IS-95 2G radio transmission technology(e.g., TD-SCDMA).

Non-Synchronous: The other group of concepts does not rely on base stationsynchronization (e.g., WCDMA).

1.3 3GPP and 3GPP2

By the end of 1998, two specification development projects were founded by theregional standardization organizations, 3GPP (3rd Generation Partnership Project)


and 3GPP2. The goal of both 3GPP and 3GPP2 was to merge a number of theIMT-2000 proposals into a single one, see figure 1.7.

3GPP: 3GPP includes the organizations which are working on evolving GSM to-wards 3G standards and beyond. 3GPP is responsible for the standardizationof GSM, GPRS, UMTS, HSPA & LTE.

3GPP2: 3GPP2 includes the organizations which are working on evolving IS-95(2G CDMA) towards 3G standards. 3GPP2 is responsible for the standard-ization of CDMA2000 1X, CDMA200 EV-DO Rev. A/B/C.

1.3.1 3rd Generation Partnership Project (3GPP)

Source: http://3gpp.org/Partners

http://3gpp.org/About-3GPP

The 3rd Generation Partnership Project (3GPP) unites six telecommunications stan-dards bodies, known as Organizational Partners and provides their members with astable environment to produce the highly successful Reports and Specifications thatdefine 3GPP technologies.

The six 3GPP Organizational Partners - from Asia, Europe and North America -determine the general policy and strategy of 3GPP.

ARIB The Association of Radio Industries and Businesses, Japan

CCSA China Communications Standards Association, China

TTA Telecommunications Technology Association, Korea

TTC Telecommunication Technology Committee, Japan

ETSI The European Telecommunications Standards Institute

ATIS The Alliance for Telecommunications Industry Solutions, USA

Other than these, 3GPP currently has three Observers. Observers are StandardsDevelopment Organizations (SDOs) who have the qualifications to become futureOrganizational Partners.

TIA Telecommunications Industries Association, USA


ISACC ICT Standards Advisory Council of Canada, Canada

ACIF Communications Alliance - former Australian Communications Industry Fo-rum, Australia

Additionally, 3GPP has also members who have the ability to offer market adviceto 3GPP and to bring into 3GPP a consensus view of market requirements fallingwithin the 3GPP scope; but does not have the capability and authority to define,publish and set standards within the 3GPP scope. These partners are called ‘MarketRepresentation Partners’.

3GPP has several market representative partners, which are IMS Forum, TD-Forum, GSA, GSM Association, IPV6 Forum, UMTS Forum, 4G Amer-icas, TD SCDMA Industry Alliance, InfoCommunication Union, SmallCell Forum, CDMA Development Group, Cellular Operators Associationof India (COAI) and NGMN Alliance.

1.3.2 3rd Generation Partnership Project 2 (3GPP2)

Source: http://www.3gpp2.com/Public html/Misc/AboutHome.cfm

The Third Generation Partnership Project 2 (3GPP2) is also a collaborative effortamong 5 North American and Asian standards development organizations whoseaim is to develop the specifications for ANSI/TIA/EIA-41 Cellular Radio telecom-munication Intersystem Operations network evolution to 3G. 3GPP2 is responsiblefor standardization of cdma2000 and its future evolutions.

Similar to 3GPP, 3GPP2 also has organizational partners, which are:

ARIB The Association of Radio Industries and Businesses, Japan7

CCSA China Communications Standards Association, China

TTA Telecommunications Technology Association, Korea

TTC Telecommunication Technology Committee, Japan

TIA Telecommunications Industry Association, USA

7ARIB, CCSA, TTA & TTC organizations are partners in both 3GPP and 3GPP2.


3GPP2 also has market representation partners which have the ability to offer mar-ket advice to 3GPP2 and to bring into 3GPP2 a consensus view of market re-quirements falling within the 3GPP2 scope. There are 4 market representativesof 3GPP2: CDMA Development Group (CDG), IPv6 Forum, Small CellForum, CDMA Certification Forum.

Figure 1.7: Standards Development Organizations responsible for forming 3GPP& 3GPP2

List of all IMT-2000 Systems

The purpose of this section is to show the complete picture of 3G. In the

whole book, we will discuss only WCDMA FDD (officially called as IMT-2000

CDMA Direct Spectrum).

For someone living in Europe, 3G, WCDMA and UMTS are synonyms. But if weanalyze carefully, it is not correct. According to ITU’s Recommendation ITU-RM.1457, there were 5 systems recommended for terrestrial radio interfaces of IMT-2000.

Source: ITU’s Recommendation ITU-R M.1457

1. IMT-2000 CDMA Direct Spread: The IMT-2000 radio-interface specifica-tions for CDMA Direct Spread technology are developed by 3GPP. This radio


interface is called Universal Terrestrial Radio Access (UTRA) FDD or Wide-band CDMA (WCDMA). In the development of this radio interface, the CNspecifications are based on an evolved GSM-MAP. However, the specificationsinclude the necessary capabilities for operation with an evolved ANSI-41-basedCN.

2. IMT-2000 CDMA Multi-Carrier: The IMT-2000 radio interface specifica-tions for CDMA multi-carrier (MC) technology are developed by 3GPP2. Thisradio interface is called cdma2000. In the development of this radio interfacethe CN specifications are based on an evolved ANSI-41 and IP network, but thespecifications include the necessary capabilities for operation with an evolvedGSM-MAP based CN, a CN based on IETF protocols, or the 3GPP EvolvedPacket Core (EPC).

3. IMT-2000 CDMA TDD: The IMT-2000 radio interface specifications for CDMATDD technology are developed by 3GPP. This radio interface is called the Uni-versal Terrestrial Radio Access (UTRA) time division duplex (TDD), wherethree options are defined:

• 1.28 Mchip/s TDD (TD-SCDMA)

• 3.84 Mchip/s TDD

• 7.68 Mchip/s TDD

4. IMT-2000 TDMA Single-Carrier: The IMT-2000 TDMA Single-Carrier ra-dio interface specifications contain two variations depending on:

• whether a TIA/EIA-41 circuit switched network component is used, or

• a GSM evolved UMTS circuit switched network component is used.

In either case, a common enhanced GSMGeneral Packet Radio Service (GPRS)packet switched network component is used. The initial focus of the followingsections has been to provide an evolution path for the TIA/EIA-136 pre-IMT-2000 radio interface to evolve to IMT-2000.

5. IMT-2000 FDMA/TDMA: The IMT-2000 radio interface specifications forFDMA/TDMA technology are defined by a set of ETSI standards. This radiointerface is called digital enhanced cordless telecommunications (DECT).

1.3.3 WiMAX as IMT-2000 System

In 2007, WiMAX was also accepted as a new member of IMT-2000 family with theofficial name of IMT-2000 OFDMA TDD WMAN. WiMAX (designated as IEEE


Std 802.16) is developed and maintained by the IEEE 802.16 Working Group onBroadband Wireless Access. It is published by the IEEE Standards Association(IEEE-SA) of the Institute of Electrical and Electronics Engineers (IEEE).

1.4 WCDMA FDD - Releases

Source: http://3gpp.org/Releases

Before 3G, the standardization work of GSM and GPRS was done by ETSI. FromR99 onwards, ETSI is one of the bodies in the collaboration of 3GPP. Hence, afterR99, we always talk about 3GPP releases instead of ETSI releases.

Table 1.3 shows the dates on which various 3GPP releases were standardized andfrozen. According to 3GPP, after freezing, a release can have no further additionalfunctions added. However, detailed protocol specifications (stage 3) may not yet becomplete.

Release Freezing Date

Ph 1 1992Ph 2 1995R96 Early 1997R97 Early 1998R98 Early 1999R99 March 2000Rel-4 March 2001Rel-5 March - June 2002Rel-6 December 2004 - March 2005Rel-7 Stage 3 freeze December 2007Rel-8 Stage 3 freeze December 2008Rel-9 Stage 3 freeze December 2009Rel-10 Stage 3 freeze March 2011

Table 1.3: 3GPP releases of WCDMA and their freezing dates

In some of the releases, dates are mentioned according to the stages (stage 1, 2, 3).The term stage has following meaning:

“Stage 1” refers to the service description from a service-users point of view.

“Stage 2” is a logical analysis, breaking the problem down into functional elementsand the information flows amongst them across reference points between func-tional entities.

1.5. WCDMA FDD - RELEASES AND FEATURES 19

“Stage 3” is the concrete implementation of the protocols appearing at physicalinterfaces between physical elements onto which the functional elements havebeen mapped.

1.5 WCDMA FDD - Releases and Features

Before we discuss the details of each 3GPP release and the corresponding features, letus have a quick look at the bit rates offered by various 2G and 3G technologies. Table1.4 shows both numbers, one which are mentioned in the technology description andthe others which are commercially used in practice. It is expected that HSDPA willbridge the gap between theoretical and practical numbers and hence, the mobileoperators will feel transparency in the system operation and description.

System GSM GPRS EDGE UMTS HSDPATypical Max Bitrate(Kbps) 9.6 50 150 384 14400Theoretical Max Bitrate(Kbps) 9.6 171 384 2048 14400

Table 1.4: Maximum bit rates of various technologies

Figure 1.8: Mobile Evolution from 2G to 4G

Release 99 or Rel-99: In December 1999, the first UMTS Release, the so-called‘Release 99’ was frozen. UMTS Rel-99 is based on the large experience ofGSM,GPRS standardization, taking over many principles of the matured GSM,GPRS network, protocol and service architecture.

• Mature GSM/GPRS Core network


• New Air IF technology (WCDMA)

• New radio network (UTRAN)

• bit rates up to 384 kbps8

Rel-99 was the start of 3G. The highlights of R99 was a CDMA based radioaccess network (UTRAN) and the new interfaces which connect UTRAN tothe existing GSM/GPRS core network. Rel. 99 specifies that transmissiontechnology on these interfaces should be ATM9.

REL-4 Continuing the 3GPP evolution, Release 4 enhanced UMTS via severalfeatures, e.g.:

• Bearer independent CS Core Network

• CAMEL CAMEL Phase 4

• Low chip rate TDD mode

• Transcoder Free Operation

There was no major enhancement to the UTRAN in Rel-4. Therefore, the bitrates of R99 and Rel-4 are identical. In CS Core Network, MSC functional-ity was split into 2 separate Units: MSC Server (MSS) and Media Gateway(MGW). This type of Core Network architecture is also called as Split Archi-tecture. The next chapter explains these issues.

REL-5 UMTS Release 5 was finalized at the end of 2002, including several CoreNetwork and Radio Interface enhancements such as:

• High Speed Downlink Packet Access; peak DL bitrate up to 14.4 Mbps

• All IP Core Network

• IP Multimedia Subsystem

• Wide Band AMR

Release 5 is a very significant release which affected all areas of UMTS. Forradio network, HSDPA improved the peak bit rates of DL beyond the 2 Mbpslimit. For transmission network, IP based Iub, Iur and Iu interfaces weredefined. In core network, IP multimedia subsystem (IMS) was defined, whichuses SIP based signalling to setup, maintain and tear down the packet sessions.

8Theoretically 2 Mbps but in practice, we do not get more than 384 kbps using conventional3G DCH resources.

9There were 3 options available: TDM, ATM or IP. ATM was chosen because of its flexibilityand QoS provisioning.


REL-6 UMTS Release 6 was frozen 09/2005, containing features such as:

• FDD Enhanced Uplink (HSUPA ); peak UL bitrate up to 5.76 Mbps

• WLAN-UMTS Interworking

• IP Multimedia Subsystem Phase 2

Release 6 was the point where both UL and DL could be High Speed. Thecommon name for HSDPA and HSUPA is HSPA. It was specified that HSUPAcannot work without HSDPA in DL.

REL-7 UMTS Release 7 has been closed end of 2007, including important UMTS &HSPA enhancements, improving the UMTS peak rates and spectral efficiency:

• Higher order Modulation: 64QAM for the DL (up to 21 Mbps), 16QAMfor the UL (up to 11.5 Mbps)

• 2x2 MIMO (up to 28 Mbps) for downlink (HSDPA)

• Continuous Packet Connectivity CPC

• Flexible RLC

• Enhanced Cell FACH

The development of HSPA in Rel-7 was focussed on 3 different objectives,which are:

• To increase the peak bit rate of HSDPA towards higher limits. This couldbe achieved by

– Higher Order Modulation (64QAM in DL & 16QAM in UL), or

– Multiple Input Multiple Output (MIMO) in DL.

• To decrease the battery consumption so that UEs could stay connectedfor a longer period even if they are inactive.

• Reduced latency (Round trip time) for better support of RT services onHSPA.

REL-8 3GPP Release 8 was frozen in 03/2009, containing further HSPA improve-ments as well as the UMTS Long Term Evolution LTE and the Evolved PacketSystem EPS:

• HSDPA further improvement using DC-HSDPA (42 Mbps) and simulta-neous operation of MIMO & 64QAM in DL.

• DC-HSUPA (23 Mbps)


• New radio access technology: E-UTRAN /Long Term Evolution (LTE)

• New purely packet switched core network Evolved Packet Core (EPC)

Release 8 pushed HSDPA peak bit rate to even higher values by using thecombined operation of 64-QAM and 2X2 MIMO. Additionally, an OFDMA-based new radio network (E-UTRAN) and a pure IP-based new core networkwas defined. This new system os commonly known as Evolved Packet System(EPS) or Long Term Evolution (LTE).

REL-9 3GPP Release 9 has been closed end of 2009, including HSPA+ enhance-ments and initial LTE-Advanced (LTE-A) definitions.

• Dual-Cell HSDPA, 2x2 MIMO & 64QAM (up to 84 Mbps).

REL-10 3GPP Release 10 was finished in early 2011; central focus will be on LTE-Advanced10 Few highlights of Rel-10 are described below.

• Furthermore, definition of Multi-Carrier HSPA for UL & DL is expected.

• LTE-Advanced (up to 1 Gbps DL & 500 Mbps UL for low mobility/Indoor)as IMT-Advanced proposal (4G).

• Multi-Carrier HSDPA (DL: up to 3 or 4 carrier delivering up to 126 &168 Mbps respectively).

• Dual-Carrier HSUPA (UL: up to 23 Mbps).

10The term 4G is quite often used without much care. The ITU guidelines and requirementsshow that only in Rel 10, LTE is able to fulfil the requirements of the 4G system. Hence, it istechnically wrong to call REL-8 LTE as 4G system.


Copyright Notices

Main reference material for this book has been technical specifications (TSs) andtechnical reports (TRs) of 3rd Generation Partnership Project (3GPP). Informationhas been interpreted and presented in a simplified manner.

In the first chapter no copyrighted material has been used. But the informationavailable on the official website of 3GPP has been the main source of information.

Text on page 16 http://3gpp.org/Partners

Text on page 16 http://3gpp.org/About-3GPP

Table 1.3 http://3gpp.org/Releases

Figure 1.1 on page 3 source: Informa Telecoms & Media

BIBLIOGRAPHY

[1] General information about 3GPP; Available athttp://www.3gpp.org/About-3GPP

[2] Information about 3GPP Organizational partners and market representatives ;Available at http://www.3gpp.org/Partners

[3] Information about 3GPP Releases ; Available at http://3gpp.org/Releases

[4] Information about mobile technology and IMT-2000; Available athttp://www.itu.int/osg/spu/imt-2000/technology.html

[5] General information about 3GPP2; Available at http://www.3gpp2.com/.

[6] Information about 3GPP Organizational partners and market representatives ;Available at http://www.3gpp2.com/Public html/Misc/PartnersHome.cfm

[7] http://www.4gamericas.org/

[8] http://www.gsma.com/aboutus/history/

[9] M.1457-11 Detailed specifications of the terrestrial radio interfaces of Interna-tional Mobile Telecommunications-2000 (IMT-2000)

[10] H.Holma and A. Toskala, ‘WCDMA for UMTS’ , 5th Edition, John Wiley& Sons.

24

CHAPTER

2

NETWORK ELEMENTS ANDFUNCTIONALITIES

To understand the network architecture and interfaces of UMTS, we must go throughthe evolution of GSM and GPRS. UMTS can be understood as a combination of theexisting pre-Rel-99 GSM/GPRS core network and a new type of radio access network(UTRAN). Hence, the core networks of 2G and 3G are the same. This aspectsignificantly reduced the 3G cost of ownership and inspired the mobile operatorsto invest in UMTS. The following sections will explain the architecture, networkelements and interfaces of an UMTS network.

Figure 2.1 shows the GSM network architecture according to its basic release (GSMPhase 1 and phase 2). The services offered by such a purely circuit switched networkcan be categorized in 2 categories.

1. CS Speech: Back in the early 90’s, the voice service was the main objectivewhile buying a mobile phone. Even today, voice is the most important servicefor the majority of the subscribers and operators.

2. CS Data: The CS Data service can be compared to “Internet access usingdial-up modem”. Compared to the modern day’s Internet access, it is differentbecause in the early days of GSM, the traffic was carried by switches insteadof routers. The switches are equipped with an interworking functionality that

25

26 CHAPTER 2. NETWORK ELEMENTS AND FUNCTIONALITIES

can convert data into a form which can be accepted at the external packetdata network.

Figure 2.1: GSM Network Architecture

2.1 Architecture of the GSM Network

A GSM network is composed of several functional entities whose functions andinterfaces are depicted in figure 2.1. It shows the layout of a generic GSM network.The GSM network can be divided into three broad subsystems or parts.

1. The Mobile Station (MS): MS is carried by the subscriber.

2. The Base Station Subsystem (BSS): BSS controls the radio link with theMobile Station.

3. The Switching Subsystem (SS): SS is also known as core network. Its mainpart is the Mobile services Switching Center (MSC) which performs the switch-ing of calls between the mobile and other fixed or mobile network users as wellas mobility management.

2.1. ARCHITECTURE OF THE GSM NETWORK 27

Not shown is the Operations and Maintenance Center (OMC) which oversees theproper operation and setup of the network. The MS and the BSS communicateacross the Um interface1. The Base Station Subsystem communicates with theMobile services Switching Center (MSC) across the A interface.

2.1.1 The Mobile Station MS

MS consists of the mobile equipment (the handset) and a smart card called theSubscriber Identity Module SIM. The SIM provides personal mobility so that theuser can have access to subscribed services irrespective of a specific terminal. Byinserting the SIM card into another GSM terminal, the user is able to receive calls atthat terminal, make calls from that terminal and receive other subscribed services.

• The mobile equipment is uniquely identified by the International Mobile Equip-ment Identity (IMEI).

• The SIM card contains the International Mobile Subscriber Identity(IMSI),which is used to identify the subscriber. SIM also contains a secret key whichis required for authentication of the user and encryption of information.

The IMEI and the IMSI are independent thereby allowing personal mobility. TheSIM card may be protected against unauthorized use by a password or personalidentity number.

IMSI is a GSM-specific number which is used for internal signalling be-tween the nodes of GSM. It is a secret information which is typicallyunknown to the subscriber. For making calls and SMS, we use anothernumber known as MSISDN number2 or simply phone number. MSISDNlooks similar to the phone numbers of fixed line telephones. In HLR, themapping between MSISDN and IMSI can be performed.

2.1.2 Base Station Subsystem BSS

The Base Station Subsystem is composed of two types of network elements, theBase Transceiver Station (BTS) and the Base Station Controller (BSC). These twocommunicate across the standardized Abis interface3. The openness is desired toallow the interconnection of BTS from one vendor to the BSC of another vendor.

1also known as the air interface or radio link2Mobile Station ISDN Number3Although Abis is planned to be an open interface but typically BTS and BSC belong to the

same vendor.


BTS

The Base Transceiver Station houses the radio transceivers that define a cell andhandle the radio link protocols with the Mobile Stations In a large urban area, therewill potentially be a large number of BTSs deployed. Thus the requirements for aBTS are ruggedness, reliability, portability and minimum cost. The most importantfunctions of BTS are:

• Physical layer processing (channel coding, interleaving, puncturing etc.)

• Uplink physical layer measurements

• Radio transmission and reception

BSC

The Base Station Controller is the most important network element in BSS. It isresponsible for radio channel assignment, allotment, maintenance and release. OneBSC can control the operations of hundreds of BTS. BSC also controls the handoverprocedures for connected mode mobility. BSC is the connection between the mobilestation and the Mobile service Switching Center MSC.

2.1.3 Switching Subsystem

Network Switching Subsystem (NSS) or Switching Subsystem (SS) is responsible forswitching the traffic from one mobile operator to another operator or to PSTN.

MSC and VLR

The central component of the this subsystem is the Mobile services Switching Center(MSC). It acts like a normal switching node of the PSTN or ISDN and additionallyprovides all the functionality needed to handle a mobile subscriber such as registra-tion, authentication, location updating, handovers4 and call routing to a roamingsubscriber. These services are provided in conjunction with several functional enti-ties which together form the switching subsystem. The MSC provides the connectionto the fixed networks such as the PSTN or ISDN. Signalling between functional en-tities in the this subsystem uses Signalling System Number 7 SS7 used for trunksignalling in ISDN and widely used in current public networks.

4in the case of Inter-BSC handovers


The Visitor Location Register (VLR) contains selected subscriber’s information fromthe HLR necessary for call control and provision of the subscribed services for eachsubscriber currently located in the geographical area controlled by the VLR. Al-though each functional entity can be implemented as an independent unit, all man-ufacturers of switching equipment implement the VLR together with the MSC sothat the geographical area controlled by the MSC corresponds to that controlledby the VLR thus simplifying the signalling required. Note that the MSC containsno information about particular mobile stations. This information is stored in thelocation registers.

The following steps take place when a MS tries to register itself with an MSC/VLR.

Step 1: A subscriber sends its request to register with an MSC/VLR (Using IMSI).

Step 2: MSC analyzes the IMSI and finds out the home operator and the HLR’saddress.

Step 3: MSC/VLR contacts the HLR and requests for subscriber’s information.

Step 4: Using this information, the serving MSC/VLR authenticates the subscriber.

Step 5: After successful authentication, VLR informs the HLR about the successfulregistration. In future, if any incoming call or SMS arrives for this subscriber,this MSC/VLR will be contacted for setting up the connection.

Gateway MSC GMSC

From basic operation and functionality, GMSC is in fact the same as MSC but itslogical role is different. GMSC is that MSC which is at the border of the PLMNand interconnects one network to another. The main function of GMSC is HLR-Interrogation. This procedure takes place when a Mobile Terminated Call (incomingcall) request comes to GMSC, and GMSC interrogates HLR regarding the currentlocation of a mobile subscriber.

To understand the role of GMSC, let us take a look at the sequence of events whichtake place when an incoming5 call comes.

Step 1: Mobile terminated call setup request arrives at GMSC (using MSISDN ofcalled party).

Step 2: GMSC queries HLR regarding the current location of subscriber(using MSISDN number).

5also known as Mobile Terminated Call (MTC)


Step 3: HLR maps MSISDN to IMSI and finds the VLR address where UE waslast reported.

Step 4: HLR contacts VLR (using IMSI).

Step 5: VLR assigns a temporary Mobile Station Roaming Number (MSRN) tothis IMSI and sends it back to HLR.

Step 6: HLR sends MSRN to GMSC and hence the call can be forwarded to theserving-MSC where the user is currently located.

The acceptance of an interrogation to an HLR is the decision of the operator. Thechoice of which MSCs can act as Gateway MSCs is for the operator to decide (i.e.all MSCs or some designated MSCs).

Home Location Register HLR

Home Location Register (HLR) is a central database that stores the informationabout the subscribers. When a SIM card is issued to a mobile user, it gets reg-istered in HLR. Afterwards, wherever the user goes, it gets registered with localMSC/VLR and that MSC/VLR contacts HLR to get the administrative informa-tion of the subscriber. In this way, HLR always keeps track of the user’s location.This information is stored in the form of signalling address of VLR. HLR and VLRcommunicate using MAP protocol of the SS7 signalling suite.

For each subscriber HLR contains a lot of information. Some of that is shown below:

• IMSI of the subscriber

• MSISDN of the subscriber

• VLR-address which is currently serving this subscriber

• List of Subscribed services

• GPRS related data

• Quality-of-service (QoS) profile

• Subscribed supplementary services (e.g., Call Waiting, Call Forwarding, etc.)

There is logically one HLR per GSM operator but as the number of subscribersgrows, there can be more than one HLR in the network. It is also better to have


another HLR node for redundancy purpose. The second node can be used for backupand for redundancy purpose. This arrangement can be used to guarantee the servicecontinuity in case of technical failure with the first node. The information aboutHLR-address can be found from the IMSI.

Equipment Identity Register EIR

The Equipment Identity Register (EIR) is a database that contains a list of allvalid mobile equipment on the network where each mobile station is identified byits International Mobile Equipment Identity IMEI. An IMEI is marked as invalid ifit has been reported stolen or is not type-approved. An EIR maintains three lists:

1. Black: The IMEI numbers of the mobile handsets which have been reportedstolen or inappropriate are stored in black list.

2. White: The while list contains the few digits of IMEI number that identify thehandset type. In white list, there is no need to have the full IMEI number.If a handset model has been approved by 3GPP standards, then its ”handsettype” is stored in the white list.

3. Grey: Under the grey list of EIR, one can find the IMEI numbers of phoneswhich are under surveillance. Every time, this handset is used to access thenetwork services, a log will be generated.

In the criminal investigation, IMEI number proves to be quite helpful. Sometimes,criminals steal the phones and start using them with their own SIM cards. Fortu-nately, the IMEI number of the handset can help the law enforcement agencies totrack the mobile equipment.

Authentication Center AuC

The Authentication Center (AuC) is a protected database that stores a copy ofthe secret key stored in each subscriber’s SIM card. The AuC always resides inthe HPLMN. This network element is the most secured node in the whole PLMN.The AuC generates security data which is used for authentication of users andencryption of data over the radio channel. The secret master key (K) never leavesthe authentication center. The AuC feeds random number (RAND) and master key(K) to a standards algorithm and generate security data. This security data is thenforwarded to the serving MSC/VLR in VPLMN.


As described, MSC/VLR perform an authentication procedure to verify the identityof the user at the time of registration. The relationship between MSC/VLR and theAuC can be illustrated in figure 2.2.

Figure 2.2: Authentication of user during roaming

2.2 Improvements of GSM Standard

Compared to the mobile systems which were available till the 90s, GSM was amagical invention and hence, a huge success in the commercial market.

The services offered by GSM could be summarized as:

• Incoming and outgoing speech calls

• Short message services

• Supplementary services e.g., call forwarding, calling line identification presen-tation etc.

• Data services e.g., email, fax, web surfing

In the next few sections, we will discuss the developments which improved the GSMsystem in terms of efficiency and user experience.

2.2. IMPROVEMENTS OF GSM STANDARD 33

2.2.1 CAMEL

Source: 3GPP TS 29.002 (MAP) & 3GPP TS 22.078, 23.078, 29.078

(CAP)

CAMEL (Customized Applications for Mobile network Enhanced Logic) is anIN6 architecture within the GSM based on 3GPP standardization. CAMEL pro-vides mechanisms to support services independently of the serving network. WithCAMEL, it is possible to offer operator-specific services (OSS), that is, intelligentnetwork services, for the subscriber while roaming outside the home PLMN.

In order to support Intelligent-Network applications:

• MSCs are often upgraded with a Service Switching Point (SSP) which residesin VPLMN.

• Operator-specific services can be generated in the Service Control Point (SCP)which lies in HPLMN.

• Inter-operator communication is guaranteed by using an open interface andcommon protocol. The Interface between SSP-SCP is well-defined open inter-face and the protocol used is called CAMEL Application Part (CAP).

CAMEL was developed under the framework of Virtual Home Environment, whichmeans that the subscriber should get the same ‘look & feel’ of the services, inde-pendent of the serving network, type of handset etc.

CAMEL within Home PLMN

Within Home PLMN (or Home Network), 2 functional entities are involved.

HLR: The HLR stores subscriber-related data, which also includes the informa-tion whether the subscriber is a CAMEL subscriber. The HLR transfers theCAMEL Subscription Information (CSI) to the network elements which needit to be able to provide CAMEL services. These network elements have tosupport CAMEL, and sending the CSI to these elements has to be allowed.

gsmSCF: The operator-specific services are executed in the gsmSCF, which con-tains the service logics invoked during originating and terminating CAMELcalls, originating SMSs, etc. The CAMEL standard does not specify the im-plementation of operator-specific services.

6Intelligent Network


Figure 2.3: CAMEL Service Architecture (Phase 1)

CAMEL within visited PLMN

The PLMN where the CAMEL subscriber is roaming is called the visited net-work (VPLMN). The VMSC, VLR & gsmSSF handle the processing of originatingCAMEL calls and forwarded calls, and terminating CAMEL calls.

Visited MSC: The VMSC sets up calls from and towards the visiting subscriber.When handling service setup, the VMSC detects whether the subscriber hasCAMEL services. If the VMSC receives CSI from VLR and the triggeringcriteria are met, an initial contact to the gsmSCF takes place. During theCAMEL call, the gsmSCF may request the VMSC to monitor and reportcertain call events.

gsmSSF: The gsmSSF acts as an interface from the MSC/GMSC towards the gsm-SCF. The gsmSSF initiates the dialogue with the gsmSCF to get instructionsfor the CAMEL call handling.

VLR: The VLR stores the CAMEL subscriber data received from the HLR of thehome network as part of the subscriber data of the subscriber roaming in theVLR area. The VLR sends the subscriber data to the VMSC during originatingor forwarded call processing, and terminating call processing.

CAMEL standard has been gradually improved in phases. Currently, there are 4phases:

• CAMEL Phase 1

2.3. GPRS NETWORK ARCHITECTURE 35

• CAMEL Phase 2

• CAMEL Phase 3

• CAMEL Phase 4

In order to identify the CAMEL phase, we must check which version of MAP &CAP protocols are supported by gsmSSF, gsmSCF & HLR.

2.3 GPRS Network Architecture

In the list of services offered by GSM, there is a circuit switched data service but ithas 2 basic problems:

• Low Bit rate (only 9.6 kbps)

• Circuit switching & time-based charging

As explained in the previous module, HSCSD was introduced to improve the GSMbit rates by roughly 5 times by allocating multiple time slots to the same subscriber.But as the name suggests, HSCSD is also a circuit switched technology which relieson time-slot management and time-dependent charging. In a data session, typicallywe never use the channel 100% of allocation time. Hence, the operator has to allocatethe resources unnecessarily and the user has to pay for this channel for the wholeduration of the connection.

This was the main motivation to develop the concept of GPRS. GPRS is a packetswitched technology where the packets are carried using routers and not usingswitches. Figure 2.4 clearly shows the combined GSM & GPRS network archi-tecture.

On a general level, GPRS connections use the resources only for a short period oftime when sending or receiving data:

• In a circuit-switched system, the line is occupied even when no data is trans-ferred.

• In a packet-switched system, the resources are released so they can be used byother subscribers.


Figure 2.4: GPRS Network Architecture

The General Packet Radio System (GPRS) is a new service that provides actualpacket radio access for mobile GSM and time-division multiple access (TDMA)users. The main benefits of GPRS are that it reserves radio resources only whenthere is data to send and it reduces reliance on traditional circuit-switched networkelements. The increased functionality of GPRS decreases the incremental cost toprovide data services and increases the penetration of data services among consumerand business users.

In addition to providing new services for today’s mobile user, GPRS is an importantmigration step toward third-generation (3G) networks. GPRS will allow networkoperators to implement an IP-based core architecture for data applications, whichwill continue to be used and expanded upon for 3G services for integrated voiceand data applications. Today, everyone knows that packets are transported usingrouters. Prior to GPRS, the packets were carried via switches (MSCs) which is veryinefficient if the nature of traffic is bursty.

2.3.1 GPRS Mobile Terminals

New mobile terminals are required because existing GSM phones do not handle theenhanced air interface nor do they have the ability to packetize traffic directly. Allthese terminals will be backward compatible with GSM for making voice calls usingGSM.


Class A terminals: Class A terminals support simultaneous circuit-switched (CS)and packet-switched (PS) traffic.

Class B terminals: Class B terminals attach to the network as both CS and PSclients but only support traffic from one service at a time. They can monitorGSM and GPRS channels simultaneously. In other words, a Class B terminalcan support simultaneous attach, activation, and monitor, but not simultane-ous traffic.

Class C terminals: Class C terminals support attach to only one type of network(either CS or PS). The user must manually select the service to which it wantsto connect. Therefore, a Class C terminal can make or receive calls from onlythe manually (or default) selected service. The service that is not selected isnot reachable.

The three modes of operation are defined in 3GPP TS 22.060.

2.3.2 GPRS Base Station Subsystem

Impact of GPRS on BSC

Each BSC will require the installation of one or more Packet Control Unit (PCUs)and a software upgrade. The PCU provides a physical and logical data interfaceout of the base station system (BSS) for packet data traffic. When either voice ordata traffic is originated at the subscriber terminal, it is transported over the airinterface to the BTS, and from the BTS to the BSC in the same way as a standardGSM call. However, at the output of the BSC the traffic is separated; voice is sentto the mobile switching center (MSC) per standard GSM, and data is sent to a newdevice called the SGSN, via the PCU over a Frame Relay interface.

Impact of GPRS on BTS

The BTS may also require a software upgrade but typically will not require hardwareenhancements. The upgrade in BTS is called Channel Control Unit (CCU) whichis responsible for adaptive coding (CS-1 , 2 , 3 and 4).

The CCU (Channel Coding Unit) in the BTS performs channel coding whose rateis adapted to the radio transmission conditions:

• CS-1 (Channel Coding Scheme 1) - 9.05 kbps





2.3.3 New Elements in the Core Network

Source : 3GPP TS 23.060

SGSN

At the hierarchical level, SGSN can be considered as an “MSC with in-built VLR forPS users”. In other words, SGSN can be viewed as a “packet-switched MSC”. Verysimilar to the CS registration with MSC/VLR, a GPRS mobile station has to registerwith SGSN. This registration process is called ‘GPRS attach’. After entering a newarea, GPRS user reports its location to the corresponding SGSN. Thus SGSN isresponsible for the registration of new mobile subscribers, and keep a record of theirlocation inside a given area. In other words, SGSN performs mobility managementfunctions such as mobile subscriber attach/detach and location management. TheSGSN is connected to the base-station subsystem via a Frame Relay connection tothe PCU in the BSC.

For a better understanding, the following section breaks down the attach process ofGRPS into several steps and explains it.

Step 1: A subscriber sends its request to register with an SGSN (Using IMSI).

Step 2: SGSN analyzes the IMSI and finds out the home operator and HLR’saddress.

Step 3: SGSN contacts HLR and requests for subscriber’s information (e.g., Sub-scriber’s service profile, QoS agreement, max bit rate etc., authentication re-lated data).

Step 4: Using this information, the serving SGSN authenticates the subscriber.

Step 5: After successful authentication, SGSN informs HLR about the successfulregistration.

At this moment, a so-called ‘MM-Context ’ is generated at MS and SGSN. In otherwords, a logical-connection has been established between MS and SGSN. This con-nection is not enough to receive/transmit IP packets because the MS does not havean IP address yet.

The main functions of SGSN can be summarized as:


• Mobility Management

• Subscriber’s registration and authentication

• Charging Data Records (CDR) collection

• Ciphering7

• Packet routing

Gateway GPRS Support Node

When we observe the GPRS network from the outside world’s viewpoint, it appearsthat GPRS is nothing but a private IP network owned by the mobile operator. Theaccess to this IP network is allowed only via a gateway router known as GGSN.Hence GGSNs are used as interfaces to external IP networks such as the publicInternet, other mobile service providers GPRS services, or enterprise intranets.

UE establishes an IP connectivity with GGSN via a procedure known as ‘PDPContext Activation’. This procedure takes place in following sequence:

Step 1: MS sends PDP activation requests by specifying the Access Point Name(APN) Access Point Name (APN) and requested Quality-of-Service (QoS).

Step 2: SGSN translates APN into the IP address of GGSN with the help of a DNSsystem.

Step 3: SGSN forwards the request to GGSN and GGSN allocates an IP addressto the mobile user.

Step 4: GGSN informs SGSN and SGSN informs MS about the successful PDPcontext activation. From this moment, MS is known in the IP world becauseit has been allocated a valid IP address.

At this point, a so-called PDP Context is generated at MS, SGSN and GGSN side.

The main functions of GGSN can be summarized as:

• Packet routing

• Charging Data Records (CDR) generation

• Firewall functionality

7(only in 2G but not in 3G SGSN)


• IP-address allocation

• QoS negotiation

• Session management (e.g., PDP context activation)

GGSNs maintain routing information that is necessary to tunnel the protocol dataunits (PDUs) to the SGSNs that service particular mobile stations.

A more detailed information about each parameter of MM-context andPDP-context goes beyond the scope of this book. 3GPP TS 23.0608

contains tables which show the information storage structures requiredfor GPRS. There, we can also find details about subscription data storedin the HLR. For proper GPRS operation, MM-context must be storedin UE & SGSN; PDP-context must be stored in UE, SGSN & GGSN.Please refer to 3GPP TS 23.060 to get more details.

2.3.4 Other Changes

The databases in the GSM network, such as the Home Location Register (HLR)that handle the mobility management in the network also require software updatesto be able to handle the GPRS functions. Other than these standard nodes, theGPRS network also requires the following network functionalities:

Border Gateway (BG)

The BG is a special firewall which connects SGSN or GGSN to GPRS RoamingExchange (GRX) which is used for inter-PLMN connectivity. To understand therole of BG, please refer to figure 2.5.

Charging Gateway (CG)

The Charging Gateway or charging gateway functionality (CGF) is used for col-lecting the CDRs from SGSN and GGSN. Quite often, the format of CDRs is notstandardized and varies strongly from one vendor to another. Charging gatewayfunctionality is used for transforming the CDRs into a standard form and forwardthem to the billing center. It helps the telecom operators to implement differentservices with little billing and charging effort as well as protecting the subscriber

8General Packet Radio Service (GPRS); Service description


and operator from wrong charging. During PDP context activation the GGSN sendsa ‘charging ID (CID)’ to the SGSN. During the billing process, CDRs are regularlysent from each network node to a central billing centre. The CID is used to mergethe records from different network nodes which apply to the same subscriber.

Domain Name System (DNS)

While activating the PDP context, UE sends Access Pint Name (APN) to SGSN.APN is a user-friendly name which is designed for the comfort of human beings.But routers cannot work with these names. GSGN uses DNS to translate the APNsinto the IP-Address of GGSN9.

Lawful Interception Gateway (LIG)

LIG is used for law enforcement agencies (like police) to monitor the activities ofsome suspicious subscriber.

Firewall

Firewall is used to filter the malicious packets and keep GPRS networks safe fromunwanted virus and other threats. Quite often, Firewall functionality is implementedin the GGSN itself.

2.3.5 GPRS Roaming Scenario

Till now, we have observed that a packet in GPRS network takes the following path:

Radio Network (BSS) � SGSN � GGSN

The path shown above is depicted in the upper half of figure 2.5. This is true as longas the SGSN and GGSN both reside in the same network. In other words, when theuser is not roaming.

However, in roaming scenarios, the most popular implementation is to use theSGSN in Visited PLMN and GGSN in the Home PLMN. This inter-PLMN connec-tion is made using a private IP-backbone owned by one of the operators or by athird party. This scenario is depicted by the lower half of figure 2.5.

We hereby like to briefly mention the two scenarios:

9The same principle is used in internet for translating URLs into an IP address.


Figure 2.5: Data Access during roaming and non-roaming scenario

1. In non-roaming scenario: In non-roaming scenario, both SGSN and GGSNare located in the same PLMN using intra-PLMN backbone commonlyknown as the Gn interface.

2. In roaming scenario: In roaming scenario, SGSN resides in the VPLMNwhereasGGSN resides in the HPLMN. The two GPRS nodes are connected to eachother using inter-PLMN backbone using Gp interface via a secure bordergateway functionality. Gp is the name of the interface between “SGSN andBorder Gateway” and “GGSN and Border Gateway”.

2.4 Migration to 3G Network Architecture

In order to re-use the investments of GSM and to minimize the rollout cost of UMTS,it was decided that the existing GSM & GPRS core network will be slightly modifiedbut the very same nodes will be utilized to provide access to both10 the radio accessnetworks. There were some minor modifications defined for 3G MSC and 3G SGSN.Many authors like to show these changes as interworking functionality IWF and

10TDMA based 2G radio network BSS and WCDMA based 3G radio network UTRAN

2.5. UTRAN 43

reuse the same conventional MSC and SGSN.

Figure 2.6: Block Diagram of Combined GSM & UMTS Network Architecture

As a starting point, we should consider combined GSM, GPRS & UMTS thenetwork architecture as a combination of the following subsystems:

1. GSM Base station Subsystem: BTS and BSC

2. GSM CS core network: MSC and GMSC

3. GPRS CN: SGSN and GGSN

4. UTRAN: newly developed WCDMA based radio access network

5. Common units: Databases, registers, application servers and billing system

From this list, all objects except UTRAN have been already discussed in this chapter.Therefore, in the following section, we will concentrate on the details of UTRAN.

2.5 UTRAN

UMTS Terrestrial Radio Access Network (UTRAN) is the brand new WidebandCDMA-based access network defined for 3G UMTS networks. UTRAN is divided


into several Radio Network Subsystems where each RNS is managed by one RNC.A RNS typically consists of hundreds of base stations known as Node B.

The Radio Network System (RNS) is the system of base station equipments (transceivers,controllers, etc. . . . ) which is viewed by the MSC through a single Iu-interface asbeing the entity responsible for communicating with Mobile Stations in a certainarea. Similarly, in PLMNs supporting GPRS, the RNS is viewed by the SGSNthrough a single Iu-PS interface. In short,the RNS consists of one Radio NetworkController (RNC) and one or more Node B.

Figure 2.7: UMTS Network Architecture

2.5.1 Node B

Node B can be simply considered as the “BTS of 3G”. The main functions of NodeB is to establish the physical implementation of Uu interface and Iub interface. Therealization of Uu interface means that Node B implements WCDMA physical chan-nels and converts the information coming from transport channels to the physicalchannels under control of RNC. For the Iub interface, Node B performs the inversefunctionality. It should be noted here that Node B owns only physical channels’resources whereas transport channels are completely managed by RNC.

• Spreading

2.5. UTRAN 45

Figure 2.8: New Interfaces defined in UTRAN Iub, Iur and Iu

• Scrambling

• Modulation

• Channel Coding

• Interleaving

• Power Control

• Synchronization

• Measurement reporting

2.5.2 RNC

Radio Network Controller (RNC) is the main controlling element in UTRAN, sinceit owns all the logical resources of Radio Network Subsystem. It is responsible forcontrolling the use and integrity of all 3G radio resources by the means of performingRadio Resource Management (RRM) procedures. This includes functions such ashandover and admission control, power control and code allocation, radio resourcecontrol (RRC) and macro diversity combining (MDC).


RNC is the central unit in 3G RAN. It also plays an important role in configurationmanagement because the radio related parameters for the whole RNS are stored inRNC. For performance management, RNC updates counters, which are later usedto calculate the key performance indicators (KPIs) for RAN. RNC also providedsupport in fault management by keeping track of the alarms in any Node B controlledby that particular RNC.

• Radio Resource Management

• Management of System information

• Alarms handling

• Interworking node Iub and Iu interfaces

• Operation and Maintenance

• Performance Measurement

RNC works as the intermediate node which connects Core Network (CN) to RAN. Itis possible that the transport technologies in RAN and Core are different (e.g., Oneside is using ATM and the other side IP). In that case, RNC performs the protocolconversion required for interworking.

2.6. LOGICAL ROLES OF RNC: S-RNC AND D-RNC 47

2.6 Logical roles of RNC: S-RNC and D-RNC

Figure 2.9: Logical Roles of RNC: SRNC and DRNC

In UMTS, while the user is moving from one cell to another, radio links are addedand deleted without breaking the connection. This is called Soft Handover. If thetwo cells belong to 2 different RNCs, then SHO is possible only if the Iur interfacebetween the two RNCs exists. Otherwise, a hard handover takes place which canbe compared to Inter-BSC handover of GSM.

As shown in figure 2.9, the logical role played by RNC can earn it 3 different titles.

Controlling RNC (CRNC): CRNC of Cell # 1 is the RNC which controls theoperation of cell by defining its load and other parameters. For all the tele-


com procedures happening in cell #1, RNC #1 is responsible. Therefore, theCRNC of cell #1 is RNC#1.

Serving RNC (SRNC): SRNC of UE is the RNC, which has a signalling connec-tion (RRC Connection) with UE. From Core Network viewpoint, UE is con-nected to only this RNC because Core Network (MSC or SGSN) receives/sendsdata from/to this RNC only. UE always has only one SRNC. Serving RNCowns all logical resources belonging to the user connection. Serving RNC isthe place where the Macro Diversity Combining (MDC) is executed.

Drift RNC (DRNC): DRNC of UE is the RNC which is involved in soft handoverbut is not the SRNC. The DRNC is CRNC of one of the cells which are involvedin Soft Handover. DRNC comes into play only if we have Inter-RNC Soft HO.Please refer to figure 2.9 for clear understanding.

Whenever we talk about Soft HO, there is always a discussion of Micro or Macro-diversity.

Micro-diversity: Micro-diversity comes into play when UE is involved in Soft han-dover with 2 cells which belong to the same Node B. This special case of softHO is called Softer HO. Micro-diversity combining takes place in Node B.

Macro-diversity: Macro-diversity comes into play when UE is involved in softhandover with 2 or more cells which belong to 2 (or 3) different Node Bs.Macro-diversity combining takes place in RNC.

2.6. LOGICAL ROLES OF RNC: S-RNC AND D-RNC 49

Summary of R99 Network Architecture

Source: 3G TS 23.002 V3.1.0; Network architecture

Figure 2.10: Configuration of a PLMN and Interfaces (Source TS 23.002)


2.7 Release 4 Modifications

Source:

• Overview of 3GPP Release 4 V1.1.2 (2010-02)

• 3GPP TS 23.205 V4.0.0; Bearer Independent CS Core Network

• 3GPP TS 23.002 V4.8.0; Network architecture

Figure 2.11: BICC Network Architecture or Split Architecture

As shown in chapter 1, after Rel-99, 3GPP stopped naming the releases after theyear as they did in Rel-95, 96, etc. The first set of modifications introduced werecalled 3GPP Rel-4. In short, the history and future follows this path: Rel-96 →Rel-97 → Rel-98 → R99 → Rel-4 → Rel-5 → Rel-6 → and so on.

3GPP Rel-4 specifications were frozen in March 2001. One of the highlights of Rel-4is known as “Bearer Independent Call Control”. In order to understand this feature,please refer to the CS part of core network in figure 2.11.

The objective of this feature is to separate the user plane (traffic) and control plane(signalling) in the Circuit Switched (CS) domain. This new scheme offers a better

2.7. RELEASE 4 MODIFICATIONS 51

transport resource efficiency and a convergence with the Packet Switched (PS) do-main transport. Also, this enables to use one single set of layer 3 protocols on topof different transport resources as ATM, IP, STM, or even new ones.

The users shall not notice whether they are connected to a “bearer independent CSnetwork” or to a classical CS domain. Also, none of the protocols used on the radiointerface is modified by this feature. This means, for example, there is no need forthe terminals to support IP even if IP is the transport protocol used in the network.

Using BICC, the traffic is switched using CS-MGW which is capable of handling allmodern codecs (e.g., 4.75 kbps AMR ). Thus the speech can be transported fromone CS-MGW to another CS-MGW without the need of transcoding. This featurehas at least three direct benefits for the operator:

Reduced cost of transmission: The utilization of ATM/IP resources reduces sig-nificantly compared to the conventional MSCs. Because speech must be transcodedinto 64 kbps TDM format so that MSCs can handle it. Using BICC, the needof transcoding arises just before the speech ‘packet’ leaves UMTS domain andenters PSTN. In conventional CS core network, the transcoding is performedas soon as the first MSC is encountered, whereas in BICC, transcoding isperformed by the last CS-MGW in the chain.

Improved capacity: By avoiding the unnecessary transcoding, the speech qualitygets improved. In CDMA networks, this turns out to be a gain in networkcapacity.

Reduced delay: If transcoding is not performed, then the delay caused by transcod-ing is also avoided. This reduces the transmission delay and improved user’sperception.

2.7.1 Architecture

The basic principle is that the MSC is split into an MSC server and a (Circuit-Switched) Media Gateway (CS-MGW), the external interfaces remaining the sameas much as possible as for a monolithic MSC.

According to 23.002, “When needed, the MSC can be implemented intwo different entities: the MSC Server, handling only signalling,and the CS-MGW, handling user’s data. A MSC Server and aCS-MGW make up the full functionality of a MSC.”

• The MSC server provides the call control and mobility management functions,and


• The CS-MGW provides the stream manipulating functions, i.e. bearer controland transmission resource functions.

The same applies to the GMSC, split into a GMSC server and a CS-MGW.

Figure 2.12: BICC Network Architecture and Interworking with PSTN

MSC Server

The MSC Server comprises all the call control and mobility control parts of an MSC.As such, it is responsible for the control of mobile originated and mobile terminatedCS domain calls. It terminates the user to network signalling and translates it intothe relevant network to network signalling. It also contains a VLR.

The MSC Server controls the parts of the call state that pertain to connection controlfor media channels in a CS-MGW.

A GMSC Server is to a GMSC as an MSC Server is to an MSC.

CS-MGW

The CS-MGW interfaces the transport part of the UTRAN/BSC with the one ofthe core network over Iu or the A interface. It interacts with the (G)MSC server forresource control.


A CS-MGW may also terminate bearer channels from a circuit switched networkand media streams from a packet network (e.g., RTP streams in an IP network).As the entity interfacing the access and the core network, the CS-MGW operatesthe requested media conversion (it contains e.g., the TRAU), the bearer control andthe payload processing (e.g. codec, echo canceller, conference bridge). It supportsthe different Iu options for CS services (AAL2/ATM based as well as RTP/UDP/IPbased).

2.7.2 New Interfaces

CS-MGW to MSC Server (Mc)

The Mc reference point describes the interfaces between the MSC Server and CS-MGW, and between the GMSC Server and CS-MGW. It supports a separation ofcall control entities from bearer control entities, and a separation of bearer controlentities from transport entities. It uses the H.248/IETF Megaco protocol, jointlydeveloped by ITU-T and IETF.

MSC-Server to MSC-Server (Nc)

Over the Nc reference point, the Network-Network based call control is performed.Examples of this are ISUP or an evolvement of ISUP for Bearer Independent CallControl (BICC).

CS-MGW to CS-MGW (Nb)

Over the Nb reference point, the bearer control and transport are performed. Dif-ferent options are possible for user data transport and bearer control.



Source:Overview of 3GPP Release 5 V0.1.1 (2010-02)3GPP TS 23.002 V5.12.0; Network Architecture

Release 5 is a very important release because HSDPA was introduced in it. Fromthe architecture perspective too, there were very significant improvements suggestedby 3GPP in REL-5 specifications. The IMS11 is standardized by 3GPP in Rel-5.Usage of IP on the transport plane was another improvement which was introducedin this release. These features are briefly illustrated below.

2.8.1 IP Transport

In Rel-99 and Rel-4, only ATM can be used at the transport layer in the variousinterfaces. Rel-5, introduces the possibility to use IP at the transport layer in theIub, Iur, Iu-Ps and Iu-Cs interfaces, as an alternative to ATM. However, the use ofATM at the link layer under IP is not precluded. For more detailed description ofthe protocol stacks, please refer to chapter 6.

The introduction of IP as a transport protocol in the radio network does not implyan end to end IP network; the UE may be given an IP address by the higher layers,but it will not be part of the UTRAN IP network (which is private), and packetswill be encapsulated in the corresponding User Plane protocol. 3GPP has made achoice for the protocols to transport the Radio and Signalling bearers over IP.

Different solutions are adopted. UDP is used in the user plane in the three interfaces,and SCTP with additional protocols is used for the signalling bearers. Addition-ally, 3GPP resulted in the following decisions on QoS and interworking with ATMtransport networks:

• Diffserv is the mechanism to provide different service levels, and several al-ternatives are allowed for the traffic flow classification. It is also allowed thatthe QoS differentiation can be provided either on a hop-by-hop basis or on aedge-to-edge basis;

• Interworking with Rel-99/Rel-4 and Rel-5 ATM nodes is required, and it canbe accomplished via a dual stack, a logical interworking function or a separateInterworking unit.

11Now a days, IMS is a very hot topic because in LTE, there is a provision of supporting IMS-based Voice service over PS-domain.


2.8.2 IP Multimedia Subsystem (IMS)

Figure 2.13: Overview of IMS architecture

Home Subscriber Server

Home Subscriber Server (HSS) is an evolved version of HLR. From Rel-5 onwards,the name of HLR is changed into “HSS” to emphasize that this database containsnot only location-related data but also subscription-related data, like the list ofservices the user is able to get and the associated parameters. It keeps track ofwhich subscribers belong to the network and their service capabilities. The CSCFconsults with the HSS before initiating SIP connections.

Media Gateway Control Function (MGCF)

MGCF performs translation of SIP signalling messages into ISUP messages whichcan be understood by the PSTN switches. As the name suggests, MGCF controlsthe functions of IM-MGW.


IP Multimedia Media Gateway Function (IM-MGW)

An IM-MGW is used to terminate bearer channels from circuit switched infrastruc-tures and media streams from packet data networks. For instance, when it interfacesan ISDN network, it takes the data of voice from i-law PCM call, processes the userdata bits with a voice codec (e.g. AMR), before forwarding the voice informationvia RTP/UDP/IP over a packet network. To do so, an IM-MGW requires its ownresources, such as codecs, echo cancellers, and conference bridges. The IM-MGWcommunications with the Media Gateway Control Function (MGCF) for resourcecontrol via the interface Mc. For this interface, the media gateway control protocolH.248 is applied.

Proxy-Call State Control Function (P-CSCF)

P-CSCF is the “first contact point” of IMS. It is located in the same network as theGGSN (visited or home network). Its main task is to select the I-CSCF of the HomeNetwork of the user. It also performs some local analysis (e.g. number translation,QoS policing,..).

Interrogating-CSCF (I-CSCF)

I-CSCF is the “main entrance point” of the home network: it selects (with the helpof HSS) the appropriate S-CSCF.

Serving-CSCF (S-CSCF)

S-CSCF performs the actual Session Control. It handles the SIP requests, performsthe appropriate actions (e.g. requests the home and visited networks to establishthe bearers), and forwards the requests to the S-CSCF /external IP network of otherend users, as applicable. The S-CSCF might be specialized for the provisioning of a(set of) service(s).


Source: Overview of 3GPP Release 6 V0.1.1 (2010-02)


2.9.1 IMS for IP-CAN or IMS phase 2

IMS was primarily designed in Rel-5 to work on top of UMTS/GPRS using SIPsignalling but in 3GPP Rel-6, it was extended to work on top on non-GPRSbased access and SIP terminal equipments. ETSI TISPAN12 has worked veryhard to adapt the IMS for requirements of fixed networks.

Figure 2.14: Usage of IMS expanded for any IP access network

As shown in figure 2.14, the access network for using IMS services is no more re-stricted to GPRS & UMTS. The name chosen for this generic access network is“IP-Connectivity Access Network (IP-CAN)”. Some of the examples of IP-CAN areDSL, Cable, Wired and Wireless LAN, LTE etc.

IP-CAN of 3GPP Rel-6 also addresses the issues like:

• Policy Control: “Policy Decision Function” in the IMS (e.g., in P-CSCF) and“Policy Enforcement Function” in the IP-CAN (e.g., in GGSN)

• Security

• User and service profile

• UE and ISIM/USIM

• IP version issues

12TISPAN: Telecommunications and Internet converged Services and Protocols for AdvancedNetworking


• SIP Compression

• Emergency calls

2.10 Rel-7 & Rel-8 Modifications

3GPP REL-7 & 8 have introduced a lot of improvements of HSDPA & HSUPAof REL-6. This bundle-of-enhancements is collectively called as evolved-HSPA orHSPA+. Since, we have not discussed the details of HSPA yet, it makes no sense totalk about HSPA+ in this module.

In nutshell, we can say that HSPA+ is trying to:

• Push the peak bit rates of HSDPA & HSUPA higher

• Reduce the battery consumption for continuous connectivity

• Reduce the latency (transfer delay)

3GPP REL-7 & 8 have also introduced some changes in the core network to optimizethe network performance towards lower latency. These changes in the PS corenetwork are popularly called as “one tunnel solution”. Figure 2.15 shows the changesintroduced in Rel. 7 & 8.

1. As in conventional GPRS, EDGE, UMTS & HSPA (R6), there are two tunnels:One between GGSN & SGSN and the other one between SGSN & RNC. Thatmeans, SGSN takes out the IP packets from one tunnel and packs it intoanother tunnel. This procedure certainly takes some time.

2. In Rel-7, there is a mechanism for “One- Tunnel- Solution”. This allowsSGSN to be involved with only a control plane, e.g., connection setup, mobilitymanagement, authentication etc. SGSN does not appear in the chain for userplane traffic flow. User data can be directly tunneled from GGSN to RNC.

Although this solution reduced the round trip time but there are some com-plications with this scheme.

(a) Volume-dependent charging at SGSN will not be possible with this solu-tion.

(b) For Lawful Interception also, SGSN will not be able to provide any detailsabout the packet transmitted during the session.

2.10. REL-7 & REL-8 MODIFICATIONS 59

3. In Rel-8, the concept of one tunnel can be extended by one more step wherethe user data is directly tunneled from GGSN to Node B. But we must notforget that this Node B is a special one. The Node B has in-built capabilityof RNC.

Figure 2.15: Direct Tunnel Solution of REL-7 & REL-8


Copyright Notices

In order to create some figures, tables and text-sections, the following reference ma-terial has been used. Information has been interpreted and presented in a simplifiedmanner. The original references are provided here.

Main reference material for this book has been technical specifications (TSs) andtechnical reports (TRs) of 3rd Generation Partnership Project (3GPP).

Figure 2.10 on page 49 Figure 1 of TS 23.002 v 3.1.0c⃝1999. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

Text on page 51 Section 4.1.1 of “Overview of 3GPP Release4 v 1.1.2”

Text about MSC Server on page52

Section 4.1.2.1 of “Overview of 3GPP Re-lease 4 v 1.1.2”

Text about CS-MGW on page 52 Section 4.1.2.2 of “Overview of 3GPP Re-lease 4 v 1.1.2”

Figure 2.11 on page 50 Figure: BICC Network Architecture of“Overview of 3GPP Release 4 v 1.1.2”

Figure 2.12 on page 52 Figure: Bearer Independent Core Networkwith A- and Iu-Interfaces of “Overview of3GPP Release 4 v 1.1.2”

Text in section 2.7.2 on page 53 Section 4.1.3.1, 4.1.3.2 & 4.1.3.3 of“Overview of 3GPP Release 4 v 1.1.2”

Text in section 2.8.1 on page 54 Section 6.1 of “Overview of 3GPP Release 5v 0.1.1”

Text about CSCF on page 56 Section 12.2 of “Overview of 3GPP Release5 v 0.1.1”

c⃝2010. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

BIBLIOGRAPHY

[1] 3GPP TS 25.401 Ver. 7.0.0 ;‘UTRAN overall description’

[2] 3GPP TS 23.002 ver. 3.1.0 ;‘Network architecture’



[5] 3GPP TS 29.002 ver. 3.0.0 ;‘Mobile Application Part (MAP) specification’

[6] 3GPP TS 22.078 ver. 9.0.0 ;‘Customised Applications for Mobile network En-hanced Logic (CAMEL) Service description’

[7] 3GPP TS 23.078 ver. 5.0.0 ;‘Customised Applications for Mobile network En-hanced Logic (CAMEL) Phase 4’

[8] 3GPP TS 29.078 ver. 5.0.0 ;‘CAMEL Application Part (CAP) specification’

[9] 3GPP TS 23.205 ver. 4.0.0;‘Bearer Independent CS Core Network’

[10] 3GPP TS 23.060 ver. 6.0.0 ;‘General Packet Radio Service (GPRS); Servicedescription’

[11] 3GPP TS 22.060 ver. 6.0.0 ;‘General Packet Radio Service (GPRS); Servicedescription’

[12] Overview of 3GPP Release 4 v 1.1.2 ; Available athttp://www.3gpp.org/ftp/Information/WORK PLAN/Description Releases/.

[13] Overview of 3GPP Release 5/ 6 / 7 /8 . . . ; Available athttp://www.3gpp.org/ftp/Information/WORK PLAN/Description Releases/.


61

CHAPTER

3

WCDMA AIR INTERFACE

The main difference between GSM of second generation and UMTS of third genera-tion is the air interface technology. The switches, routers and databases in the corenetwork behave in the the same manner in both the technologies. Therefore, un-derstanding the concepts of UMTS air interface is a very important part in learning3G fundamentals. This module tries to cover the basic principles about spreading,code multiplexing and physical layer processing of the data in UMTS.

3.1 Duplex Methods

Because commercial mobile networks are used to send as well as receive data fromUE, they are duplex systems. This is different from simplex transmission as in TVor radio broadcast where the user only receives but does not send data. Hence, inmobile communication we use full-duplex. There are two popular methods whichcan be used to separate the signals from UE to Node B, Uplink and Node B to UE,Downlink. They are:

FDD: As shown in figure 3.1, in FDD scheme, user sends his data on one frequencyand receives on another one. These 2 frequencies must be separated by severalMHz. FDD can only operate in paired band. For every uplink frequency, there

62

3.2. MULTIPLE ACCESS TECHNOLOGIES 63

Figure 3.1: Popular duplexing methods - FDD & TDD

is a downlink frequency. This pair of frequencies forms a carrier. For example,GSM is a FDD system.

TDD: In contrast with FDD, TDD operates in an unpaired spectrum. The samefrequency is used for both uplink and downlink. This is achieved by organizingthe time into time slots and assigning some lots to uplink and remaining slotsfor downlink.

According to 3GPP, UMTS can operate both in FDD and TDD mode. But FDD hasbeen a more popular choice among the commercial telecom operators. Accordingto common practice and usage, when someone speaks of “UMTS”, we undoubtedlyassume that UMTS-FDD is referred to. But for TDD, it must be explicitly men-tioned that we are referring to the UMTS-TDD version. Both technologies havetheir advantages and disadvantages but we will investigate only the FDD part inthis book due to its popularity.

3.2 Multiple Access Technologies

In the previous section, we saw 2 methods to separate the uplink and downlinkstreams. Now, if we imagine a cell with several users simultaneously accessing the

64 CHAPTER 3. WCDMA AIR INTERFACE

Figure 3.2: Popular multiple-access methods

services, their individual signals will interfere with each other and cause distur-bance in the transmission and reception. In order to avoid or minimize the effect ofinterference from other users, several multiple access schemes have been designed.

In other words, multiple access technique is a method by which multiple users canshare the same radio resources. This sharing can be in time domain, frequencydomain or in power domain. Hence, we have several options for multiple accessschemes. Some of them are briefly1 mentioned here:

3.2.1 Frequency Division Multiple Access

FDMA is a multiple access scheme where the total frequency spectrum is dividedinto small radio channels and each user is allocated one radio channel. This is one ofthe oldest radio techniques which was used in 1G cellular systems like NMT, C-Nets,AMPS etc. Figure 3.2 shows FDMA principle in the left upper subfigure.

In FDMA, several users use the radio resources at their allocated section of frequencyspectrum.

1The discussion is kept very short because generally these topics are well known.

3.3. UMTS OPERATING BANDS AND SPECTRUM 65

3.2.2 Time Division Multiple Access

In the TDMA multiple access scheme, the time resource is structured into TDMAframes and each frame is further divided into time slots. Each user is allocated onetime slot every TDMA frame. Therefore, in TDMA we can accommodate only asmany users as the number of time slots per TDMA frame. In GSM, such a schemewith 8 slots per frame is used.

In TDMA, several users use the radio resources at their scheduled time intervals.

3.2.3 Code Division Multiple Access

CDMA is the main topic to be discussed in this chapter because air interface tech-nology used in UMTS air interface is based on Wideband CDMA.

In CDMA, several users are allowed to use the same frequency resource at the sametime but their signals are separated by codes. Theoretically, we can accommodateas many simultaneous users as the number of codes. It sounds like magic butthis scheme has its limitation. The communication with acceptable quality can bemaintained as long as the interference at the receiver is within allowed limits. Ifthe interference rises, the transmitter should increase the power to fight against thedisturbance. But the power of UE and Node B are finite. Therefore, CDMA systemsare also called as interference limited systems.

3.2.4 Orthogonal Frequency Division Multiple Access

Orthogonal FDMA is a relatively new technology where different frequencies areallocated to different users. Therefore, it is a frequency division multiple accessscheme but with one basic difference. In OFDMA, the allocated frequency is furtherdivided into smaller sub-carriers which makes it very robust against inter-symbolinterference, multipath fading and other radio disturbances.

Radio access technology used in E-UTRAN (LTE), WiMAX and WLAN is basedon OFDMA principles.

3.3 UMTS operating Bands and Spectrum

Source: 3GPP TS 25.104 ; Base Station (BS) radio transmission andreception (FDD)


The spectrum allocated for IMT-2000 deployment was declared in WRC-92 whichincluded the bands shown in figure 3.3. This is a country-independent data whichmight suit one geographical region but may be conflicting with other radio systemsin another part of world. The allocated spectrum had separate frequency regions ofterrestrial communication systems and mobile satellite communication systems.

Figure 3.3: Operating frequency bands for IMT-2000 System (BAND I)

In the same figure (3.3), the core band of UMTS has also been illustrated whichis chosen by 3GPP for the UMTS deployment in Europe. This figure shows boththe TDD and FDD regions of the UMTS core band. Other than the Core Band orBAND I, UTRA/FDD is designed to operate in the paired bands shown in table3.1. Nominal channel spacing is 5 MHz. The channel raster is 200 kHz for all bands,which means that the center frequency must be an integer multiple of 200 kHz. Thisrule is generally true but for some specific bands, the center frequencies are shiftedby 100 kHz relative to the channel raster. These frequencies are explicitly listed intable 5.0 & 5.1 in 3GPP TS 25.104.

In UTRAN FDD Band I, there is 2× 60 MHz. Hence, there can be 12 FDD carriersin this band. For example, the center of the first carrier will be 1922.4 MHz foruplink and 2112.4 MHz for DL. Similarly, the center of the last carrier in this bandis at 1977.6 MHz for uplink and 2167.6 MHz for downlink.

3.4 Timing in WCDMA

In UMTS, the smallest time unit is called TChip which is equal to 13.84Mcps

= 0.26µs.Quite often, other important time units are specified as multiples of TChip. The three

3.4. TIMING IN WCDMA 67

Operating Band Uplink Freq. Downlink Freq. TX-RXFreq.separation

I 1920-1980 MHz 2110 -2170 190 MHzII 1850 -1910 MHz 1930 -1990 MHz 80 MHzIII 1710-1785 MHz 1805-1880 MHz 95 MHzIV 1710-1755 MHz 2110-2155 MHz 400 MHzV 824 - 849MHz 869-894 MHz 45 MHzVI 830-840 MHz 875-885 MHz 45VII 2500 - 2570 MHz 2620 - 2690 MHz 120 MHzVIII 880 - 915 MHz 925 - 960 MHz 45 MHzIX 1749.9 - 1784.9 MHz 1844.9 - 1879.9 MHz 95 MHzX 1710-1770 MHz 2110-2170 MHz 400 MHzXI 1427.9 - 1447.9 MHz 1475.9 - 1495.9 MHz 48 MHzXII 699 - 716 MHz 729 - 746 MHz 30 MHzXIII 777 - 787 MHz 746 - 756 MHz 31 MHzXIV 788 - 798 MHz 758 - 768 MHz 30 MHzXV - XVIII Reserved Reserved -XIX 830 845 MHz 875 -890 MHz 45 MHzXX 832 - 862 MHz 791 - 821 MHz 41 MHzXXI 1447.9 - 1462.9 MHz 1495.9 - 1510.9 MHz 48 MHz

Table 3.1: UTRAN FDD Bands, reproduced from 3GPP TS 25.104

most important time units discussed in UMTS & HSPA are illustrated in figure 3.4.

Figure 3.4: Time units used in WCDMA air interface

1. Radio Frame: A radio frame is a processing duration which consists of 15 slots.


The length of a radio frame corresponds to 38400 chips. In other words, a radioframe is 10 ms long and can accommodate 38,400 chips.

2. Slot: A slot is a duration which consists of fields containing bits. The length ofa slot corresponds to 2560 chips. Compared to the 2G combination of TDMAframe & Time Slot, 3G uses a combination of Radio Frame & Slot. One RadioFrame of 3G is further divided into 15 Slots but all the times slots are allocatedto the same users. The main purpose of having Slots in 3G is so that controlinformation can be sent to the UE at a regular and very fast interval. Oneslot is 2/3 ms long.

3. Sub-frame: A sub-frame is the basic time interval for E-DCH and HS-DSCHtransmission and E-DCH and HS-DSCH-related signalling at the physicallayer2. The length of a sub-frame corresponds to 3 slots (7680 chips).

3.5 Spreading Principles

UMTS air interface is based on code division multiple access scheme where thebandwidth after spreading is 5 MHz wide. The narrowband signal is converted towideband with the help of a spreading code. The exact details of the codes will beshown in the next section but for the current discussion, they are simply called code.

Figure 3.5 shows 4 users using the same 5 MHz wideband carrier. The time isorganized in 10 ms radio frame. Each user is allowed to transmit or receive in theentire 10 ms period. Therefore, the users are using the same frequency & timedomain resources. It is natural for them to interfere with each other. In order tokeep the interference to a minimum level, it is desirable that each users uses as littlepower as possible. This reduction in power3 is achieved by spreading the wholeenergy over a wide frequency band. The spreading technique allows the operator tosimultaneously allocate the same time and frequency resources to many users.

There are two resources in CDMA world, which are (1) code and (2) power. Let usanalyze them one by one:

1. Codes: In general, the users must be identified by codes. A new user cannot beadmitted until there is a code available for him. Hence, the number of activeusers can be limited by unavailability of codes.

2Please note: Prior to the introduction of HSDPA in 3GPP Rel-5, there was no discussion aboutsub-frame. Therefore, for R99 channels (DCH, FACH, RACH etc.) the term ‘sub-frame’ has nosignificance.

3Power spectral density

3.5. SPREADING PRINCIPLES 69

Figure 3.5: Principle of Spreading

2. Power: Code itself is not enough to allow a radio connection in CDMA.

2.a In Uplink: In Uplink, the received power at the Node B’s receivershould be under the manageable limits. If the interference at the receiverbecomes very high, then the desired signal cannot be reconstructed fromthe received signal. This is a very common reason for blocking in CDMAnetworks. In other words, CDMA systems are interference limited sys-tems.

2.b In Downlink: In Downlink, the transmitted power of Node B is theresource which limits the number of subscribers. With each connecteduser, Node B needs to spend aome finite power for each active user.Therefore, in DL Node B transmit power is the shared resource.

Figure 3.6 illustrates how the spreading & despreading mechanism can be used tosuppress interference. After spreading, when the wideband signal is transmitted,it gets interfered by both narrowband and wideband interference. In the receiver,during despreading, the narrow band interference gets spread and its power spec-tral density gets reduced. After despreading, when the output is passed through alowpass filter then despreaded data signal can be derived.

The received data signal can be used to regenerate the actual data only if the receivedbit energy is greater than the overall noise energy by at least Eb

No[dB].

If CDMA is successfully used in commercial networks, it should be robust againstthe interference from the other user interference. This principle is illustrated infigure 3.7. For example, imagine that the transmitter shown in this picture depictsthe transmitter in Node B, which spreads the data for user 1 with code # 1 anddata for user 2 with code # 2. As expected, the spread signal for both the users willinterfere at the radio interface. Now, the User 1 will try to despread the received


Figure 3.6: Spreading and despreading to suppress the interference

signal with code # 1. UE has the knowledge about the codes by prior signallingwith RNC.

As a result of despreading, the data of user 1 can be reconstructed. In the samefigure, we can see that spread signal of user 2 does not get despreaded at the receiverof UE 1. This is possible if:

• Code # 1 and code # 2 are orthogonal to each other. [AND]

• Codes at the transmitter and receiver are synchronized to each other.

In commercial cellular networks, operators want that one cell should cover a largegeographical area. In other words, communication should be possible between basestation and a distant user equipment. This can be achieved if the sensitivity ofthe base station and user equipment is good. While performing despreading, thereceiver can manifold amplify the received signal. This gain is called Processinggain. Processing gain can be mathematically expressed as:

Processing Gain = 10 · log 3.84 Mcps

Rbit

[dB]

3.5. SPREADING PRINCIPLES 71

Figure 3.7: Multiple access using different codes for 2 users

Figure 3.8: Processing gain at the receiver side

Figure 3.9 shows a fast code sequence whose symbol duration is fixed by 3GPP


specifications. This small symbol is called a chip. According to 3GPP, in onesecond, there can be 3.84 million such chips. Hence, each chip is 0.26 µs long.

The channelization codes used for spreading always use this fast code. As a result,the product is always 3.84 Mcps. The bandwidth required to transmit this fastwaveform is also very large. In UMTS, the licensed bandwidth is 5 MHz but theeffective transmission takes place in 3.84 MHz.

Figure 3.9 also illustrates that for various services, the symbol rate can vary but thechip rate is always constant and fixed.

• For a high bit rate service, the symbol duration is short. Therefore,the SF is also small.

• For a low bit rate service, the symbol duration is very large andtherefore, the SF is also very high.

• In other words Bit Rate ∝ 1

SF

Figure 3.9: Effect of SF on bitrate and symbol duration

3.6 Codes in UMTS

Source: 3GPP 25.213 Spreading and Modulation (FDD)

3.6. CODES IN UMTS 73

According to the definition used by 3GPP TS 25.213, spreading consists of twooperations. The first is the channelization operation, which transforms every datasymbol into a number of chips, thus increasing the bandwidth of the signal. Thesecond operation is the scrambling operation, where a scrambling code is applied tothe spread signal. Hence, there are two types of codes used in UMTS.

1. Scrambling Codes: Scrambling codes do not perform any spreading of band-width. These codes are used to super-impose the identity of transmitter on thephysical layer signals. Scrambling codes are not orthogonal. They are derivedusing sequence generators consisting of shift registers.

2. Channelization Codes: According to section 4.3.1.1 of 3GPP TS 25.213, theChannelization codes are the codes which perform spreading of bandwidth.Therefore, sometimes, these codes are also called as spreading code. Channel-ization codes define the user bit rate. These codes are Orthogonal VariableSpreading Factor (OVSF) codes that preserve the orthogonality between auser’s different physical channels. The OVSF codes can be defined using thecode tree shown in figure 3.10.

The number of chips per data symbol is called the Spreading Factor (SF).

3.6.1 Channelization Code

Channelization Codes have similar properties in DL and UL. As stated earlier,

Bit Rate ∝ 1

SF. Therefore, the user bit rate is defined by the channelization code.

• In UL, Channelization codes are used to separate control and data chan-nels from the same UE (DPDCH and DPCCH).

• In DL, Channelization codes are is used to separate the users within acell.

In order to calculate the L1 data rate for each spreading factor, we use followingformula:

Symbol Rate =Rchip

SF=

3.84Mcps

SF

It will be explained in the next section that UL modulation is BPSK and DL mod-ulation is QPSK. Therefore, for the same SF, UL & DL bit rates are different. ForQPSK, one symbol corresponds to two bits whereas in BPSK one symbol equals onebit only. This concept is illustrated in Table 3.2.


SFSymbol Rate (ksps)

=[Rchip

SF

]=

[3.84Mcps

SF

] bit rate (kbps) on DLDPCH

bit rate (kbps) on ULDPDCH

512 7.5 15 -256 15 30 15128 30 60 3064 60 120 6032 120 240 12016 240 480 2408 480 960 4804 960 1920 960

Table 3.2: SF and the corresponding L1 bitrate

Figure 3.10: Code Tree for generation of Orthogonal codes

3.6.2 Scrambling Code

As stated earlier in the introduction part, the scrambling codes do not performany spreading of bandwidth. These codes are used to super-impose the identity oftransmitter on the physical layer signals. As a result of scrambling, some ‘0’s become‘1’s and some ‘1’s become ‘0’s, but the time-duration of each chip does not alter.Hence, the scrambling procedure does not affect the bandwidth of the transmittedsignal. Spreading is achieved by Channelization code alone. The following sectionstries to investigate the usage of scrambling codes in UL and DL.


UL Scrambling Codes

UL Scrambling codes are used as user identity in Uplink. All uplink physical chan-nels are scrambled with a complex-valued Scrambling code. The dedicated physicalchannels may be scrambled by either a long or a short scrambling code.

There are 224 long and 224 short uplink scrambling codes. The usage of longscrambling codes in UL is very popular. Therefore, in this book we willonly discuss the long codes. The sequence generator used to generate the longUL scrambling codes is shown in figure 3.11. The shift registers with 24 bit delaycapability and can be used to create 224 − 1 or 16.7 Million UL scrambling codes.

Uplink scrambling codes are assigned by RRC signalling.

Figure 3.11: Configuration of uplink scrambling sequence generator

DL Scrambling Codes

DL (primary) scrambling codes are used as a physical layer cell-id in UMTS. The DLscrambling codes are generated using the sequence generator shown in figure 3.12.There are 18 shift registers in the sequence generator. Hence, we can get a total of218 − 1 = 262, 143 scrambling codes. But not all of the SC are used. Only 8192DL scrambling codes are allowed in UMTS which are further divided into512 groups.

Each group contains one primary Scrambling code and 15 secondaryscrambling codes. Figure 3.14 illustrates this arrangement.

The Scrambling code sequences are constructed by combining two real sequences into


Figure 3.12: Configuration of downlink scrambling sequence generator

a complex sequence. Each of the two real sequences are constructed as the positionwise modulo 2 sum of 38400 chip segments of two binary m-sequences generatedby means of two generator polynomials of degree 18. The resulting sequences thusconstitute segments of a set of Gold sequences. The scrambling codes are repeatedfor every 10 ms radio frame.

The primary scrambling codes n : n = 16 ∗ i where i = 0 . . . 511

The i:th set of secondary scrambling codes: 16 ∗ i+ k, where k = 1 . . . 15

Each cell is allocated one and only one primary Scrambling code. The primaryCCPCH, primary CPICH, PICH, AICH and S-CCPCH carrying PCH shall alwaysbe transmitted using the primary scrambling code. The other downlink physicalchannels may be4 transmitted with either the primary scrambling code or a sec-ondary scrambling code from the set associated with the primary scrambling codeof the cell.

The set of primary scrambling codes is further divided into 64 Scrambling codegroups, each consisting of 8 primary scrambling codes. The j:th scrambling codegroup consists of primary scrambling codes 16*8*j+16*k, where j=0..63 and k=0..7.

4Use of secondary scrambling code is not very popular in practice. Therefore, this book willfurther assume that in DL only primary scrambling code is used.


Figure 3.13: Total 8192 DL Scrambling Codes and 512 Primary SC

Figure 3.14: 512 SC divided into 64 Groups of 8 codes each


3.6.3 Summary of Scrambling Codes

In the last few sections, the details about channelization and scrambling codes weregiven. Table 3.3 shows a brief summary of the codes in UMTS.

• In UL, the users are separated by using different UL scrambling codes.There are 224 - 1 = 16.7 Million UL scrambling codes. RNC allocatesone SC to one user at connection setup. SC are unique within oneRNC area. The number of SC available in one RNC are defined by thehardware capacity of RNC.

• In DL, the cells are separated by DL scrambling codes. There are 512primary scrambling codes which are organized in 64 code groups having 8codes per group ( 64 × 8 = 512)). DL SC are planned by radio planners.

3.6.4 Summary of Codes in UMTS

At this point, it is quite normal for the readers to feel confused and lost in details.Therefore, table 3.3 shows the summary of the previous section by highlighting themain aspects of the codes used in UMTS.

Scrambling Code Channelization Code

UsageUL: User Id UL: To separate control and data

channels from UEDL: Cell Id DL: User Id

Spreading Does not perform spreading Performs spreading

# of codesUL : 16.7 Million UL: Depends on the SF ( 256 ,. . . ,

4)DL : 8192 (512 Primary SC and therest are secondary SC)

DL: Depends on the SF (512,. . . , 4)

Orthogonality Non-orthogonal Orthogonal

LengthUL : There are 2 options

• Option 1: long Codes 38400chips

• Option 2: Short codes 256 chips

UL: 4 to 256 chips

DL: 10 ms (38400 Chips) DL: 4 to 512 chips

Code Genera-tion

Using Shift Register based sequencegenerator

Using Walsh Code Tree matrix

Table 3.3: Main aspects about the codes used in UMTS

3.7. MODULATION 79

3.7 Modulation

The modulation schemes used in UMTS uplink and downlink are illustrated infigure 3.15. The same figure also shows the codes used in spreading and scrambling.For example, in UL, we use user-specific scrambling codes and in DL, cell-specificscrambling code.

Figure 3.15: Spreading and Modulation in UL & DL

• The modulation used in downlink is Quadrature Phase Shift Keying (QPSK)which involves 2 bits per symbol. For example,

SF = 256 ⇒ 15 ksps = 30 kbps

• The modulation used in uplink is Binary Phase Shift Keying (BPSK ) whichinvolves 1 bits per symbol. For example,

SF = 256 ⇒ 15 ksps = 15 kbps

Figure 3.15 illustrates the spreading and modulation for the uplink dedicated phys-ical channels & DL dedicated channel. In Uplink, data modulation is dual branchQPSK, that is, the I and Q channels are used as two independent BPSK channels.


Copyright Notices



Text about UMTS operatingBands on page 66

Section 5.4.1 & 5.4.2 of 3GPP TS 25.104v9.6.0

Table 3.1 on page 67 Table 5.0 of 3GPP TS 25.104 v9.6.0c⃝2011. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

Figure 3.11 on page 75 Figure 5 of 3GPP TS 25.213 v 8.4.0Figure 3.12 on page 76 Figure 10 of 3GPP TS 25.213 v 8.4.0Text in section 3.6 on page 72 Section 4.1 of 3GPP TS 25.213 v 8.4.0Text in section 3.6 on page 73 Section 4.3.1.1 of 3GPP TS 25.213 v 8.4.0Text about UL Scrambling Codeson page 75

Section 4.3.2.1 of 3GPP TS 25.213 v 8.4.0

Text about DL Scrambling Codeson page 75

Section 4.1 of 3GPP TS 25.213 v 8.4.0

Text in section 3.4 on page 66 Section 5 of 3GPP TS 25.211 v 9.1.0c⃝2009. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

BIBLIOGRAPHY

[1] 3GPP TS 25.201 ver. 6.0.0 ;‘Physical layer - General description’

[2] 3GPP TS 25.211 ver. 6.0.0 ;‘Physical channels and mapping of transport chan-nels onto physical channels (FDD)’

[3] 3GPP TS 25.212 ver. 6.0.0 ;‘Multiplexing and Channel Coding (FDD)’

[4] 3GPP TS 25.213 ver. 6.0.0 ;‘Spreading and Modulation (FDD)’

[5] 3GPP TS 25.214 ver. 6.0.0 ;‘Physical Layer Procedures (FDD)’

[6] 3GPP TS 25.104 ver. 6.0.0 ;‘Base Station (BS) radio transmission and reception(FDD)’


[8] Chris Johnson, ‘Radio Access Networks For UMTS ; Principles AndPractice’ , John Wiley & Sons.

81

CHAPTER

4

LOGICAL, TRANSPORT & PHYSICALCHANNELS

In order to master the fundamentals of 3G radio transmission and reception, it isessential to get acquainted with the channels used in UMTS and HSPA. Channelsare simply a method to organize the information into some categories dependingon some common aspects. This chapter is written to provide the most essentialdetails about them. According to UTRAN specifications, there are three hierarchiesof channels.

• Logical channels

• Transport channels

• Physical channels

The concept of channel was used in GSM as well. In 2G, there are logical andphysical channels. The concept of Transport channel is new in UMTS. This pagetries to illustrate the difference between the three types of channels and later in thischapter more details can be found about each of them.

A Logical channel is used to describe what type of information is being

transported by it (e.g., control signalling or user data).

82

4.1. CHRONOLOGY: FIRST 3G AND THEN 3.5G 83

A Transport channel is used to describe the characteristics with which it

transports the information carried by it (e.g., using common channels of the

cell or dedicated channels especially allocated to one user).

A Physical channel is used to describe the physical aspects of it (e.g., fre-

quency, scrambling code, channelization code and slot format).

4.1 Chronology: First 3G and then 3.5G

As we all know, 3G is constantly evolving and getting better with each 3GPP release.Therefore, we should study the changes in chronological order. It is highly recom-mended that readers must try to learn channels in the same order. The learningbecomes much easier if we break the whole process in three steps.

Step 1, R99 Channels: R99 channels are the topic of this particular chapter.Here, we will discuss common control channels and dedicated channels ofUMTS.

Step 2, HSDPA Channels: HSDPA channels will be discussed in chapter 7. Allthe channels which have something to do with HSDPA, start with HS-. Thereare only 3 new channels introduced in Rel-5 for HSDPA operation.

Step 3, HSUPA Channels: HSUPA channels will be discussed in chapter 8. Allthe channels which have something to do with HSUPA, start with E-. Thereare only 5 new channels introduced in Rel-6 for HSUPA operation.

As we can see, there will be a lot of channels to learn and discuss. Therefore, wewill start building our knowledge on the strong foundation of R99 UMTS channels.

4.2 Logical Channels

Source: 3GPP TS 25.301, 25.211, 25.212, 25.213

As explained in the first section of this chapter, Logical channels are used to describewhat is being transported. According to 3GPP TS 25.301, logical channels aredivided into two groups:

1. Control channels: for the transfer of control plane information, &

84 CHAPTER 4. LOGICAL, TRANSPORT & PHYSICAL CHANNELS

2. Traffic channels: for the transfer of user plane information.

Figure 4.1 illustrates the distribution of uplink and downlink logical channels. It canbe seen that there are 6 logical channels in UMTS, 2 for traffic and 4 for control plane.Some of these channels are only in DL e.g., (BCCH, PCCH and CTCH) whereas theother 3 channels are bidrectional (CCCH, DCCH and DTCH). Splitting the analysisin DL and UL makes it much easier to understand.

While describing the logical channels, we do not discuss the issues about power, bitrates, bit error rate, block error rates, etc. At this level, we only consider the natureof data being transported.

Figure 4.1: UL & DL Logical channels

4.2.1 Logical Channels for Control Plane Information

In this section, all 6 logical channels are described.

1. BCCH, Downlink only ↓ BCCH channel is used for system control informa-tion broadcasting. It exists only in the downlink.

4.2. LOGICAL CHANNELS 85

2. PCCH, Downlink only ↓ PCCH channel is used to transmit the paging mes-sages. RNC can generate paging after getting the paging requests from corenetwork or generate the paging by itself to page the packet-switched users whoare in RRC power saving stand-by states.

3. CCCH, Uplink and Downlink ↕ CCCH is a bi-directional channel. It carriescontrol information between the network and the UE. This channel is used bythose UEs which access a new cell after cell re-selection as well as by UEswhich do not have a RRC connection.

4.DCCH, Uplink and Downlink ↕ This is a point-to-point bi-directional chan-nel which is set up in the RRC connection establishment procedure. It carriesdedicated control information between RNC and the UE.

4.2.2 Logical Channels for User Plane Information

5. CTCH, Downlink only ↓ This point-to-multipoint channel is used to carrydedicated information in the downlink to all or a group of UEs. For example,stock market updates, sports results, weather updates, business promotionsand service area broadcast.

6. DTCH, Uplink and Downlink ↕ DTCH is a dedicated point-to-point chan-nel which can be used in the uplink as well as in the downlink. This channelcarries user traffic like CS speech, video, streaming video, emails with andwithout attachments, file transfer etc.

As a quick summary, table 4.1 lists all the logical channels. In this table, we can seewhich channels are used to carry control data and which channels for traffic. Thesame table also shown whether the channels are unidirectional or bidirectional.

Logical Channels for Control Plane

1. BCCH Broadcast Control Channel DL only2. PCCH Paging Control Channel DL only3. CCCH Common Control Channel UL & DL4. DCCH Dedicated Control Channel UL & DLLogical Channels for User Plane

5. CTCH Common Traffic Channel DL only6. DTCH Dedicated Traffic Channel UL & DL

Table 4.1: List of all Logical channels in UMTS


4.3 Transport Channels

Source: 3GPP TS 25.301, 25.302, 25.321

The main task of a transport channel is to describe the characteristics with whichthe data will be transported. At this moment, it is quite normal for the readers todoubt why do we need transport channels?

As we have seen in the previous section, there is only one logical channel DTCH fordescribing the one-to-one user traffic, for example, voice, video, streaming and NRTdata. We cannot expect the transport conditions of CS voice and FTP file transferbe same. Typically, there are the following preferences:

• CS Voice needs low but constant bit rate with strict delay requirements. Voiceservice is insensitive to bit error rates and we do not re-transmit the speechframe in case of errors.

• File transfer requires high bit rate which can tolerate the bit-rate fluctua-tions. The end-to-end delay can also be flexible but file transfer is very strictabout bit errors which are achieved using negative acknowledgements and re-transmissions.

Furthermore, the packets sessions can be of various natures:

1. Packet session with small amount of infrequent data transmission.

2. Packet session with high amount of data transmission.

3. Packet session with small amount of packets but very frequently transmitted.

Medium Access Control Layer (MAC) in RNC & UE is responsible for map-

ping logical channels to transport channels. This procedure is illustrated in

figure 4.2.

Hence, one can argue that UMTS needs different types of transport channels tofulfill the different types of needs. There are 2 types of transport channels definedfor UMTS.

• 1. Common transport channels

• 2. Dedicated transport channels

4.3. TRANSPORT CHANNELS 87

Figure 4.2: UL & DL Transport channels ; Logical � Transport channel mapping

Common Transport Channels

BCH Broadcast Channel DL onlyPCH Paging Channel DL onlyFACH Forward Access Channel DL onlyRACH Random Access Channel UL onlyDedicated Transport Channels

DCH Dedicated Channel UL & DL

Table 4.2: List of all Transport channels in UMTS1

4.3.1 Common Transport Channels

In the common transport channels, if UE addressing is required, then explicit ad-dressing is used.

BCH BCCH V BCH. (Logical channel BCCH is mapped on the transport channelBCH.) The Broadcast Channel (BCH) is a downlink transport channel that isused to broadcast system- and cell-specific information. The BCH is always


transmitted over the entire cell and has a single transport format.

PCH PCCH V PCH. (Logical channel PCCH is mapped on the transport channelPCH.) The Paging Channel (PCH) is a downlink transport channel. ThePCH is always transmitted over the entire cell. The transmission of the PCH isassociated with the transmission of physical-layer generated Paging Indicators,to support efficient sleep-mode procedures.

RACH RACH is a well-known name for people who are familiar with 2G. In GSM,RACH is used to make the initial access to the network and ask for dedicatedsignalling resources. Here in 3G also, the same functions are performed byRACH channel.

But in UMTS, RACH can also be used to transmit small amount of NRT PSdata in uplink2. Hence, RACH can generate some revenue for the operator.

FACH In 2G, the answer to RACH is received on Access Grant Channel AGCH.In UMTS, the same task has been given to Forward Access Channel (FACH).Hence, FACH is used to inform the users about allocated dedicated signallingresources in response to the RACH request.

But in UMTS, FACH can also be used to transmit small amount of NRT PSdata in downlink3. Hence, FACH can generate some revenue for the operator.

4.3.2 Dedicated transport channels

Dedicated Channel DCH is a transport channel allocated to one UE. It can beused either for uplink or downlink. This channel is controlled through the innerpower control. DCH bit rate is variable depending on the channel conditionsand the allocated bearer. Bit rate variations can be performed every 10 ms.

4.4 Physical Channels

According to 3GPP TS 25.211, a physical channel is defined by:

• a specific carrier frequency,

• scrambling code,

• channelization code,

23G RACH = 2G RACH + Small amount of UL NRT PS traffic.33G FACH = 2G AGCH + Small amount of DL NRT PS traffic.

4.4. PHYSICAL CHANNELS 89

• time start & stop (giving a duration) &

• on the uplink, relative phase (0 or π/2).

Scrambling and channelization codes are specified in chapter 3. Time durations aredefined by start and stop instants, measured in integer multiples of chips. Suitablemultiples of chips also used in specification are:

Figure 4.3: Slot, Subframe and Radio Frame as used in WCDMA

1. Radio frame: A radio frame is a processing duration which consists of 15 slots.The length of a radio frame corresponds to 38400 chips or 10 ms.

2. Slot: A slot is a duration which consists of fields containing bits. The length ofa slot corresponds to 2560 chips or 2/3 ms.

3. Sub-frame: A sub-frame is the basic time interval for E-DCH and HS-DSCHtransmission and E-DCH and HS-DSCH-related signalling at the physicallayer. The length of a sub-frame corresponds to 3 slots (7680 chips) or 2ms.

Physical layer (L1) in Node B & UE is responsible for mapping transport

channels to physical channels. This procedure is illustrated in figure 4.4.

As shown in figure 4.4, there are some physical channels which do not have anycorresponding transport or logical channels. These channels are, in fact, physicalsignals which are generated by physical layer of transmitter (e.g., Node B) and usedby the physical layer of the receiver (e.g., UE). The scope of these channels arerestricted to only physical layer. These physical channels exist to support somespecial functions of physical layer e.g., synchronization, channel estimation etc.


The default time duration for a physical channel is continuous from the instantwhen it is started to the instant when it is stopped. Physical channels that are notcontinuous will be explicitly described.

UMTS has been designed in such a way that physical layer maps various transportchannels to physical channels. When more than one transport channel is multi-plexed, this composite channel is called composite coded transport channel (CC-TrCH). This composite transport channel (CCTrCH) is mapped to the data part ofa physical channel. In addition to data parts, there also exist control parts whichare locally generated and inserted by the physical layer.

Figure 4.4: UL & DL Physical channels ; Transport � Physical channel mapping

In chapter 3, the basics about channelization and scrambling were discussed. Theunique combinations of these codes works as the identity of various physical channels.

Example: Let us consider two physical channels and investi-gate their physical layer attributes. First channel is the Primary-common pilot channel (P-CPICH) of the cell and the second one a DLdedicated physical channel (DPCH) allocated to a specific user.

• P-CPICH is a physical channel that uses


– Frequency FDL, that has been assigned to the cell by radioplanner,

– Scrambling code SCCell, assigned by the planner while radioplanning,

– & the Channelization Code4, CC256, 0.

• Downlink DPCH allocated to a particular user is a physical channelthat uses

– Frequency FDL, that has been assigned to the cell by radioplanner,

– Scrambling code SCCell, assigned by the planner while radioplanning,

– & the Channelization Code5, CCSF, Code Number which is allo-cated by RNC at the time of call or session setup.

There are a lot of physical channels defined for UMTS. In order to make the under-standing easier, we will discuss them in four groups:

1. UL Common Channels: PRACH

2. UL Dedicated Channels: DPDCH and DPCCH

3. DL Common Channels: P-SCH, S-SCH, P-CPICH, P-CCPCH, S-CCPCH,AICH and PICH

4. DL Dedicated Channels: DPCH

Please refer to figure 4.5 and table 4.3 to keep an overview about the physicalchannels. There is only one UL common channel and there are 2 UL dedicatedchannels. Similarly in DL, there are 7 common channels and one dedicated channels.

4.4.1 UL Common Channel

There is only one UL common physical channel PRACH. The next section explainsmore details about it.

4This is a standard code which is used in all UMTS networks for primary-common pilot channel(P-CPICH).

5Here SF is decided based on the allocated bit rate while code number is a random choice basedon the codes availability.


DL Common Channels UL Common Channels

P-SCH Primary Synchronization Ch.

PRACH Physical Random Access Ch.

S-SCH Secondary Synchronization Ch.P-CPICH Primary Common Pilot Ch.P-CCPCH Pri. Common Control Physical Ch.S-CCPCH Sec. Common Control Physical Ch.PICH Paging Indication Channel Ch.AICH Acquisition Indication Channel Ch.

DL Dedicated Channels UL Dedicated Channels

DPCH Dedicated Physical ChannelDPDCH Dedicated Phy. Data Ch.DPCCH Dedicated Phy. Control Ch.

Table 4.3: List of all R99 Physical channels

Figure 4.5: Summary of all R99 Channels

Physical Random Access Channel (PRACH)

In section 4.3, we discussed about an UL transport channel RACH. Physical layerof UE maps this transport channel to a physical channel called ‘Physical Random


Access CHannel (PRACH)’. Therefore, PRACH is used by user for making initialcontact with the UTRAN and also to transmit some small amount of non-real time(NRT) data.

PRACH physical channel can be used to carry transport channel RACH, whichin turn, carries logical channel DTCH and CCCH.

Logical Ch. V Transport Ch. V Physical Ch.

CCCH V RACH V PRACH

DTCH V RACH V PRACH

While making the initial access to UTRAN, UE has no idea about the amount thetransmitted power which is sufficient to reach Node B. Therefore, the UE uses amechanism called Open Loop Power Control. This mechanism is explained in fulldetails in chapter 5 in section 5.7.1. This procedure is illustrated in figure 4.6.

Figure 4.6: PRACH procedure in UMTS

In short, this procedure can be summarized as following.

Step 1: UE transmits a PRACH preamble with a very small power which is calcu-lated by UE, based on path loss calculations and some system parameters.

Step 2: UE waits for the response to this preamble on a DL channel called ‘Acqui-sition Indication Channel’ (AICH). At this point, 3 scenarios can take placewhich are explained in the step 3-a, 3-b & 3-c.


Step 3-a: If there is a positive response from Node B on AICH, UE sends thePRACH message part. Using this message, UE informs RNC about its inten-tions and asks for dedicated resources.

Step 3-b: If there is no response from Node B on AICH, then UE ramps up thetransmission power and sends another preamble. UE keeps on ramping itspreamble power until it hears a reply from Node B.

Step 3-c: If there is a negative response from Node B on AICH, UE aborts therandom access procedures.

The preamble is a sequence of 16 chips which are repeated 256 times. Hence, thelength of a PRACH preamble is 256 × 16 = 4096 chips. Table 4.4 shows all the 16preamble signature sequences defined by 3GPP. This table can be found in 3GPP TS25.211. Operators can define how many and which preambles are allowed to be usedin a cell and broadcast this information using system information. UE randomlyselects one of the allowed preamble signatures and forms its preamble.

PreambleSignature

Sequence

P0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

P1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1

P2 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1

P3 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1

P4 1 1 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1

P5 1 -1 1 -1 -1 1 -1 1 1 -1 1 -1 -1 1 -1 1

P6 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 1 1

. . . . . .

P14 1 1 -1 -1 -1 -1 1 1 -1 -1 1 1 1 1 -1 -1

P15 1 -1 -1 1 -1 1 1 -1 -1 1 1 -1 1 -1 -1 1

Table 4.4: PRACH preamble signatures

4.4.2 DL common Channel

There are 7 DL common channels which are referred to as R99 common channels.The next sections discuss some essential details of these channels. Each section isnumbered from one to seven for convenience.


1. P-SCH

At switch-on, UE looks for P-SCH and tries to identify the beginning of atime slot by using a globally unique code called primary synchronizationcode. Hence, P-SCH is the starting point of all UMTS activities.

The Synchronization Channel (SCH) is a downlink signal used for cell search. TheSCH consists of two sub channels, the Primary and Secondary SCH. The 10 msradio frames of the Primary and Secondary SCH are divided into 15 slots, each oflength 2560 chips. Figure 4.8 illustrates the structure of the SCH radio frame.

P-SCH is transmitted for only first 10% of each slot. One slot corresponds to 2/3 msor 2560 chip. Therefore, P-SCH consists of a unique code, Primary SynchronizationCode (PSC) which is modulated and transmitted at the beginning of every slot.This is illustrated in figure 4.8. The PSC is the same for every cell in the UMTSsystem irrespective of the country or operator. The value of code itself goes beyondthe scope of our discussion. If you are interested in knowing more about the PSC,please refer to section 5.3.3.5 of 3GPP TS 25.213.

Figure 4.7: Timing of Synch. Channels; sent on the first 10 % of every slot

At the beginning, UE is not synchronized to the Node B timing. Therefore, it isimpossible to perform spreading and scrambling. Hence, P-SCH is sent without anyspreading. In other words, P-SCH does not consume any channelization code.

2. S-SCH

After finding the beginning of Slot using P-SCH, UE searches for S-SCH andtries to identify the beginning of radio frame by using a sequence of sec-ondary synchronization code. This sequence is shared by all cells belong-ing to that scrambling code group.


SC GroupSlot #

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Group 0 1 1 2 8 9 10 15 8 10 16 2 7 15 7 16Group 1 1 1 5 16 7 3 14 16 3 10 5 12 14 12 10Group 2 1 2 1 15 5 5 12 16 6 11 2 16 11 15 12Group 3 1 2 3 1 8 6 5 2 5 8 4 4 6 3 7Group 4 1 2 16 6 6 11 15 5 12 1 15 12 16 11 2Group 5 1 3 4 7 4 1 5 5 3 6 2 8 7 6 8

...

. . .

. . .

. . .Group 61 9 10 13 10 11 15 15 9 16 12 14 13 16 14 11Group 62 9 11 12 15 12 9 13 13 11 14 10 16 15 14 16Group 63 9 12 10 15 13 14 9 14 15 11 11 13 12 16 10

Table 4.5: Table 4: Allocation of SSCs for secondary SCH (from TS 25.213)

Just like P-SCH, the Secondary SCH is also transmitted in the first 10 % of eachtime slot only. The information transmitted on S-SCH repeats after every 15 slots.Therefore, S-SCH is transmitting a unique sequence of secondary synchronizationcodes. These sequences are well defined in 3GPP TS 25.2136.

SSC is a 256 chip long sequence and there are only 16 Secondary SynchronizationCodes (SSC). By arranging them in different order, different sequences could beformed. As we know, there are 64 primary scrambling code groups. Therefore,there are only 64 sequences defined for secondary synchronization codes, as shownin table 4.5.

From table 4.5, one can say “if a cell belongs to scrambling code group # 0,the it will broadcast SSC # 1 on slot #0, SSC # 1 on slot # 1, . . . , SSC # 16on slot # 14 of S-SCH channel.” Similarly for a cell belonging to scramblingcode group # 63, S-SCH will broadcast SSC # 9 on slot # 0, , SSC # 12 onslot # 1, . . . , SSC # 10 on slot # 14. This principle is illustrated in figure4.8.

Just like P-SCH, S-SCH is also transmitted without any spreading. Hence, S-SCHalso does not consume any channelization code.

This sequence on the Secondary SCH indicates which of the code groups the cell’sdownlink Scrambling code belongs to. In the cell-search procedure, from 512 options

63GPP TS 25.213, section ’Code allocation of SSC’


Figure 4.8: Content of Primary and Secondary SCH ; PSC and SSC

UE has narrowed down to 8. There are 8 cells which belong to one SC group.Therefore, the information on S-SCH is the same in all the cells of one SC Group.4.5 is copied from 3GPP TS 25.213.

As shown in figure 4.9, the radio planners have two choices while allocating SC to anew cell.

Minimize the # of SC Groups: In this scheme, the neighbouring cells are allo-cated the SC from the same group. Once the SC in that group are all used,then they start with the next group. This scheme is shown as Option 1 infigure 4.9.

Minimize the # of SC Groups: In this scheme, the neighboring cells are allo-cated the SC from two different groups. When all 64 Groups have been used,then they go to the first group again and pick the next SC from that group,and so on. This is shown as Option 2 in figure 4.9.


Figure 4.9: Cells belonging to the same SC group can be adjacent or distant

3. Primary Common Pilot Channel (P-CPICH)

P-CPICH, or simply ‘Pilot channel’, is probably the most commonly dis-cussed channel by radio planners and optimizers. P-CPICH is used for SCidentification and channel estimation. If this channel’s received level is notsatisfactory, UE tries for cell reselection or handover. P-CPICH is measuredby 2 quantities, CPICH RSCP [dBm] & CPICH Ec/No [dB].

The Primary Common Pilot Channel (P-CPICH) has the following characteristics:

• The same channelization code is always used for the P-CPICH (Cch,256,0)7,

• The P-CPICH is scrambled by the primary scrambling code of the cell,

• There is one and only one P-CPICH per cell, and

• The P-CPICH is broadcasted over the entire coverage area of the cell.

Due to its fixed SF (256), the bit rate of this DL control channel is also fixed.P-CPICH can carry 30 kbps information.

7Cch,256,0 = [1 1 1 1 1 1 1 1 1 1 . . . 1 1 1 1], or 256 chips long sequence of all 1’s


Figure 4.10: Primary Common Pilot Channel

The Primary CPICH is a phase reference for the following downlink channels: SCH,Primary-CCPCH, AICH, PICH and the Secondary-CCPCH. By default, the Pri-mary CPICH is also a phase reference for downlink DPCH.

4. P-CCPCH

Although P-CCPCH is a complicated name but it is simply a physical channelwhich is used to bring system information from UTRAN to UE.

CCCH V BCH V P-CCPCH

The Primary CCPCH is a DL control channel which has a fixed SF=256 & a fixedrate 30 kbps. This downlink physical channels used to carry the BCH transportchannel (system information).

As shown in figure 4.11, the Primary CCPCH is not transmitted during the first256 chips of each slot. Instead, Primary SCH and Secondary SCH are transmittedduring this period. Hence, P-CCPCH has an activity factor of 90% which reducesthe effective bit rate to 27 kbps. System information is organized in blocks knownas System Information Block or SIB # N where N = 1, 2, 3,. . . .

5. S-CCPCH

S-CCPCH can be compared to Swiss Army Knife which is one tool thatperform several functions.

BCCH V FACH V S-CCPCH


Figure 4.11: Primary-CCPCH Structure: ON & OFF periods

DCCH V FACH V S-CCPCH

DTCH V FACH V S-CCPCH

CTCH V FACH V S-CCPCH

CCCH V FACH V S-CCPCH

and

PCCH V PCH V S-CCPCH

S-CCPCH physical channel carries FACH and PCH transport channels. Therecould be 1, 2 or more S-CCPCH per cell.

The Secondary CCPCH is used to carry the FACH and PCH. The frame structureof the Secondary CCPCH is shown in the figure 4.12 above.

S-CCPCH can have a spreading factor in a range from 256 to 4. As usual, the usedspreading factor decides the total number of bits per downlink Secondary CCPCHslot.

The FACH and PCH can be mapped to the same or to separate Secondary CCPCHs.By having separate S-CCPCHs for FACH & PCH, the physical layer overhead in-creases but the paging & FACH capacity can be increased.

• The main difference between a S-CCPCH and a downlink dedicated physicalchannel (DPCH) is that an S-CCPCH is not inner-loop power controlled.

• The main difference between the Primary and Secondary CCPCH is that thetransport channel mapped to the Primary CCPCH (BCH) can only have afixed predefined transport format combination, while the Secondary CCPCHsupport multiple transport format combinations using TFCI.


Figure 4.12: Secondary Common Control Physical Channel

Figure 4.13: Paging Process in UMTS; First Paging Indication & then Paging

6. PICH

PICH is a wake-up call which carries either ‘1’ or ‘0’. Each idle mode UEkeeps on monitoring PICH on periodic intervals.

If PICH = ‘1’: UE wakes up and reads the PCH on S-SCCPCH which fol-lows 3 slots after PICH.

If PICH = ‘0’: UE stays idle and checks PICH on the next PICH occasion.

Figure 4.13 illustrates the two step paging process in UMTS. First the UEs in sleep-ing mode wake up and read the paging indicator channel (PICH). If there is a pagingindicator, they read the S-SCCPH and decode the paging message which carries UEidentity (e.g., IMSI).

The Paging Indicator Channel (PICH) is a fixed rate (SF=256) physical channel usedto carry the paging indicators. The PICH is always associated with an S-CCPCHto which a PCH transport channel is mapped.

Figure 4.14 illustrates the frame structure of the PICH. One PICH radio frame oflength 10 ms consists of 300 bits (b0, b1, . . . ,b299). Of these, 288 bits (b0, b1, . . . ,


Figure 4.14: Slot format of PICH for Np = 18, 36, 72 and 144

b287) are used to carry paging indicators. The remaining 12 bits are not formallypart of the PICH and shall not be transmitted.

In each PICH frame, Np paging indicators, where Np =18, 36, 72, or 144.

Further, the PI calculated by higher layers is associated with the value of the pagingindicator Pq. If a paging indicator in a certain frame is set to “1” it is an indicationthat UEs associated with this paging indicator and PI should read the correspondingframe of the associated S-CCPCH.

7. AICH

AICH channel is used to inform UE that its PRACH preamble has been ac-quired by Node B. From this, UE concludes that the currently used trans-mission power is sufficient to communicate with Node B. At this point, OpenLoop Power Control is finished.

AICH is a common DL channel whose operation is closely related to UL PRACHchannel. As shown in figure 4.6, the response to the successful PRACH preambleis sent on the AICH channel. Hence, AICH is a channel that carries AcquisitionIndicators (AI). The Acquisition Indicator channel (AICH) is spreaded by a fixedSF = 256. Acquisition Indicator AIs corresponds to signature ‘s’ on the PRACH.AICH is aligned with Primary CPICH for the phase reference and timing.

Figure 4.15 illustrates the structure of the AICH. The AICH consists of a repeatedsequence of 15 consecutive access slots (AS), each of length 5120 chips. Each accessslot consists of two parts:


Figure 4.15: Acquisition Indication Channel

Acquisition-Indicator (AI) part: an Acquisition-Indicator (AI) part consistingof 32 real-valued symbols a0, . . . , a31.

No Transmission part: For last 1024 chips AICH is switched off8.

According to 3GPP TS 25.211, the real-valued symbols, aj are given by

aj =15∑s=0

AIs · bs,j (4.1)

In equation 4.1, there are two terms on right hand side, AIs and bs,j. Let us inves-tigate more about them step-by-step.

1. AIs: AI can have 3 values:

• If an Acquisition Indicator is set to +1, it represents a positive acknowl-edgement.

• If an Acquisition Indicator is set to -1, it represents a negative acknowl-edgement.

• 0

2. bs: bs is chosen depending on the signature used by UE on PRACH preambleusing table 4.6 which has been defined by 3GPP9.

The real-valued symbols, aj, are spread and modulated in the same fashion as bitswhen represented in +1, -1 form.

8PRACH Preamble is also 256× 16 = 4096 chips93GPP TS 25.211


Sbs,j ,

where

j=

0,1,2,...,

31

01

11

11

11

11

11

11

11

11

11

11

11

11

11

11

11

1

11

1-1

-11

1-1

-11

1-1

-11

1-1

-11

1-1

-11

1-1

-11

1-1

-11

1-1

-1

21

11

1-1

-1-1

-11

11

1-1

-1-1

-11

11

1-1

-1-1

-11

11

1-1

-1-1

-1

31

1-1

-1-1

-11

11

1-1

-1-1

-11

11

1-1

-1-1

-11

11

1-1

-1-1

-11

1

41

11

11

11

1-1

-1-1

-1-1

-1-1

-11

11

11

11

1-1

-1-1

-1-1

-1-1

-1

51

1-1

-11

1-1

-1-1

-11

1-1

-11

11

1-1

-11

1-1

-1-1

-11

1-1

-11

1

61

11

1-1

-1-1

-1-1

-1-1

-11

11

11

11

1-1

-1-1

-1-1

-1-1

-11

11

1

71

1-1

-1-1

-11

1-1

-11

11

1-1

-11

1-1

-1-1

-11

1-1

-11

11

1-1

-1

81

11

11

11

11

11

11

11

1-1

-1-1

-1-1

-1-1

-1-1

-1-1

-1-1

-1-1

-1

91

1-1

-11

1-1

-11

1-1

-11

1-1

-1-1

-11

1-1

-11

1-1

-11

1-1

-11

1

10

11

11

-1-1

-1-1

11

11

-1-1

-1-1

-1-1

-1-1

11

11

-1-1

-1-1

11

11

11

11

-1-1

-1-1

11

11

-1-1

-1-1

11

-1-1

11

11

-1-1

-1-1

11

11

-1-1

12

11

11

11

11

-1-1

-1-1

-1-1

-1-1

-1-1

-1-1

-1-1

-1-1

11

11

11

11

13

11

-1-1

11

-1-1

-1-1

11

-1-1

11

-1-1

11

-1-1

11

11

-1-1

11

-1-1

14

11

11

-1-1

-1-1

-1-1

-1-1

11

11

-1-1

-1-1

11

11

11

11

-1-1

-1-1

15

11

-1-1

-1-1

11

-1-1

11

11

-1-1

-1-1

11

11

-1-1

11

-1-1

-1-1

11

Tab

le4.6:

AIC

HSign

ature

pattern

s


4.4.3 UL Dedicated Channels

In the uplink, there are only two dedicated physical channels, the uplink ‘Dedi-cated Physical Data Channel (uplink DPDCH)’ and the uplink ‘Dedicated PhysicalControl Channel (uplink DPCCH)’.

Uplink Dedicated Physical Channel

As stated above, there are 2 dedicated physical channels in UL, the DPDCH andthe uplink DPCCH. The DPDCH and the DPCCH are I/Q code multiplexed whichmeans they are modulated by carrier waves which have 90 degree phase difference.

Figure 4.16: Slot format of UL DPDCH and DPCCH Channel

1. DPDCH: The uplink DPDCH is used to carry the DCH transport channel.In other words, DPDCH carries user data and L3 control signalling10.According to 3GPP specifications, there could be several DPDCHs per radiolink, but in practice however, we use only one DPDCH per radio link (peruser). This channel has a variable spreading factor which can assume anyvalue from 256 to 4.

2. DPCCH: As shown in figure 4.16, the uplink DPCCH is carries control informa-tion which is added by Layer 1. Layer 1 control information contains followingfields:

1. Pre-known pilot bits for channel estimation for coherent detection,

10Note! It is a common misunderstanding that L3 messages are sent using DPCCH. In factDPCCH is physical channel which does not have any corresponding transport or logical channel.Therefore, DPCCH can be called as L1 control channel.


2. Transmit power-control (TPC) commands,

3. Feedback information (FBI) (used only if DL transmit diversity is usedon DL DPCH channel) and

4. A Transport-format combination indicator (TFCI) which is optional.

The transport-format combination indicator (TFCI) serves the duty of inform-ing the receiver receiver about the current transport format combination of thetransport channels mapped to the uplink DPDCH radio frame sent in the sameslot. It is not allowed to have less than or more than one DPCCH channel perradio link.

Due to a fixed SF = 256, the DPCCH bit rate equals 15 kbps in UL.

Figure 4.16 shows the frame structure of the uplink DPDCH and the uplink DPCCH.Each radio frame of length 10 ms is split into 15 slots, each of length Tslot = 2560chips, corresponding to one power-control period. The DPDCH and DPCCH arealways frame-aligned with each other.

Having one power control command per time slot means 15 power control commandsper radio frame (or 10 ms). This simply implies that in UMTS, when UE is usingdedicated physical channels, its power can be modified 1500 times per second.

Since DPDCH is our main UL data channel, it is crucial to know about the possiblebit rates that can be achieved.

DPDCH can have SF = 256, 128, 64, 32, 16, 8 and 4 which corresponds to15, 30, 60, 120, 240, 480 and 960 kbps respectively. Hence, variable bit rateservices can be achieved using variable spreading factors. Please refer to table4.7 for more details.

The modulation used in UL is BPSK.

4.4.4 DL Dedicated Channels

There is only one type of downlink dedicated physical channel, the Downlink Dedi-cated Physical Channel (downlink DPCH).

Downlink Dedicated Physical Channel

In uplink, L1 control and data are transmitted on two separate physical chan-

nels (DPDCH and DPCCH) but in downlink both L1 control and data is car-

ried by the same physical channel known as DPCH. Here DPCH is a combi-

nation of DPDCH & DPCCH.


SFSymbol Rate (ksps)

=[Rchip

SF

]=

[3.84Mcps

SF

] bit rate (kbps) on DLDPCH

bit rate (kbps) on ULDPDCH

512 7.5 15 -256 15 30 15128 30 60 3064 60 120 6032 120 240 12016 240 480 2408 480 960 4804 960 1920 960

Table 4.7: SF and the corresponding Channel bitrate

Figure 4.17: Slot format of DL DPCH Channel

As stated above, there is only one type of downlink dedicated physical channel, thedownlink DPCH. Within one downlink DPCH, the following information is trans-mitted:

User Data, DTCH logical Channel

L3 Control Information, DCCH logical channel

L1 Control Information, Physical signals, generated by L1

The physical control information consistes of (1) pilot bits, (2) TPC commands, and(3) an optional TFCI ). Therefore, DL DPCH can be considered as time multiplexof a downlink DPDCH and a downlink DPCCH.

As usual, the timing is organized into 10 ms radio frames which equals 15 time slots.If we carefully examine the conents of a slot in figure 4.17, various fields of DPCH


can be identified. Since there is one TPC command every 2/3 ms, the DL powercontrol also happens at 1500 times per second (just like uplink).

DL DPCH can have SF = 512,11 256, 128, 64, 32, 16, 8 and 4 which corre-sponds to 30, 60, 120, 240, 480, 960 and 1920 kbps respectively. Hence, vari-able bit rate services can be achieved using variable spreading factors. Pleaserefer to table 4.7 for more details.

The modulation used in DL is QPSK.

4.4.5 Summary of DCH Channels

DCH is the main channel used for transferring user data in UMTS. Therefore, it isbetter to understand the slot format of UL and DL DCH channel. In figure 4.18,the slot format of both UL and DL DCH channels is shown.

In order to understand the fast inner loop power control of UMTS, this section isvery important.

Figure 4.18: Slot format of UL and DL DPCH Channel

In figure 4.19, an example is illustrated where 3 different UEs are using 3G servicesin a cell which is operating at UL frequency fUL and DL frequency fDL. The DLprimary scrambling of the cell is 511 and the UL scrambling codes allocated to the3 UEs are 1,000,111, 1,000,222 & 1,000,333.

11Some vendors do not support SF 512

4.5. CELL SEARCH PROCEDURE 109

Figure 4.19: Example of DCH usage, 3 DCH users shown here

This example has been specially included to explain the usage of channelization codein UL and DL.

• In uplink, the control and data channel from the same UE is identified by ULchannelization codes.

• In downlink, channelization code is used to identify the UEs because frequencyand DL Scrambling code is the same for all users in that cell.

4.5 Cell Search Procedure

Source: 3GPP TS 25.214, Annexure C (quoted Word-by-word)

During the cell search, the UE searches for a cell and determines the downlinkScrambling code and frame synchronization of that cell. The cell search is typicallycarried out in three steps:

Step 1: Slot synchronization

During the first step of the cell search procedure the UE uses the SCHs primarysynchronization code to acquire slot synchronization to a cell. This is typicallydone with a single matched filter (or any similar device) matched to the primarysynchronization code which is common to all cells. The slot timing of the cell canbe obtained by detecting peaks in the matched filter output.


Step 2: Frame synchronization and code-group identification

During the second step of the cell search procedure, the UE uses the SCHs sec-ondary synchronization code to find frame synchronization and identify the codegroup of the cell found in the first step. This is done by correlating the receivedsignal with all possible secondary synchronization code sequences, and identifyingthe maximum correlation value. Since the cyclic shifts of the sequences are uniquethe code group as well as the frame synchronization is determined.

Step 3: Scrambling code identification

During the third and last step of the cell search procedure, the UE determinesthe exact primary Scrambling code used by the found cell. The primary Scramblingcode is typically identified through symbol-by-symbol correlation over the CPICHwith all codes within the code group identified in the second step. After the primaryScrambling code has been identified, the Primary CCPCH can be detected and thesystem- and cell specific BCH information can be read. If the UE has received in-formation about which scrambling codes to search for, steps 2 and 3 above can besimplified.

4.6. HSDPA CHANNELS IN SHORT 111

4.6 HSDPA Channels in Short

Although the channels and other details about HSDPA will be discussed in chapter7, a list of all HSDPA related physical channels is included in this chapter. Thereare 3 new physical channels which are illustrated in figure 4.20.

Figure 4.20: HSDPA operation explained using the physical channels.

HS-PDSCH: HS-PDSCH is a shared channel; it is shared between all active HS-DPA users in the cell. Each radio frame is divided into 2 ms sub-frames inHSDPA. There are 3 timeslots within one HSDPA sub-frame. The main fea-tures about HS-PDSCH are listed below:

• High Speed Physical Downlink Shared Channel

• Only in DL

• Carries User data and scheduled by Node B

• SF is fixed, SF = 16

• Uses adaptive modulation, QPSK and 16QAM

• No Soft Handover, no fast power control

• Shorter transmission time interval (TTI), TTI = 2ms

HS-SCCH: The High Speed Shared Control Channel (HS-SCCH) is a downlinkcontrol channel that is specially designed to inform UE about the schedulingdecisions made by Node B. The information on HS-SCCH is absolutely essen-tial for HS-PDSCH reception. This channel indicates when there is data onthe HS-PDSCH that is addressed to this UE.


• High Speed Shared Control Channel

• Carries control information for HS-PDSCH:

– Channelization code set information

– Modulation scheme

– Transport block size

– Hybrid ARQ process id

– Redundancy and constellation version

– New data indicator

– UE identity = H-RNTI

HS-DPCCH: In the uplink direction, there is the High Speed Dedicated PhysicalControl Channel (HS-DPCCH) that is used for sending feedback informationto Node B.

• High Speed Dedicated Physical Control Channel

• Carries L1 feedback information from a UE:

– L1 H-ARQ NACK/ACK

– Channel Quality Indicator (CQI)

4.7. HSUPA CHANNELS IN SHORT 113

4.7 HSUPA Channels in Short

A detailed description of HSUPA can be found in chapter 8. In this section a verybrief introduction to HSUPA channels is given.

Figure 4.21: HSUPA operation explained using the physical channels.

As shown in figure 8.23, there are 2 UL channels and 3 DL channels in relation tothe HSUPA operations.

E-DPDCH: E-DPDCH is the main data channel of HSUPA. In UL, UE can have1, 2 or 4 E-DPDCHs. The main parameters about E-DPDCH are:

• E-DCH Dedicated Physical Data Channel

• Carries UL user data up to 5.76 Mbps

• Variable SF; SF = 256, 128, 64, 32, 16, 8, 4 & 2

• Uses same modulation as the UL DCH, BPSK

• Uses soft Handover & fast power control

• Shorter transmission time interval (TTI) , TTI = 10 ms & 2ms (optional)

E-DPCCH: E-DPCCH is used to carry L1 control information related to E-DPDCH.The E-DPCCH is time-aligned with the uplink DPCCH.

• E-DCH Dedicated Physical Control Channel

• Carries control information for E-DPDCH:H:

– Retransmission sequence number (RSN), 2 bits

– E-TFCI, 7 bits

– Happy bit, 1 bit


E-AGCH: The E-AGCH is a downlink physical channel used to transmit absolutegrants to a UE or a group of UEs. The absolute grant consists of a 5 bit grantvalue which is between 0 and 31. The definition of grant is the ratio betweenthe transmit powers of E-DPDCH and DPCCH.

Grant represents the maximum E-DPDCH to DPCCH power ratio theUE may use in the next transmission.

Grant =Ptx,E-DPDCH

Ptx,DPCCH

E-RGCH: The E-RGCH carries relative grants that are used in the schedulingprocess to gradually increment or decrement the allowed UE grant.

• E-DCH Relative Grant Channel

• Carries relative grants for uplink E-DCH scheduling

• Relative grants transmitted with signature sequences

E-HICH: The E-HICH carries the HARQ acknowledgement indicator, ACK orNACK.

• E-DCH Hybrid ARQ Indicator Channel

• Carries hybrid ARQ ACK/NACK indicator

• HARQ acknowledgment indicators transmitted with signature sequences

4.7. HSUPA CHANNELS IN SHORT 115

Copyright Notices



Text in section 4.2 on page 83 Section 5.3.1.1.1 of 3GPP TS 25.301 v 7.0.0Text in section 4.2.1 on page 84 Section 5.3.1.1.1 of 3GPP TS 25.301 v 7.0.0Text in section 4.2.2 on page 85 Section 5.3.1.1.1 of 3GPP TS 25.301 v 7.0.0c⃝2006. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

Text in section 4.4 on page 88 Section 5 of 3GPP TS 25.211 v 9.1.0.Text about P-CPICH on page 98 Section 5.3.3.1.1 of 3GPP TS 25.211 v 9.1.0.Text about S-CCPCH on page100

Section 5.3.3.4 of 3GPP TS 25.211 v 9.1.0.

Text about PICH on page 101 Section 5.3.3.10 of 3GPP TS 25.211 v 9.1.0.Text about P-SCH on 95 Section 5.3.3.5 of 3GPP TS 25.211 v 9.1.0.Text about AICH on 103 Section 5.3.3.7 of 3GPP TS 25.211 v 9.1.0.Text about Cell Search Procedurein section 4.5 on page 109

Quoted word-by-word from Annex C of3GPP TS 25.214 v 9.1.0.

Figure 4.10 on page 99 Figure 13 of 3GPP TS 25.211 v 9.1.0.Figure 4.11 on page 100 Figure 15 of 3GPP TS 25.211 v 9.1.0.Figure 4.12 on page 101 Figure 17 of 3GPP TS 25.211 v 9.1.0.Figure 4.15 on page 103 Figure 21 of 3GPP TS 25.211 v 9.1.0.Figure 4.16 on page 105 Figure 1 of 3GPP TS 25.211 v 9.1.0.Figure 4.17 on page 107 Figure 9 of 3GPP TS 25.211 v 9.1.0.Table 4.4 on page 94 Table 3 of 3GPP TS 25.213 v 8.4.0.Table 4.5 on page 96 Table 4 of 3GPP TS 25.213 v 8.4.0.Table 4.6 on page 104 Table 22 of 3GPP TS 25.211 v 9.1.0.c⃝2009. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

BIBLIOGRAPHY

[1] 3GPP TS 25.201 ver. 6.0.0 ;‘Physical layer - General description’

[2] 3GPP TS 25.211 ver. 6.0.0 ;‘Physical channels and mapping of transport chan-nels onto physical channels (FDD)’




[6] 3GPP TS 25.104 ver. 6.0.0 ;‘Base Station (BS) radio transmission and reception(FDD)’

[7] 3GPP TS 25.301 ver. 6.0.0 ;‘Radio Interface Protocol Architecture’


[9] Chris Johnson, ‘Radio Access Networks For UMTS ; Principles AndPractice’ , John Wiley & Sons.

For HSDPA-secific details, the version of these specs should be 5.0.0 orhigher & for HSUPA-specific details, it shold be 6.0.0 or higher.

116

CHAPTER

5

RADIO RESOURCE MANAGEMENT

Source:

• 3GPP TR 25.922 ver. 7.0.0 ; ‘Radio resource management strategies’

• H.Holma and A. Toskala, ‘WCDMA for UMTS’ , 5th Edition, John

Wiley & Sons.

Radio Resource Management or RRM is a collective term used for the algorithmsand features designed for the optimized operation of radio networks. Radio Resourceis a generic term which is applicable to all radio access technologies. In a TDMAbased system, radio resource is a time slot, whereas, in a FDMA system it is afrequency channel. Similarly in our CDMA-based cellular systems, UMTS & HSPA,radio resource can be identified as a combination of:

• frequency,

• Scrambling code,

• channelization code &

• power.

Radio resources are valuable resources which directly contribute to the revenue ofthe service provider. Therefore, it is very crucial to have a well-tuned radio resource

117

118 CHAPTER 5. RADIO RESOURCE MANAGEMENT

management working in the network. The tuning is generally performed by variousparameters defined at RNC, Node B or cell level. Other than these, for properhandover and mobility, there are parameters which can separately affect the mobilityfrom one source cell to different target cells. The most common approach for RRMimplementation is to take decisions based on cell load where the word load refers toas received power at Node B receiver for Uplink and transmitted power from NodeB transmitter for downlink.

In short, the functions of Radio Resource Management can be summarized as:

1. Maximize Capacity: If the current load in a cell is less than the planned targetload, there should be a mechanism to increase the resources of Non-real Time(NRT) data users and utilize the total cell resources.

This feature will have at least two advantages: the increased cell throughputfrom the operator perspective and improved user experience from end-userperspective. This can be achieved by smart packet scheduling in RNC. Withthe introduction of HSDPA & HSUPA, there are new schedulers introduced inNode B which can respond much quicker to the variations in radio conditionsand adapt the throughput according. This well-known concept is called linkadaptation.

2. Guarantee the Planned Coverage: In CDMA-based networks, if a cell ex-periences overload, then the interference becomes higher than usual. To over-come this, UEs are asked to increase the transmit power. At this moment,the UEs at cell edge, which are already transmitting with maximum power,cannot increase their power and find themselves out-of-coverage area due tothis overload mechanism. This well-known mechanism is called cell breathing.Therefore, there should be some mechanism, which will prevent the cell to gointo overload. This is achieved by an effective admission control algorithm inRNC.

If admission control algorithm is too relaxed, then there will be admission ofnew users even if the cell is close to overload, which will cause instability. Onthe other hand, if admission control algorithm is over-protective, then therewill be very high blocking although there are some free resources left in thecell. Therefore, proper parameter setting to tune the admission control is verycrucial to the network performance.

3. Provide good Quality of Service: In order to achieve an acceptable bit errorrate (BER), there must be sufficient quality at the physical link. There arethree important QoS attributes which are quite often used in RRM, in orderto guarantee a good link quality. They are:

5.1. INPUTS FOR RRM FUNCTIONALITY 119

1. Signal to Interference Ratio (SIR) [in dB]

2. Bit Energy to Noise Energy Ratio (Eb/No) [in dB]

3. Block Error Rate (BLER) [in %]

While admitting a new bearer, admission control already takes into accountthe Planned Required EbNo, BLER target and SIR Target values. Based onthese values, admission control makes an estimate of the increment in the cellload caused by this particular bearer. Once the bearer is admitted, the powercontrol mechanism tries to maintain the power level at an absolute minimumlevel which will be enough to meet the quality criterion1.

4. Priority Handling: The services can be broadly categorized into 4 traffic classesnamely: (1 = Highest priority)

1. Conversational

2. Streaming

3. Background

4. Interactive

Generally, Conversational class has the highest priority followed by Streaming,Interactive and then Background. Therefore, Conversational class users aregiven the highest importance while admitting the service. (e.g., Voice or videocalling). Rest 3 classes are subjected to buffering and scheduling according totheir relative priorities.

5.1 Inputs for RRM Functionality

In this section, we will discuss the inputs which are used by RRM functions. Thereare 4 main inputs which are illustrated in figure 5.1.

1. Radio parameters stored in RNC’s database

2. Node B measurements

(a) Common Measurements

(b) Dedicated Measurements

3. UE measurements

4. RNC’s internal calculation and measurements


Figure 5.1: Inputs for RRM functionality

Let’s us discuss them one by one.

5.1.1 RNC Parameter Database

RNC is responsible for storing the radio parameters for the whole radio networksubsystem. Among other parameters, it also stores the cell specific uplink loadtarget and downlink load target.

For example, if the target DL load is 75% and the current load is 65%, RRM caneasily decide about the next strategy. Therefore, the parameters stored in RNC’sdatabase are an important input for RRM functionality.

Figure 5.2 shows three regions according to the cell load status.

• The planned area is the safe operation area where the load is under con-trollable limits and neither coverage nor the quality of active connections getsaffected. The threshold which defines the upper limit of planned area is de-cided in co-ordination with radio network planning strategy.

Generally in this situation, admission control is advised to allow more RABsand packet scheduler is advised to schedule higher bit rates.

1Transmit power should be much as required, as little as possible.


• The marginal area is the safety window between ‘normal’ and ‘overload’states. In this situation, the new real-time calls are generally denied. Ongoingpacket sessions continue but their bit rates are neither throttled not increased.The threshold which defines the upper limit of marginal area is decided by theplanner and defined relative to the threshold for the planned area, for example,1 dB above the threshold for planned area.

• The overlaod area is the area where the cell load is beyond the controllablelimits. This can severely affect the quality and coverage of the cell-edge users.Generally, in this state, the admission control stops allowing more real timeRABs in the cell and packet scheduler tries to reduce the load by schedulingless bit rates.

Figure 5.2: Load Regions used in Radio Resource Management

5.1.2 Node B Measurements

Source: 3GPP TS 25.433, UTRAN Iub interface Node B Application

Part (NBAP) signalling

One central difference between the RRM of 2G family of systems (GSM, GPRS &EDGE) and 3G family of systems (WCDMA & HSPA) is the exact knowledge aboutcurrent actual load.


• In 2G, the RRM is located at BSC/PCU and it knows exactly how many timesslots have been allocated. The decisions about resource allocation is purely inthe hand of BSC. BTS does not have the authority to modify the resourcesautonomously. Thus, there is no confusion about the current load in thecell.

• In 3G, the RRM is located at the RNC site. But the exact knowledge aboutthe cell load (UL received power and DL transmitted power) is available at theNode B. RNC makes decisions about the initial, minimum and maximumpower of each connection but the instantaneous power can be modified byNode B using power control feature. RNC has to completely depend on themeasurements performed by Node B and reported to RNC.

The interface connecting Node B & RNC is Iub. The signalling protocol on Iubis called Node B Application Part (NBAP). There are two types of measurementreports, common measurements and dedicated measurements.

Figure 5.3: Common NBAP measurement management, source: 3GPP TS 25.433

Common Measurement Report

These reports are handled by C-NBAP protocol. The word common here means“common to the cell”. Hence we have one such report at scheduled intervals decidedby operator specific parameters2. Typical values reported in this report are:

• Total Carrier Power (TCP)

2Typically one such report is sent from Node B to RNC at several 100 ms, e.g., 400 ms.


• Transmitted carrier power of all codes not used for HS transmission

• Received Total Wideband Power (RTWP)

• Acknowledged PRACH Preambles

• HS-DSCH Required Power

• E-DCH Provided Bit Rate

Dedicated Measurement Report

These reports are handled by D-NBAP protocol. The word dedicated here means“dedicated to one radio link”. Using this measurement report, Node B can informRNC about the transmit power of a particular radio link in downlink. Typical valuesreported in this report are:

• SIR

• SIR Error

• Transmitted Code Power

NBAP protocol uses 2 special identifiers for this purpose. They are called Node B UEcontext ID and CRNC Communication Context ID. These IDs are like ‘nicknames’that were chosen by Node B and RNC at the time of initial radio link establishment.

Due to multitude of dedicated measurements, these reports are sent at lower fre-quency compared to common measurement reports3.

5.1.3 UE Measurements

According to 3GPP, the measurements performed by UE can be either periodicor event-triggered. Event triggered option requires parameters to be set toclearly define an event.

Source: 3GPP TS 25.215, Physical layer - Measurements (FDD)

Other than the measurements performed by Node B, UE physical layer also performsvarious measurements which are reported back to RNC for optimum functionalityof RRM functions e.g., handover mobility, bit-rate modification etc.

According to 3GPP TS 25.215, some of the crucial UE measurements are:

3Typically every few seconds. e.g., 3s.


Figure 5.4: Dedicated NBAP measurement management, source: 3GPP TS 25.433

• P-CPICH RSCP

• P-CPICH Ec/N0

• UTRA carrier RSSI

• GSM carrier RSSI (BCCH RxLev of GSM)

• Transport channel BLER

• UE transmitted power

• UE Rx-Tx time difference

• SFN-SFN Observed time difference

• . . .

In order to read more about the definition of these quantities, please refer to section5.1 & 5.2 in 3GPP TS 25.215. Section 5.1 describes the UE measurement abilitiesand section 5.2 explains UTRAN measurement abilities.

Please note that not all the measurements are performed periodically. Accordingto 3GPP specifications4, the measurements can be either periodic, or on demand orevent-based. This simply implies that there is a great deal of freedom which canbe used by infrastructure vendors for controlling the UE reporting whereas the UEsmust be capable of measuring these quantities.

4TS 25.302, section 9.2 and TS 25.215


It has been observed, that the vendors have opted for event-based triggeringof measurements. Therefore, the UE looks out for some special scenarios to takeplace. For example, UE monitors a new target cell whose CPICH signal is almost-equally-strong as the serving cell. When such a scenario happens, UE sends a RRC:Measurement Report Message with the details of the target cell scrambling codeand signal strength. Such a scenario is called Event 1A. In the similar fashion,various events have been defined by 3GPP which will be discussed later in thismodule.

5.1.4 Internal RNC Measurements

RNC is the central controlling unit of the RAN. Therefore, RNC keeps on performingcertain calculations, estimations and measurements to guarantee the stability of cellswithin its controlling area. For example,

• For packet users, RNC keeps on performing measurement on ‘DL TransportChannel Traffic Volume’. If the data volume exceeds a given threshold, it cannotify the packet scheduler to:

– Perform state transition from CELL FACH to CELL DCH or

– Upgrade the bit rate of allocated DCH

• Once a DCH channel is established for a UE, RNC keeps on measuring the ‘ac-tual’ throughput in UL and DL. Based on these measurements, packet sched-uler can:

– Decrease the allocated bit rate in next scheduling decision, or

– Release the allocated bit rate in next scheduling decision, or

– Increase the allocated bit rate if throughput measurements indicate avery high utilization.

• Another example is when admission control admits a new real-time (RT) RAB.Admission control informs the load estimation entity of RRM about this ‘inac-tive’ bearer. This procedure makes sure that the load-calculation entity alwayshas the knowledge about load which is as close to reality as possible.

• Similarly, after scheduling a PS bearer, packet scheduler informs the load-calculation entity about its estimate of the load caused by PS bearers.

• . . .


5.2 Load Estimation

Source:

• 3GPP TR 25.922 ver. 7.0.0 ; ‘Radio resource management strategies’

• H.Holma and A. Toskala, ‘WCDMA for UMTS’ , 5th Edition, John

Wiley & Sons.

The following section is inspired from the book ‘WCDMA for UMTS’ byH.Holma and A. Toskala, where these topics are explained with a step-by-step mathematical analysis and description. In ‘Let’s Learn 3G in 10Days’, the author has tried to summarize the final result of the analysis.The advanced readers should refer to the above mentioned reference toget more details.

For the proper functionality of RRM, the RNC must periodically estimate the UL& DL load in order to decide the actions for admission control and packet scheduler.The following section explains the procedure of ‘current cell load estimation’,in both uplink and downlink. Let us start the discussion with uplink cell loadestimation.

5.2.1 Uplink Load Estimation

RNC can estimate the current uplink load in 2 different ways.

1. Uplink cell load estimation based on ‘Received Total Wideband Power(RTWP)’, and

2. Uplink cell load estimation based on ‘Total Uplink Throughput’

Option 1: Received Total Wideband Power-based UL load Estimation

In all CDMA-based systems, UL capacity is directly affected by the noise rise gen-erated by users in the uplink. Typically, an operator restricts the acceptable uplinkload to a certain UL noise rise. The noise rise in the UL is the increase in noisecompared to the noise floor of the Node B:

Noise Rise, NRUL =Prx,total

Pnoise

(5.1)

5.2. LOAD ESTIMATION 127

Without going into the mathematical derivation, we will write the final relationbetween Noise Rise (NR) and the cell load ηUL:

NR =1

1− ηUL

or ηUL = 1− 1

NR(5.2)

Received Total power (RTWP) consists of three components:

1. System and equipment noise (or background noise),

2. Interference caused by ‘OWN CELL USERS’ &

3. Interference caused by ‘OTHER CELL USERS’

Or,RTWP = PNoise + IntOwn cell + IntOther cell (5.3)

As explained earlier, Node B keeps on reporting the current Received Total Wide-band Power (RTWP) to RNC. RNC uses this RTWP measurements and comparesit with the Pnoise. This indicates the amount of noise which has risen.

This scheme has a limitation, because:

• RTWP does not differentiate between own cell interference and other cell in-terference. RTWP is simply the measured received power at Node B receiverwhich might be caused by users in the own cell or neighbouring cells.

• RTWP also includes PNoise, as depicted in equation 5.3. If the noise level itselffluctuates, then the RTWP cannot indicate the UL loading in an accuratemanner.

In order to overcome the problems listed above, it is better to combine the power-based load estimation with another scheme described below.

Option 2: Throughput-based UL Load Estimation

Throughput-based UL load estimation utilizes the concepts of fractional load causedby one user and summing the load of all the users to calculate the total cell load.

Throughput based UL load can be depicted by LThr,Cell where

LThr,Cell =∑

i∈All DCH in Cell

LDCH,i (5.4)


where the individual DCH of bit rate Ri kbps, causes a load LDCH,i which is calcu-lated by:

LDCH,i =1

1 +W/Ri

(Eb/No)i· 1

AFi

(5.5)

where Eb/No is the signal energy per bit divided by noise spectral density that isrequired to meet a predefined block error rate, W is WCDMA chip rate, Ri is thebit rate of user i & AFi is the activity factor5 for uses i.

5.2.2 Downlink Load Estimation

Transmitted Power-based DL load Estimation

In the section related to Node B measurements, it was shown that Node B keeps onreporting the current Total Transmitted Carrier Power (TCP) or Ptx,total to RNC.RNC uses this Ptx,total measurements and compares it with the PBTS,Max. Thisindicates what percentage of the Node B Power Amplifier’s power has been utilizedin the current measurement period.

ηDL =Ptx,total

PBTS,Max

(5.6)

The operator must define the DL load target. DL load target is defined as a ratioof maximum Node B power amplifier value. For example, in a 20 W carrier, if weplan to use ηDL = 75%, then the cell is in normal state up to Ptx,total < 15W .

Throughput-based DL Load Estimation

In principle, the throughput-based DL load estimation can be utilized in the samemanner as discussed in the previous section for Uplink. But in DL, the power basedmeasurements are quite reliable. Therefore, there is not much need for a separateestimation of DL load based on throughput. The implementation is vendor specific.

5For voice 0.5-0.7 & for Data service 1.0

5.3. RADIO RESOURCE MANAGEMENT STRATEGIES 129

5.3 Radio Resource Management Strategies

Source: ‘Section 12: Congestion Control’ of 3GPP TR 25.922,

‘Radio resource management strategies’

In UMTS, congestion control mechanism takes care of the situations where systemhas reached a congestion state and therefore the QoS guarantees can be at at risk.This feature is implemented in the packet scheduler of RNC. 3GPP only gives roughguidelines about these feature. The exact rules of this feature are decided by theequipment vendors. Some of these features are optional. Therefore, it is possiblefor the operators to enable only those feature, which sound useful to them. But inprinciple, the congestion control mechanism should perform the following tasks:

1. Congestion detection: Periodically Node B reports the cell load to RNC andRNC compared the reported load with the target load. After this comparison,RNC declares whether congestion has been detected.

2. Congestion resolution. Various steps can be taken by RNC’s packet schedulerto resolve the state of congestion.

• Prioritization: Ordering the different users from lower to higher priority(e.g., from those that expect a lower grade of service to those with morestringent QoS requirements).

• Load reduction: Two main actions could be taken:

(a) Selective blocking of new connections while in congestion

(b) Reducing the maximum transmission rate

• Load check: Load reduction actions can be carried on until the consideredload factor is below a given threshold for a certain amount of time (i.e.,the system can enter the congestion recovery status).

3. Congestion recovery: It is possible to attempt to restore the transmission pa-rameters used before the congestion was triggered, by using a “time schedul-ing” on a user by user basis.

5.4 Admission Control

Imagine an empty party hall. The first two guests arrive and start their small-talk at a comfortable volume. As few more guests arrive, they also start talkingin pairs or groups. Later, when the room is full and everyone is busy in


the conversation with their partner, the first two guests realize that they areactually speaking much louder compared to the situation when they were allalone in the hall.

From this small story, one can understand that every subscriber that gets admittedin UMTS cell, adds its contribution to the overall interference. If we want to keepthe interference within a controlled limit, the admission control must play an activerole and stop admitting new users after a certain limit.

For admission control, the following strategies must be used:

• Admission control should be performed according to the Quality of Service.Typically, the admission control is very strict while admitting guaranteed bitrate (GBR) services like voice, because once admitted, RNC has no authorityto drop the connection if resource congestion is detected.

On the contrary, for non-GBR services like email, web-browsing, FTP, etc.,admission control is quite relaxed. These bearers are allowed to setup be-cause later if congestion is detected, the resource allocation can be reduced oreliminated.

• Admission control should take the decision after considering the current systemload and the required service. The quality can be defined in terms of requiredBlock Error Rate (BLER) or required Eb/No.

Admission control should use these quality parameters and estimate the in-crement in load that will be caused if this bearer is admitted.

Imagine a room with 10 chairs where already 8 chairs are occupied. 3more persons want to enter this room. Should admission control allowthem to enter?

I am sure your answer is No. From this simple example, we can learn that admissioncontrol not only considers the existing load but also the hypothetical or simulatedload for the connections for which admission control is deciding. This clearly showsthat admission control algorithm prepares for the worst-case scenario before sayingyes to a new bearer.

There are various scenarios where admission control must step in and make thedecisions. The following section describes these situations.

1. AC at the time of RRC Connection Setup. This signalling is depictedin figure 5.5

5.4. ADMISSION CONTROL 131

Figure 5.5: Admission Control in RNC at RRC Connection Establishment

In RRC Connection request, UE specifies the cause of establishment. Forexample, mobile originated call, mobile terminated call, interactive session,emergency call, registration and so on. At this moment, admission controlcan prioritize the RRC connection for certain causes. It is quite obvious thatRRC connection to set up an emergency call must be treated with the highestpriority.

2. AC at the time of RAB Setup. This signalling is depicted in figure 5.6.The procedure of RAB establishment is started by core network. Either MSCor SGSN requests RNC to establish a RAB with certain QoS parameters.For example, traffic class, max bit rate, guaranteed bit rate, SDU error ratio,traffic handling priority, allocation retention priority, etc. From these QoSparameters, RNC finds out the radio bearer attributes like Eb/No target,Signal-to-Interference target & block error rate (BLER) target. RNC typicallyuses some look-up table to do so.

Using these attibutes, admission control can estimate the increment in loadcaused by the RAB in question.

(a) For RT RAB setup, AC works independently.

RT RABs have certain guaranteed bit rates. Therefore, if the resourcesfor these GBR service are not available, the RT RABs are denied.

(b) For NRT RAB setup, AC works in close co-ordination with packet sched-uler (PS). Therefore, NRT RAB admission is performed by AC but thesubsequent scheduling of resources is performed by PS.

3. AC at the time of SHO diversity branch addition. This signallingis depicted in figure 5.7. The decision about handover is taken in SRNC


Figure 5.6: Admission Control in RNC at RAB Establishment

whereas the admission control takes place in the target cell’s CRNC. In general,admission control is a little bit relaxed for the handover decisions. Admissioncontrol allows handover to take place up to a higher load limit compared tothe admission control for a new RAB setup.

5.5 Code Allocation

As discussed in the chapter related to CDMA, Spreading and air interface technology,we have learnt that there are 4 types of codes used in WCDMA which are:

1. DL Scrambling Code

2. DL Channelization Code

3. UL Scrambling code

4. UL Channelization Code

1. DL Scrambling Code: Used as the physical cell id. There are totally 512Primary-Scrambling codes in DL, which are used as L1 identity of anyWCDMA

5.5. CODE ALLOCATION 133

Figure 5.7: Admission Control in RNC at Inter-RNC SHO

cell. After 512, these codes can be repeated. Therefore, we never face conges-tion or blocking in DL Scrambling. Therefore, RRM has not much role to playin DL SC.

2. DL Channelization Code: The channelization codes used for spreading areOrthogonal Variable Spreading Factor (OVSF) codes that preserve the or-thogonality between physical channels. In DL, Channelization codes are usedto differentiate among the individual users. Hence, as the need for capacity in-creases, the DL Channelization codes face congestion. Code-tree optimizationprocedure is explained in section 5.5.1.

3. UL Scrambling Code: UL Scrambling codes are used as user Id for Uplinksignal separation. According to 3GPP specification, more than 16 MillionUL SC have been defined. Out of which, one RNC can utilize a subset ofthose based on the hardware limitation of RNC (for example 50,000 codes).Therefore, shortage of UL SC is also not a very common cause for congestion.

4. UL Channelization Code: UL channelization code is used to differentiate amongthe various channels transmitted from the same UE. For example:

• In Rel-99 Configuration: DPDCH & DPDCH


• In Rel-5 configuration: DPDCH, DPDCH & HS-DPCCH

• In Rel-6 configuration: DPDCH, DPDCH, HS-DPCCH, E-DPCCH &E-DPDCH

In Uplink, every user uses a different Scrambling code. Therefore, every UEhas its own code tree. Hence, the same UL CC can be re-used within thesame cell. This is the reason why we never observe congestion in the ULchannelization code tree.

Summary: DL channelization code is a rare radio resource and must be usedvery efficiently. In most of 3G cellular networks, 3G and HSDPA are deployed.HSDPA makes use of multiple code allocation to one user. This further in-creases the code utilization. In order to reduce the code blocking, a techniquecalled code tree optimization is used by RNC (see section 5.5.1).

Code allocation deals with the problem how different codes are allocated to differentconnections. The channelization codes used for spreading are Orthogonal VariableSpreading Factor (OVSF) codes that preserve the orthogonality between physicalchannels. The OVSF code is shown in figure 5.8.

5.5.1 Code Tree Optimization

RNC has a smart algorithm which either periodically or based on some threshold,re-organizes the DL channelization code tree. The main purpose of this feature is toavoid the fragmentation of a code tree. Figure 5.9 depicts the same with examplewhere CC16,2 code was allocated to user 1 and CC16,10 is allocated to another user.As a result, CC8,1 and CC8,5 are forbidden to be used in the same cell. This happensdue to the fragmented nature of code allocation.

In RRM framework, there should be a smart code allocation algorithm that canrelease CC16,10 and re-assign CC16,3 to the same UE. Because the SF remains un-changed, the net bit rate does not get affected. Therefore, this procedure happensonly at physical layer, without disturbing the higher6 protocols layers.

5.6 Packet Scheduler

With the introduction of GPRS into the mobile world, it became clear that packetswitched IP-based data services are going to be an important part of the services

6MAC, RLC and PDCP

5.6. PACKET SCHEDULER 135

Figure 5.8: OVSF code Tree

offered by future mobile systems. That is why Packet Scheduler is introduced inRNC to handle the packet traffic more efficiently. The main function of packetscheduler are:

• Transport Channel Type Selection: Logical channel DTCH can be mappedon either common channels, dedicated channels or on shared channels. PS isresponsible to select the channel type and later on, if needed, channel typeswitching7.

• Transport Format Combination Set (TFCS) construction: At the time

7HS-DSCH ↪→ DCH channel type switching can be understood as HSDPA to R99 handover.


Figure 5.9: DL Channelization Code Tree Optimization to avoid code congestion

of radio bearer setup, the PS decides about the possible transport formats(transport block size, TB set size, TTI, channel coding scheme, coding rate,etc.).

• RRC state handling: PS is responsible to handle the UE state. This conceptis explained later in section 5.6.1.

• Priority handling: All the PS bearers to be scheduled are put into queueand PS picks the bearer according to their relative priorities.

• Overload Control: If the cell load goes to overload, it is PS which reducedthe bit rates and thereby tries to bring back the load to normal state.

• Bit Rate Adaptation: Other than these, PS also keeps an eye on the re-source allocation & utilization. For example, if allocated bit rate is higherand actual throughput is not high, then the bit rate can be reduced to avoidwastage of resources.


In order to transmit data in uplink, UE can use RACH, DCH or E-DCH transportchannels. Similarly UE can receive downlink data on FACH, DCH or HS-DSCHtransport channels. This mapping between logical channels and transport channelsis performed by the MAC layer which is implemented in RNC’s packet scheduleralgorithm. With the introduction of HSDPA & HSUPA, the packet schedulingfunction is distributed, which is described below:

RACH (↑), FACH (↓) & DCH (↕): For these transport channels, the packetscheduling is performed by RNC. The main input for the scheduler decisionare: the amount of data to be transmitted, actual throughput measured inpast few TTIs, cell load status, priorities of the bearers etc8.

HS-DSCH (↓) HS-DSCH is the DL transport channel used by HSDPA system.The scheduler for this channel is located at Node B and known as MAC-hsscheduler. CQI plays a central role in selecting which HSDPA user will beserved in the next TTI and what transport block size will be selected.

E-DCH (↑) Finally, E-DCH is the UL transport channel used by HSUPA. Thescheduler for this channel is also located at Node B and known as MAC-escheduler. The main input to these schedulers are the feedback reports fromUE. Each UE keeps on reporting the status of its buffer, power control head-room and the priority of the logical channel whose data is to be transmitted.Scheduling request happens periodically, e.g., every 100 ms. Meanwhile UEkeeps on reporting one bit information called ‘Happy Bit’ which indicated theUE’s wish for an upgrade in UL resources.

5.6.1 RRC States

Source : 3GPP TS 25.331 RRC Protocol Specification9

RRC is the central L3 protocol in UTRAN. RRC protocol is implemented in UEand RNC. Therefore, whenever UE & RNC want to communicate, they use RRCprotocol. Some important procedures of RRC protocols are RRC connection estab-lishment, Radio Bearer Management, Measurement control and reporting, Systeminformation transfer, Paging etc.

The RRC states introduced in 3G are a compromise of the following aspects:

8Please note that Radio conditions (CPICH Ec/No or CQI) is not a factor for RNC basedpacket scheduler. This happens because UE reporting to RNC is so slow that RNC cannot keeptrack of radio condition of all the users.

9TS 25.331 is perhaps the most bulky specification of UTRAN. Developments in HSDPA,HSUPA & HSPA+ domain have further increased the details available in this this document.


• Which physical channels that are allocated to the UE, and thus which trans-port channels that can be used. This factor affects the effective utilization ofUTRAN resources.

• Which type of RRC connection mobility procedures that are used. For exam-ple, in one state UE performs handovers whereas in another one Cell Reselec-tion.

• The level of UE activity, e.g. whether it is known on cell or URA level andwhether or not it uses DRX. This is a deciding factor for UE battery consump-tion and longer standby time. In principle, UE should be in a power savingstate, if inactive. At the same time, it should be possibly to quickly make astate transition from stand by state to active state10.

In nutshell, the UE behaviour is broadly decided by the state in which it currentlyis. Therefore, the knowledge about RRC state is very crucial in 3G understanding.

There are two modes: idle mode and connected mode. When UE is in connectedmode, its behaviour is decided by the sub-state in which it is. There are 4 sub-statesdefined. They are, Cell DCH, Cell FACH, Cell PCH & URA PCH.

• [1. IDLE Mode]

When a UE is in Idle Mode, there is no RRC connection between the UE andthe RNC. In other words, RNC does not even know that this UE exists inits area. In such a situation, UE keeps on listening to system information ofthe cell and periodically reads paging channel. After being paged, UE canestablish an RRC connection.

Similarly, to initiate a call, UE can establish and RRC connection with RNCand use it to perform call control signalling.

• [2. Connected mode]

2.a Cell DCH: The CELL DCH state is characterized by:

– A dedicated physical channel is allocated to the UE in uplink anddownlink.

– The UE is known on cell level according to its current active set.

– UE shall use the connected mode measurement control informationreceived in other states until new measurement control informationhas been assigned to the UE.

10The words standby and active mentioned above are used as English words rather than telecomspecific technical words.


– It shall perform measurements and transmit measurement reportsaccording to the measurement control information.

– UE performs handover in this state - soft, softer or hard handover.

– Battery consumption is the highest in Cell DCH state (≈ 300 -400mA11).

– From Operator’s perspective, this state is very expensive because cer-tain dedicated radio resources have to be reserved for one subscriber.

2.b Cell FACH: The Cell FACH state is characterized by:

– Neither an uplink nor a downlink dedicated physical channel is allo-cated to the UE.

– The UE continuously monitors FACH tranport channel in the down-link (mapped on S-CCPCH physical channel).

– The UE is assigned a default common transport channel in the up-link (e.g. RACH) that it can use anytime according to the accessprocedure defined by system information.

– The UE is known on cell level according to the cell where the UE lastmade a cell update. It performs cell reselection and upon selecting anew UTRAN cell, initiates a cell update procedure.

– UE is identified by a C-RNTI on common transport channels. Thescope of C-RNTI is limited to a cell. If a new cell is selected, a newC-RNTI must be allocated.

– UE must monitor a FACH to receive signalling messages or user dataaddressed to the UE or any broadcast messages.

– UE performs measurements and transmits measurement reports ac-cording to the measurement control information.

– Battery consumption in this state is lower than that in Cell DCHstate but yet very high(≈ 150-200 mA).

Therefore, Cell FACH should not be considered as standby state. Itis an active state. The difference compared to Cell DCH is the usageof common channel rather than a dedicated channel.

2.c Cell PCH: The Cell PCH state is characterized by:

– Neither an uplink nor a downlink dedicated physical channel is allo-cated to the UE.

– The UE uses DRX for monitoring a PCH via an allocated PICH.

11UE battery consumption strongly depends on the handset’s hardware, features and configura-tion. Therefore, the number mentioned here should be used as approximate value for understandingpurpose.


– No uplink activity is possible. If the UE wants to make an uplinkaccess, it autonomously shall enter the Cell FACH state and informRNC about it using cell Update signalling message.

– The UE is known on cell level according to the cell where the UElast made a cell update in CELL FACH state.

– In this state, UE shall monitor the paging occasions according to theDRX cycle and receive paging information on the PCH.

– UE shall acquire system information on the BCH and use the mea-surement control information according to that system informationwhen no dedicated measurement control information has been as-signed to the UE.

– Perform cell reselection and upon selecting a new UTRA cell, enterthe CELL FACH state and initiate a cell update procedure.

– Perform measurements according to the measurement control infor-mation. Consequently, when needed, enter CELL FACH state andtransmit measurement reports.

– In Cell PCH state, the UE battery consumption is very small (≈ 5-15mA).

2.d URA PCH: The URA PCH state is very similar to the CELL PCHstate. Therefore, a [X] sign has been printed in front of those pointswhich differentiate between these two states. Other points are commonin both the states. The URA PCH state is characterized by:

– Neither an uplink nor a downlink dedicated physical channel is allo-cated to the UE:

– The UE uses DRX for monitoring a PCH via an allocated PICH.

– No uplink activity is possible. If the UE wants to make an uplinkaccess it autonomously enters the Cell FACH state.

X The UE is known on URA level according to the URA assigned tothe UE during the last URA update in CELL FACH state.

– In this state, the UE shall monitor the paging occasions according tothe DRX cycle and receive paging information on the PCH.

– Acquire system information on the BCH and use the measurementcontrol information according to that system information when nodedicated measurement control information has been assigned to theUE.

X Perform cell reselection and upon selecting a new UTRA cell thatdoes not match the URA assigned to the UE, enter the CELL FACHstate and initiate a URA update procedure.


– Perform measurements according to the measurement control infor-mation when needed according to the measurement control informa-tion, enter CELL FACH state and transmit measurement reports.

– Just like the CELL PCH state, in URA PCH state also, the UEbattery consumption is very small (≈ 5-15 mA).

Some advanced readers might notice that there are a lot of details about RRCstates that could be added in the previous section. Their thoughts are absolutelyright. I wanted to keep is simple and short. For more details, readers areadvised to refer to TS 25.331.

5.6.2 RRC States Transitions

For the discussion about RRC State transition, URA PCH will not be discussed.This will simplify our learning. Afterwards, the same concepts can be extended byinvolving URA PCH as well.

From inactive to active transitions

This subsection will mainly treat the transition, which results in Idle to connectedmode transition, DCH allocation or DCH bit rate upgrade.

1. RRC Idle to CELL DCH Transition: From RRC IDLE, UE can directlyenter CELL DCH or Cell FACH state depending on the establishment causespecified by UE in the RRC Connection Request message. The completesignalling flow is shown in figure 5.5.

2. CELL FACH to CELL DCH Transition: This transition takes placewhen UE has no DCH allocated. In this scenario, it can use RACH in UL& FACH in DL. But if the UE requires higher bitrates in either DL or UL,a request is received at RNC either from UE or from within RNC. This istypically called as Capacity Request.

This capacity request is generated when the UE or RNC buffer contains data[in Bytes] which exceeds a certain threshold. In UL, the capacity request isofficially known as Event 4A.

3. CELL DCH to CELL DCH Transition: This special case is not a statetransition but we should still discuss it. When a UE has been allocated somebit rates in UL & DL and yet the amount of data [in Bytes] exceeds a certainthreshold, then DCH is upgraded to a higher bit rate, if allowed by the cellload condition.


Figure 5.10: RRC State Transition: From Inactive � Active behaviour

4. Cell PCH to Cell FACH Transition: If a packet session remains inactivefor several seconds or minutes, the UE will enter Cell PCH state. In this state,there is no possibility to transmit or receive any data.

If RNC receives data from SGSN for the UE in DL: RNC will page theUE in the Cell where it last performed a Cell Update. UE in return re-sponds to this paging with another Cell Update message where the causewill be explicitly specified as Paging Response. This response will go toRNC using RACH and UE will enter Cell FACH state where once againthe data transmission can take place.

If UE has some data to send in UL: On the contrary, if the UE has somedata to send, it autonomously enters into the CELL FACH state. Onceagain, on RACH it sends a Cell Update message to RNC where the causeis specified as Uplink Data transmission.

From Active to Inactive Transitions

In contrast to the discussion in the previous section, this subsection will mainlytreat the transition which happens, if the UE becomes inactive. We will start by


imagining the UE has been allocated some DCH channel with N kbps in UL andM kbps in DL. Now let us discuss the UE behaviour if it becomes inactive for a fewseconds.

Figure 5.11: RRC State Transition: From Active � Inactive behaviour

1. CELL DCH to Cell FACH Transition: In CELL DCH state, UE hasa dedicated code and power allocation. If RNC’s Packet scheduler detectsinactivity in UL & DL, the dedicated resources are taken back from UE andit can be sent to CELL FACH state. The timer value used in figure 5.11 isto give a rough idea about the range which this parameter should take. Inpractice, network optimizers can change these values to control the wastage ofresources in cell.

2. CELL FACH to Cell PCH Transition: As it was shown in section 5.6.1,CELL FACH state is a state where UE constantly monitors FACH channel.This causes very high battery consumption in UE. Therefore, if inactivity isdetected in this state, the UE moves to the real power saving state known asCell PCH.

3. Cell PCH to RRC IDLE Transition: In Cell PCH, UE can generally stayinctive for a longer period because neither it is holding any network resourcenor it is wasting its battery power.


5.7 Power Control

As we have seen in the sections 5.2.1 & 5.2.2, transmit power in any CDMA-basedsystem is directly connected to the capacity of a cell. Therefore, it is desired tokeep the transmit power level at a minimum level which will be just enough tomeet the quality target but not exceed the desired quality. In UMTS, this task isaccomplished by 3 types of power control algorithms, which are explained in thissection.

DL Common Channels UL Common Channels

P-SCH Primary Synchronization Ch.

PRACH Physical Random Access Ch.

S-SCH Secondary Synchronization Ch.P-CPICH Primary Common Pilot Ch.P-CCPCH Pri. Common Control Physical Ch.S-CCPCH Sec. Common Control Physical Ch.PICH Paging Indication Channel Ch.AICH Acquisition Indication Channel Ch.

DL Dedicated Channels UL Dedicated Channels

DPCH Dedicated Physical ChannelDPDCH Dedicated Phy. Data Ch.DPCCH Dedicated Phy. Control Ch.

Table 5.1: List of all R99 Physical channels

Table 5.1 shows a list of all UL & DL physical channels of R99 UMTS. Among these:

• The DL common channels do not undergo any power control. The power ofthese channels is decided by radio network planners and remains fixed through-out the operation. Their power values can be changed as an optimization effortby the optimization engineers but RRM plays no role in dynamically changingthe power of DL common channels.

• UL Common channel PRACH is used for making initial access to the net-work. Additionally, in UMTS, PRACH can carry small amount of UL NRTdata traffic. The power control on PRACH is known as Open Loop PowerControl.

• From the table 5.1, the only remaining channels are UL & DL dedicated chan-nels. These are the main traffic channels in 3G. These channels undergo twopower control mechanisms in parallel, known as Inner Loop Power Controland Outer Loop Power Control.

5.7. POWER CONTROL 145

5.7.1 Open Loop Power Control

Source : 3GPP TS 25.211, 25.214, 25.331

According to Open Loop Power Control of PRACH channel, UE transmits a PRACHpreamble with a certain initial power (see equation 5.7). If it does not receive anyresponse in downlink on the Aquisition Indication channel (AICH), it ramps up thepower and sends the next preamble with a higher power. UE keeps on doing it untilit receives the response from Node B.

According to the procedure defined by 3GPP TS 25.331 (section 8.5.7), UE calcu-lates the power for the first preamble as:

Preamble Initial Power = Primary CPICH TX power

− CPICH RSCP

+ UL interference

+ Constant Value (5.7)

• “Primary CPICH Tx power” and “Constant value” are broadcasted bysystem information in System Information Block type 5;

• “UL interference” is broadcasted by system information in System Infor-mation Block type 7;

• and the CPICH RSCP is measured by UE;

As expressed by equation 5.7, the initial preamble’s strength can be controlled bya constant value. This parameter can be in the range of [-35 . . . -10] dB. Once, thevalue of this parameter is fixed, then the equation can be simplified as

Preamble Initial Power ∝ Primary CPICH TX power− CPICH RSCP

∝ Path Loss (5.8)

From equation 5.8, we can conclude that transmission power of first preamble isdirectly proportional to the path loss experienced by the UE. Hence, further awaythe UE is, stronger will be the initial preamble.


After transmitting the initial preamble UE will wait for a certain time12. Within thisperiod if there is no response from the Node B, UE will send the next preamble withan increased power. This power ramping is called Open Loop power Control.The word Open Loop means that this power control works autonomously in thetransmitter (UE) without any feedback from the receiver (Node B). The moment UEreceives a feedback from Node B, open loop PC is finished because its purpose wasonly to calculate the minimum initial UL power which will allow UE to communicatewith Node B.

As defined in 3GPP TS 25.214 (section 6.1), before the physical random-accessprocedure can be initiated, Layer 1 shall receive the following information from thehigher layers (RRC): (The parameters related to Open Loop Power Control are indicatedby [X].)

• The message length in time, either 10 or 20 ms.

X The AICH Transmission Timing parameter [0 or 1].

• The set of available signatures and the set of available RACH sub-channels for eachAccess Service Class (ASC).

X The power-ramping factor Power Ramp Step [integer > 0].

X The parameter Preamble Retrans Max [integer > 0].

X The Power offset P p-m = (Pmessage-controlPpreamble), measured in dB, between thepower of the last transmitted preamble and the control part of the random-accessmessage.

In order to know more about the RACH procedure in UMTS, advanced readers are advisedto refer to 3GPP TS 25.214, (section: ‘Physical random access procedure’). PRACHprocedure has also been discussed in chapter 4 of this book in section ULcomCH. As aquick summary, please refer to figure 5.12.

5.7.2 Inner Loop Power Control

In order to understand the fast inner loop power control of UMTS, let us review ourknowledge about UL and DL dedicated channel. As shown in figure 5.13, there are twophysical channels in UL (DPDCH and DPCCH) and only one physical channel in DL(DPCH).

12The exact time can be calculated by reading the “AICH transmission timing” from systeminformation.


Figure 5.12: Open loop Power Control on PRACH physical Channel

Figure 5.13: Slot format of UL and DL DPCH Channel

• On UL DPCCH, UE sends Pilot bits whose quality is measured by NodeB. In response, Node B sends TPC Command on DL DPCH. Basedon this TPC Command, UE can increase or decrease its transmissionpower. In figure 5.13, this phenomenon is highlighted by oval shapes.

• Similarly, on DL DPCH, Node B sends Pilot bits whose quality is mea-sured by UE. In response, UE sends TPC Command on UL DPCCH.Based on this TPC Command, Node B can increase or decrease its trans-mission power used on that particular radio link. 5.13, this phenomenonis highlighted by triangle shapes.


Source : 3GPP TS 25.214;

Section 5.1 Uplink power control,

Section 5.2 Downlink power control

The concept of power control mechanism is very easy but to understand the mathematicaldescription available in TS 25.214, we require some acquaintance with these procedures.In the following section, we will try to simplify the explanation. The exact details shouldbe studied from the reference mentioned above.

Let us discuss the uplink and downlink power control procedures one by one. First we willstart with uplink.

Uplink Inner Loop PC

3GPP TS 25.214 (section 5.1.2.2.1) provides the general description of uplink inner-looppower control. UL inner loop PC adjusts the UE transmit power in order to keep thereceived uplink signal-to-interference ratio (SIR) at a given SIR target, SIRTarget.

The serving cells (cells in the active set) should estimate signal-to-interference ratio SIREst

of the received uplink using the Pilot Bits in UL DPCCH.

On Node B side, this decision has to be taken:

• if SIREst > SIRTarget then the TPC command to transmit is “0”.

• if SIREst < SIRTarget then the TPC command to transmit is “1”.

If UE is in soft handover with 2 or more cells, it is possible that it received different TPCCommands from different cells. For example, in 2 cells TPC Command = 1 and one cellTPC command = 0.

UE must combine the multiple TPC commands and derive one final TPC command thatwill be effective in that slot. TPC Command is “0” if at least one cell is sendingTPC command = “0” and TPC Command is “1” only if all the cells are sending TPCcommand =“1”.

To convert the binary values (0 or 1) to the power step (+1 dB, +2 dB, -1 dB, 0 dB orany other value), UE uses following guidelines:

• If the received TPC command is equal to 0, then TPC cmd for that slot is -1.

∆DPCCH = ∆TPC · TPC cmd

(or) Ptx,DPCCH (n+ 1) = Ptx,DPCCH (n)−∆TPC (5.9)


• If the received TPC command is equal to 1, then TPC cmd for that slot is +1.

∆DPCCH = ∆TPC · TPC cmd

(or) Ptx,DPCCH (n+ 1) = Ptx,DPCCH (n) + ∆TPC (5.10)

On UE side, the TPC command is interpreted according to the power control algorithmselected by operator.

[PCA 1 Power Control Algorithm 1 (3GPP TS 25.214 section 5.1.2.2.2)]

• When PCA 1 is selected, UE responds to TPC commands every time slot. Inother words, Power control happens at a rate of 1500 times per second. Therules for TPC cmd calculation are explained in equations 5.10 & 5.9.

• ∆TPC = 1 dB or 2 dB, which is derived from the UE-specific higher-layerparameter “TPC-StepSize”. This parameter value is signalled to UE by RNCusing L3 RRC signalling at the time of DCH allocation.

[PCA 2 Power Control Algorithm 2 (3GPP TS 25.214 section 5.1.2.2.3)]

• When the PCA 2 is selected, then UE responds to TPC command every 5th

time slot. This reduces the frequency of power control from 1500 to 300 timesper second.

– For first four slots in set, TPC cmd = 0.

– For the 5th time slot, UE follows following rule:

∗ If all 5 TPC commands within a set are 1 (i.e., 11111) thenTPC cmd = +1 in the 5th slot.

∗ If all 5 TPC commands within a set are 0 (i.e., 00000) thenTPC cmd = −1 in the 5th slot.

∗ Otherwise, TPC cmd = 0 in the 5th time slot.

• ∆TPC = 1 dB. For Algorithm 2, ∆TPC shall always take the value 1 dB.

After doing all this analysis, UE knows TPC cmd = ‘0’ or ‘1’ in every slot.

Two algorithms shall be supported by the UE for deriving a TPC cmd. Which of thesetwo algorithms is used is determined by a UE-specific higher-layer parameter, “PowerCon-trolAlgorithm”, and is signalled to UE by RNC using L3 RRC signalling at the time ofDCH allocation.

Summary of uplink fast power control algorithms:


Power Control Algorithm 1: If the power control algorithm is PCA 1,then the UE responds of TPC commands as following:

If TPC bit = ‘1’ ⇒ Increase the power by 1 or 2 dB

If TPC bit = ‘0’ ⇒ Decrease the power by 1 or 2 dB

Power Control Algorithm 2: PCA 2 means:

If 5 consecutive TPC bits are = ‘11111’ ⇒ Increase the power by 1 dB

If 5 consecutive TPC bits are = ‘00000’ ⇒ Decrease the power by 1 dB

If 5 consecutive TPC bits are = ‘01101’ ⇒ Ignore the commands


If 5 consecutive TPC bits are = ‘. . . ’ ⇒ Ignore the commands

Please refer to section 5.1 Uplink power control in 3GPP TS 25.214 for the exact math-ematical analysis and more details about the UL inner loop power control. Now let usfocus on the DL power control mechanism.

Downlink Inner Loop PC

We must remember, Node B is transmitting several physical channels simul-taneously. The power control explained in this section works independentlyon all the DL DPCHs. In other words, if there are 10 users using speechservice in a cell, the power used for each user is calculated separately andindependently.

As explained in the introductory remarks about power control, the DL inner loop PC ad-justs the Node B transmit power to maintain the received Downlink signal-to-interferenceratio (SIR) at a given SIR target, SIRTarget. Node B adjusts it transmit power accordingto the TPC commands received from UE in UL DPCCH. UE calculates the value of TPCcommand by comparing the desired Target SIR and actually measured SIR.

Figure 5.14, shows that DPDCH and DPCCH are time-multiplexed to form DPCH. TheDL power control algorithm controls the DL transmit power of the ’pilot bits’ field ofDPCCH. From this figure, one can notice the power offsets as following:

P01: The power offset between TFCI fields of DPCCH and the DPDCH.

P02: The power offset between TPC fields of DPCCH and the DPDCH.

PO3: The power offset between PILOT BITS fields of DPCCH and the DPDCH.


Figure 5.14: Slot format of DL DPCH Channel

As power control takes place, the relative power offsets between the DPCCH and DPDCHare not changed.

According to 3GPP TS 25.214 (section 5.2.1.2.1 UE behaviour), the UE shall generateTPC commands to control the network transmit power and send them in the TPC fieldof the uplink DPCCH. The UE shall check the downlink power control mode (DPCMode)before generating the TPC command. The DPC MODE parameter is a UE specificparameter controlled by the UTRAN.

• If DPCMode = 0: the UE sends a unique TPC command in each slot and the TPCcommand generated is transmitted in the first available TPC field in the uplinkDPCCH;

• If DPCMode = 1: the UE repeats the same TPC command over 3 slots and the newTPC command is transmitted such that there is a new command at the beginningof the frame.

According to 3GPP TS 25.214 (section 5.2.1.2.2 UTRAN behaviour), upon receiving theTPC commands, UTRAN shall adjust its downlink DPCCH/DPDCH power accordingly.For DPCMode = 0, UTRAN shall estimate the transmitted TPC command TPCest to be0 or 1, and shall update the power every slot. If DPCMode = 1, UTRAN shall estimatethe transmitted TPC command TPCest over three slots to be 0 or 1, and shall update thepower every three slots.

According to 3GPP TS 25.214, the power control step size can take four values: 0.5, 1,1.5 or 2 dB. It is mandatory for UTRAN to support the step size of 1 dB, while supportof other step sizes is optional.

Summary of downlink fast power control algorithms:


DPCMode = 0: If the power control algorithm is DPC Mode=0, the thenNode B responds of TPC commands as following:

If TPC bit = ‘1’ ⇒ Increase the power by a fixed step size

If TPC bit = ‘0’ ⇒ Decrease the power by a fixed step size

DPCMode = 1: If the power control algorithm is DPC Mode=1, the thenNode B responds of TPC commands as following:

If 3 consecutive TPC bits are = ‘111’ ⇒ Increase the power by a fixed step size

If 3 consecutive TPC bits are = ‘000’ ⇒ Decrease the power a fixed step size



If 3 consecutive TPC bits are = ‘. . . ’ ⇒ Ignore the commands

5.7.3 Outer Loop Power Control

Outer Loop Power Control adjusts the SIR target (SIRTarget), in order to achieve a desiredTarget Block Error Rate (BLERTarget). Therefore, the decisions to increase or decreasethe SIR Target are made based on the comparison of estimated (measured) BLER withTarget BLER.

DL Outer Loop PC

DL outer loop power control is mainly implemented within the user equipment. At thebeginning of connection setup, RNC informs UE about the desired value of block errorrate (BLERTarget). When UE receives the data, it calculates the actual value of BLERreceived in the current TTI. This procedure is illustrated in figure 5.15.

• If Estimated BLER is < Target BLER then the DL Target SIR is reduced.

• If Estimated BLER is > Target BLER then the DL Target SIR is increased.

• If Estimated BLER is = Target BLER then the DL Target SIR is not modified.

Figure 5.15 illustrates both DL innerloop and DL outerloop power control mechanisms.The DL outerloop function appears to be an autonomous algorithm which tries to reachthe BLERTarget as informed by the RNC at the beginning of connection setup. Hence, theUE handset vendors have some degree of freedom while implementing the DL outer loopPC.


Figure 5.15: Functionality of DL Outer Loop & Inner Loop PC

UL Outer Loop PC

Figure 5.16: Functionality of UL Outer Loop & Inner Loop PC

In uplink, the Outer Loop Power Control takes place in RNC. The whole procedure isillustrated in figure 5.16. The same sequence of steps are described in the following text:


1. At connection setup, (RRC or RAB), RNC’s admission control decides the UL BLERTarget.

2. Admission control also decides the initial, minimum and maximum SIRTarget.

3. RNC informs Node B about the initial SIRTarget.

4. On physical layer between UE and Node B, UL inner-loop power control tries toachieve this target value of SIR. The process is briefly described below.

(a) UE transmits pilot bits on UL DPCCH channel.

(b) Node B estimates the Signal-to-interference-ratio (SIREst) & decides the po-larity of TPC bits.

• if SIREst > SIRTarget then the TPC command to transmit is ‘0’

• if SIREst < SIRTarget then the TPC command to transmit is ‘1’

(c) This communication between UE and Node B happens once every slot (onceevery 2/3 ms).

5. After receiving the data from UE, the Node B forms a frame protocol frame. Thisframe has 2 parts, header and payload. Payload is for the received data from UE,but the header contains some control information. Among other things, the headerfield contains frame reliability information.

6. (In case of Soft handover), UE is connected to more than one cell or Node B. RNCreceives the frames from all the Node Bs and looks into the frame reliability infor-mation. Based on this information, RNC decides, which frame should be forwardedto the core network.

7. After combining the frames from all the Node Bs, RNC estimates the BLEREst andcompares it with BLERTarget. Based on the result from this last step, the SIR targetis either reduced, increased or kept unchanged.

8. RNC informs Node B about the modified target of SIR and the whole process repeatsonce again (steps 3, 4, 5, 6 & 7).

5.8 Handover Control

In early 90s, people were amazed to know that while talking they can movefrom one cell to another, without disconnecting the call. Now a days, we treatit as a basic functionality of cellular networks. We have certainly come a longway.

Handover is a mechanism where a UE in connected mode can move from one WCDMA cellto another cell. The target cell can be of the same radio access technology or a differentone e.g., GSM. This brings us to the point where we should classify the type of handovers

5.8. HANDOVER CONTROL 155

in WCDMA. In RRM framework, the handover control makes decisions that will be madebased on the measurement results reported primarily by the UE but also by measurementsin the network or various parameters set for each cell. In general, the handovers in allthe systems can be categorized into two families, namely Soft HO & Hard HO. A briefintroduction to both is given below.

(a) Soft Handover: Soft Handover is a handover in which the mobile station adds andremoves radio links in such a manner that the UE always keeps at least one ra-dio link to UTRAN. This can be performed on the same carrier frequencyonly. For this reason, Soft Handover allows easily the provision of macro diversitytransmission. As a result of this definition, there are areas of the UE operation inwhich the UE is simultaneously communicating via a number of radio links towardsdifferent cells.

With reference to Soft Handover, the Active Set is defined as the set of radio linkssimultaneously involved in the communication between the UE and UTRAN (i.e.,the UTRA cells currently assigning a downlink DPCH to the UE constitute theactive set). Typically, max Active Set Size = 3.

(b) Hard Handover: A Hard handover is a handover in which the mobile station has toremove all the active radio links before establishing a new radio link with the targetcell. A need of hard handover arises when:

• The target cell is a WCDMA cell but operating at a frequency other than thefrequency used in the source cell.

• The target cell belongs to a different radio access technology.

• The source and target cell are both operating at same frequency but a SHO isnot possible13.

Another way of classification of handover is based on the Radio frequency and technologyused in the source cell and the same used in the target cell. Based on this criterion, thehandover in WCDMA can be categorized in 3 groups:

1. Intra Frequency Handover: This scenario happens when the source cell is a WCDMAcell with operating frequency f1 & the target cell is also a WCDMA cell with thesame operating frequency. These kinds of handovers are typically:

• Soft HO: Inter Node B soft HO

• Softer HO: Intra Node B soft HO

• Hard HO: Inter-RNC HO but no Iur interface between the two RNC’s.

13This happens in the case of Inter-RNC Handover without Iur interface support.


2. Inter Frequency Handover (IFHO): In GSM, the neighbouring cells generally op-erate on different frequency. Therefore, while moving from one cell to another issimply an Inter Frequency HO, but there is a big difference between TDMA-based2G system and CDMA-based 3G system. In CDMA systems, UE is constantlyreceiving & transmitting on its serving frequency. Therefore, UE cannot measureanother carrier without interrupting its reception on the serving UTRAN frequency.Hence we need some kind of scheme where some well-defined gaps are created inwhich UE can perform measurements of signal strength of P-CPICH of the inter-frequency target cell. This concept is called Compressed Mode and will be discussedlater in this section.

Concept of compressed measurement is also needed for 3G to 2G Handover or ISHO.

3. Inter System Handover (ISHO): In the early days of UMTS deployment, it can beanticipated that the service area will not be as contiguous and extensive as existingsecond generation systems. It is also anticipated that UMTS network will be anoverlay on the 2nd generation network and utilize the latter, in the minimum case,as a fall back to ensure continuity of service and maintain a good QoS as perceivedby the user.

Therefore, the majority of 3G mobile devices will be a multimode equipment, capableof using both 2G & 3G. This concept is beneficial for both the technologies. Where3G gets some kind of coverage safety belt from the underlying legacy 2G network,at the same time, 2G investments can be reused in the modern 3G technology. Thisbackward compatibility of 3G to 2G is a major driving force in the success of UMTS.

5.8.1 Active, Monitored and Detected cells

According to 3GPP TS 25.331 (section 8.4.0 ‘Measurement related definitions’), cells thatthe UE is monitoring are grouped in the three mutually exclusive categories:

Active Set Cells: Cells, which belong to the active set. User information is sent fromall these cells. The cells in the active set are involved in soft handover. The UEshall only consider active set cells included in the variable CELL INFO LIST formeasurement; i.e., active set cells not included in the CELL INFO LIST shall notbe considered in any event evaluation and measurement reporting.

Monitored Cells: Cells, which are not included in the active set, but are included inthe CELL INFO LIST belong to the monitored set. In common man’s language, wecan call these cells as defined neighbours.

Detected Cells: Cells detected by the UE, which are neither in the CELL INFO LISTnor in the active set belong to the detected set. Reporting of measurements of thedetected set is only applicable to intra-frequency measurements made by UEs in theCELL DCH state. These cells can be understood as missing neighbours.


5.8.2 Soft/Softer Handover

The only difference between soft and softer handover is:

• In Soft Handover, the cells taking part in HO are served by two different Node Bs,whereas, in Softer handover, they belong to the same Node B.

• In Soft Handover, RNC receives the data from two (or more) Node Bs. Both ofthese data flow can have different block error rates (BLER). RNC can select thedata with less BLER and ignore the other one. This procedure in called MacroDiversity Combining (MDC). An example of this was shown in the UL outer loopPC section (see figure 5.16).

In Softer HO, there is no MDC because it is Node B which performs the combiningof two uplink radio links.

• Another difference between the Soft & Softer HO is in terms of Iub utilization. InSofter Handover, the data is sent/received on Iub only on one link, where as inSot handover at least two Iub links are used and in worst case, even an Iur link isrequired if the two Node Bs are controlled by two different RNCs.

Otherwise from the RF perspective, Soft and Softer HO are very similar. Therefore, inthe next sections the word Soft Ho will be used for both types of HO.

Soft handovers areMobile Evaluated Handovers, MEHO. Therefore, it is UE which initiatesthe handover procedure. As defined in section 5.1.3, UE can inform RNC about the needfor handover either periodically or based on some events.

According to 3GPP TS 25.331 (section 14.1.1 ‘Intra-frequency measurement quantities’),a measurement quantity is used to evaluate whether an intra-frequency event has occurredor not. It can be:

1. Downlink Ec/No.

2. Downlink path loss. For FDD:

Pathloss in dB = Primary CPICH Tx power− CPICH RSCP

For Primary CPICH Tx power, the IE “Primary CPICH Tx power” shall be usedwhich is signalled to UE in system information (SIB 5). The unit is dBm. CPICHRSCP is the result of the CPICH RSCP measurement. The unit is dBm.

3. Downlink received signal code power (RSCP) after despreading.

In practice, most commonly, CPICH Ec/No is chosen as a measurement quan-tity for Soft HO decisions. For Inter-frequency and Inter-System handover,both CPICH RSCP and CPICH Ec/No are used to trigger the handover mea-surements.


For Soft handover, there are three main events defined in the specifications 3GPP TS25.331. Within Measurement Control message, the UTRAN notifies the UE which eventsshould trigger a measurement report. The listed events are the toolbox from which theUTRAN can choose the reporting events that are needed for the implemented handoverevaluation function, or other radio network functions.

In the description about the SHO related events, we will assume that Intra-frequency measurement quantity is CPICH Ec/No. The explanation is a sim-plified version of the complicated (and complete) procedure explained in 3GPPTS 25.331.

• [Event 1A:] A Primary CPICH enters the reporting range.

Figure 5.17: Event 1A triggered

Commonly network planners and optimizers define event 1A as Event1A is used to ADD a cell to the active set.

As shown in figure 5.17, event 1A can take place when the UE has an active set =1 or 2. The threshold value of CPICH Ec/No is calculated with reference to thebest active set cell. Therefore, if a neighbour cell is to be added to the active set,its CPICH Ec/No should be greater than the threshold shown in the figure. Thethreshold does not have an absolute value but relative to the best active set cell.

In right sub-figure of figure 5.17, there are 2 cells in AS but the threshold forhandover evaluation is calculated with reference to the cell with SC ‘a’ because it isthe strongest cell in AS.

(CPICH Ec/No)Neighbour Cell > (CPICH Ec/No)Best, AS Cell −Add Window (5.11)


– UE � RNC: Measurement ReportAfter event 1A gets triggered, UE reports this to RNC by sending a L3 RRC:Measurement Report massage. In this, UE specifies the DL SC of the neigh-bour cell along with the CPICH Ec/No value. This signalling scenario wasillustrated in figure 5.7 in admission control section.

– RNC � UE: Active Set UpdateAt this moment, RNC performs admission control for the target cell. Onsuccessful addition decision, RNC informs UE by sending a L3 RRC: ActiveSet Update message.

– UE � RNC: Active Set Update CompleteIn response, UE finally replies with RRC: Active Set Update Complete.

Adding another cell to the active set makes the neighbours of the added cell alsothe neighbours for UE. Therefore, RNC performs neighbour list combining andinforms UE about its decision using RRC: Measurement Control message.

• [Event 1B:] A primary CPICH leaves the reporting range .

Figure 5.18: Event 1B triggered

Commonly network planners and optimizers define event 1B as Event1B is used to DELETE a cell from the active set.

As shown in figure 5.18, e1B takes place when the UE has an active set = 2 or3. Just like e1A, here also the threshold value of CPICH Ec/No is calculated withreference to the best active set cell. Therefore, if a neighbour cell is to be deletedor removed from the the active set, its CPICH Ec/No should be weaker than the


threshold shown in the figure. The threshold does not have an absolute value butrelative to the best active set cell.

In the left sub-figure of figure 5.18, there are 2 cells in the AS and in the rightsub-figure there are 3 cells in AS. In both the scenarios, the threshold for handoverevaluation is calculated with reference to the cell with SC ‘a’ because it is thestrongest cell in AS.

(CPICH Ec/No)AS,Cell < (CPICH Ec/No)Best, AS Cell −Drop Window (5.12)

The signalling procedures explained in the case of event 1A are also valid in thiscase. The name of messages are the same. In short:

– UE � RNC: Measurement Report

– RNC � UE: Active Set Update

– UE � RNC: Active Set Update Complete

After deleting an AS cell, RNC performs neighbour list combining and informsUE about its decision using RRC: Measurement Control message.

• [Event 1C:] A non-active primary CPICH becomes better than an active primaryCPICH.

Figure 5.19: Event 1C triggered

Commonly network planners and optimizers define event 1C as Event 1C isused to REPLACE a ‘weak AS Cell’ with a ‘Stronger one outsidethe AS’.


As shown in figure 5.19, e1C can only take place when the UE has an active set = 3. Inother words, when the AS is full. In contrast to e1A & e1B, where the threshold value ofCPICH Ec/No is calculated with reference to the best active set cell, for e1C, the thresholdis calculated with reference to the Weakest active set cell. Therefore, if a neighbour cellis to be replaced with one of the AS cells, its CPICH Ec/No should be stronger than thethreshold shown in figure 5.19.

In figure 5.18, there are 3 cells in AS. The threshold for handover evaluation is calculatedwith reference to the cell with SC ‘c’ because it is the weakest cell in AS.

(CPICH Ec/No)Neighbour Cell > (CPICH Ec/No)Weakest, AS Cell +Replacement Window(5.13)

The signalling procedures explained in the case of event 1A & 1B.

As a summary, the SHO mechanism can be summarized by figure 5.20. This figure hasbeen copied from ‘Figure 5-1: Example of Soft Handover Algorithm’ of 3GPP TR 25.922V7.0.0 which explains Radio resource management (RRM) strategies. Advanced readerswho might be interested in more details, are advised to refer to section 5.1.4.2 in TR25.922.

Figure 5.20: Summary of Soft Handover Mechanism (from TR 25.922)


5.8.3 ISHO and IFHO Triggering

In CDMA, the UEs with only one receiver are only monitoring the DL frequency used bythe active set cells. Therefore, to start the inter-frequency or inter-system measurements,certain events must take place. In general, there are several reasons to start an IFHO orISHO. The following is a non-exhaustive list for causes that could be used for the initiationof a handover process.

• Uplink quality (e.g.BLER)

• Downlink quality (e.g. Transport channel BLER)

• Downlink signal measurements (e.g. CPICH RCSP, CPICH Ec/No, Pathloss)

• UE transmit power

• Node B radio link Power

• Traffic load (or Load Based HO)

• Pre-emption

• Change of service (service based HO)

• . . .

• . . .

The exact strategies implemented in the RAN depends on infrastructure vendors. Fromthose strategies, the network optimizers can enable only a subset (or all the strategies)that will control inter-system and inter-frequency handover. In this book, we will discussthe ISHO/IFHO due to downlink pilot channel measurements (e.g. CPICH RCSP, CPICHEc/No).

As depicted by the left sub-figure of figure 5.21, the downlink signal of the active set cellhas become very weak. According to 3GPP TS 25.331, there are specific events describedfor these scenarios.

Event 1F: A Primary CPICH becomes worse than an absolute threshold. Thestrength of P-CPICH can be measured in terms of CPICH RCSP, CPICH Ec/No. Inorder to trigger an event 1F, either of the two quantities has to fall below a certainthreshold. In figure 5.21(see left sub-figure), these thresholds are depicted as ‘N’ dBfor Ec/No and ‘M’ dBm for RSCP.

Please note: A UE can be in SHO with 2 or 3 cells. If 1F is triggered for one ofthe AS cells, UE reports this to RNC but RNC does not start the measurementmechanism because there are still other AS cells, which can maintain the servicewith adequate quality. Only when the e1F is triggered for the last AS cell, themeasurements procedure is started.


Figure 5.21: Event 1E & 1F triggered

Event 1E: A Primary CPICH becomes better than an absolute threshold. Inorder to trigger an event 1E, either of the two quantities has to rise above a certainthreshold. In figure 5.21 (see right sub-figure), these thresholds are depicted as ‘N+ ∆1’ dB for Ec/No and ‘M + ∆2’ dBm for RSCP.

In simple words, event 1E can be called as Cancel previously reported event 1F.

Summary: Event 1F is a method by which UE informs RNC about its poor3G coverage and the need for an IFHO or ISHO and Event 1E is a method bywhich UE informs RNC about its 3G reception with acceptable signal quality.

For a more detailed information, readers should refer to 3GPP TS 25.331. Section 14.1.2.5describes the details of Event 1E & 14.1.2.6 illustrates Event 1F.

5.8.4 Inter-Frequency Measurements

Source: 3GPP TS 25.331, section 14.2.0a Inter-frequency measurement

quantities

Within the measurement reporting criteria field in the MEASUREMENT CONTROL mes-sage, UTRAN notifies the UE which events should trigger the UE to send a MEASURE-MENT REPORT message. The listed events are the toolbox from which the UTRAN


can choose the reporting events that are needed for the implemented handover evaluationfunction or other radio network functions. The measurement quantities are measured onthe monitored primary common pilot channels (CPICH) in the FDD mode. In order tounderstand the events of IF measurements, we need to define 2 terms:

1. Non-used Frequency: A “non-used frequency” is a frequency that the UE has beenordered to measure upon but is not used for the connection.

2. Used Frequency: A “used frequency” is a frequency that the UE has been orderedto measure upon and is also currently used for the connection.

The following events are described in section 10.3.7.19 of 3GPP TS 25.331. This sectionis about Inter-frequency measurement reporting criteria.

1. Event 2a: Change of best frequency.

2. Event 2b: Event 2b is triggered when following 2 conditions are fulfilled:

• The estimated quality of the currently used frequency is below a certain thresh-old, and

• the estimated quality of a non-used frequency is above a certain threshold.

3. Event 2c: The estimated quality of a non-used frequency is above a certain threshold.

4. Event 2d: The estimated quality of the currently used frequency is below a certainthreshold.

5. Event 2e: The estimated quality of a non-used frequency is below a certain threshold.

6. Event 2f: The estimated quality of the currently used frequency is above a certainthreshold.

5.8.5 Inter-System Measurements

Source: 3GPP TS 25.331, section 14.3.0a Inter-RAT measurement quantities

At the time of writing of this book, the commonly used inter-system handover from anUTRAN cell are towards a GERAN cell (2G) or a E-UTRAN cell (LTE). We will discussonly the handovers from 3G to 2G.

A measurement quantity is used by the UE to evaluate whether an inter-RAT measurementevent has occurred or not is described below:

Measurement quantity for UTRAN: The measurement quantity for UTRAN is usedto compute the frequency quality estimate for the active set, as described in the nextsubclause, and can be:


• Downlink Ec/No.

• Downlink received signal code power (RSCP) after despreading.

Measurement quantity for GSM: The measurement quantity for GSM can be:

• GSM Carrier RSSI

Within the measurement reporting criteria field in the MEASUREMENT CONTROL mes-sage, UTRAN notifies the UE which events should trigger the UE to send a MEASURE-MENT REPORT message. The listed events are the toolbox from which the UTRANcan choose the reporting events that are needed for the implemented handover evaluationfunction or other radio network functions. The measurement quantities are measured onthe monitored primary common pilot channels (CPICH) in the FDD mode. In order tounderstand the events of inter-system measurements, we need to define 2 terms:

1. Other System: “Other system” is e.g., GSM or E-UTRA14. But in this book, we willdiscuss on the GSM case.

2. Used Frequency: A “used UTRAN frequency” is a frequency that the UE have beenordered to measure upon and is also currently used for the connection to UTRAN.

Following events are described in section 10.3.7.30 of 3GPP TS 25.331. This section isabout Inter-RAT measurement reporting criteria.

1. Event 3a: Event 3a is triggered when the following two conditions are fulfilled:

• The estimated quality of the currently used UTRAN frequency is below acertain threshold, and

• The estimated quality of the other system is above a certain threshold.

2. Event 3b: The estimated quality of the other system is below a certain threshold.

3. Event 3c: The estimated quality of the other system is above a certain threshold.

4. Event 3d: Change of the best cell in the other system.

5.8.6 Compressed Mode

In the previous section, we saw how a UE informs RNC about the need for handover toanother frequency UTRAN cell or a cell with another RAT (e.g. GSM). In this section,we will try to investigate the method by which the UE can perform measurements on

14LTE


another frequency while resuming the service on its serving frequency. This method iscalled Compressed Mode15.

According to 3GPP TR 25.922, Compressed Mode can be avoided if the device supportsdual-receiver. UE can signal this capability to RNC using at the time of RRC establish-ment. But the majority of UEs, which are commercially available, have only one receiver,therefore, the radio planners cannot rely on this option. It is assumed that UEs do notsupport dual-receivers and therefore, compressed mode is very much needed.

Methods of Compressed Mode

Spreading Factor by 2 or SF/2: This method has advantages and also disadvantages:

Adv: This method allows us to achieve the same bitrate in compressed frames asin the normal frame.

Disadv: In compressed frames, the SF becomes half, therefore, the power require-ment becomes double. This causes problems in terms of coverage and capacity.

Higher Layer Scheduling: This method also has advantages and disadvantages:

Adv: This method allows us to transmit with the same power in compressed framesand normal frames.

Disadv: The bit rate in compressed mode is reduced because “higher” layers havescheduled less data in compressed frame.

5.8.7 Inter System HO Signalling

The signalling procedures involved with Inter-system HO is explained in chapter section9.9. In short, the steps involved in this procedure are:

1. Phase 1: ISHO triggers

2. Phase 2: Compressed Mode measurements for BCCH RSSI

3. Phase 3: Measurement Reports (UE to RNC)

4. Phase 4: Compressed Mode measurements for BSIC verification


6. Phase 6: HO decision

7. Phase 7: Signalling between SRNC & BSC

15This has nothing to do with data compression as we know from our computer and IP knowledge.


8. Phase 8: Communication between UE and GERAN

9. Phase 9: Confirmation about successful HO to RNC

Please refer to section 9.9 for the signalling flow and more explanation.


Copyright Notices

In order to create some figures, tables and text-sections, the following reference materialhas been used. Information has been interpreted and presented in a simplified manner.The original references are provided here.

Main reference material for this book has been technical specifications (TSs) and technicalreports (TRs) of 3rd Generation Partnership Project (3GPP).

Figure 5.3 on page 122 Figure 13 of 3GPP TS 25.433 v 7.0.0.Figure 5.4 on page 124 Figure 40 of 3GPP TS 25.433 v 7.0.0.Figure 5.20 on page 161 Figure 5-1 of 3GPP TS 25.922 v 7.0.0.Text about RRM Strategies insection 5.3 on page 129

Section 12 of 3GPP TS 25.922 v 7.0.0.

Text about Common-NBAP mea-surements on page 122


Text about Dedicated-NBAPmeasurements on page 123


Text about UE measurements onpage 123

Section 5.1 & 5.2 of 3GPP TS 25.215 v 7.0.0.

Text about Initial PRACHPreamble on page 145

Section 8.5.7 of 3GPP TS 25.331 v 6.9.0.

Text about Active, Monitoredand Detected cells on page 156


Text about Intra-frequency mea-surement quantities on page 157

Section 14.1.1. of 3GPP TS 25.331 v 6.9.0.

Text about IF measurementquantities on page 164

Section 14.2.0a of 3GPP TS 25.331 v 6.9.0.

Text about Event 2A to 2F onpage 164


Text about IS measurementquantities on page 164

Section 14.3.0a of 3GPP TS 25.331 v 6.9.0.

Text about Event 3A to 3D onpage 165




Text about Open Loop PC pa-rameters on page 146

Section 6.1 3GPP TS 25.214 v 6.9.0.

Text about UL Inner Loop PC onpage 148

Section 5.1.2.2.1 3GPP TS 25.214 v 6.9.0.

Text about UL PC Algorithm 1on page 149

Section 5.1.2.2.2 3GPP TS 25.214 v 6.9.0.

Text about UL PC Algorithm 2on page 149

Section 5.1.2.2.3 3GPP TS 25.214 v 6.9.0.

Text about DL PC (UE be-haviour) on page 151

Section 5.2.1.2.1 3GPP TS 25.214 v 6.9.0.

Text about DL PC (UTRAN be-haviour) on page 151

Section 5.2.1.2.2 3GPP TS 25.214 v 6.9.0.

Figure 5.12 on page 147 Figure 31 of 3GPP TS 25.211 v 9.1.0.c⃝2009. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

BIBLIOGRAPHY

[1] 3GPP TS 25.211 ver. 6.0.0 ;‘Physical channels and mapping of transport channelsonto physical channels (FDD)’




[5] 3GPP TS 25.214 ver. 6.0.0 ;‘3GPP TS 25.215, Physical layer - Measurements (FDD)’



[8] 3GPP TS 25.413 ver. 6.0.0 ;‘UTRAN Iu interface RANAP signalling’

[9] 3GPP TS 25.433 ver. 6.0.0 ;‘UTRAN Iub interface Node B Application Part (NBAP)signalling’

[10] 3GPP TS 25.331 ver. 7.0.0 ;‘Radio Resource Control (RRC) protocol specification’

[11] 3GPP TR 25.922 ver. 7.0.0 ;‘Radio resource management strategies’

[12] 3GPP TR 25.931 ver. 8.0.0 ;‘UTRAN functions, examples on signalling procedures’

[13] H.Holma and A. Toskala, ‘WCDMA for UMTS’ , 5th Edition, John Wiley & Sons.

[14] Chris Johnson, ‘Radio Access Networks For UMTS ; Principles And Prac-tice’ , John Wiley & Sons.

For HSDPA-specific details, the version of these specs should be 5.0.0 orhigher & for HSUPA-specific details, it should be 6.0.0 or higher.

170

CHAPTER

6

PROTOCOLS & INTERFACES

Abbreviations

In this module, a lot of abbreviation will be used. Therefore, it is better to introduce alist of all the abbreviations used in the coming sections.

• AAL2/5: ATM adaptation Layer type 2 / Type 5

• ATM: Asynchronous Transfer Mode

• BMC: Broadcast/Multicast Control Protocol

• BSSAP: Base Station System Application Part Protocol

• FP: Frame Protocol

• GMM: GPRS Mobility Management

• SM: (GPRS) Session Management

• GTP: GPRS Tunneling Protocol

• luUP: Iu User Plane Protocol

• MAC: Medium Access Control

171

172 CHAPTER 6. PROTOCOLS & INTERFACES

• MAP: Mobile Application Part

• MM: Mobility Management

• MTP-3B: Message Transfer Part Level 3B

• NBAP: NBAP Node B Application Part

• PDCP: Packet Data Convergence Protocol

• ALCAP: Access Link Control Application Part

• RANAP: Radio Access Network Application Protocol

• RLC: Radio Link Control Protocol

• RNSAP: Radio Network Subsystem Application Part

• RRC: Radio Resource Control

• RTCP: Real Time Control Protocol

• RTP: Real Time Protocol

• SCCP: Signalling Connection Control Part

• SCTP: Stream Control Transmission Protocol

• SMS: SMS Short Message Service

• SS: Supplementary Services

• SSCOP: Service Specific Connection-Oriented Protocol

• SSCF-NNI: Service Specific Coordination Function - Network-Network Interface

• SSCF-UNI: Service Specific Coordination Function - User-Network Interface

• UDP: User Datagram Protocol

6.1 Overview

Source: 3GPP TS 25.401; UTRAN overall description

Figure 6.1 shows the general protocol model for UTRAN interfaces. While designing thisstructure, it was planned to keep the layers and planes logically independent of each other.This strategy was designed so that protocol stacks and planes can be modified accordingto the future requirements.

6.1. OVERVIEW 173

Figure 6.1: General Protocol Model for UTRAN Interfaces (TS 25.401)

6.1.1 Horizontal Layers

The Protocol Structure consists of two main layers, Radio Network Layer, and TransportNetwork Layer. A description for both is available in 3GPP TS 25.401 (section 11.1.2).

1. Radio Network Layer: All UTRAN related issues are visible only in the Radio Net-work Layer. It defines the procedures related to the operation of Node B. The radionetwork layer consists of a radio network control plane and a radio network userplane.

2. Transport Network Layer: Transport Layer defines the procedures for establishingphysical connections between Node B and the RNC. It represents standard transporttechnology that is selected to be used for UTRAN, but without any UTRAN-specificrequirements.

6.1.2 Vertical Planes

Similarly, the UTRAN protocol structure is vertically divided into 3 planes. The descrip-tion is available in section 11.1.3 of 3GPP TS 25.401.


Interface Control Plane User Plane

Iub NBAP FPIur RNSAP FPIu-CS RANAPIu-PS RANAP GTP-U

Table 6.1: Main Protocols used on UTRAN Terrestrial Interfaces

1. Control Plane: The Control Plane consists of protocols which have functionalitypurely designed for the UMTS operation. On the Iu-CS & Iu-PS interface, thecontrol plane protocol is RANAP. On the Iur interface it is RNSAP and on Iub in-terface it is NBAP. In addition, the control plane also includes the Signalling Bearerfor transporting the Application Protocol messages.

Application Protocol is used for setting up bearers. The Signalling Bearer for theApplication Protocol may or may not be of the same type as the Signalling Protocolfor the ALCAP. The Signalling Bearer is always set up by O & M actions.

2. User Plane: The User Plane Includes the Data Stream(s) and the Data Bearer(s) forthe Data Stream(s). The Data Stream(s) is/are characterized by one or more frameprotocols specified for that interface.

3. Transport Network Control Plane: The Transport Network Control Plane doesnot include any Radio Network Layer information, and is completely in the Trans-port Layer. It includes the ALCAP protocol(s) that is/are needed to set up thetransport bearers (Data Bearer) for the User Plane. It also includes the appropriateSignalling Bearer(s) needed for the ALCAP protocol(s).

4. Transport Network User Plane: The Data Bearer(s) in the User Plane, and theSignalling Bearer(s) for Application Protocol also belong to Transport Network UserPlane. As described in the previous section, the Data Bearers in the Transport Net-work User Plane are directly controlled by the Transport Network Control Planeduring real time operation but the control actions required for setting up the Sig-nalling Bearer(s) for Application Protocol are considered O & M actions.

Figure 6.2 shows the UMTS network architecture with only the most essential networkelements. Here, various network elements are connected using well-defined standard in-terfaces called Iub, Iur & Iu, whre Iu itself has 2 versions. One towards CS core network,called as Iu-CS and the other one towards the Packet core network, called as Iu-PS.

These four are also called as UTRAN interfaces. All of these interfaces are used to carrysignalling as well as the traffic which is depicted by dashed and solid lines respectively inthe figure 6.2. On each interface, a shaded box is drawn to indicate the name of Interface,protocol used for control plane and the protocol used for user plane data transfer.

6.2. QOS AND BEARER 175

Other than the UTRAN interfaces, the figure 6.2 also illustrated the UTRAN RadioInterface protocols. The network element which controls the whole radio network is RNC.Therefore, UE & RNC need to communicate very often in UMTS. This communicationhappens using the radio protocols. Physical realization of this signalling transfer happensusing the Uu Interface ( UE � Node B) and Iub Interface (Node B � RNC).

Figure 6.2: Overview of all UTRAN Interfaces and Protocols

6.2 QoS and Bearer

Source : 3GPP TS 23.107 ; Quality of Service (QoS) concept and architecture

End-to-End Service: End-to-end service means the service as perceived by the end user.For example, the end-to-end service from one Terminal Equipment (TE) to another TE,or from laptop to web server. In order to provide a certain QoS to a user, there must bea bearer with well-defined characteristics and functionality.

End-to-end service is like a chain of several smaller links (or bearers) andit is a well-known fact that a chain is never stronger than the weakest list.Therefore, the weakest bearer in the chain will define the QoS of end-to-endservice.

End-to-end service = UMTS bearer “ + ” External Bearer.

External bearer is beyond the scope of UMTS technology. Therefore, the operator has torely on the QoS provided by the external bearer. If the external bearer is between GMSC


Figure 6.3: UMTS QoS Architecture and Bearer Concept (3GPP TS 23.107)

and external PSTN exchange, then these links can be the PCM lines which have excellentQoS with guaranteed bit rate. On the other hand, if these external bearers are betweenGGSN and some web server, then the external bearer is implemented on the IP link. TheQoS in IP is a configurable thing. But we will not discuss it here and restrict ourself tothe UMTS bearer.

The UMTS bearer can be understood as a chain of three smaller bearers.

UMTS Bearer = [Radio Bearer] “ + ” [Iu Bearer] “ + ” [CoreNetwork Bearer].

where , [Radio Bearer “ + ” Iu Bearer] is often called as RadioAccess Bearer (RAB).

Radio Access Bearer can be considered as a service provided by lower layers to higherlayers. Using RAB, the information is transferred between UE and core network (MSCor SGSN). In order to have a RAB, UE must have a radio bearer and Iu bearer. Radiobearers are managed by RNC. Therefore, while RAB setup, core network requests RNCand after successful response from RNC, the RAB is established.

Please note! RB Reconfiguration and RAB Reconfiguration sound very similarand quite often people mix them up.

6.2. QOS AND BEARER 177

We should remember that Radio Bearer (RB) Reconfiguration is a local sig-nalling procedure between UE and RNC, whereas, RAB Reconfiguration hap-pens with the involvement of core network. RB reconfiguration happens veryoften and can be seen from L3 radio messages, but to analyze the signallingof RAB reconfiguration we must use the signllinng traces on Iu-CS or Iu-PSinterface.

Please refer to section 6.1 of TS 23.107 for more details.

6.2.1 UMTS QoS Classes

The QoS is simply a phrase. For implementation, we define it using a list of parameters.One of these parameters is the Traffic Class. According to 3GPP TS 23.107, all theservices can be classified into 4 groups:

• Conversational class

• Streaming class

• Interactive class

• Background class

The delay sensitivity of traffic is the main criteria for this classification. Conversationalclass traffic is affected very badly the bearer is lost for few hundred ms where as thebearer background class will not be affected so badly even if the bearer is unavailable forfew seconds.

Other than this classification, we can also group the services in two groups: Real-Time(RT) and Non-Real-Time (NRT) services. Conversational and Streaming classes aremainly used for carrying real-time traffic flows whereas the Interactive and Backgroundtraffic classes are suitable for carrying Non-Real-Time traffic.

Conversational Class

The most well-known use of this scheme is telephony speech (e.g. GSM). But with Internetand multimedia, a number of new applications will require this scheme, for example,voice over IP and video conferencing tools. Real time conversation is always performedbetween peers (or groups) of live (human) end-users. This is the only scheme where therequired characteristics are strictly given by human perception. Real time conversation -fundamental characteristics for QoS:

• Preserve time relation (variation) between information entities of the stream;

• Conversational pattern (stringent and low delay).


Streaming Class

When the user is looking at (listening to) real time video (audio), the scheme of real timestreams applies. The real time data flow is always aiming at a live (human) destination.It is a one way transport.

Real time streams - fundamental characteristics for QoS:

• Preserve time relation (variation) between information entities of the stream.

Interactive Class

When the end-user, that is either a machine or a human, is on line requesting data fromremote equipment (e.g. a server), this scheme applies. Examples of human interaction withthe remote equipment are: web browsing, data base retrieval, server access. Interactivetraffic - fundamental characteristics for QoS:

• Request response pattern;

• Preserve payload content.

Background Class

When the end-user, that typically is a computer, sends and receives data files in thebackground, this scheme applies. Examples are background delivery of E-mails, SMS,download of databases and reception of measurement records. Background traffic - fun-damental characteristics for QoS:

• The destination is not expecting the data within a certain time;

• Preserve payload content.

6.3 Access Stratum and Non-Access Stratum

According to 3GPP TR 21.905 ‘Vocabulary for 3GPP Specifications’ , the definition ofStratum is as follows:

Stratum: Grouping of protocols related to one aspect of the servicesprovided by one or several domains.

In simple words, Stratum is similar to ‘a stack of protocols’. There are two types ofstratums that are often discussed. They are Access Stratum (AS) & Non-Access-Stratum(NAS). The same concept is illustrated in figure 6.4.

6.3. ACCESS STRATUM AND NON-ACCESS STRATUM 179

Figure 6.4: Access Stratum & Non-access Stratum Signalling

Access Stratum: Access Stratum protocols are defined in close co-ordination with thetechnology and medium of transport. AS protocol in radio interface is RRC, whichclearly defines the communication between UE and RNC. Similarly, the AS protocolin Iu Interface is RANAP. RANAP is used to control the communication betweenRNC and Core network. AS also works like a delivery service for NAS messages. Forexample, PAGING REQUEST is a NAS signalling message that must be deliveredfrom MSC to UE. Higher layers (NAS) use the services of access stratum protocolsRANAP and RRC to deliver this signalling message to UE. This mechanism is calledDirect Transfer (DT).

Please note that in UMTS, the paging procedure between RNC and UE is differ-ent from the paging procedure in GSM between BSC and MS. Therefore, the ASprotocols are access-aware protocols.

Non-access Stratum: Non-access stratum is a set of protocols which are access-agnostic.In other words, these protocols are higher layer end-to-end protocols which do notdepend on the underlying access network. One example of such protocol is MobilityManagement protocol of UMTS. The same MM is used in GSM for procedures likelocation update, authentication, paging etc.

NAS protocol messages can be carried over a TDMA-based 2G access networkor CDMA-based 3G access network. The structure of these protocols remain un-changed.

There are totally 6 NAS protocols defined which will be discussed in section 6.9.


6.4 Radio Protocols

Source:

3GPP TS 25.301: Radio Interface Protocol Architecture.

3GPP TS 25.321: MAC Protocol Specification.

3GPP TS 25.322: RLC Protocol Specification.

3GPP TS 25.323: PDCP Protocol Specification.

3GPP TS 25.324: BMC Protocol Specification.

3GPP TS 25.331: RRC Protocol Specification.

These specifications contain the details of UMTS, HSDPA as well as HSUPA.But we should pay attention to the version. For HSDPA, the version numbershould be 5.0.0 or higher. Similarly, for HSUPA-specific information, theversion number has to be 6.0.0 or higher.

Radio Protocols are the set of protocols which control the communication between UEand RNC. This section will investigate those set of protocols. As usual, we will focus oncontrol plane and user plane separately.

6.4.1 Control Plane

The main signalling protocol in 3G is RRC protocol but RRC is a higher layer protocol,which uses the services of underlying layers L2 (MAC and RLC) and L1 (PHY layer). Thecomplete protocol stack is shown in figure 6.5. The functions of each individual protocollayer is explained in the coming sections. This figure also shows the protocol terminationpoint. The physical layer is implemented by UE and Node B. Similarly, it can be seenthat MAC, RLC and RRC protocols are implemented in UE and RNC.

Figure 6.5: Protocol Termination for DCH, control plane(from TS 25.301)

6.4. RADIO PROTOCOLS 181

As seen in figure 6.5, downlink signalling messages can be either generated by RNC or theymight arrive from the core network which must be forwarded to the user(s). Similarly, inuplink, the signalling messages from UE can be either processed by RNC or forwarded tocore network.

• Signalling message coming from/going to Core Network: for example, Paging re-quest/response, authentication request/response, etc.

NAS Signaling from CN → RRC Signalling → RLC → MAC → PHY

Hence, we can identify the first function of RRC layer which is NAS message trans-port in the uplink and downlink.

• Signalling message generated from/terminated within RNC: for example measure-ment control/report, handover commands, system information broadcast, etc.

RRC Signalling → RLC → MAC → PHY

This category of RRC messages are used by RNC to control the behaviour of UE.Similarly, UE can contact RNC and inform about some event that took place.

Note! The details shown in figures 6.5 & 6.6 are applicable to DCH transport channelonly. In order to keep this book at an overview level, the protocol termination for transportchannels RACH & FACH is not shown here. Readers are advised to refer to section 5.6.2of 3GPP TS 25.301 to learn more. Details about of HS-DSCH and E-DCH will be shownin their respective module.

6.4.2 User Plane

There are many similarities between the control plane and user plane protocols on theradio interface. By comparing the figures 6.5 & 6.6, we observe that the RRC protocol isonly for CP whereas in UP we have 2 new protocols: PDCP for packet switched UP andBMC for the broadcast services.

As we know, in UMTS, the same transport channel (DCH) is used for voice, video, text,data, streaming and more. Therefore, depending on the service carried by it, the user planeprotocol stack gets slightly modified. In this section, we will learn the set of protocols inthe path of CS service, PS services and broadcast & multicast service.

CS Services

On the transmitter side, the protocol stack for UP is as follows:

CS data streams → RLC → MAC → PHY


Figure 6.6: Protocol Termination for DCH, User Plane(from TS 25.301)

PS Services

On the transmitter side, the protocol stack for UP is as follows:

IP Data flow → PDCP → RLC → MAC → PHY

Broadcast & Multicast Services

On the transmitter side, the protocol stack for BC services is as follows:

Common Traffic or CBS → BMC → RLC → MAC → PHY

6.4.3 RRC-layer Functions

3GPP TS 25.331 is a bulky document with more than 1200 pages (in Rel-6). The detailsabout all the RRC procedures, RRC messages and their parameters can be found in it.According to Section 5.1 of TS 25.331, RRC layer performs following functions:

• Non-access stratum message broadcast

• Access stratum related information broadcast

• RRC Connection Management

• Radio Bearer Management


• Management of radio resources for RRC Connection and radio bearers

• Connected mode mobility functions (handover, cell update, URA update, etc.)

• Paging

• Control of requested QoS

• Control of UE measurement reporting

• Outer loop power control

• Control of ciphering

• Initial cell selection and re-selection in idle mode

• Initial Configuration for CBS

• . . .

6.4.4 RLC-layer Functions

This section provides an overview on services and functions provided by the RLC sublayer.The RLC sublayer is a part of L2 in the Radio interface protocol stack. The detaileddescription of RLC is available in 3GPP TS 25.322. Depending on the type of informationcarried in the RLC SDU, the RLC layer can be configured in 3 modes:

1. Transparent Mode (TM): In this mode, RLC layer processing is very minimal. Thename transparent mode shows that it appears as if the RLC layer is not present inthe processing chain. This mode is generally used for real time user plane serviceslike voice or video telephony. In this mode, there is no feedback from the receiverand there is no re-transmission mechanism.

The service provided by RLC layer in TM are:

• Segmentation and reassembly,

• Transfer of user data, and

• SDU discard.

Please note! Ciphering is an important function of the RLC layer. But in thelist above, ciphering is missing. Does it mean that there is no ciphering for theservices which use RLC transparent mode? In other words, is our voice sent withoutencryption in UMTS?

Answer is No. When the RLC-sublayer is configured in the Transparent mode, theciphering is performed by the MAC sublayer.


2. Unacknowledged Mode (UM): In the unacknowledged mode, there is no guaran-tee of delivery because there is no retransmission mechanism. This mode can beused for Voice over IP which is possible with HSPA solution. The following functionsare needed to support unacknowledged data transfer:

• Segmentation and reassembly.

• Concatenation.

• Padding.

• Transfer of user data.

• Ciphering.

• Sequence number check.

• SDU discard.

• Out of sequence SDU delivery.

• Duplicate avoidance and reordering.

• Provisioning of sequence number.

Unacknowledged mode of RLC can be compared to UDP transport, which doesnot provide guarantee of delivery but is still a popular transport method due to itsreduced protocol overhead compared to more expensive alternative, i.e., TCP.

3. Acknowledged Mode: The third mode of RLC configuration uses a ACK/NACKfeedback from the receiver and performs re-transmission. Therefore, it is the mostreliable mode which provides some guarantee of delivery. But at the same time,this mode is most expensive one if we compare the size of the RLC header and theprocessing delay. The following functions are needed to support acknowledged datatransfer:

• Segmentation and reassembly.

• Concatenation.

• Padding.

• Transfer of user data.

• Error correction.

• In-sequence delivery of upper layer PDUs.

• Duplicate detection.

• Flow Control.

• Protocol error detection and recovery.

• Ciphering.

• SDU discard.


Other than this, RLC layer also performs the following functions:

• Maintenance of QoS as defined by upper layers.

• Notification of unrecoverable errors.

6.4.5 MAC-layer Functions

Source: 3GPP TS 25.321; Medium Access Control (MAC) protocol specifica-tion

It can be said that the MAC sublayer is the brain of modern communicationsystems like UMTS, HSDPA, HSUPA & LTE. It is the MAC layer who takesdecisions about scheduling and bit rate adjustments. Without the MAC layer’spriority handling capability, we would not be discussing QoS concept in moderntelecom systems.

The functions of MAC include:

• Mapping between logical channels and transport channels;

• Selection of appropriate Transport Format for each Transport Channel dependingon instantaneous source rate;

• Priority handling between data flows of one UE;

• Priority handling between UEs by means of dynamic scheduling;

• Identification of UEs on common transport channels;

• Identification of MBMS services on common transport channels;

• Multiplexing/demultiplexing of upper layer PDUs into/from transport blocks deliv-ered to/from the physical layer on common transport channels;

• Multiplexing/demultiplexing of upper layer PDUs into/from transport block setsdelivered to/from the physical layer on dedicated transport channels;

• Segmentation and reassembly of upper layer PDUs;

• Traffic volume measurement;

• Transport Channel type switching and

• Ciphering for transparent mode RLC.

HSDPA-specific MAC (MAC-hs) and HSUPA-specific MAC(MAC-e/es) willbe discussed in their respective modules.


6.4.6 PDCP-layer Functions

Source: 3GPP TS 25.323; Packet Data Convergence Protocol (PDCP) speci-fication

This section provides an overview on services and functions provided by the Packet DataConvergence Protocol (PDCP).

Header compression and decompression: Header compression and decompression ofIP data streams (e.g., TCP/IP and RTP/UDP/IP headers) at the transmitting andreceiving entity, respectively. The header compression method is specific to theparticular network layer, transport layer or upper layer protocol combinations e.g.TCP/IP and RTP/UDP/IP.

Transfer of user data: Transmission of user data means that PDCP receives PDCPSDU from the NAS and forwards it to the RLC layer and vice versa.

Support for lossless SRNS relocation or lossless DL RLC PDU size change: Maintenanceof PDCP sequence numbers for radio bearers that are configured to support losslessSRNS relocation or lossless DL RLC PDU size change.

6.5. IU-CS INTERFACE PROTOCOLS 187

Till now, we were focussing on the radio interface protocols. Now, we will draw ourattention towards the protocols used on the UTRAN interfaces Iu-PS, Iu-CS, Iub and Iur.

Due to various options available in transport (IP, ATM, IP over ATM) and then separateprotocol stacks for control plane and user plane, it is very difficult to keep an overview ofthe protocol stacks. Therefore, instead of going into the details of every protocol, we willaim at getting a big picture about the protocols used on every interface. The interestedreaders are advised to refer to the 3GPP specs mentioned in the following sections1.

6.5 Iu-CS Interface Protocols

From protocol description description, Iu-CS and IU-PS are simply referred to as Iu interface.The following section is written with the reference from following specifications.

Source :

3GPP TS 25.410: ‘‘UTRAN Iu Interface: general aspects and principles’’

3GPP TS 25.411: ‘‘UTRAN Iu Interface Layer 1’’

3GPP TS 25.412: ‘‘UTRAN Iu Interface Signalling Transport’’.

3GPP TS 25.413: ‘‘UTRAN Iu Interface RANAP Signalling’’.

3GPP TS 25.414: ‘‘UTRAN Iu Interface Data Transport and Transport

Signalling’’

3GPP TS 25.415: ‘‘UTRAN Iu Interface User Plane Protocols’’.

6.5.1 Control Plane - Iu-CS

Iu-CS interface connects RNC to the CS-domain of the core network. Therefore, theprotocols stack shown here is implemented in RNC and MSC.

The protocol stacks for the Iu-CS Domain are shown in figure 6.7.

As shown in figure 6.7, there are two options for the realization of transport network, theyare:

• ATM-based transport, &

• IP-based transport

6.5.2 User Plane - Iu-CS

User plane protocols on Iu-CS are shown in figure 6.8. Both ATM-based transport optionand the IP-based transport options are shown.

1TS 25.41x for Iu, 25.42x for Iur and 25.43x for Iub.


Figure 6.7: Iu-CS control plane protocol architecture (TS 25.410)

Figure 6.8: Iu-CS user plane protocol architecture (TS 25.410)

Figures 6.7 & 6.8 are drawn with the help of Figure 6.1 in 3GPP TS 25.410.

6.5. IU-CS INTERFACE PROTOCOLS 189

6.5.3 RANAP Functions

RANAP provides the signalling service between UTRAN and CN, which are described in3GPP TS25.413. In this book, we will not dig into the details of each function. A list ofthe functions performed by RANAP lyer are listed below:

Relocating serving RNC,

Overall RAB management,

Queuing the setup of RAB,

Requesting RAB release,

Release of all Iu connection resources,

SRNS context forwarding function,

Controlling overload in the Iu interface,

Resetting the Iu,

Sending the UE Common ID to the RNC,

Paging the user,

Transport of NAS information between UE and CN. This function has two sub-classes:

• 1. Transport of the initial NAS signalling message from the UE to CN.

• 2. Transport of subsequent NAS signalling messages between UE and CN.

Controlling the security mode in the UTRAN,

Controlling location reporting,

Location reporting,

Data volume reporting function,

Reporting general error situations,

Location related data, and

Information Transfer.


6.6 Iu-PS Interface Protocols

Iu-PS interface connects RNC to the PS-domain of core network. Therefore, the protocolsstack shown here is implemented in RNC and SGSN.

6.6.1 Control Plane - Iu-PS

The protocol stacks for the Iu PS Domain is shown in figure 6.9. The standard allowsoperators to choose one out of the three standardized protocol suites for transport of SCCPmessages.

Figure 6.9: Iu-PS control plane protocol architecture (TS 25.410)

• ATM-based transport,

• IP-based transport &

• IP over ATM-based transport

6.6.2 User Plane - Iu-PS

There are two options for the transport layer for data streams over Iu-PS.

6.6. IU-PS INTERFACE PROTOCOLS 191

• ATM-based Transport (ATM transport option)

• IP-based Transport (IP transport option)

Figure 6.10: Iu-PS user plane protocol architecture (TS 25.410)

Figures 6.9 & 6.10 are drawn with the help of Figure 6.3 in 3GPP TS 25.410.


6.7 Iub Interface Protocols

Source :

3GPP TS 25.430: ‘‘UTRAN Iub Interface: general aspects and principles’’.

3GPP TS 25.431: ‘‘UTRAN Iub Interface Layer 1’’.

3GPP TS 25.432: ‘‘UTRAN Iub Interface Signalling Transport’’.

3GPP TS 25.433: ‘‘UTRAN NBAP Specification’’.

3GPP TS 25.434: ‘‘UTRAN Iub Interface: Data Transport & Transport

Signalling for Common Transport Channel Data Streams’’.

3GPP TS 25.435: ‘‘UTRAN Iub Interface: User Plane Protocols for

Common Transport Channel Data Streams’’.

Iub interface is used to connect Node B and RNC. For network operation, they mustcommunicate with each other at regular periods. Whenever a radio link is established,NBAP protocol is used. Similarly, Node reports the measurements about current ULinterference and DL transmission power to RNC. Based on these reports, RNC performsRadio Resource Management.

Figure 6.11: Iub control plane protocol architecture (TS 25.430)

6.7.1 Control Plane - Iub CP

The Signalling Bearer for NBAP is a point-to-point protocol. There may be multiplepoint-to-point links between an RNC and a Node B. As shown in figure 6.11, the standardallows operators to choose one out of two protocol suites for transporting the NBAPmessages.

6.7. IUB INTERFACE PROTOCOLS 193


• IP-based transport

6.7.2 User Plane - Iub UP

This section specifies the transport layers that support Common Transport Channel(FACH, RACH, PCH, DSCH, HS-DSCH) data streams. As usual, there are two op-tions for protocol suites for transport of RACH, FACH, DSCH and HS-DSCH Iub datastreams, which are shown in figure 6.12.


• IP-based transport.

Figure 6.12: Iub user plane protocol architecture (TS 25.430)

6.7.3 NBAP Functions

The functions performed by NBAP protocol layer are specified in section 7 of 3GPPTS 25.433. NBAP procedures are divided into common procedures and dedicatedprocedures.

• NBAP common procedures or C-NBAP are procedures that are not relatedto one particular subscriber or radio link. C-NBAP procedures are common to acell.


• NBAP dedicated procedures or D-NBAP are procedures that are related toa specific subscriber who is identified by Node B Communication Context in NodeB.

The full NBAP specifications are available in 3GPP TS 25.433. From the same specifica-tion, the functions performed by NBAP are listed below:

Cell Configuration Management,

Common Transport Channel Management,

System Information Management,

Resource Event Management,

Measurements on Common Resources,

Radio Link Management,

Radio Link Supervision,

Compressed Mode Control,

Measurements on Dedicated Resources,

Reporting of General Error Situations,

Physical Shared Channel Management,

Information Exchange,

Bearer Rearrangement, and

MBMS Notification.

6.8. IUR INTERFACE PROTOCOLS 195

6.8 Iur Interface Protocols

Source :

3GPP TS 25.420: ‘‘UTRAN Iur interface general aspects and principles’’

3GPP TS 25.421: ‘‘UTRAN Iur Interface: Layer 1’’

3GPP TS 25.422: ‘‘UTRAN Iur Interface: Signalling Transport’’

3GPP TS 25.423: ‘‘UTRAN Iur Interface: RNSAP Signalling’’

3GPP TS 25.424: ‘‘UTRAN Iur Interface: Data Transport & Transport

Signalling’’

3GPP TS 25.426: ‘‘UTRAN Iur & Iub Interface: Data Transport & Transport

Signalling for DCH Data Streams’’.

Iur interface is the link between any two RNCs within the UTRAN. Its main purpose is tohandle Inter-RNC mobility within UTRAN and hide this mobility from the core network.If Iur is not present between the two RNCs, then the Inter-RNC soft handover cannottake place. In this case, a hard handover will be performed instead. For multi-vendoroperability, it is recommended that Iur should be an open interface. Iur interface is notonly used for signalling but also for carrying data streams. RNC-to-RNC interface is alogical description. It can be implemented even if there is no direct physical connectionbetween two RNCs.

6.8.1 Control Plane - Iur CP

Due to the similarity between the control plane protocol stack of Iur and Iu-PS, thedescription is not given in order to avoid repetition. The protocol stack of control planesignalling over Iur is shown in figure 6.13. The main control plane protocol on Iur interfaceis RNSAP. The word RNS in UMTS means one RNC and several Node B controlled byit.

All three transport options are shown in figure 6.13.

6.8.2 User Plane - Iur UP

The user plane protocol stack on Iur interface is illustrated in figure 6.14. As we can easilyidentify, the protocol stack resembles the user plane protocol stack on Iub. Therefore, thedescription can be avoided here as well.

6.8.3 RNSAP functions

The full RNSAP specifications are available in section 7 of 3GPP TS 25.423. The functionsperformed by RNSAP are listed below:


Figure 6.13: Iur Interface Protocol Architecture for Control Plane

Figure 6.14: Iur Interface Protocol Architecture for User Plane

Radio Link Management,

Physical Channel Reconfiguration,

Radio Link Supervision,

Compressed Mode Control,

6.8. IUR INTERFACE PROTOCOLS 197

Measurements on Dedicated Resources,

DCH Rate Control,

CCCH Signalling Transfer,

Paging,

Common Transport Channel Resources Management,

Relocation Execution,

Reporting of General Error Situations,

Measurements on Common Resources,

Information Exchange, and

Resetting the Iur.


6.9 Non-Access Stratum Protocols

Till now, in this chapter we have discussed the access stratum. Now it is time for someNAS signalling. The term access stratum and non-access stratum was explained in section6.3 at the beginning of this chapter. The fact, that NAS protocols are access-agnostic,is illustrated on figure 6.15. In this figure, there are 2 access technologies, TDMA-basedBSS (2G) and CDMA-based UTRAN (3G). The NAS messages are depicted with thebidirectional arrows which flow between UE and core network. The structure of NASmessage does not depend on the underlying access network.

Figure 6.15: Principle of NAS signalling

In figure 6.16, we can see that there are three sublayers in the overall protocol architecture.These sublayers are:

The Access Stratum (AS) sublayer: The AS sublayer performs the duties of a post-man and transports NAS signalling messages between UE & core network.

The Mobility Management sublayer: The MM sublayer provides its services to CM.The MM sublayer contains two protocol entities:

• The MM protocol for mobility related signalling towards the CS core networkdomain, and

• The GMM protocol for mobility related signalling towards the PS core networkdomain.

The Connection Management sublayer: The CM sublayer consists of four basic pro-tocol entities: CC, SM, SMS and SS.

If we ignore the AS sublayer and focus on only NAS sublayers, we can conclude thatthere are following protocol entities which together constitute the NAS domain. Those sixentities are identified by their protocol discriminator field as shown in table 6.2.

In LTE/EPS, the concept of AS and NAS protocols is reused and the definitions are alsonot changed. The protocols which carry signalling messages between UE and Evolved

6.9. NON-ACCESS STRATUM PROTOCOLS 199

Figure 6.16: NAS protocols in UMTS

Name of NAS protocol Protocol Discrimina-tor

Call Control (CC) 3Mobility Management 5GPRS Mobility Management 8SMS 9Session Management 10Supplementary Services 11

Table 6.2: NAS protocols and the protocol discriminator values

Packet Core (EPC) are called NAS protocols and they include 2 protocols: EMM andESM. The words MM and SM are already known from 2G & 3G, ‘E’ stands for EPS orEvolved packet System.


Copyright Notices



Text in section 6.5.3 on page 189 Section 7 of 3GPP TS 25.413 v 7.0.0.c⃝2005. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

Figure 6.1 on page 173 Figure 10 of 3GPP TS 25.401 v 7.0.0.Figure 6.5 on page 180 Figure 11 of 3GPP TS 25.301 v 7.0.0.Figure 6.6 on page 182 Figure 12 of 3GPP TS 25.301 v 7.0.0.Figure 6.7 on page 188 Figure 6.1 of 3GPP TS 25.410 v 7.0.0.Figure 6.8 on page 188 Figure 6.1 of 3GPP TS 25.410 v 7.0.0.Figure 6.9 on page 190 Figure 6.3 of 3GPP TS 25.410 v 7.0.0.Figure 6.10 on page 191 Figure 6.3 of 3GPP TS 25.410 v 7.0.0.Figure 6.11 on page 192 Figure 7 of 3GPP TS 25.430 v 7.0.0.Figure 6.12 on page 193 Figure 7 of 3GPP TS 25.430 v 7.0.0.Figure 6.13 on page 196 Figure 4 of 3GPP TS 25.420 v 7.0.0.Figure 6.14 on page 196 Figure 4 of 3GPP TS 25.420 v 7.0.0.Text about RRC Protocol func-tions on page 182

Section 5.1 of 3GPP TS 25.331 v 6.9.0.

Text about Protocol Layers onpage 173


Text about Protocol Planes onpage 173


Text in section 6.7.3 on page 193 Section 7 of 3GPP TS 25.433 v 7.0.0.Text in section 6.8.3 on page 195 Section 7 of 3GPP TS 25.423 v 7.0.0.c⃝2006. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

6.9. NON-ACCESS STRATUM PROTOCOLS 201

Figure 6.3 on page 176 Figure 1 of 3GPP TS 23.107 v 7.0.0.Text in section 6.2.1 on page 177 Section 6.3 of 3GPP TS 23.107 v 7.0.0.c⃝2007. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

Text in section 6.4.4 on page 183 Section 6 of 3GPP TS 25.322 v 9.0.0.Text in section 6.4.6 on page 186 Section 5 of 3GPP TS 25.323 v 9.0.0.c⃝2010. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

BIBLIOGRAPHY

[1] 3GPP TS 23.107 ver. 7.0.0 ;‘Quality of Service (QoS) concept and architecture’


[3] 3GPP TS 25.321 ver. 7.0.0 ;‘MAC protocol specification’

[4] 3GPP TS 25.322 ver. 7.0.0 ;‘RLC protocol specification’

[5] 3GPP TS 25.323 ver. 7.0.0 ;‘PDCP protocol specification’

[6] 3GPP TS 25.324 ver. 7.0.0 ;‘BMC protocol specification’



[9] 3GPP TS 25.410 Ver. 7.0.0 ;‘UTRAN Iu Interface: general aspects and principles’

[10] 3GPP TS 25.411 Ver. 7.0.0 ;‘UTRAN Iu Interface: Layer 1’

[11] 3GPP TS 25.412 Ver. 7.0.0 ;‘UTRAN Iu Interface: Signalling Transport’

[12] 3GPP TS 25.413 Ver. 7.0.0 ;‘UTRAN Iu Interface: RANAP Signalling’

[13] 3GPP TS 25.414 Ver. 7.0.0 ;‘UTRAN Iu Interface: Data Transport and TransportSignalling’

[14] 3GPP TS 25.415 Ver. 7.0.0 ;‘UTRAN Iu Interface: User Plane Protocols’

[15] 3GPP TS 25.420 Ver. 7.0.0 ;‘UTRAN Iur Interface: general aspects and principles’

[16] 3GPP TS 25.421 Ver. 7.0.0 ;‘UTRAN Iur Interface: Layer 1’

[17] 3GPP TS 25.422 Ver. 7.0.0 ;‘UTRAN Iur Interface: Signalling Transport’

[18] 3GPP TS 25.423 Ver. 7.0.0 ;‘UTRAN Iur Interface: RNSAP Signalling’

202

BIBLIOGRAPHY 203

[19] 3GPP TS 25.424 Ver. 7.0.0 ;‘UTRAN Iur Interface: Data Transport and TransportSignalling’

[20] 3GPP TS 25.426 Ver. 7.0.0 ;‘UTRAN Iur & Iub Interface: Data Transport & Trans-port Signalling for DCH Data Streams’

[21] 3GPP TS 25.430 Ver. 7.0.0 ;‘UTRAN Iub Interface: general aspects and principles’

[22] 3GPP TS 25.431 Ver. 7.0.0 ;‘UTRAN Iub Interface: Layer 1’

[23] 3GPP TS 25.432 Ver. 7.0.0 ;‘UTRAN Iub Interface: Signalling Transport’

[24] 3GPP TS 25.433 Ver. 7.0.0 ;‘UTRAN Iub Interface: NBAP Signalling’

[25] 3GPP TS 25.434 Ver. 7.0.0 ;‘UTRAN Iub Interface: Data Transport & TransportSignalling for Common Transport Channel Data Streams’

[26] 3GPP TS 25.435 Ver. 7.0.0 ;‘UTRAN Iub Interface: User Plane Protocols for Com-mon Transport Channel Data Streams’



For HSDPA-specific details, the version of these specs should be 5.0.0 orhigher & for HSUPA-specific details, is should be 6.0.0 or higher.

CHAPTER

7

HIGH SPEED DOWNLINK PACKETACCESS

Source: 3GPP TS 25.308,

High Speed Downlink Packet Access (HSDPA); Overall description;

Overview of 3GPP Release 5; available at:

http://www.3gpp.org/ftp/Information/WORK PLAN/Description Releases/

7.1 Why HSDPA?

Actually the question should be Why HSPA? HSDPA (and later HSUPA) was designedto overcome the limitations of the Rel-99 WCDMA air interface. If an operator disablesHSDPA services from any cell, the maximum bit rate drops from Mbps to kbps range.UMTS in its basic form (Rel-99 and Rel-4) can theoretically achieve 2 Mbps, bothin uplink and downlink. But these theoretical numbers are very far from the popularimplementation. In most common deployments across the globe, Rel-99 UMTS is able toshow the peak bit rates of only 384 kbps and that too with a very limited coverage. Dueto this, the end-user experience is very poor.

From an operator’s perspective, in order to get high cell throughput, it should be possibleto have several simultaneous users with high bit rates. But due to high fractional load of

204

7.2. HSDPA STANDARDIZATION, 3GPP RELEASES AND EVOLUTION 205

data bearers, unfortunately only a few simultaneous users are possible.

This indirectly also affects the handset manufacturers because all the smart phones, padsand tablets are useless if they cannot provide fast wireless internet access to the subscribers.Let us discuss some limitations of Rel-99 UMTS.

End user experience: Due to limited practical bit rates, the end user does not experi-ence good throughput.

Poor coverage for data bearers: In WCDMA, coverage is separately calculated foreach service. As the service bit rate increases, the coverage area decreases. Usermust be in excellent radio condition and the cell load should be quite low, only thenthe user can experience the bit rates of several hundred kbps.

Cell capacity: Although the load in cell depends on various factors, but it has beenobserved that only a few users of 384 kbps bearer can block the entire cell capacity.This is very bad for the operator’s revenue and also network accessibility KPI.

Cost of usage: 3G was expected to fulfill the dream which was started by GPRS. Ev-eryone expected that affordable “unlimited data usage” plans will become popular.But unfortunately due to the high cost of operation, it did not happen. Hence, oneof the requirements while designing HSDPA was to reduce the cost-per-bit from theoperator’s perspective so that more affordable data plans could be introduced.

Latency: UMTS experiences very high control plane and user plane latency.

Revenue vs. Investment: Due to high cost of spectrum licences, mobile operators ex-pected a huge revenue which unfortunately did not happen.

3G or no 3G?: People often described 3G as “a system with 2 new services – Videotelephony and broadband data access”. Video telephony never became popularand data rates in 3G were quite limited. Therefore, the GSM operators were unableto decide whether they should go for 3G or just settle down with EDGE1. At thesame time operators started comparing 3G with Mobile-WiMAX solution.

7.2 HSDPA Standardization, 3GPP Releases and

Evolution

Source: 3GPP TS 25.306 ; UE Radio Access capabilities

HSDPA is just a milestone in the journey of High Speed Packet Access (HSPA). Due tothe urgency and demand of higher bit rates in DL, the HSDPA standard was released and

1EDGE can offer > 200 kbps (practically) & operators do not need to wait/pay for new 3Glicences.

206 CHAPTER 7. HIGH SPEED DOWNLINK PACKET ACCESS

in the next 3GPP release, its counterpart HSUPA was standardized. The terminologyof 3GPP specifications & releases is quite complicated. Therefore, we will try to explainonly the most important features of each 3GPP release in terms of PS NRT data access.Table 7.1 describes the new categories that were defined when HSDPA was standardizedin Rel. 5. In later releases, newer devices with more advanced features were introduced.The following section will take us through this journey in a few steps.

ReleaseUE

CategoryMod MIMO

DC-HSDPA

PeakBitrate

Release 5 1 to 12QPSK,16QAM

No No 14.4 Mbps

Release 6 Same as Rel-5

Release 7 13 to 18QPSK,16QAM,64QAM

2X2 with16QAM

No28 or 21Mbps

Release 8 19 to 24QPSK,16QAM,64QAM

2X2 with64QAM

2 Carriers 42 Mbps

Table 7.1: HSDPA features in REL-5, REL-7 & REL-8 (Source TS 25.306, Table5.1a)

7.2.1 Release 99 & Rel-4

• Basic 3G

• Downlink data services available on FACH and DCH transport channels

• Uplink data services available on RACH and DCH transport channels

• RACH, FACH & DCH are scheduled by RNC’s packet scheduler

• Peak bit rates UL: 384 kbps & DL: 384 kbps

• No concept of CQI reporting, UE categories etc.

• DCH uses a fast power control but no link adaptation mechanism

7.2.2 Release 5

• Commonly called as 3.5G

• DL HSDPA operation without UL HSUPA

7.2. HSDPA STANDARDIZATION, 3GPP RELEASES AND EVOLUTION 207

• DL HSDPA and UL R99 DCH

• DL packet scheduling is done by Node B based on CQI feedback from the UE

• Supported UE categories: 1 to 12

• Peak bit rates in UL: 384 kbps & DL: 14.4 Mbps

7.2.3 Release 6

• HSDPA + HSUPA = HSPA

• Just like HSDPA R5, HSPA is also commonly called as 3.5G

• DL HSDPA operation is a must for UL HSUPA. Hence, HSPA is a synonym forHSUPA.

• Channel scheduling is done by Node B based on feedback from the UE (e.g., databuffer status, power headroom, etc.)

• Supported HSDPA UE categories: 1 to 12 (no change compared to R5)

• Supported HSUPA UE categories: 1 to 6

• Peak bit rates in UL: 5.76 Mbps & DL: 14.4 Mbps

7.2.4 Release 7

• Commonly called as evolved HSPA or HSPA+

• Supported HSDPA UE categories: 1 to 12 & 13 to 18

• Support of 2 X 2 MIMO or 64QAM modulation in DL

• Supported HSUPA UE categories: 1 to 6 & 7

• Supported 16QAM Modulation in UL

• Peak bit rates UL: 11.2 Mbps & DL: 28 Mbps

7.2.5 Release 8

• Commonly called as evolved HSPA or HSPA+ (just like Rel-7)

• Supported HSDPA UE categories: 1 to 12 & 13 to 18 & 19 to 24

• Support of Simultaneous “64QAM with MIMO operation” or DC-HSDPA


• Supported HSUPA UE categories: 1 to 6 & 7

• Peak bit rates UL: 11.2 Mbps & DL: 42 Mbps

The points listed in previous section are summarized in table 7.1.

7.3 HSDPA Operation

This section explains the operation of HSDPA from an higher-layer perspective. Therewill be a detailed discussion about L1 physical channels and L2 protocols in the latersections. In this section, we are trying to find an answer to the question ‘ ‘how doesHSDPA operation start?” We will analyze in this process by breaking it into two steps.

1. HSDPA Operation: Between UE and RNC

2. HSDPA Operation: Between Node B and RNC

7.3.1 HSDPA Operation: Between UE and RNC

Figure 7.1: Signalling to initiate an HSDPA session

7.3. HSDPA OPERATION 209

The HSDPA-capable user equipment (mobile phone, smart phone, USB stick modem,tablet etc.) starts the connection setup in the same manner as a R99 device. Therefore,on higher layers (L3 and NAS protocols), there are no HSDPA specific messages andprocedures. In other words, the call flow of packet switched connection setup of Rel-99and Rel-5 are the same which is illustrated in figure 7.1.

At the time of transport channel type selection, if the DL transport channel is HS-DSCH,in uplink, RNC can choose either DCH or E-DCH based on the UE device capability. UE isinformed about this channel selection by RRC: Radio Bearer Setup or RRC: Radio BearerReconfiguration messages. Using this message, UE comes to know about its HSDPA-specific id H-RNTI and the HSDPA configuration of the cell.

HSDPA without HSUPA: HS-DSCH in DL and DCH in UL, or

HSDPA with HSUPA: HS-DSCH in DL and E-DCH in UL. This option is availableonly for Rel-6 or newer UEs.

7.3.2 HSDPA Operation: Between Node B and RNC

The most remarkable difference between UMTS and HSDPA is the presence of an addi-tional scheduler in Node B for scheduling the resources to HSDPA users. If the transmittedpackets are not acknowledged, then Node B performs re-transmission. Therefore, it is re-quired to buffer the user data at Node B. The transfer of data from RNC to Node B takesplace in such a way that the buffer at Node B does not over flow. This procedure is calledIub flow control and accomplished by the two messages illustrated in figure 7.2.

Figure 7.2: Iub Flow Control

Step 1: RNC asks Node B, “How much can I send for a particular UE”? As shownin the first message in figure 7.2, the ‘Capacity Request’ message provides the


Node B with information regarding the RNC buffer occupancy for a specific priorityqueue belonging to a specific MAC-d flow.

Step 2: Node B informs RNC about the suitable amount. As shown in the sec-ond message in figure 7.2, the ‘Capacity Allocation’ message is sent from theserving Node B to the controlling RNC. Its primary purpose is to provide the RNCwith permission to transfer MAC-d PDU belonging to a specific MAC-d flow pri-ority queue towards the Node B at a specific maximum rate. This message has 3important parameters:

1. number of credits,

2. time interval, and

3. repetition period.

For example, if the number of credits is 50, the time interval is 20 ms and the repetitionperiod is 10, then the RNC is permitted to transfer 50 MAC-d PDU every 20 ms duringthe next 200 ms. A repetition interval of ‘0’ is interpreted as unlimited repetition, i.e.,if the repetition period in the previous example was ‘0’, the RNC would be permitted totransfer 50 MAC-d PDU every 20 ms for an indefinite period.

7.4. WHAT’S NEW IN HSDPA? 211

7.4 What’s new in HSDPA?

HSDPA can be better understood by comparing it with the Rel-99 DCH transport channel.In other words, we can focus on the new features introduced for HS-DSCH transportchannel.

• Adaptive modulation and coding

• Shorter and fixed TTI (2 ms)

• Node B based packet scheduling

• Multi-code Operation

• L1 H-ARQ retransmission

• MAC-hs protocol in Node B

• Serving Cell Change instead of Soft Handover

7.4.1 Adaptive Modulation & Coding

The Node B selects the modulation and the coding for each TTI for each userbased on an estimate of the downlink. Each UE reports an indicator of theDL channel quality in the uplink signalling.

One of the main drawbacks of R99 DCH channel is its inflexibility. If the UE comes closeto Node B, power control decreases the transmission power but the bit rate remains thesame. In DCH, bit rate modification is not very easy because the scheduler is locatedat RNC and it does not know anything about the current radio conditions. In contrastto this, in HSDPA, the transport block size for HS-DSCH channel can be changed everyTTI. In other words, 500 times in one second, the bit rates can be adjusted to matchthe radio conditions. Table 7.2 illustrates the effect of modulation and coding on the netuser throughput. The number of codes is also a deciding factor in determining the net bitrates.

7.4.2 Shorter and Fixed TTI

Transmission Time Interval is defined as the inter-arrival time of Transport Block Sets,i.e. the time it should take to transmit a Transport Block Set. In general, if this timeis big, then the information bits from higher layer will be buffered at MAC layer beforebeing delivered to the lower layers for transmission.


Modulation Coding Rate # codesGross Bit

RateNet BitRate

QPSK 1/4 5 2.4 Mbps 600 kbpsQPSK 1/2 5 2.4 Mbps 1.2 MbpsQPSK 3/4 5 2.4 Mbps 1.8 Mbps

QPSK 1/4 10 4.8 Mbps 1.2 MbpsQPSK 1/2 10 4.8 Mbps 2.4 MbpsQPSK 3/4 10 4.8 Mbps 3.6 Mbps

16QAM 1/2 10 9.6 Mbps 4.8 Mbps16QAM 3/4 10 9.6 Mbps 7.2 Mbps16QAM 4/4 10 9.6 Mbps 9.6 Mbps

16QAM 1/2 15 14.4 Mbps 7.2 Mbps16QAM 3/4 15 14.4 Mbps 10.8 Mbps16QAM 4/4 15 14.4 Mbps 14.4 Mbps

Table 7.2: Effect of Modulation and Coding scheme on net bit rate

For the DCH Transport channel, TTI can be either 10, 20, 40 or 80 ms. For HS-DSCH,TTI has been fixed and its value is 2 ms. In simple words, every 2ms one2 MAC-hstransport block can be delivered to the physical layer for transmission.

Shorter TTI interval helps in reducing the round trip time (RT) for the user plane.

If HS-DSCH is used for L3 signalling, then the control plane latency can also be reduced.

7.4.3 Node B-based Packet Scheduling

In R99, the packet scheduling is purely handled by RNC. Due to the dynamic nature of theradio conditions, it is impossible to inform the scheduler about the user’s radio channel’squality. Therefore, the bit rate upgrade/downgrade is only possible by RNC. To illustratethis, two methods are briefly explained below:

High Traffic Volume Measurement: User data might be buffered at UE for Uplinktransmission or in RNC for DL transmission:

• If the amount of data (in Bytes) buffered in user-specific buffer at RNC’s sideexceeds a certain threshold, then RNC automatically tries to upgrade the DLDCH bitrate (For example, DCH128 to DCH256).

2From R7 onwards, more than one TB can also be transmitted but that is possible only withMIMO. From R8 onwards, DC-HSDPA operation can also deliver 2 TABS per TTI.


• If the amount of data (in Bytes) buffered in user equipment’s buffer exceeds acertain threshold, then UE sends a measurement report to RNC and informsabout this event3. After receiving this measurement report, RNC automati-cally tries to upgrade the UL DCH bitrate.

High Throughput Measurement: If a DCH has been allocated to a user in UL & DL,RNC constantly keeps on measuring the actual throughput in terms of kbps. If thethroughput in UL or/and DL drops/exceeds some operator specific thresholds, thenthe allocated bitrates in that direction can be reduced or increased. This mechanismis called Throughput Based Bitrate Adaptation.

Although the two methods explained above are very effective in adjusting the bitrateallocation to the UE’s requirements but this mechanism is very slow and it takesseveral hundred ms before the bit rate modification takes place. These delays arecaused because the scheduler is residing in RNC and the signalling between UE &RNC is not very frequent.

By introducing a MAC-hs scheduler at Node B and CQI reporting mechanism, itis possible to look into the instantaneous channel quality and select the scheduleduser in current TTI. Furthermore, the TB size in that TTI can also be adapted tothe current radio conditions. This is explained in more details in CQI section.

In fact, the dynamic sharing of HS-PDSCH among users is only possible if thedecisions are made by Node B-based scheduler. This changed behaviour is beneficialfor both end-user and the operator. The end-user benefits by always getting thesuitable bitrate and reduced number of retransmission. On the other hand, theoperator can more often allocate resources to the users in favorable conditions andimprove the cell throughput.

7.4.4 Multi-code Operation

• In Rel-99 DCH, the flexibility in bit rates (8, 16, 32, . . ., 384) is achieved by usingvariable spreading factor from SF4 to SF256.

• Whereas, in HSDPA, the SF is fixed to 16. Therefore, the flexibility in bit ratescomes from:

– varying the number of SF16 codes simultaneously allocated to a user,

– varying the modulation scheme, and

– varying the channel coding scheme.

CQI reporting is a mechanism where UE suggests the Node B about the suitable modu-lation, number of codes and suitable transport block size.

3Commonly known as Capacity Request or Event 4a


A user can be allocated up to 15 HS-PDSCH channel codes. But the instantaneous actualmulticode allocation is decided by UE handset category, instantaneous CQI and the currentload in the cell.

CQI reports one value at a time from the CQI report definition. CQI report definition is atable containing 31 values, each of which is defined with N parameters. These parametersshall consist of one or more of the following:

• the transport block size,

• the coding rate,

• the number of HS-PDSCH codes,

• modulation,

• power offsets, etc.

For every UE category, there is a CQI table defined in 3GPP TS 25.214. Since thesespecifications are readily available on 3GPP website, we will not show all the tables.Instead, we will use only two table and try to understand its fields. In the examples, wewill take a low-end device category 6 & a high-end device category 14.

CQI table for UE Category 6

HS-DSCH Category 6 UE has following features

Modulation: QPSK & 16QAM only

Max. # of codes: 5

Category 6 HSDPA device uses CQI table A which is shown in table 7.3

CQI table for UE Category 14

Category 14 has following features

Modulation: QPSK, 16QAM & 64QAM

Max. # of codes: 15

For example, category 14 device uses CQI table D (from 3GPP TS 25.214, not includedin this book), if 64QAM is not configured and table G if 64QAM is configured. CQI tableG is shown in table 7.4.


CQI valueTransport Block

SizeNumber ofHS-PDSCH

ModulationReference poweradjustment ∆

0 N/A Out of range1 137 1 QPSK 02 173 1 QPSK 03 233 1 QPSK 04 317 1 QPSK 05 377 1 QPSK 06 461 1 QPSK 07 650 2 QPSK 08 792 2 QPSK 09 931 2 QPSK 010 1262 3 QPSK 011 1483 3 QPSK 012 1742 3 QPSK 013 2279 4 QPSK 014 2583 4 QPSK 015 3319 5 QPSK 0

16 3565 5 16QAM 017 4189 5 16QAM 018 4664 5 16QAM 019 5287 5 16QAM 020 5887 5 16QAM 021 6554 5 16QAM 022 7168 5 16QAM 023 7168 5 16QAM -124 7168 5 16QAM -225 7168 5 16QAM -3

26 7168 5 16QAM -427 7168 5 16QAM -528 7168 5 16QAM -629 7168 5 16QAM -730 7168 5 16QAM -8

Table 7.3: CQI Table A, taken from Table 7A of TS 25.214

Observations from the CQI tables

By carefully analyzing the information available in CQI tables and comparing the samefor two different device categories, we can make following observations:


CQI valueTransport Block

SizeNumber ofHS-PDSCH

ModulationReference poweradjustment ∆

0 N/A Out of range1 136 1 QPSK 02 176 1 QPSK 03 232 1 QPSK 04 320 1 QPSK 05 376 1 QPSK 06 464 1 QPSK 07 648 2 QPSK 08 792 2 QPSK 09 928 2 QPSK 010 1264 3 QPSK 011 1488 3 QPSK 012 1744 3 QPSK 013 2288 4 QPSK 014 2592 4 QPSK 015 3328 5 QPSK 0

16 3576 5 16QAM 017 4200 5 16QAM 018 4672 5 16QAM 019 5296 5 16QAM 020 5896 5 16QAM 021 6568 5 16QAM 022 7184 5 16QAM 023 9736 7 16QAM 024 11432 8 16QAM 025 14424 10 16QAM 0

26 15776 10 64QAM 027 21768 12 64QAM 028 26504 13 64QAM 029 32264 14 64QAM 030 38576 15 64QAM 0

Table 7.4: CQI Table G, taken from Table 7G TS 25.214

Observation # 1. TB Size divided by 2ms TTI length gives the MAC-hs throughput.

Observation # 2. As the CQI becomes better, TB size, # of HS-PDSCH codes and


modulation scheme is improved.

Observation # 3. Cat 6 & Cat 14 UEs have a similar TB size for poor & medium CQIs.Therefore, a high-end device experiences better throughput only in the excellentradio conditions.

Observation # 4. 64QAM modulation of Cat. 14 is only available at CQI ≥ 26.

Observation # 5. In table 7.3, the maximum TB size, max # of codes and the bestmodulation is already used at CQI = 15. Therefore, as the CQI becomes better,there is a reference power adjustment factor. This factor is a negative factor whoseabsolute value increases as the radio channel becomes better.

7.4.5 L1 H-ARQ Retransmission

Here the word ARQ stands for Automatic Retransmission Query. In other words, if thepacket received by receiver is erroneous, it will send a negative-acknowledgement whichwill trigger the retransmission of the same packet. Some books also call it backward errorcorrection (BEC) because we take the action after the errors have occurred.

In contrast to backward error correction, there is another scheme called forward errorcorrection (FEC) or channel coding. In FEC, we add some extra redundant bits to improvethe channel conditions and to fight against the errors. FEC is called so because FEC stepsare performed at the transmitter end before the errors have actually occurred.

The scheme used in HSDPA is a mixture of both FEC and BEC. Therefore, it is calledhybrid -ARQ. The specialty of HSDPA is that this H-ARQ happens at MAC-hs layerbetween Node B and UE. UE also needs to play an active part in this scheme. If UEreceives a packet with a lot of errors, it sends a negative-Ack and stores a copy of thiserroneous reception. Later on, after receiving the retransmitted packet, UE has to softlycombine these two versions. This soft combining capacity is decided by the number of softchannel bits in the handset.

Retransmission on negative acknowledgement can be done in many ways, e.g.,

• Stop-and-Wait

• Go Back ‘N’

• Selective Repeat

• . . .

The method chosen for HSDPA retransmission is Stop-and-Wait (SAW) proce-dure, where the transmitter sends a transport block and waits for the receiver’s responsebefore sending a new block or retransmitting the erroneous one.


In its basic form, stop-and-wait mechanism is not very efficient, since the transmitter isinactive until it gets a response. This eventually reduces the throughput. Therefore, inHSDPA, 3GPP chose a smart way to improve the existing stop-and-wait algorithm. InHSDPA, Node B can configure up to six parallel H-ARQ processes active for one user.While Node B is waiting for a feedback from UE for process # 1, data can be transmittedfrom process # 2, 3, 4, 5 or 6. Hence, Node B can transmit without interrupting the dataflow.

Figure 7.3: Ilustration of parallel processes of HSDPA H-ARQ scheme

7.4.6 MAC-hs Protocol in Node B and UE

It won’t be any exaggeration if we say that MAC-hs is the brain of HSDPA.Prior to HSDPA, MAC layer was implemented at RNC. Therefore, only RNChad the authority to perform packet scheduling for Rel-99 channels.

Please refer to section 7.5 for detailed information about MAC-hs protocols and also itsinterworking with it others protocols. In short, the MAC-hs protocol is responsible for:

• packet scheduling,

• transport format combination (TFC) selection,

• L1 Hybrid-ARQ, and

• Iub flow control etc.


7.4.7 Serving Cell Change Instead of Soft HO

UE in HSDPA connected mode does not perform soft handover. While moving from oneHSDPA cell to another HSDPA cell, UE undergoes serving cell change. As a result ofserving cell change, UE stops receiving data from one Node B and starts receiving fromanother one. This topic is explained in more details in carefully in section 7.10. In short,the serving cell change mechanism is divided into three phases (as shown in figure 7.4).

Figure 7.4: HS-DSCH Serving Cell Change; 3 phases

The figure 7.4, explains the serving cell change procedure by dividing into three chrono-logical steps.

1. When UE is in Source Cell: UE has no radio link with the target cell. HS-DSCHas well as the associated-DCH channels are only between the UE and the Node Bof the source cell.

2. When UE is in overlapping area of the 2 cells: In the overlapping area, UE sendsa measurement report to RNC and performs soft handover for the associated-DCH(A-DCH) channel. But the HS-DSCH channel is only received from the source cell.

3. When UE is in Target Cell After leaving the overlapping area, if UE comes to thetarget cell’s area, it will maintain the radio link only with the Node B of the targetcell.


When the cell change action is triggered, there is always some interruption of HS-DSCHbut the end-user sees it as a reduced throughput. During this procedure, the user databuffered at old Node B cannot be transferred to the new Node B. In case of Inter-NodeB serving cell change, the old Node B flushes (or discards) the buffered data and the newNode B receives the same data from RNC. In case of Intra-Node B serving cell change,both the source and the target cells are served by the same Node B. Therefore, the samedata can be delivered to UE in the target cell.

7.5. HSDPA PROTOCOL ARCHITECTURE 221

7.5 HSDPA Protocol Architecture

Figure 7.5: MAC-hs Protocol in UE and Node B

Figure 7.5 shows the user plane protocol stack of HSDPA operation. In conventional Rel-99 operation, MAC-d PDUs are transmitted from RNC to Node B using Frame Protocol(FP) for DCH. For HSDPA operation, a new ‘FP for HS-DSCH’ is introduced. MAC-dflows from RNC are buffered at Node B. The data flow on Iub is controlled by MAC-hsprotocol and the procedure is known as Iub Flow Control. Figure 7.5 illustrates a FP dataframe from RNC to Node B.

After getting the CQI reports from UE, Node B can decide the size of MAC-hs transportblock, which is used by Node B to calculate the number of MAC-d PDUs that can bemultiplexed in MAC-hs PDU. Please note that the size of MAC-hs PDU can change everyTTI. Therefore, UE must also be informed about it. The information about the numberof MAC-d PDUs and their sizes is signalled to UE using the header field of MAC-hs PDU.

7.5.1 MAC-hs entity - UE Side

According to section 4.2.3.3 of 3GPP TS 25.321, the functions performed by MAC-hsentity on UE side is depicted in figure 7.6. These functions are listed in table 7.5. Let’sdiscuss them one-by-one.

1. HARQ: The HARQ functional entity handles all the tasks that are required for hy-brid ARQ. It is responsible for generating ACKs or NACKs. In the case of re-transmission, UE has to perform soft combining of previous erroneous reception andnew received transport block. There are two popular algorithms for this: ChaseCombining CC and Incremental Redundancy IR. These two schemes are de-scribed using figure 7.7.


On Node B Side On UE side

1. Flow Control

2. Scheduling/PriorityHandling

3. HARQ

4. TFRC selection

1. HARQ

2. Reordering Queue dis-tribution:

3. Reordering

4. Disassembly

Table 7.5: Summary of MAC-hs protocol functions

Figure 7.6: MAC-hs Protocol in UE Side (from TS 25.321)

Chase Combining: Chase combining is also called as ‘identical retransmis-sion’. As shown in the upper part of figure 7.7, in chase combining, whenNode B gets a negative acknowledgement for an MAC-hs transport block, itretransmits exactly the same amount of bits as the original transmission. Inother words, the same Redundancy Version (RV) is used for the original trans-mission and re-transmission. We can also say that the coding schemes used in


Figure 7.7: Chase Combining (upper) and Incremental Redundancy (lower)schemes for HSDPA HARQ

transmission and subsequent re-transmissions are identical.

Incremental Redundancy: Incremental redundancy scheme is illustrated in thelower subfigure of figure 7.7. IR has the liberty to change the redundancyversion after getting a negative acknowledgement.

2. Reordering Queue distribution: Using the QUEUE ID field of MAC-hs header,UE’s MAC-hs protocol entity forwards the MAC-hs PDUs to the correct reorderingbuffer.

3. Reordering: On UE side, one reordering entity is configured for each Queue ID. Themain purpose of this function is to deliver the MAC-hs PDUs with consecutiveTrasnmission Sequence Number (TSN) to the disassembly function. If MAC-hsPDUs with lower TSN are missing, MAC-hs PDUs are not delivered to the disas-sembly function.

4. Disassembly: A MAC-hs PDU contains three fields: (1) MAC-hs header, (2) MAC-dPDUs & and (3) padding bits. Disassembly function removes the other two partsand extracts the useful part, which is MAC-d PDUs. These MAC-d PDUs aredelivered to the MAC-d protocol layer.


7.5.2 MAC-hs entity - UTRAN Side

In the previous section, we discussed the MAC-hs entity on the UE side. Now we willfocus on the same protocol entity on UTRAN side. In UTRAN, MAC-hs is implementedin Node B which is shown in figure 7.8. These functions are described in section 4.2.4.3of 3GPP TS 25.321 and listed in table 7.5.

Figure 7.8: MAC-hs Protocol in UTRAN Side (from TS 25.321)

1. Flow Control: Flow control mechanism has already been discussed in section 7.3 andfigure 7.2.

Flow control function in MAC-d provides a controlled data flow between the MAC-d (RNC) and MAC-hs (Node B), taking the transmission capabilities of the airinterface into account in a dynamic manner. In other words, the flow control’sfunction is to negotiate the numbers of MAC-d PDUs transferred from RNC toNode B. Node B is in a better position to decide this for individual HSDPA userbecause of the received CQI feedback from each user.

The aim of flow control is to limit the layer 2 signalling latency and minimize thediscarded and retransmitted data which can happen due to HS-DSCH congestion.


In case of congestion, Node B can decrease the number of credits which means RNCwill send less amount of MAC-d data. This avoids buffer overflow and makes theIub transmission more effective. Flow control is provided independently by MAC-dflow for a given MAC-hs entity.

2. Scheduling & Priority Handling: Every TTI Node B has to allocate HS-DSCHresources between HARQ entities and data flows according to their priority class.Based on UE’s feedback in uplink, Node B decides whether new transmission orretransmission should be transmitted.

3. HARQ: One HARQ entity is responsible for managing the hybrid ARQ functionalityfor one user. As explained in an earlier section (see figure 7.3), we can have up tosix parallel processes per HARQ entity. These multiple processes are used to avoidthe interruption in continuous data flow caused by stop-and-wait HARQ algorithm.There can be only one HARQ process per HS-DSCH per TTI.

In HSDPA, up to six parallel HARQ processes can be configured. There can be oneHARQ process per TTI, whose identity is signalled to UE using L1 signalling. Formore information, please read about the information delivered on HS-SCCH channelin a later part of this chapter (section 7.6.2).

4. TFRC selection: Transport Format and Resource Combination selection for the datato be transmitted on HS-DSCH is very strongly attached to the link adaptation. Asdiscussed earlier, after receiving the feedback from UE, Node B decides:

• the size of MAC-hs Transport block,

• number of HS codes,

• channel coding rate, &

• modulation scheme etc.


7.6 Channels and Physical Layer

Source: 3GPP TS 25.211 Physical channels and mapping of transport channelsonto physical channels

In chapter 4, we discussed about the logical, transport and physical channels and restrictedour discussion to only Release 99 channels. With HSDPA development, there is no newlogical channel introduced in the system. But a new transport channel is designed whichis known as High speed- downlink shared channel (HS-DSCH). This transport channel isspecially used to carry DTCH logical channel4. In R99, the logical channel DTCH5 couldbe mapped to FACH and DCH transport channels. But with Rel-5, RNC has the optionsto select from the choices shown below.

From Rel-5 onwards, the DL logical channel DTCH is mapped to:

=

FACH if data volume is very smallDCH if data volume is large but HSDPA not supportedHS-DSCH if data volume is large and HSDPA is supported

Supported means that both UE device and the UTRAN must be capable of HSDPAfunctionality.

The transport channel HS-DSCH is further mapped to HS-PDSCH (HighSpeed-Physical Downlink Shared Channel).

Log. Ch. DTCH → Tra. Ch. HS-DSCH → Phy. Ch. HS-PDSCH

In the final section of chapter 4, there was brief overview of the HSDPA related channelsin section 4.6. For clarity, the same figure is shown in figure 7.9.

Now, we will focus on the functionality of L1 signalling for HSDPA operation. As shown infigure 7.1, the decision to use HS-DSCH is taken by RNC. After this, RNC informs NodeB and UE about the HSDPA configuration to kick-start the HSDPA operation. RNC canonly select the transport channel type but the actual scheduling is done by Node B. As weknow, HS-DSCH is a shared channel which is shared among all the users in a cell. NodeB has to notify the UEs about its scheduling decisions.

The procedure described in figure 7.9 can be understood in 4 steps.

Step 1: Every UE reports its radio conditions in the form of a Channel Quality Indicator(CQI ). The UL channel used for this feedback is HS-DPCCH.

4Optionally DCCH can also be carried by HS-DSCH. This is called Signalling Radio Bearer(SRB) on HSPA.

5Dedicated Traffic Channel

7.6. CHANNELS AND PHYSICAL LAYER 227

Figure 7.9: HSDPA related physical channels

Step 2: The MAC-hs scheduler at Node B calculates the Priority Metric for all the usersand selects the User (or Users)6, who will get scheduled in the next TTI.

Each scheduled user is individually notified using an HS-SCCH channel.

Step 3: Exactly 2 slots after the HS-SCCH, Node B transmits data on HS-PDSCH chan-nel to the scheduled users. There can be maximum 15 HS-PDSCH per cell. Oneuser can be allocated 1 to 15 HS-PDSCH codes. Therefore, it is also possible toallocate the whole cell resources to one user.

Step 4: After receiving and decoding the data, each scheduled UE transmits ACK orNACK in UL. The uplink channel used for this purpose the same as used in step 1,that is, HS-DPCCH.

In the section below, we will try to investigate these 3 physical channels in more depth.

7.6.1 HS-DPCCH

HS-DPCCH is a dedicated UL channel for sending HSDPA related feedbackinformation to Node B.

• HS-DPCCH is a dedicated channel. In simple words, if there are, for example, 50users in HSDPA active mode, then each user will transmit its own UL feedbackchannel.

• The timing of HS-DPCCH is organized in sub-frame which is 2ms or 3 slots long.

6The number of scheduled users is decided by the number of HS-SCCH configured in the cell.We can have at least one and at most 4 such channels. The most popular choices are 3 and 4.


Figure 7.10: Frame structure for uplink HS-DPCCH (TS 25.211)

• The HARQ-ACK is carried in the first slot of the HS-DPCCH sub-frame.

• The CQI is carried in the second and third slot of a HS-DPCCH sub-frame.

• SF for HS-DPCCH is 256.

• Bit Rate = 15 kbps. Therefore, 30 bits can be sent in UL every TTI.

• 10 bits are used for ACK/NACK and 20 bits for CQI7.

• CQI repetition cycle can be configured by operator.

Figure 7.10 shows that there are ‘N’ users in a cell and every UE is sending L1 feedback inuplink using HS-DPCCH channel. The same figure also shows that a 10 ms radio frame isbroken down into 5 sub-frames of 2ms. Each sub-frame can accommodate three slots andthese three slots of HS-DPCCH sub-frame carry two fields.

1. CQI: An active HSDPA UE is bound to report the DL channel conditions back to theNode B. The network signals the periodicity of channel condition indicator (CQI )reporting, and whether it is repeated (optionally). The UE measures the receivedP-CPICH & uses a proprietary algorithm to calculate CQI. CQI value also stronglydepends on the ratio of HS-PDSCH Power to Total Carrier power. For example,

7After channel coding 1 bit of ack/nack becomes 10 bits and 5 bits of CQI become 20 bits


6W out of 20W is allocated to HSDPA. Therefore, UE must get this information byhigher layer signalling.

The reported value indicates the maximum amount of data the UE estimates it couldreceive given the current channel conditions and UE capabilities. The network canthen use this value as a guideline when it schedules the next block of data. NodeB can of course, perform some vendor specific compensation to this reported CQI.There are 30 different CQI values for each UE category, so a CQI can be addressedusing 5 bits. However, CQI values are coded using a robust (20,5) code, so thechannel coder output is 20 bits long and fills completely the two slots allocated forCQI.

2. ACK/NACK: After the UE has received the HS-PDSCH frame and successfullydecoded it, it has to send an ACK (or NACK in case of errors) back to Node Busing a HS-DPCCH channel. The UE has approx. 7.5 slots (5 ms) to complete thisprocedure. ACK/NACK channel coding is very robust, because the input consistsof only one bit (ACK=1, NACK=0), and the channel coder simply repeats this tentimes, so the output is ten bits long.

7.6.2 HS-SCCH

Figure 7.11: Subframe structure for the HS-SCCH (TS 25.211)


HS-SCCH is a common DL channel which can be read by every HSDPA users.Each user reads this channel (or channels) every 2 ms to find out if he hasbeen scheduled.

If not: UE ignores the content of HS-SCCH (or HS-SCCHs).

If Yes: UE finds out which codes, how many codes, which modulation &,which Transport Block (TB) Size has been scheduled for him.

• HS-SCCH is a common channel. Operator can configure 1, 2, 3 or 4 such channelsper cell.

• SF for HS-SCCH is 128.

• Bit Rate = 60 kbps. Therefore, 120 bits can be sent in DL on each channel everyTTI.

• It is used to informs all the UEs how and when to receive the HS-PDSCH.

• For example, if 3 such channels are configured then 15 HS-PDSCH codes can bedivided into 3 ‘blocks’ every TTI ( e.g., ‘5+5+5’ or ‘2+8+5’ or ‘3+10+2’ etc.).

Figure 7.11 shows a cell with several users. In this example, the cell has been configuredwith only one HS-SCCH channel. In this example, only one UE can be scheduled inone TTI. Therefore, the cell uses pure time-multiplexing principle. It is also allowed tohave more than one HS-SCCH in a cell. This alternative, increases the overhead in codeand power domain but allows the operator to serve more than one UE in one TTI whichallows us to have code multiplexing of resources. Figure 7.11 also shows that HS-SCCHtransmission is two slots ahead of actual data transmission of HS-PDSCH. In short, wecan say that HS-SCCH informs and prepares the UE to receive HSDPA data on sharedresources.

HS-SCCH channel carries the following fields: .

Channelization Code Set, 7 bits: The CCS field indicates the number of SF16 codesand the code offset that are used for the HS-DSCH during the specific 2 ms TTI.

Modulation Type, 1 bit: This bit indicates the modulation type. In Rel-5 & Rel-6,there are only two options. Therefore, one bit is sufficient. But from Release 7,the third option of 64QAM is also available. Hence, if 64QAM is configured in thecell, then 7 bits of CCS and 1 bit modulation type should be considered together toidentify the modulation.

Transport Block Size, 6 bits:

Hybrid-ARQ Process ID, 3 bits:

Redundancy and Constellation Version, 3 bits:


New Data Indicator, 1 bit: This bit toggles (0 to 1 or 1 to 0) for every new transmis-sion and remains the same in case of retransmission.

• 7 bits of ‘Channelization Code Set’ and 1 bit of ‘Modulation Type’ aremultiplexed together. These 8 bits are channel coded and the result issent on the first slot of HS-SCCH sub-frame.

• 6 bits of ‘Transport Block Size’, 3 bits of ‘HARQ process ID’, 3 bits of‘Redundancy and Constellation Version’ & 1 bit of ‘New Data Indicator’fields are multiplexed together. These 13 bits are channel coded and senton 2nd and 3rd slot of HS-SCCH sub-frame.

Several times, it has been stated that HS-SCCH carries the UE identity. But that identityfield is missing from the list shown above. This list is actually copied from section 4.6.2of 3GPP TS 25.212. Are we missing something?

Yes, we are missing the concept of masking UE identity on the CRC field.

From the aforementioned 21 bits (8 + 13 bits) of HS-SCCH fields, a 16-bit CRC is calcu-lated by Node B. The CRC is masked with a 16-bit user specific identity called H-RNTI.H-RNTI is allocated by RNC at the time of radio bearer setup or radio bearer reconfig-uration, if the HS-DSCH transport channel is selected. Although HS-SCCH transmissionis on three slots of a sub-frame, UE can read the UE identity from the first slot itself.

UE must monitor all HS-SCCHs in the HS-SCCH set. If the UE did detect controlinformation intended for this UE in the previous subframe, it is sufficient to only monitorthe same HS-SCCH used in the previous subframe. If a UE detects that one of themonitored HS-SCCHs carries control information intended for this UE, the UE shall startreceiving the HS-PDSCHs indicated by this control information.

For more details, readers are advised to refer to 3GPP TS 25.212; Multiplexing and channelcoding (FDD).

7.6.3 HS-PDSCH

HS-PDSCH is the main DL channel which carries DL data for the subscribers.

• HS-PDSCH is a shared channel. There can be up to 15 such channels per cell

• SF for HS-PDSCH is 16

• Bit rate = 240 ksps per code8

• No soft handover

8To get kbps, multiply by #bits per symbol, 2 for QPSK, 4 for 16QAM and 6 for 64QAM


Figure 7.12: Subframe structure for the HS-PDSCH (TS 25.211)

• No fast inner-loop power control

The High Speed Physical Downlink Shared Channel (HS- PDSCH) is used to carry theHigh Speed Downlink Shared Channel (HS-DSCH). A HS-PDSCH corresponds to onechannelization code of fixed spreading factor SF=16 from the set of channelization codesreserved for HS-DSCH transmission. Multi-code transmission is allowed, which translatesto UE being assigned multiple channelization codes in the same HS-PDSCH subframe,depending on its UE capability. According to the principles of channelization codes, thereare 16 codes of SF=16, but one of them CC16,0 is forbidden to use because a SF 256(CC256,0) code from the same branch is used for P-CPICH in the same cell. Therefore, tomaintain orthogonality on DL, it is decided to use only 15 codes for HSDPA transmission.This concept is described in figure 7.12. The same figure also shows the subframe and slotstructure of HS-PDSCH.

An HS-PDSCH may use QPSK, 16QAM or 64QAM modulation symbols. All relevantLayer 1 information is transmitted in the associated HS-SCCH i.e. the HS-PDSCH doesnot carry any Layer 1 information. The slot formats for HS-PDSCH are shown in table7.6. The three rows of this table emphasize the effect of modulation on channel bit rate.


Slot format#i

Channel BitRate (kbps)

Channel SymbolRate (ksps)

SFBits/ HS-DSCH

subframe

0 (QPSK) 480 240 16 960

1 (16QAM) 960 240 16 1920

2 (64QAM) 1440 240 16 2880

Table 7.6: HS-DSCH fields (TS 25.211)

Figure 7.13: All Channels in REL-5 Configuration (including A-DCH)

7.6.4 Associated DCH

A-DCH or associated DCH is the new name used for the well-known R99 DCHchannels when these channels are used in association with HSDPA channels.

Uplink: In UL, the Control channel (DPCCH) and Data channel (DPDCH) are codemultiplexed. DPCCH is used for carrying L1 Control9 bits & DPDCH is used forcarrying for user data and signalling radio bearer (SRB or L3 signalling)

Downlink: In DL Control channel and Data channel are time multiplexed. The multi-plexed channel is called DPCH. Hence, DPCH is used for L1 control, User Data andSRB.

One again, we would emphasize that A-DCHs are dedicated channels. Therefore, if thereare 50 active HSDPA users then there will be 50 UL channels and 50 DL channels. Dueto this, every active user’s A-DCH will cause additional UL interference and DL code &power congestion.

9TFCI, Pilot Bits and TPC


Figure 7.14: Fractional DPCH Channel as reduced version DL DPCH (TS 25.211)

7.6.5 Fractional-DPCH

As the name implies, F-DPCH is a fractional version of the normal DL DPCHchannel. For every active HSDPA user, one DL DPCH is needed but one F-DPCH can be used by upto 10 users. This solves DL code and power congestionup to some extent.

An F-DPCH carries control information generated at layer 1 (TPC com-mands) for one uplink DPCCH.

As explained in section 7.6.4, every active HSDPA user requires one SF256 from DLchannelization code tree. At the time of writing this book (August 2012), vendors aresupporting more than 70 active HSDPA users per cell. If conventional A-DCH is used,then for every active user a DL SF256 code will be reserved for DPCH. To solve thisproblem, 3GPP has introduced DL Fractional-DPCH which can be used as a replacementfor DL DPCH. But there are a few prerequisites for using F-DPCH.

• F-DPCH is possible for HSDPA+HSUPA.

• SRB on HSPA must be configured because DL RRC signalling cannot be conveyedon F-DPCH.

As shown in figure 7.14, Normal DPCH with SF 256 can be used to transmit 20 bits pertime slot. But in Fractional DPCH, the transmitter is ‘OFF’ for 18 bits and ‘ON’ for onlytwo bits. These two bits are DL TPC (Transmit Power Control) command. The users areallocated a slot format number (0, 1, 2, . . . , 9). Based on the slot number, UE finds outwhen TPC bits are transmitted for him. In the remaining 90% of time, other nine usersare provided with their respective TPC commands. In the same figure, an example of slotformat # 4 is shown. The exact definition of each slot format # can be found in table 7.7.

7.7. TIMING OF HSDPA CHANNELS 235

Slot FormatSF

Total NOFF1 NTPC NOFF2

# Bits/Slot Bits/Slot Bits/Slot Bits/Slot

0 256 20 2 2 161 256 20 4 2 142 256 20 6 2 123 256 20 8 2 104 256 20 10 2 85 256 20 12 2 66 256 20 14 2 47 256 20 16 2 28 256 20 18 2 09 256 20 0 2 18

Table 7.7: F-DPCH fields (from 3GPP TS 25.211)

7.7 Timing of HSDPA Channels

Source: 3GPP TS 25.211;

section 7; Timing relationship between physical channels

A simplified HSDPA operation is depicted in figure 7.15. In the example shown in thisfigure, we have assumed that there is only one HS-SCCH in the cell and the UEs areexpected to send CQI reports every 2 ms. UE # 1 is scheduled in first TTI, UE #2 andUE # 3 in the 2 next TTIs and UE #2 is again scheduled in the 4th TTI. The samefigure (fig. 7.15) also shows the behaviour of UE # 1 and UE # 2 from the reception andtransmission perspective.

x

It can be seen that CQI reports are sent periodically. If the HSDPA user gets scheduled,it receives data and sends either positive or negative acknowledgement. A/NACK are senton the first time slot of HS-DPCCH channel.

Timing of HS-SCCH: This downlink channel has the same reference and frame timingas P-SCH, S-SCH, P-CPICH and P-CCPCH. The start of HS-SCCH subframe #0is aligned with the start of the P-CCPCH frames.

Timing of HS-PDSCH: Figure 7.15 illustrates the timing structure for the HS-DSCHcontrol signalling. The fixed time offset between the HS-SCCH information and thestart of the corresponding HS-DSCH TTI equals 2× time slots (2*Tslot=5120chips).

Timing of HS-DPCCH: The timing of HS-DPCCH is calculated in relation to the DLHS-PDSCH reception time and UL DPCCH/DPDCH transmission time. The rela-tive timing between DPCCH/DPDCH and HS-DPCCH is kept constant.


Figure 7.15: Summary of HSDPA operation and timing

• The start of HS-DPCCH subframe which carries Ack/Nack for the receivedHS-PDSCH data is approx. 7.5 Time slot after the reception of correspondingHS-PDSCH subframe at UE receiver.

• The time offset between UL DPCCH/DPDCH and HS-DPCCH is a multipleof 256 chip (n × 256 chips).

7.8 HSDPA UE Categories

Quite often the network performance is limited by the population of low-end HSDPAdevices on the network. Therefore, it is quite important to learn about the maximum bitrates that can be achieved by a certain UE category. Every 3GPP release has added newfunctionalities to HSDPA operation and thereby defined new device categories. Accordingto 3GPP Rel-9, there are 28 HSDPA UE categories, whose details are readily available in3GPP TS 24.306. The purpose of this book is to make the learning easier. Therefore, wewould focus on the device categories according to each release.

7.9. HSDPA PEAK BITRATE CALCULATION 237

Category Modulation Max. Codes

11 & 12 Only QPSK 5

1 to 6QPSK & 16QAM

57 & 8 109 & 10 15

Table 7.8: UE categories according to Rel-5 & Rel-6

Category Modulation Max. Codes MIMO Support

11 & 12 Only QPSK 5 No

1 to 6 QPSK & 16QAM 5 No

7 & 8 QPSK & 16QAM 10 No

9 & 10 QPSK & 16QAM 15 No

13 & 14 QPSK & 16QAM & 64QAM 15 No

15 & 16 QPSK & 16QAM 15 Yes

17 & 18 QPSK & 16QAM & 64AM 15 No17 & 18 QPSK & 16QAM 15 Yes

Table 7.9: UE categories according to Rel-5, Rel-6 & Rel-7

7.9 HSDPA Peak Bitrate Calculation

In this section, we will investigate the maximum bit rates that can be achieved with anHSDPA device of certain category. The wordmaximum here means the peak instantaneousbit rate for 2ms TTI. In order to calculate the average throughput, we should also considerthose TTIs where the user was not scheduled.

Data Rate per code =

[Rchip

SF

]Symbols/second

Bit Rate per code = [Data Rate [ksps] × Bits per Symbol] kbps ,

Bits per Symbol =

2 if Modulation is QPSK,4 if Modulation is 16QAM,6 if Modulation is 64QAM .

Max. Gross Bit Rate = [Bit Rate per code × Max. # of codes supported] kbps

Max. Net Bit Rate = [Gross Bit Rate] × [Channel Coding Rate] kbps

Let us take examples of device categories 12, 6, 8, 10, 14 & 16 and calculate the peak netbit rates achieved. In this example, we will assume channel coding rate of 3/4. Pleaserefer to table 7.10.


UECat.

SymbolRate

Best Mod-ulation

Bit Rate#

codesRbit

(Gross)Rbit (Net)

12 240 Ksps QPSK 480 kbps 5 2.4 Mbps 1.8 Mbps

6 240 Ksps 16QAM 960 kbps 5 4.8 Mbps 3.6 Mbps




16 240 Ksps 16QAM 960 kbps 1528.8

Mbps101.8 Mbps

Table 7.10: Example of peak bit rate calculation for several devices categories

While doing the same calculation for a UE which supports MIMO operation, the finalresult can be multiplied by 2. Because in the MIMO scheme, where 2 transport blocks aremultiplexed on the same TTI, the peak bit rates are doubled.

7.10. SERVING HS-DSCH CELL CHANGE 239

7.10 Serving HS-DSCH Cell Change

Figure 7.16: Inter-Node B serving HS-DSCH cell change (TS 25.308)

According to 3GPP TS 25.308, “A serving HS-DSCH cell change facili-tates the transfer of the role of ‘serving HS-DSCH radio link’ from one radiolink belonging to the source HS-DSCH cell to a radio link belonging to thetarget HS-DSCH cell”.

As discussed in chapter 5, mobile in CELL DCH mode performs soft-handover or hard-handover in order to maintain the connectivity with UTRAN. However, for HS-PDSCHallocation for a given UE belongs to only one of the radio links assigned to the UE, theserving HS-DSCH radio link. The cell associated with the serving HS-DSCH radio link isdefined as the serving HS-DSCH cell. While moving, UE can perform serving HS-DSCHcell change. Quite often, people call it HSDPA Serving Cell Change (SCC).

This mechanism is almost similar to a hard handover with a small difference that duringtransition UE may perform soft handover on A-DCH channels with source and targetcells. Hence for HS-DSCH, UE does not perform Soft handover but for the associated-DCH (A-DCH) it does. The source and the target cells can be controlled by the same NodeB or two different Node Bs. Thus, we need to discuss two different mobility scenarios:

In 3GPP 25.308, several ways to classify the Serving HS-DSCH Cell change proceduresare defined. We will discuss the classification which is based on the serving HS-DSCHNode B. The signalling scenarios related to these procedures are discussed in chapter 9.


Intra-Node B serving HS-DSCH cell change: In this scenario, the source and thetarget cells are two adjacent sectors of the same site (Node B). Therefore, theunacknowledged data which is buffered at Node B can be transmitted to the userusing new radio link. There is no need to flush the data. Intra-Node B SCC hasless interruption in service.

Inter-Node B serving HS-DSCH cell change: In contrast to the earlier case, in thiscase, the source and the target cells are controlled by two different Node Bs. There-fore, when the user moves into the new cell, the unacknowledged buffer data at oldNode B must be flushed and the new Node B must get the same from RNC. Asexpected, this causes delay and increases the service interruption time.

For UE it is irrelevant whether the serving HS-DSCH cell change procedure is of a intra-Node B or inter-Node B nature. The cell change decisions are always made by UTRAN.Hence SCC procedure of HSDPA is known as network-controlled serving HS-DSCH cellchange. A network controlled HS-DSCH cell change is performed as an RRC layer sig-nalling procedure and is based on the existing handover procedures in CELL DCH state.

The detailed signalling between UE and RNC related to both Inter-Node B and Intra-Node B Serving Cell Change is described in the in chapter 9 along with other interstingsignalling scenarios related to UMTS and HSPA.

7.11. SUMMARY: HSDPA OPERATION IN SHORT 241

7.11 Summary: HSDPA Operation in Short

The whole communication between UE and Node B can be explained using the 3 physicalchannels designed for HSDPA operation. This procedure is illustrated in figure 7.17. Inshort, the various steps are as following:

Figure 7.17: HSDPA operation explained using the physical channels.

Channel Direction Function SF Modulation Ch. Coding

HS-PDSCH ↓ Carries DL userdata

16QPSK &16QAM

1/3 Turbo coding

HS-SCCH ↓ Carriesscheduling info

128 QPSK1/3

Convolutionalcoding

ACK =‘1111111111’

HS-DPCCH

↑ Used to send ULfeedback

256 BPSKNACK =

‘0000000000’CQI = (20,5)Block coding

Table 7.11: Summary of HSDPA channels


Copyright Notices



Table 7.3 on page 215 Table 7A of 3GPP TS 25.214 v 9.1.0.Table 7.4 on page 216 Table 7G of 3GPP TS 25.214 v 9.1.0.Figure 7.10 on page 228 Figure 2A of 3GPP TS 25.211 v 9.1.0.Figure 7.11 on page 229 Figure 26A of 3GPP TS 25.211 v 9.1.0.Figure 7.12 on page 232 Figure 26B of 3GPP TS 25.211 v 9.1.0.Table 7.6 on page 233 Table 26 of 3GPP TS 25.211 v 9.1.0.Figure 7.14 on page 234 Figure 12B of 3GPP TS 25.211 v 9.1.0.Table 7.7 on page 235 Table 16C of 3GPP TS 25.211 v 9.1.0.Text in section 7.7 on page 235 Section 7 of 3GPP TS 25.211 v 9.1.0.c⃝2009. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

Text in section 7.5.1 on page 221 Section 4.2.3.3 of 3GPP TS 25.321 v 7.7.0.Text in section 7.5.2 on page 224 Section 4.2.4.3 of 3GPP TS 25.321 v 7.7.0.Figure 7.6 on page 222 Figure 4.2.3.3.1 of 3GPP TS 25.321 v 7.7.0.Figure 7.8 on page 224 Figure 4.2.4.3.1 of 3GPP TS 25.321 v 7.7.0.c⃝2008. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

7.11. SUMMARY: HSDPA OPERATION IN SHORT 243

Table 7.1 on page 206 Table 5.1a of 3GPP TS 25.306 v 9.1.0.Table 7.8 on page 237 Table 5.1a of 3GPP TS 25.306 v 9.1.0.Table 7.9 on page 237 Table 5.1a of 3GPP TS 25.306 v 9.1.0.Text in section 7.6.2 on page 229 Section 4.6 of 3GPP TS 25.212 v 9.3.0.c⃝2010. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

BIBLIOGRAPHY


[2] 3GPP TS 25.308 ver. 7.0.0 ;‘High Speed Downlink Packet Access (HSDPA); OverallDescription;’

[3] 3GPP TS 25.306 ver. 9.0.0 ;‘UE Radio Access capabilities’












[15] H.Holma and A. Toskala, ‘HSDPA/HSUPA for UMTS’ , 1st Edition, John Wiley& Sons.


244

CHAPTER

8

HIGH SPEED UPLINK PACKETACCESS

Source: 3GPP TS 25.319; Enhanced uplink; Overall description

After learning the important facts about High Speed Downlink Packet Access (HSDPA)in the previous chapter, the next logical step is to investigate the improvements in uplink.These new set of improvements are known as “High Speed Uplink Packet Access (HSUPA)or Enhanced Uplink1”.

The first release of HSDPA standard was available in 3GPP Rel-5. HSUPA was standard-ized in 3GPP Rel-6. Once again, the design targets are very similar to HSDPA. But inUplink, there are some additional requirements which need to be met. These requirementsare discussed in 3GPP 25.319. Some of those points are mentioned below.

8.1 Requirements

• The uplink coverage for R99 DCH channel is generally very limited. Therefore, theend user experience in wide area cells is not very good.

1Enhanced Uplink (EUL) is the official name chosen by 3GPP but due to popularity of HSDPA,the term HSUPA is also very widely used.

245

246 CHAPTER 8. HIGH SPEED UPLINK PACKET ACCESS

The Enhanced Uplink feature is targeted at providing a significant improvements interms of user experience (throughput and delay) and/or capacity. The coverage isone of the aspects which affect the user experience. For an operator, it is desirableto have good coverage to provide consistency of performance across the whole cellarea. Therefore, it is expected that HSUPA should serve a wider cell area. Hence,coverage will be one of the main design criterion while development. In contrast tothis, in HSDPA, the focus was on DL throughput.

• HSUPA should be designed to serve urban, sub-urban and rural deployment scenar-ios.

• HSUPA should support full mobility. Undoubtedly, the system is best optimized forstationary users but it should perform well for fast-moving users as well.

• HSUPA should be designed with least complexity so that the user equipment’s (UE)& network elements’ cost is not very high. In R99 specification, there were a lotof features that are practically not used anywhere. In HSUPA development, suchfeatures should be avoided so that the time-to-market can be reduced.

• It is required that HSUPA should provide improved QoS compared to R99 UL ded-icated channels. The main focus should be on the services of streaming, interactiveand background traffic classes.

• There is always a trade-off between performance improvement & complexityof upgrades. HSDPA introduced a lot of changes in hardware and protocol archi-tecture. It is desirable that changes caused by HSUPA should be as little as possible.

According to 3GPP TS 25.319: “New techniques or group of techniques shall there-fore provide significant incremental gain for an acceptable complexity”.

• The improvements should be designed in such a away that HSUPA can be introducedto a network which has UEs of different radio capabilities, i.e., R6 UEs and the UEsfrom R99, R4 and R5.

• A terminal supporting the Enhanced Uplink feature must support HSDPA. There-fore, the term HSPA can be used to describe the combination of HSDPA andHSUPA. In our further discussions, we will use HSPA as a synonym for HSUPA.

From the end-user point of view, HSUPA is an enhancement to Rel-99 UTRAN whichallows him to achieve higher Uplink peak bit rates in a wider service area compared toclassical R99 solution for Uplink data transmission. This is an important upgrade becausethe UL bit rates of R99 DCH are very low when the UE is at cell-edge.

8.2. COMPARISON WITH HSDPA 247

8.2 Comparison with HSDPA

As the names indicate, HSDPA and HSUPA sound very similar. Therefore, we commonlyassume that HSUPA is nothing but ‘HSDPA for Uplink’. This is not exactly true. Toinvestigate this issue further, let’s discuss the commonalities and differences between thetwo technologies.

8.2.1 Commonalities with HSDPA

Node B based scheduling: The transport channels used to carry the user data in R99UMTS are RACH (↑), FACH (↓) & DCH (↕). All of these channels are scheduledby RNC’s packet scheduler. This concept was explained in HSDPA module.

HSDPA transport channel HS-DSCH and HSUPA transport channel E-DCH areboth scheduled by Node B based packet scheduler.

Fast L1 H-ARQ: In HSUPA, the data transmitted via E-DCH transport channel re-quired immediate acknowledgements from Node B. This concept was introducedin HSDPA where the role of transmitter is played by Node B and UE sends theacknowledgment.

Multicode Operation: The peak UE bit rates in HSDPA are achieved by sending datato a user on multiple SF16 codes. Similarly, in HSUPA, UE can send uplink dataon either 1, 2 or 4 channelization codes.

Link Adaptation: Based on the UE radio conditions, data volume and many otherconditions, UE resource allocation can be modified. This concept is common inHSDPA and HSUPA.

• Rel-5 HSDPA devices support QPSK & 16QAM modulation2. Therefore, linkadaptation happens by adaptive modulation and coding (AMC).

• Rel-6 HSUPA devices support only BPSK modulation. Therefore, the linkadaptation happens mainly by adaptive coding (AC) only.

Shorter TTI: The Rel-99 transport channel DCH supports the TTI length of 10, 20, 40or 80 ms. HSDPA utilizes a significantly shorter TTI of 2 ms. In HSUPA:

• 10 ms TTI is a mandatory for every network and the UE. This is to ensurethat UE will be able to use HSUPA when it finds itself in a poor coverage area.

• 2 ms TTI is optional. 2 ms will allow the user to achieve higher peak bit ratesand lower latency, but 2ms TTI can be used only if the UE is in good radioconditions.

2Except special category 11 & 12 UEs


8.2.2 Differences from HSDPA

Power Control: In HSDPA, all 3 slots in a subframe are transmitted at a constantpower. In other words, there is no fast inner loop PC for HSDPA. But in HSUPA,the power control is very crucial for minimizing the near-far effect.

In HSDPA, there is a central transmitter in Node B whereas in HSUPA, the trans-mitters are distributed across the whole cell coverage area. Therefore, managementof interference requires more signalling in HSUPA.

Soft Handover: HSDPA performs a (hard) Serving Cell Change whereas, in HSUPA theE-DCH channel can be in soft-handover with up to 3 Cells.

Variable Spreading factor: In HSDPA, the SF = 16, which is fixed. But in HSUPA,UE gets a resource grant from Node B and decides which SF to use. It is allowed touse eight possible spreading factors (SF 256, 128, ..., 2). This is shown in table 8.4.

Overall Procedure: In HSDPA, the scheduler resides in Node B and data is also bufferedat Node B & RNC side. Therefore, Node B can very well decide how much bitratewill satisfy the need of the user. On the contrary, in uplink, the scheduler needs toknow the status of the UE buffer. There has to be some periodic reporting of thebuffer status.

• In HSUPA, we have some kind ofRequest → Grant → Data Transmission → Acknowledgementmechanism. Whereas,

• In HSDPA, we haveNotification to UE → Data Transmission → Acknowledgementtype of mechanism.

8.3 HSUPA User Plane Protocols

A detailed description of PDCP, RLC and MAC-d protocols is available in chapter 6.HSUPA related MAC protocols are MAC-e and MAC-es, which are explained later in thischapter.

In this section, we will examine the HSUPA transmission only in an overview manner.

1. On UE Side • PDCP layer compresses the headers belonging to higher layers e.g.,TCP/IP or RTP/UDP/IP.

• RLC layer performs segmentation on the big data block received from PDCPlayer. The size of RLC PDU is explicitly signalled to the user via RRC sig-nalling3. RLC also performs ciphering. If the Acknowledged Mode (AM) ofRLC is configured, then RLC layer keeps track of L2 retransmissions.

3in RB setup or RB Reconfiguration message.

8.3. HSUPA USER PLANE PROTOCOLS 249

Figure 8.1: HSUPA User Plane Protocols

• MAC-d layer in UE generates the MAC-d flows. MAC-d layer is transparentin HSUPA. Therefore, the MAC-d PDU is exactly the same as RLC PDU.

• MAC-es layers combines MAC-d PDUs of the same logical channel and samesize into one MAC-es PDU. MAC-es layer adds a Transmission Sequence Num-ber which will help the RNC to re-order the correctly received MAC-es PDUs.

• MAC-e layer in UE, combines several MAC-es PDUs and form a MAC-e PDU.

• Physical layer in UE carries on L1 processing and transmits the data onWCDMA air interface.

2. On Node B Side • Node B’s Physical layer receives the data coming from UE’sphysical layer.

• MAC-e layer in Node B checks for L1 H-ARQ and decides whether an Ack orNack has to be sent.

• MAC-e layer demultiplexes the MAC-e PDU and extracts the MAC-es PDUswhich are sent towards RNC.

3. On RNC Side • By looking into the ‘transmission sequence number (TSN)’, MAC-es layer of RNC re-orders the correctly received MAC-es PDUs. It demulti-plexes the MAC-es PDUs to extract the MAC-d pdus. In HSUPA, UE canbe in soft handover with more than one cell. Therefore, MAC-es layer alsoperforms Macro Diversity Combining (MDC) to achieve the link diversity.

• Finally, the correctly received MAC-d PDUs are forwarded to the MAC-d layer.

• RLC layer in RNC checks whether a L2 Ack or Nack has to be sent to the UE.On RNC side, the RLC layer performs reassembly of several RLC blocks andconstructs a big data block to be delivered to the PDCP layer.


• PDCP layer in RNC performs header decompression and restores the originalheader of higher layer application.

Summary of HSUPA Operation (according to TS 25.401):“The E-DCH MAC (MAC-e/MAC-es) entity in the UE trans-fers MAC-e PDUs to the peer MAC-e entity in the Node B andMAC-es PDUs to the peer MAC-es entity in the RNC using theservices of the Physical Layer”.

8.4 HSUPA Configuration Options

At first sight, one can guess that E-DCH transport channel is mainly designed for carryinguplink user data (Logical channel DTCH). Similarly HS-DSCH transport channel is mainlydesigned to transmit downlink user data.

But if we carefully examine options available for mapping the Signalling Radio Bearers(SRB) on transport channels, operators have two choices. This section investigates bothoptions. The general channel structure of UMTS was discussed in chapter 4.

Figure 8.2: HSUPA Control Plane Protocols - SRB on DCH

Option 1: SRB on DCH: In this configuration, HS-DSCH channel and E-DCH chan-nel is used to carry the DTCH logical channel whereas the logical channel DCCHor RRC signalling4 is still sent via UL & DL DCH channels. Obviously this optionis not the best option because it includes a lot of DCH overhead channels. Thecontrol plane protocol stack for this option is exactly the same as Rel-99 controlplane protocol stack as shown in figure 8.2.

SRB on DCH option does not reduce the control plane latency.

4also known as Signalling Radio Bearer SRB or L3 Signalling

8.5. E-DCH UE CATEGORIES AND BIT RATES 251

Figure 8.3: HSUPA Control Plane Protocols - SRB on HSPA

Option 2: SRB on HSPA: Alternatively, HS-DSCH and E-DCH channels can be con-figured to send both User data DTCH and DCCH. This option is commonly knownas SRB on HSPA. The control plane protocol stack for this configuration is illus-trated in figure 8.3.

This option significantly reduces the amount of DCH overhead channels and controlplane latency.

SRB on HSPA is a pre-requisite for some other smart features, for example, Fractional-DPCH (F-DPCH).

8.5 E-DCH UE Categories and Bit Rates

Source: 3GPP TS 25.306 ; UE Radio Access capabilities

In HSDPA, we have learnt about a variety of UE categories. Up to Release 9, thereare 28 HS-DSCH UE categories defined for HSDPA operation. Similarly, there existsome standard UE categories for HSUPA operation too. In order to follow the HSUPAdevelopment in chronological order, the E-DCH UE categories are illustrated in threedifferent tables.

• Rel. 6: Category 1, 2, 3, 4, 5 & 6 are introduced.

• Rel. 7: Category 7 UE has been added to the list of UE categories. Main enhance-ment is 4-PAM modulation on E-DPDCH channel (which is quite often referred toas 16-QAM).


• Rel. 8: No new Category defined in Rel-8.

• Rel. 9: Category 8 & 9 Categories have been added which support Dual Cell-HSUPA(or DC-HSUPA) operation.

E-DCHCategory

Maxno. ofE-DCHCodes

Min.SF

SupportedTTI

Max. TBSize [bits]in 10 msTTI


Modul.

Cat. 1 1 SF4 10 ms only 7110 - BPSKCat. 2 2 SF4 10 ms & 2 ms 14484 2798 BPSKCat. 3 2 SF4 10 ms only 14484 - BPSKCat. 4 2 SF2 10 ms & 2 ms 20000 5772 BPSKCat. 5 2 SF2 10 ms only 20000 - BPSKCat. 6 4 SF2 10 ms & 2 ms 20000 11484 BPSK

Table 8.1: E-DCH UE Categories introduced in 3GPP Rel. 6 (25.306)

E-DCHCategory

Maxno. ofE-DCHCodes

Min.SF

SupportedTTI



Modul.

Cat. 7 4 SF2 10 ms & 2 ms 20000 22996 4-PAM

Table 8.2: Additional E-DCH UE Categories in 3GPP Rel. 7 (25.306)

E-DCHCategory

Maxno. ofE-DCHCodes

Min.SF

SupportedTTI



Modul.

Cat. 8 4 SF2 10 ms & 2 ms 20000 11484 BPSKCat. 9 4 SF2 10 ms & 2 ms 20000 22996 4-PAM

Table 8.3: Additional E-DCH UE Categories in 3GPP Rel. 9 (25.306)

After observing the tables 8.1, 8.2 & 8.3, we can make some remarks about the variousUEs of different categories.

1. Multi-code Support: Some UEs do not support multi-code operation on E-DPDCH(for example Cat. 1 UE), some support upto 2 codes (for example Cat. 2, 3, 4, &5) while some UEs support upto 4 code transmission (for example UE cat. 6, 7, 8& 9).

8.6. STARTING OF HSUPA OPERATION 253

2. Min. SF: SF2 was introduced in 3GPP REL-6 for E-DPDCH channel. But all theUEs cannot use SF2. This aspect of their radio access capabilitis is shown in thecolumn ‘Min. SF’ in the UE categories tables.

3. TTI Support: Both 2 ms and 10 ms TTI have their own advantages and disadvan-tages. 10 ms TTI is a mandatory feature which is supported by all UEs but 2 msTTI operation is possible only for UE cat. 2, 4, 6, 7, 8 & 9.

4. Modulation: Cat. 1 to 6 and cat. 8 can transmit data using BPSK modulation (onebit per symbol) only whereas the UE category 7 & 9 can also use 4PAM; modulation(2 bits per symbol).

5. DC-HSUPA: Only Rel. 9 categories UEs, i.e. Category 8 & 9 UEs, can supportDC-HSUPA operation.

8.6 Starting of HSUPA Operation

As discussed in the chapter 5 about the Radio Resource Management, we saw that RNC’sPS is responsible for deciding the ’transport channel type selection’. This procedure canyield 4 possible outcomes:

1. RACH & FACH

2. DCH & DCH

3. DCH & HS-DSCH

4. E-DCH & HS-DSCH

As shown in figure 8.4, every HSUPA device starts the signalling procedure as if it werea simple R99 UE. After performing GPRS ATTACH, the serving SGSN, UE acquires aP-TMSI and knows about the Routing area ID of the cell. As a result of GPRS attach,there is a MM context stored in UE and SGSN. Later, UE establishes a PDP context andtries to acquire an IP address and negotiate the QoS.

Later on, when UE feels the need of UL resources, it sends an UL capacity request tothe RNC. RNC performs the channel type selection and decides one of the options listedabove. Up to this point in signalling, a 3G R99 UE and HSUPA UE behave almost thesame.

In case, RNC chooses to use E-DCH in UL, the use of HS-DSCH becomes mandatary.If HS-DSCH resources are also available, RNC sends the information regarding the cellspecific HSDPA and HSUPA details to user in a L3 RRC message Radio Bearer Recon-figuration.


Figure 8.4: Signalling to initiate an HSUPA session

8.7 HSUPA Protocol Architecture

Source: 3GPP TS 25.321; Medium Access Control (MAC) Protocol Specifi-cation

Earlier in section 8.3, the user plane protocol architecture of HSUPA & data-flow wasdescribed but the details about MAC-e and MAC-es were not discussed. In the same sec-tion, figure 8.1 described the overall functionality of HSUPA using the user plane protocolstack. In the following section, we will investigate the MAC layer of HSUPA in depth.

On UTRAN side, for each UE that uses E-DCH, one MAC-e entity per Node-B and oneMAC-es entity in the SRNC are configured. Whereas on UE side, both MAC-e & MAC-esare configured in the user equipment.

MAC-e/es entity - UE Side

Figure 8.5 is copied from ‘Figure 4.2.3.4.1a: UE side MAC architecture / MAC-e/es details(FDD)’ of 3GPP TS 25.321. The MAC-es/e handles the E-DCH specific functions. Thesplit between MAC-e and MAC-es in the UE is not detailed. In the model below, the

8.7. HSUPA PROTOCOL ARCHITECTURE 255

Figure 8.5: UE side MAC-e/es details (25.321)

MAC-e/es comprises the following entities:

1. H-ARQ: The HARQ entity is responsible for handling the MAC functions relat-ing to the HARQ protocol. It is responsible for storing MAC-e payloads andre-transmitting them. The detailed configuration of the hybrid ARQ protocol isprovided by RRC over the MAC-Control SAP. The HARQ entity provides the E-TFC, the retransmission sequence number (RSN), and the power offset to be usedby L1. Redundancy version (RV) of the HARQ transmission is derived by L1 fromRSN, CFN and in case of 2 ms TTI from the sub-frame number. RRC signallingcan also configure the HARQ entity to use RV=0 for every transmission.

2. Multiplexing and TSN setting: Figure 8.6 illustrates multiplexing of multiple MAC-d PDUs into MAC-es PDU. After this, MAC-e layer further multiplexes severalMAC-es PDUs into MAC-e PDUs, as shown by figure 8.7. PDU sizes directly affectthe user bit rate. Therefore, these decisions are done by E-TFC selection function.UE also sets the TSN while concatenating multiple MAC-d PDUs into MAC-esPDUs.

3. E-TFC selection: This entity is responsible for E-TFC selection according to thescheduling information, Relative Grants and Absolute Grants, received from UTRAN


via L1 and Serving Grant value signalled through RRC, and for arbitration amongthe different flows mapped on the E-DCH. The detailed configuration of the E-TFC entity is provided by RRC over the MAC-Control SAP. The E-TFC selectionfunction controls the multiplexing function.

Figure 8.6: MAC-es PDU

Figure 8.7: MAC-e PDU

As shown in figure 8.1, MAC-es sits on top of MAC-e and receives PDUs directly fromMAC-d. Figure 8.6 illustrates that MAC-es SDUs (i.e. MAC-d PDUs) of the same size,coming from a particular logical channel are multiplexed together into a single MAC-es


payload. There is one and only one MAC-es PDU per logical channel per TTI (since onlyone MAC-d PDU size is allowed per logical channel per TTI). To this payload is prependedthe MAC-es header.

The number of PDUs, as well as the one DDI value identifying the logical channel,the MAC-d flow and the MAC-es SDU size are included as part of the MAC-eheader. In case sufficient space is left in the E-DCH transport block or if SchedulingInformation needs to be transmitted, an SI will be included at the end of the MAC-ePDU. Multiple MAC-es PDUs from multiple logical channels, but only one MAC-e PDUcan be transmitted in a TTI.

In the example shown in figure 8.7, the field DDI0 is referring to the specific DDI valuethat indicates that there is an SI included in the MAC-e PDU. This header will not beassociated with a new MAC-es payload.


MAC-es entity - UTRAN Side

Figure 8.8: UTRAN side MAC-es details(25.321)

For each UE, there is one MAC-es entity in the SRNC. The MAC-es sublayer handlesE-DCH specific functionality,which is not covered in the MAC-e entity in Node B. TheMAC-es comprises the following entities:

1. Reordering Queue Distribution: The reordering queue distribution function routesthe MAC-es PDUs to the correct reordering buffer based on the SRNC configuration.


2. Reordering: This function reorders received MAC-es PDUs according to the receivedTSN and Node B tagging i.e. (CFN, subframe number). MAC-es PDUs with consec-utive TSNs are delivered to the disassembly function upon reception. Mechanismsfor reordering MAC-es PDUs are left to the implementation. The number of re-ordering entities is controlled by the SRNC. There is one Reordering Queue perlogical channel.

3. Macro diversity selection: The function is performed in the MAC-es, in case of softhandover with multiple Node Bs (The soft combining for all the cells of a Node Btakes place in the Node B). This means that the reordering function receives MAC-esPDUs from each Node B in the E-DCH active set. The exact implementation is notspecified. However, the model below is based on one Reordering Queue Distributionentity receiving all the MAC-d flow from all the Node Bs, and one MAC-es entityper UE.

4. Disassembly: The disassembly function is responsible for disassembly of MAC-esPDUs. When a MAC-es PDU is disassembled the MAC-es header is removed, theMAC-d PDU’s are extracted and delivered to MAC-d.

MAC-e entity - UTRAN Side

There is one MAC-e entity in the Node B for each UE and one E-DCH scheduler functionin the Node B. The MAC-e and E-DCH scheduler handle HSUPA specific functions in theNode B. In HSUPA, the MAC-e and E-DCH scheduler comprises the following entities:

1. E-DCH Scheduling: This function manages E-DCH cell resources between UEs.Based on scheduling requests, Scheduling Grants are determined and transmitted.The general principles of the E-DCH scheduling are described by 3GPP but theactual implementation is not specified (i.e. depends on RRM strategy).

2. E-DCH Control: The E-DCH control entity is responsible for reception of schedulingrequests and transmission of Scheduling Grants.

3. De-multiplexing: This function provides de-multiplexing of MAC-e PDUs. MAC-esPDUs are forwarded to the associated MAC-d flow.

4. HARQ: One HARQ entity is capable of supporting multiple instances (HARQ pro-cesses) of stop and wait HARQ protocols. Each process is responsible for generatingACKs or NACKs indicating delivery status of E-DCH transmissions. The HARQentity handles all tasks that are required for the HARQ protocol.


Figure 8.9: UTRAN side MAC-e details(25.321)

8.8 Channels and Physical Layer

In the previous section, we learnt about the L2 MAC sub-layer functionality for HSUPAoperation. Now we will take a closer look at L1 Physical layer and learn about the HSUPAphysical channels. All the channels related to HSUPA operation have a name which startwith ‘E-’.

One by one, we will discuss the following physical channels:

1. E-DPDCH

2. E-DPCCH

3. E-RGCH

4. E-HICH

5. E-AGCH


8.8.1 E-DPDCH

Figure 8.10: Subframe Structure of E-DPDCH and E-DPCCH Channels

The E-DPDCH is the principal channel which is used to carry the E-DCH transportchannel. There may be zero, one, 2 or 4 E-DPDCH on each radio link. The E-DPCCHis a physical channel used to transmit control information associated with the E-DCH.There is at most one E-DPCCH on each radio link.

Figure 8.10 shows the E-DPDCH and E-DPCCH (sub)frame structure. Each radio frameis divided in 5 subframes, each of length 2 ms; the first subframe starts at the start ofeach radio frame and the 5th subframe ends at the end of each radio frame.

Just like Rel. 99 DPDCH channel, REL-6 E-DPDCH channel can also have variablespreading factor. E-DPDCH support 8 different SF as shown in table 8.4 by row number1 to 8. Various slot formats actually represent a combination of ‘SF and Modulation’.

An E-DPDCH may use BPSK (all UE categories) or 4PAM modulation symbols (Category7 and 9 only). Table 8.1, 8.2 & 8.3 show various UE categories and their physical layercapabilities.

In the basic form of HSUPA (3GPP release 6), there are 6 UE categories defined. As anexample, we try to calculate the peak L1 bitrate of category 6.


Slot format #i Channel BitRate (kbps)


SF Bits/ E-DPDCHsubframe

0 (BPSK) 15 15 256 30

1 (BPSK) 30 30 128 60

2 (BPSK) 60 60 64 120

3 (BPSK) 120 120 32 240

4 (BPSK) 240 240 16 480

5 (BPSK) 480 480 8 960

6 (BPSK) 960 960 4 1920

7 (BPSK) 1920 1920 2 3840

8 (4PAM) 1920 960 4 3840

9 (4PAM) 3840 1920 2 7680

Table 8.4: E-DPDCH slot formats (from TS 25.211)

E-DPDCH Code # 1 : SF4 = 960 ksps

+ E-DPDCH Code # 2 : SF4 = 960 ksps



= Sum of all 4 E-DPDCH Codes = 5760 ksps

or Cat. 6 UE supports only BPSK Modulation ⇒ 5760 kbps

Hence, by sending Uplink data on 4 channelization codes ( 2×SF2+2×SF4 ), UE is ableto achieve a L1 bit rate of 5.76 Mbps. The knowledge of channel coding rate is needed tofind out the L2 user bit rate. Same calculation can be done for UE of category 7, whichsupports both BPSK and 4PAM modulation. 4PAM modulation uses 2 bits to generateone modulation symbol. For 4-PAM case, 5760 ksps = 11200 kbps or 11.2 Mbps.

8.8.2 E-DPCCH

The E-DPCCH is a physical channel carrying control information for the E-DPDCH. TheE-DPCCH is sent with a power offset relative to the DPCCH. The power offset is signalledby RRC. E-DPCCH has a fixed spreading factor 256 which allows UE to send 15 kbpscontrol signalling. In a 2 ms subframe, UE can send maximum 30 bits on E-DPCCH. Outof these 30 bits, only 10 carry useful information and the remaining 20 bits are used forthe reliability or channel coding. The details can be found in 3GPP TS 25.212.


For both 2 ms and 10 ms TTI, the information carried on the E-DPCCH consists of 10bits in total.

E-TFCI, 7 bits: An E-DCH Transport Format Combination Indicator (E-TFCI) iden-tifies the transport block size on E-DCH (7 bits). SRNC signals which E-DCHTransport Block Size table should be used by the UE5.

RSN, 2 bits: The Retransmission Sequence Number (RSN) is used to convey the uplinkHARQ transmission number. The combination of the RSN and the transmissiontiming allows the receiver to determine the exact transmission number. The lengthof the RSN field is 2 bits. 2 bits of RSN are interpreted as:

• ‘00’ ⇒ Original Transmission

• ‘01’ ⇒ First Re-transmission

• ‘10’ ⇒ Second Re-transmission

• ‘11’ ⇒ Third or higher retransmission

Happy Bit, 1 bit: One bit of the E-DPCCH is used to indicate whether or not the UEis satisfied (‘happy’) with the current Serving Grant. This bit is always be presentduring uplink transmission of E-DPCCH. According to section 11.8.1.5 of 25.321,UE indicates that it is ‘unhappy’ if the following criteria are met:

1. UE is transmitting as much scheduled data as allowed by the current ServingGrant;

2. UE has enough power available to transmit at higher data rate;

3. Total buffer status would require more than Happy Bit Delay Conditionms to be transmitted with the current Serving Grant.‘Happy Bit Delay Condition’ is an operator configurable parameter.

53GPP TS 25.321, annexure B shows all the tables for E-DCH FDD mode.

• If the UE is configured with E-TFCI table 0 and 2ms TTI, use Annex B.1


• If the UE is configured with E-TFCI table 2 and 2ms TTI, use Annex B.2a

• If the UE is configured with E-TFCI table 3 and 2ms TTI, use Annex B.2b




Slot format #i Channel BitRate (kbps)


SF Bits/ E-DPDCHsubframe

0 (BPSK ) 15 15 256 30

Table 8.5: E-DPCCH slot formats (from TS 25.211)

8.8.3 E-AGCH

The E-DCH Absolute Grant Channel (E-AGCH) is a downlink physical channel with fixedspreading factor (SF=256). In other words, the E-AGCH has a bit rate 30 kbps. In asubframe of 2 ms, Node B can send 60 bits. E-AGCH transmission is:

• Over one sub-frame if E-DCH TTI is set to 2ms.

• Over one frame if E-DCH TTI is set to 10ms.

The sequence of 60 bits are mapped to the corresponding E-AGCH sub-frame. If the E-DCH TTI is equal to 10 ms, the same sequence of bits is transmitted in all the E-AGCHsub-frames of the E-AGCH radio frame. In other words, the same 2 ms sub-frame ofE-AGCH is re-transmitted four times (sent total 5 times).

E-AGCH channel is used to carry the uplink E-DCH Absolute Grant. Figure 8.11 illus-trates the frame and sub-frame structure of the E-AGCH.

Figure 8.11: Subframe Structure of E-AGCH

The absolute grant channel carries six bits which are concatenated with 16 bit CRC. Theuser identity E-RNTI is masked on the CRC. After channel coding, E-AGCH becomes 90bits long. A Rate Matching procedure is used to select selected 60 bits and those bits aretransmitted in E-AGCH sub-frame. The six data bits of E-AGCH channel are:


Index Absolute Grant Value

31 (168/15)2 ∗ 630 (150/15)2 ∗ 629 (168/15)2 ∗ 428 (150/15)2 ∗ 427 (134/15)2 ∗ 426 (119/15)2 ∗ 425 (150/15)2 ∗ 224 (95/15)2 ∗ 423 (168/15)2

22 (150/15)2

21 (134/15)2

20 (119/15)2

19 (106/15)2

......

11 (42/15)2

10 (38/15)2

9 (34/15)2

8 (30/15)2

7 (27/15)2

6 (24/15)2

5 (19/15)2

4 (15/15)2

3 (11/15)2

2 (7/15)2

1 ZERO GRANT0 INACTIVE

Table 8.6: Mapping of Absolute Grant Value (from 3GPP TS 25.321)

Absolute Grant Value, 5 bits: This field indicates the maximum E-DCH traffic to pi-lot ratio (E-DPDCH/DPCCH) that the UE is allowed to use in the next transmis-sion. The length of the Absolute Grant Value field is 5 bits.

Absolute Grant =Ptx,E-DPDCH

Ptx,DPCCH

Absolute Grant Scope, 1 bit: This field indicates the applicability of the AbsoluteGrant. It can take two different values, “Per HARQ process” or “All HARQ pro-cesses”, allowing to indicate whether the HARQ process activation/de-activation


will affect one or all processes. The Absolute Grant Scope is encoded in 1 bit.When the E-DCH is configured with 10ms TTI, only the value “All HARQ pro-cesses” is valid. In case, Identity Type is ‘Secondary’, only the value “All HARQprocesses” is valid.

8.8.4 E-RGCH

The E-DCH Relative Grant Channel (E-RGCH) is a downlink physical channel with fixedspreading factor (SF=128). Hence, this channel can carry information at 60 kbps. E-RGCH carries dedicated uplink E-DCH relative grants. The word ‘Relative’ means, incomparison to the current grant used by UE. Figure 8.15 illustrates the structure of theE-RGCH. A relative grant can have one of the following three values.

• UP

• DOWN

• HOLD

E-RGCH channel can be transmitted either in 3, 12 or 15 consecutive slots and in eachslot a sequence of 40 ternary values is transmitted (Up, Down or Hold).

E-RGCH transmission on 3 slots: Used on an E-RGCH transmitted to UEs for whichthe cell transmitting the E-RGCH is in the E-DCH serving radio link setand for which the E-DCH TTI is 2 ms.

E-RGCH transmission on 12 slots: Used on an E-RGCH transmitted to UEs for whichthe cell transmitting the E-RGCH is in the E-DCH serving radio link setand for which the E-DCH TTI is 10 ms.

E-RGCH transmission on 15 slots: Used on an E-RGCH transmitted to UEs for whichthe cell transmitting the E-RGCH is not in the E-DCH serving radio link set.For non-serving E-DCH RLS, the duration of E-RGCH transmission is irrespectiveof the E-DCH TTI.

The next section has been written with the help of 3GPP TS 25.321 as reference material.For the following discussion, it is assumed that UE’s E-DCH active set is more than one.Hence, UE is in soft handover for E-DCH with two or more cells.

Serving Relative Grant: Transmitted in downlink on the E-RGCH from all cells inthe serving E-DCH RLS, the serving relative grant allows the Node B schedulerto incrementally adjust the serving grant of UEs under its control. By definition,there can only be one serving relative grant command received at any time. Thisindication can take three different values, ‘UP’, ‘DOWN’ or ‘HOLD’.


Non-serving Relative Grant: Transmitted in downlink on the E-RGCH from a non-serving E-DCH RL, the non-serving relative grant allows neighboring Node Bs toadjust the transmitted rate of UEs that are not under their control in order to avoidoverload situations. By definition, there could be multiple non-serving relative grantcommands received by MAC at any time. This indication can take two differentvalues, ‘DOWN’ or ‘HOLD’.

Figure 8.12: Subframe Structure of E-RGCH & E-HICH

The sequence bi,0, bi,1 . . . , bi,39 is calculated as

[bi,0, bi,1 . . . , bi,39] = a ∗ [40 bit long Signature Sequence], where:

a =

+1 if Relative Grant is ‘UP’,0 if Relative Grant is ‘HOLD’,

−1 if Relative Grant is ‘DOWN’.

The orthogonal signature sequences are defined by 3GPP TS 25.21. Figure 8.14 showsa table with all of these 40 signature sequences which are numbered from CSS,40,0 toCSS,40,39. Each HSUPA user is assigned one signature sequence for E-HICH and anothersequence for E-RGCH. Hence, every user requires at least two signature sequences. Thisis a nice trick which consumes only one channelization code for E-RGCH and E-HICH forup to 20 HSUPA users. The principle of creating 40 dedicated channels using only onechannelization code is illustrated in figure 8.13.

In figure 8.13, UE1 has been assigned a signature sequence # 0 for E-RGCH and # 1 forE-HICH. Similarly the other users are also assigned 2 signature sequences per UE.

If there are more than 20 HSUPA users in a cell, then additional channelization codesmust be allocated for additional E-RGCH and E-HICH channels.


Figure 8.13: Signature Multiplexing Scheme for E-RGCH and E-HICH

Which Grant to be Respected: AGCH or RGCH?

According to 3GPP TS 25.321, UEs configured with an E-DCH transport channel shallmaintain a Serving Grant and the list of active HARQ processes based on the absoluteand relative grant commands decoded on the configured E-AGCH and E-RGCH(s). TheUE will only act on a relative grant command if all of the following are true:

• The current serving grant is not set to ZERO GRANT.

• The UE has not received a new absolute grant within 1 HARQ Round Trip Time(40 ms for 10 ms TTI, 16 ms for 2 ms TTI).

• The UE was expecting to receive an ack/nack on the E-HICH at the same timeas the network sent the E-RGCH command (an ack/nack sent for a E-DPDCHtransmission that just contained MAC-e Scheduling Information alone does not meetthis criteria).

Now the question is:“If Serving Relative Grant is UP, how much should the SG be increased?Similarly, if serving Relative Grant is down, how much should the SG bedecreased?”

According to TS 25.321, the answer to this question can be found by using two param-eters: “3-index-step threshold” and “2-index-step threshold” that are configuredby higher layers.


Figure 8.14: E-RGCH and E-HICH signature sequences (from TS 25.211)

If the UE received a Serving Relative Grant ‘UP’: UE determine the Serving Grantas follows:

• if SG < “3-index-step threshold”: Serving Grant (SG) = [MIN(SG + 3, 37)].

• if “3-index-step threshold” <= SG < “2-index-step threshold”: Serving Grant(SG) = [MIN(SG + 2, 37)].

• if SG <= “2-index-step threshold”: Serving Grant (SG) = [MIN(SG + 1, 37)].

If the UE received a Serving Relative Grant ‘DOWN’: UE determine the Serv-ing Grant as follows:

• Serving Grant (SG) = [MAX(SG -1, 0)]


Index Scheduled Grant

37 (168/15)2 ∗ 636 (150/15)2 ∗ 635 (168/15)2 ∗ 434 (150/15)2 ∗ 433 (134/15)2 ∗ 432 (119/15)2 ∗ 431 (150/15)2 ∗ 230 (95/15)2 ∗ 429 (168/15)2

28 (150/15)2

27 (134/15)2

26 (119/15)2

25 (106/15)2

......

11 (21/15)2

10 (19/15)2

9 (17/15)2

8 (15/15)2

7 (13/15)2

6 (12/15)2

5 (11/15)2

4 (9/15)2

3 (8/15)2

2 (7/15)2

1 (6/15)2

0 (5/15)2

Table 8.7: Scheduling Grant Table (from 3GPP TS 25.321)

8.8.5 E-HICH

The E-DCH Hybrid ARQ Indicator Channel (E-HICH) is a fixed rate (SF=128) dedicateddownlink physical channel carrying the uplink E-DCH hybrid ARQ acknowledgement in-dicator. Figure 8.15 illustrates the structure of the E-HICH. A hybrid-ARQ acknowledge-ment indicator is transmitted using 3 or 12 consecutive slots and in each slot, a sequenceof 40 binary values is transmitted. The 3 and 12 slot duration shall be used for UEs whoseE-DCH TTI is set to 2 ms and 10 ms respectively.

3GPP TS 25.212 shows the mapping for E-HICH ACK/NACK. The same concept is briefly


Figure 8.15: Subframe Structure of E-RGCH & E-HICH

mentioned below.

In a radio link set containing the serving E-DCH radio link set, the hybrid-ARQacknowledgement indicator ‘a’ is set to:

• ‘+1’: If Node B wants to send a positive Acknowledgement

• ‘-1’: If Node B wants to send a negative Acknowledgement

In a radio link set not containing the serving E-DCH radio link set, the hybridARQ acknowledgement indicator ‘a’ is set to:

• ‘+1’: If Node B wants to send a positive Acknowledgement

• ‘0’ or ‘DTX’: If Node B wants to send a Negative Acknowledgement

The sequence bi,0, bi,1 . . . , bi,39 is calculated as

[bi,0, bi,1 . . . , bi,39] = a ∗ [40 bit long Signature Sequence], where :

a =

+1 if H-ARQ Indication is “ACK”,0 if H-ARQ Indication is “NACK” & Cell is not in serving E-DCH radio link set]

−1 if H-ARQ Indication is “NACK” & Cell is in in serving E-DCH radio link set.


8.8.6 F-DPCH

Although F-DPCH was described in HSDPA chapter, but it is not allowedto use F-DPCH until the uplink is on E-DCH. HSDPA without HSUPAconfiguration cannot use F-DPCH for the users.

The F-DPCH carries control information generated at layer 1 (TPC commands). It is aspecial case of downlink DPCCH. Figure 8.16 shows the frame structure of the F-DPCH.Each frame of length 10 ms is split into 15 slots, each of length Tslot = 2560 chips,corresponding to one power-control period.

Figure 8.16: Frame Structure of F-DPCH

The exact number of bits of the OFF periods and of the F-DPCH fields (NTPC) is describedin table 8.8. Each slot format corresponds to a different set of OFF periods within theF-DPCH slot.

Slot format #i SF Bits/Slot NOFF1

Bits/slotNTPC

Bits/slotNOFF2

Bits/slot

0 256 20 2 2 161 256 20 4 2 142 256 20 6 2 123 256 20 8 2 104 256 20 10 2 85 256 20 12 2 66 256 20 14 2 47 256 20 16 2 28 256 20 18 2 09 256 20 0 2 18

Table 8.8: F-DPCH Fields

8.9. SUMMARY: SERVING AND NON-SERVING RLS 273

8.9 Summary: Serving and Non-serving RLS

When I started learning HSUPA, it was fun to learn about the L1 and L2modifications. But I want to honestly admit that I had a very hard time ingetting comfortable with the words ‘Serving E-DCH Radio Link Set’ and ‘Non-serving E-DCH Radio Link Set’. Therefore, in this section, I have tried tosummarize those concepts which will help the readers to clear some doubts.For more information, please refer to TS 25.319 and TS 25.321.

When a UE has an active HSUPA session, it is mandatory to have HSDPA configuredin downlink. HS-DSCH channel undergoes Hard serving cell change, whereas E-DCHchannel undergoes normal soft handover. Therefore, we need to define a few new termswhich will help us in understanding HSUPA operation. In our discussion, we will take thehelp of figure 8.17. In this figure, there are 3 cells which are named as ‘A’, ‘B’ & ’C’. TheUE shown in this figure happens to receive DL HS-DSCH from cell ‘A’ only but its uplinkE-DCH is in soft handover with all the three cells shown in this figure.

Let us try to find out the answers to following questions:

1. Which cell is E-DCH Serving Cell?

2. Which cell(s) form the E-DCH Active Set?

3. Which cell(s) belong to Serving E-DCH RLS?

4. Which cell(s) belong to Non-serving E-DCH RLS?

Serving E-DCH Cell: Serving E-DCH cell is the same cell as serving HS-DSCH cell.HS-DSCH channel cannot be in soft handover. Because HS-DSCH has only onecell delivering DL data, there is no confusion in deciding which cell is our E-DCHserving cell.

In other words, E-DCH serving cell is the cell from which the UE receives AbsoluteGrants. A UE has only one Serving E-DCH cell. In figure 8.17, cell ‘A’ is our sevingE-DCH cell.

E-DCH Active Set Cells: This is a set of cells with which a UE has active E-DCHconnection. In figure 8.17, cell ‘A’, ‘B’ & ’C’ are our E-DCH active set cells.

Serving RLS Cells: It was stated earlier,“for each UE that uses E-DCH, we have oneMAC-e entity per Node-B”. If cell ‘A’ is our Serving E-DCH cell, then the ‘main’MAC-e entity will be in the Node B which controls cell ‘A’. If the same Node Balso controls cell ‘B’, then the E-RGCH and E-HICH in these two cells will carrythe same information. There will be an ‘additional’ MAC-e entity at the NodeB which controls cell ‘C’. This additional MAC-e entity does not have authority tosend E-AGCH or to send an ‘UP’ command on E-RGCH. The information sent onE-RGCH and E-HICH from these two MAC-e entities can be different or the same.


Figure 8.17: E-DCH Cell Status: Serving RLS and Non-serving RLS

Hence, the cells that belong to that Node B which controls the Serving E-DCHcell, form Serving E-DCH RLS. The UE has only one Serving E-DCH RLS. In ourexample of figure 8.17, cell ‘A’ & ‘B’ belong to Serving E-DCH RLS. The contentof E-RGCH and E-HICH in these cells can have the following values:

On E-RGCH UP, DOWN or HOLD

On E-HICH +1 for ACK and -1 for NACK

Non-serving RL: Cell which belongs to the E-DCH active set but does not belong tothe Serving E-DCH RLS and from which the UE can receive one Relative Grant.The UE can have zero, one or several non-serving E-DCH RL(s). In figure 8.17, cell‘C’ is in non-serving E-DCH RLS.

On E-RGCH DOWN or HOLD

On E-HICH +1 for ACK and ’DTX’ for NACK

8.9. SUMMARY: SERVING AND NON-SERVING RLS 275

The following are the main takeaways from this section:

Once again, please have a look at figure 8.17 and observe the E-AGCH, E-RGCH & E-HICH behaviour.

• E-AGCH comes only from Serving E-DCH Cell.

• E-RGCH comes from all the Active Set Cells, but:

– If Cell belongs to Serving E-DCH RLS, E-RGCH can have 3 values:UP, DOWN & HOLD.

– If Cell belongs to Non-Serving E-DCH RLS, E-RGCH can have 2values: DOWN & HOLD.

• E-HICH also comes from all the Active Set Cells. But:

– If Cell belongs to Serving E-DCH RLS, E-HICH can have 2 values:ACK (+1) & NACK (-1).

– If Cell belongs to Non-Serving E-DCH RLS, E-RGCH can have 2values: ACK (+1) & NACK (0).


8.10 E-TFC Selection Procedure

As we have learnt in the discussion so far, Node B only sends a grant value to UE and itis UE’s duty to select the transport block size, transport format combination and otherL1 parameters such as spreading factor, number of codes, coding rate, etc.

This whole procedure is explained in a chronological order in the next few pages. Thestarting of HSUPA operation was explained in section 8.6. In short, when RNC decidesto allocate E-DCH transport channel to the UE in uplink, an ‘initial serving grant’ isassigned to it. This grant is generated by Node B but UE receives it from RNC using RRCsignalling. Once, HSUPA operation begins, UE and Node B can perform L1 signallingwithout bothering RNC for each message transfer.

In HSUPA, UE and Node B are in constant touch and maintain a ‘REQUEST-GRANT’mechanism. Let us begin by analyzing how UE requests uplink resources from Node Band follow the steps after that. This description is broken down into 10 steps.

8.10.1 Step 1: UE sends Scheduling Requests to Node B

In order to start the whole HSUPA operation, UE has to send some feedback or requesttowards Node B to indicate its desire to send uplink data and therefore, its wish to getscheduled. This can be done via two methods: Happy Bit and Scheduling Info.

Figure 8.18: Scheduling Information format

1. Happy Bit, 1 bit: As explained in the section 8.8.2, Happy bit is a single bit infor-mation sent on E-DPCCH which indicates whether the UE demands an upgrade inthe resource allocation or not.

2. Scheduling Info, 18 bits: The Scheduling Information is located at the end of theMAC-e PDU and is used to provide the serving Node B with a better & moredetailed view of the amount of system resources needed by the UE and the amountof resources it can actually make use of. The transmission of this information will beinitiated due to the quantization of the transport block sizes that can be supported.Figure 8.18 is copied from 3GPP TS 25.321 which shows the information fieldsincluded in Scheduling Information. These fields are briefly explained below:

• Highest priority Logical channel ID (HLID): The HLID field identifies unam-biguously the highest priority logical channel with available data. If multiple

8.10. E-TFC SELECTION PROCEDURE 277

logical channels exist with the highest priority, the one corresponding to thehighest buffer occupancy will be reported. The length of the HLID is 4 bits.In case the TEBS is indicating index 0 (0 byte), the HLID shall indicate thevalue “0000”.

• Total E-DCH Buffer Status (TEBS): The TEBS field identifies the total amountof data available across all logical channels for which reporting has been re-quested by the RRC and indicates the amount of data in number of bytesthat is available for transmission and retransmission in the RLC layer. WhenMAC is connected to an AM RLC entity, control PDUs to be transmitted andRLC PDUs outside the RLC Tx window shall also be included in the TEBS.RLC PDUs that have been transmitted but not negatively acknowledged bythe peer entity shall not be included in the TEBS. TEBS index is signalled tothe Node B which can be from 0 to 31. 0 indicated TEBS = 0 and 31 indicatedTEBS > 37642 Bytes.

• Highest priority Logical channel Buffer Status (HLBS): The HLBS field in-dicates the amount of data available from the logical channel identified byHLID, relative to the highest value of the buffer size range reported by TEBSwhen the reported TEBS index is not 31, and relative to 50000 bytes when thereported TEBS index is 31. The length of HLBS is 4 bits.

• UE Power Headroom (UPH): The UPH field indicates the ratio of the maxi-mum UE transmission power and the corresponding DPCCH code power. Thelength of UPH is 5 bits.

8.10.2 Step 2: Serving Grant Value

The UE must be able to receive Absolute Grants from the Serving E-DCH cell and RelativeGrants from the Serving E-DCH RLS. The UE shall handle the Grant from the ServingE-DCH RLS and determine a Serving Grant.

Many times in this chapter, we have discussed grants. Let us summarize the conceptsabout grant. We have seen three types of grants.

1. Absolute Grant: Absolute Grant is the value which is signalled to the user on theE-AGCH channel. AG Value can be from 0 to 316.

2. Relative Grant: Relative Grant can be either UP, DOWN or HOLD. This grantis signalled to UE using E-RGCH channel. The word Relative in RGCH meansRelative to the current Serving Grant.

3. Serving Grant: The E-TFC selection function of MAC-e/es entity of UE is respon-sible to find out the Serving Grant value from:

6Absolute Grant Value: INACTIVE (Index 0), ZERO GRANT (Index 1), & Index 2 , 3, . . . 31.


• Relative Grants and Absolute Grants, received from UTRAN via L1.

• Serving Grant value signalled through RRC.

UE maintains a Serving grant value which can be from 0 to 37. Serving Grant7 valueswere described in table 8.7.

8.10.3 Step 3: Find Power Offset

After calculating the Serving Grant (SG), UE reads the actual E-DPDCH to DPCCHpower offset from the Serving Grant table as shown in table 8.7. This is a straightforwardmechanism of reading look-up table. Therefore, it requires no further explanation.

8.10.4 Step 4: “Reference E-TFCI & Power Offset” Curve

At the time of HSUPA session setup, there is a lot of information exchanged from SRNCto UE. In figure 8.19, this section of signalling is illustrated with the emphasis on theinformation elements which are crucial for HSUPA operation. The detailed informationabout each information of this RRC message is available in 3GPP TS 25.331. Amongother parameters, RNC indicates up to 8 pairs of ‘Reference E-TFCI’ and ‘Reference E-TFCI-PO’ values. In figure 8.19, these values are highlighted by drawing an oval shapearound them. Using these set of paired-values, UE can plot a 2-dimensional curve, whichlooks like the one shown in figure 8.20.

8.10.5 Step 5: Calculate E-TFCI Allowed by Grant Value

In step 3, UE calculated the power offset allowed by the serving grant. Now it has to mapthe power offset on the x-axis of the curve made in step 4 and calculate the E-TFCI indexfrom the y-axis.

The numbers shown in figure 8.21 are just for explaining the principle. Their actual valueshould not be considered for quantitative analysis. For the exact numbers, it is suggestedto refer to TS 25.211, TS 25.212 and TS 25.331.

8.10.6 Step 6: Calculate TB Size

In the RRC signalling shown in figure 8.19, SRNC informs the user about the TB SizeTable to be used while E-TFC selection procedure. All the tables are defined in theannexure of 3GPP TS 25.321. Just for the illustration purpose, a section of Table B.3from TS 25.321 is shown in Table 8.9. In 3GPP specifications, this table is known as Table‘0 for 10 ms TTI case’.

7Serving Grant Value: (5/15)2(Index 0), (6/15)

2(Index 1), . . . , Index 37


Figure 8.19: RB Reconfiguration Message with emphasis on E-DCH info.

This step is also quite straight forward. Because once the E-TFCI index is known (fromstep 5), in step 6, UE simply needs to look up the corresponding TB size in the relevantTB size table.

8.10.7 Step 7: Select Channelization Code & L1 Parameters

This step is performed by UE based on some standard algorithms defined by 3GPP. InStep 7, UE will determine following items.

• SF,


Figure 8.20: ”Reference E-TFCI & Power Offset” Curve

• Modulation scheme (from R7 onwards),

• and number of physical channels needed.

This step will not be explained in detail in this book. If you are interested in the detailsof this procedure, please refer to ‘section 4.8.4.1 of 3GPP TS 25.212’.

8.10.8 Step 8: UL Transmission on E-DCH

Let’s assume the ‘number of physical channels needed’ = 4 from the calculation performedin Step 7. It implies that there will be 4 E-DPDCH physical channels along with oneE-DPCCH. The scenario of uplink transmission will look like the one depicted in figure8.22.

E-DPDCH: E-DPDCH is mainly designed for carrying user data but additionally wecan send SRB on this channel. In addition to that, periodically UE can send 18 bitscheduling information. At the time when SI transmission is scheduled, then SI bitswill be attached to the MAC-e PDU, as shown in figure 8.7.


Figure 8.21: Calculating the E-TFCI from Power Offset

Figure 8.22: HSUPA transmission from UE

E-DPCCH: E-DPCCH is used to carry L1 control information related to HSUPA dataon E-DPDCH. One such information is the famous ‘Happy Bit’.

8.10.9 Step 9: Feedback from Node B on E-HICH

Node B checks whether the received MAC-e PDU has been received with acceptable qual-ity. If yes, then Node B sends positive ACK to the UE using E-HICH channel and sends


E-TFCI TB Size(bits) E-TFCI TB Size(bits) E-TFCI TB Size(bits)

0 18 43 660 85 36341 120 44 687 86 37842 124 45 716 87 39413 130 46 745 88 41054 135 47 776 89 42755 141 48 809 90 44526 147 49 842 91 46367 153 50 877 92 4828

. . . . . . . . . . . . . . . . . .

38 539 80 2966 123 1700139 561 81 3089 124 1770640 584 82 3217 125 1844041 608 83 3350 126 1920442 634 84 3489 127 20000

Taken from Annex B.3 of 3GPP TS 25.321E-DCH Transport Block Size Table 0 for 10ms TTI

Table 8.9: E-DCH TB Size Selection Table (example)

the Data block in a E-DCH Frame Protocol frame. If not, then Node B sends negativeacknowledgement to the UE using E-HICH channel.

8.10.10 Step 10: Feedback from Node B on E-RGCH

The scheduler at Node B takes various factors into account and decides whether an UP,DOWN or HOLD command should sent to the user. Some of these factors are receivedHappy Bit’s value, scheduling info (SI), current UL interference in the cell etc.

8.11. SUMMARY: HSUPA OPERATION IN SHORT 283

8.11 Summary: HSUPA Operation in Short

Figure 8.23: HSUPA operation explained using the physical channels.

Channel Direction Function SF Modulation

E-DPDCH ↑ Carries UL user data 256 to 2 BPSK & 4PAM

E-DPCCH ↑ Carries L1 Signalling 256 BPSK

E-RGCH ↓ Grant (Up, Down, Hold) 128 QPSK

E-HICH ↓ ACK or NACK 128 QPSK

E-AGCH ↓ Grant (Absolute value) 256 QPSK

Table 8.10: Summary of HSUPA channels


Copyright Notices



Text in section 8.1 on page 245 Section 5 of 3GPP TS 25.319 v 7.0.0.Figure 8.1 on page 249 Figure 26 of 3GPP TS 25.401 v 7.0.0.

c⃝2006. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA, TTA, andTTC who jointly own the copyright for them. They are subject to further modificationsand are therefore provided to you as is for information purposes only. Further use isstrictly prohibited.

8.11. SUMMARY: HSUPA OPERATION IN SHORT 285

Text in section 8.7 on page 254 Section 4.2.3.4 of 3GPP TS 25.321 v 7.7.0.Figure 8.5 on page 255 Figure 4.2.3.4.1a of 3GPP TS 25.321 v 7.7.0.Text in section 8.7 on page 258 Section 4.2.4.4 of 3GPP TS 25.321 v 7.7.0.Figure 8.8 on page 258 Figure 4.2.4.4-1 of 3GPP TS 25.321 v 7.7.0.Text about Relative Grant onpage 266

Section 9.2.5.2.1 of 3GPP TS 25.321 v 7.7.0.

Text about Interpretation of RGvalue on page 268


Text about Absolute Grant onpage 264


Text about Scheduling Info onpage 276


Text about Happy Bit setting onpage 263

Section 11.8.1.5 of 25.321 v 7.7.0.

Text in section 8.7 on page 259 Section 4.2.4.5 of 3GPP TS 25.321 v 7.7.0.Figure 8.9 on page 260 Figure 4.2.4.5-1a of 3GPP TS 25.321 v 7.7.0.Figure 8.6 on page 256 Figure 9.1.5.1 of 3GPP TS 25.321 v 7.7.0.Figure 8.7 on page 256 Figure 9.1.5.2a of 3GPP TS 25.321 v 7.7.0.Table 8.7 on page 270 Table 9.2.5.2.1.1 of 3GPP TS 25.321 v 7.7.0.Table 8.9 on page 282 Table B.3 in Annex B of 3GPP TS 25.321 v

7.7.0c⃝2008. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

Figure 8.10 on page 261 Figure 2B of 3GPP TS 25.211 v 9.1.0.Figure 8.15 on page 271 Figure 12A of 3GPP TS 25.211 v 9.1.0.Figure 8.16 on page 272 Figure 12B of 3GPP TS 25.211 v 9.1.0.Table 8.8 on page 272 Table 16C of 3GPP TS 25.211 v 9.1.0.Table 8.4 on page 262 Table 5B of 3GPP TS 25.211 v 9.1.0.Table 8.5 on page 264 Table 5C of 3GPP 3GPP TS 25.211 v 9.1.0.Figure 8.13 on page 268 Figure 16A of 3GPP TS 25.211 v 9.1.0c⃝2009. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.


Table 8.1 on page 252 Table 5.1g of 3GPP TS 25.306 v 9.1.0.Table 8.2 on page 252 Table 5.1g of 3GPP TS 25.306 v 9.1.0.Table 8.3 on page 252 Table 5.1g of 3GPP TS 25.306 v 9.1.0.Table 8.6 on page 265 Table 16B of 3GPP TS 25.212 v 9.3.0.c⃝2010. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

BIBLIOGRAPHY


[2] 3GPP TS 25.319 ver. 7.0.0 ;‘High Speed Uplink Packet Access (HSUPA); Overalldescription’

[3] 3GPP TS 25.306 ver. 9.0.0 ;‘UE Radio Access capabilities’














287

APPENDIX 8.1

Source:3GPP TS 25.211: “Physical channels and mapping of transport channels ontophysical channels (FDD)”.3GPP TS 25.212: “Multiplexing and channel coding (FDD)”.3GPP TS 25.213: “Spreading and modulation (FDD)”.3GPP TS 25.214: “Physical layer procedures (FDD)”.3GPP TS 25.215: “Physical layer - Measurements (FDD)”.

In this book, we have seen the physical channels of the three technologies: UMTS, HSDPA& HSUPA. This appendix is written for advanced readers who might be interested inknowing the exact channelization code that is used for a particular physical channel. Forsome of the channels, there are fixed code allocations; for some channels, there are standardrules to decide the code and for some channels, RNC allocates the code when the needarises.

8.12 UL Channelization Codes

In total, there are five types of uplink physical channels. These are shown in figure 8.24.The DPDCH, the DPCCH, the E-DPDCH, the E-DPCCH and the HS-DPCCH are I/Qcode-multiplexed, where I and Q denote real and imaginary parts, respectively. This figurehas been copied from 3GPP TS 25.213.

The coding takes place in 2 steps: channelization and scrambling.

288

8.12. UL CHANNELIZATION CODES 289

During the channelization coding process, data symbols on I- and Q-branches are indepen-dently spread by OVSF8 codes and during the scrambling operation, the resultant signalson the I- and Q-branches are further multiplied by complex-valued Scrambling code. Thefollowing section describes the codes used on each of these uplink channels.

Figure 8.24: Spreading for uplink dedicated channels (Source: 25.213)

1. Code Allocation for DPCCH: There can be only one DPCCH channel per UEwhich is used for sending L1 control information from UE to Node B. According toTS 25.213, the channelization code used for DPCCH is always cc = Cch,256,0.

2. Code Allocation for DPDCH: According to Rel-99 specifications, it is possible tohave 1, 2, 3, 4, 5 or 6 DPDCH channels from one UE. It is also specified that if aUE transmits more than one DPDCH, then the SF of all of these channels will beSF=4. But from practical implementation viewpoint, this case is not so interesting.In popular deployments around the world, we have maximum one DPDCH per UE.

DPDCH channel is a variable bit rate channel which can have seven possible spread-ing factors; SF = 4, 8, 16, 32, 64, 128 or 256. The exact spreading code can befound by CCH,SF, SF/4, where SF is the spreading factor.

Channelization Code for DPDCH1 = CCH,SF, SF/4

3. Code Allocation for HS-DPCCH: Since there is an ‘HS-’, in the name of thischannel, one can easily identify that this channel is related to HSDPA. The officialname of HS-DPCCH channel is ‘uplink Dedicated Control Channel associated

8Orthogonal Variable Spreading Factor

290 BIBLIOGRAPHY

with HS-DSCH transmission’. I have often heard people calling it as ‘HighSpeed DPCCH’ or ‘HSDPA Feedback channel’. In fact, this channel is used to senduplink feedback (CQI and Ack/Nack) for HSDPA transmission.

HS-DPCCH is always spread with SF = 256 and the exact code number is dependentof ‘Max Number of R99 DPDCH’ channels, which can be 1 to 6.

The HS-DPCCH shall be spread with code which is decided by the following rules:

Code for HS-DPCCH =

Cch,256,33 if NMax, DPDCH = 0,Cch,256,64 if NMax, DPDCH = 1,Cch,256,1 if NMax, DPDCH = 2, 4, 6Cch,256,32 if NMax, DPDCH = 3, 5

These rules are described in the section 4.3.1.2.2 of 3GPP TS 25.213.

This section shows all the possible cases but only the first two cases arepopularly used. NMax, DPDCH = 0 is possible if the L3 signalling (SRBs)are mapped on HSPA.

HS-DPCCH shall be mapped to the I-branch in case NMax, DPDCH is 2, 4 or 6, andto the Q-branch otherwise (NMax, DPDCH = 0, 1, 3 or 5).

4. Code Allocation for E-DPCCH: Now it’s turn of HSUPA related channels. Justlike R99 DPCCH, in HSUPA also, we have a E-DPCCH channel which carries L1control information in uplink. This L1 signalling is related to the data transmissionin E-DPDCH.

E-DPCCH is a fixed rate channel which always uses SF =256. According to 3GPPTS 25.213, the DPCCH is always spread by code cc = Cch,256,1 and always mappedon the I-branch.

5. Code Allocation for E-DPDCH: The data channel which is used for carrying up-link HSUPA data is called E-DPDCH. Just like Rel-99 DPDCH, E-DPDCH is alsoa variable bit rate channel with two improvements:

1. Smallest SF of DPDCH is 4, whereas E-DPDCH can also use SF = 2.

2. The modulation used in Rel-99 DPDCH is always BPSK. In Rel-6, E-DPDCHcannot use any higher order modulation. But from REL-7 onwards, E-DPDCHis allowed to use both BPSK and 4PAM modulations.

Hence, E-DPDCH channel can have 8 possible spreading factors: SF = 2, 4, 8, 16,32, 64, 128 or 256. In order to achieve multi-Mbps speeds, UE can combine severalcodes and transmit them together in uplink. Once again, the channelization code(s)used for E-DPDCH(s), depends on if NMax, DPDCH. Table 8.11 is taken from 3GPPTS 25.213, where the rules for code allocation are described with full details.

8.13. DL CHANNELIZATION CODES 291

if NMax, DPDCH E-DPDCHk Channelization Code Ced,k

0 E-DPDCH1 Cch, SF, SF/4 if SF ≥ 4Cch, 2, 1 if SF = 2

E-DPDCH2 Cch, 4, 1 if SF = 4Cch, 2, 1 if SF = 2

E-DPDCH3 Cch, 4, 1

E-DPDCH4

1 E-DPDCH1 Cch, SF, SF/2

E-DPDCH2 Cch, 4, 2 if SF = 4Cch, 2, 1 if SF = 2

Table 8.11: Channelisation code for E-DPDCH

8.13 DL Channelization Codes

The channelization codes used on DL physical channels are the same codes as used in theuplink namely ‘Orthogonal Variable Spreading Factor (OVSF)’ codes that preserve theorthogonality between downlink channels of different rates and spreading factors.

8.13.1 R99 DL Channels

1. & 2. Synchronization Channels: As an exception, P-SCH and S-SCH channels arenot spread using any channelization codes.

3. Primary-CPICH: The channelization code for the Primary-CPICH is fixed to Cch,256,0in all 3G networks around the world. Please refer to section 5.2.1 of 3GPP TS 25.213.

4. Primary-CCPCH: The channelization code for the Primary CCPCH is fixed toCch,256,1. This rule is specified is also specified in section 5.2.1 of 3GPP TS 25.213.

Other R99 Common Channels: The channelization codes for all other physical chan-nels are assigned by UTRAN.

5. PICH: SF of Paging Indicator Channel (PICH) is fixed and equal to 256. Theexact code number is broadcasted to UEs via system information (BCH).

6. AICH: SF of Acquisition Indicator Channel (AICH) is also fixed and equal to256. Similar to PICH, the code number of AICH is also broadcasted via systeminformation (BCH).

7. S-CCPCH: Secondary Common Control Physical Channel (S-CCPCH) is usedto carry the FACH and PCH transport channels. The FACH and PCH canbe mapped to the same or to separate secondary-CCPCHs. Spreading fac-tor of S-CCPCH can have 7 possible values; SF = 4, 8, 16, 32, 64, 128 or

292 BIBLIOGRAPHY

256. The spreading factor, code number and other details about S-CCPCHconfiguration, are broadcasted using system information.

8. DL DPCH: Dedicated physical channel (DPCH) is the main data channel in R99(UMTS). Its spreading factor can take one value from the 7 possible options; SF =4, 8, 16, 32, 64, 128 or 256. RNC is responsible for performing the code allocationon demand. RNC chooses the ‘SF & Code Number’ based on required bit rate andthe code availability. UE gets the information about code allocation by explicit L3(RRC layer) signalling. Some famous messages in this category are ‘RRC ConnectionSetup’, ‘Active Set Update’, ‘Radio Bearer Setup’, ‘Radio Bearer Reconfiguration’,etc.

8.13.2 HSDPA-related DL Channels

1. HS-SCCH: 3GPP has fixed the spreading factor of HS-SCCH to 128. As mentionedearlier in this book, there can be 1 or more HS-SCCH(s) per cell. Their configuration& code number must be signalled to the user by RNC at the beginning of HSDPAsession using RRC signalling. For example, messages like ‘Radio Bearer Setup’,‘Radio Bearer Reconfiguration’, etc. are used to inform UE about the operator-defined cell-specific details of HSDPA & HSUPA.

2. HS-PDSCH: For HS-PDSCH, the spreading factor is always 16. Since the nameitself says ‘shared’ channel, there is no static allocation of these channels to a UE.The Node B’s MAC-hs scheduler makes the decision about Code(s) allocation andinforms all the UEs in cell using HS-SCCH channel.

8.13.3 HSUPA Related DL Channels

1. & 2. E-HICH & E-RGCH: For E-HICH and for E-RGCH, the spreading factor isalways 128. The E-RGCH and E-HICH are sent on the same channelization code.The exact code number must be signalled to the user by RNC at the beginning ofthe HSUPA session.

3. E-AGCH: For E-AGCH, the spreading factor is 256. The exact code number mustbe signalled to the user by RNC at the beginning of HSUPA session. If the cellsupports both 10ms and 2ms TTI on E-DCH transport channel, there must be twoseparate E-AGCHs:

• E-AGCH for 10 ms E-DCH TTI &

• E-AGCH for 2 ms E-DCH TTI.

8.13. DL CHANNELIZATION CODES 293

Copyright Notices



Figure 8.24 on page 289 Figure 1 of 3GPP TS 25.213 v 8.4.0.Table 8.11 on page 291 Table 1E of 3GPP TS 25.213 v 8.4.0.Text about DPCCH/DPDCHchannelization codes on page 289


Text about HS-DPDCH channel-ization codes on page 289


Text about E-DPCCH/E-DPDCH channelization codes onpage 290


Text about channelization codesof R99 DL channels on page 291


Text about channelization codesof HSDPA DL channels on page292


Text about channelization codesof HSUPA DL channels on page292



BIBLIOGRAPHY




294

CHAPTER

9

SIGNALLING

Source:

• 3GPP TR 25.931 ver. 8.0.0 ;‘UTRAN functions, examples on signalling

procedures’

• H.Holma and A. Toskala, ‘WCDMA for UMTS’ , 5th Edition, John Wiley

& Sons.

• Chris Johnson, ‘Radio Access Networks For UMTS; Principles And Practice’ ,

John Wiley & Sons.

This chapter is inspired from the book ‘Radio Access Networks For UMTS;Principles And Practice’ by Chris Johnson, where various signalling scenariosare illustrated with the help of diagrams, signalling traces and elaborative text.

In ‘Let’s Learn 3G in 10 Days’, the author has tried to explain the sameby skipping some details. The advanced readers should refer to the abovementioned reference to get more details, which is an excellent source of 3Gfundamentals.

In order to establish any service, certain information much be exchanged between variousnodes in the network. For example, subscriber has to request for radio resources fromRNC and services from core network. To fully understand the functionality of UMTS andHSPA, we should understand these signalling mechanisms.

295

296 CHAPTER 9. SIGNALLING

9.1 Building Blocks of 3G Signalling

Any signalling diagram of 3G is a combination of 2 or more building blocks that arediscussed below. In the following section, we will make ourselves familiar with these termswhich are very commonly used in 3G. These words have been used several times in thisbook which proves their importance. We will define 5 items here:

1. RRC Connection

2. Radio Bearer

3. Radio Access Bearer

4. Radio Link

5. Non-Access Stratum (NAS) Signalling Connection

9.1.1 RRC Connection

RRC connection is a dedicated connection between RRC peer entities on UEand UTRAN side (in RNC). It is used to carry dedicated control channel(logical channel DCCH) in both directions (i.e., UE to RNC, as well as RNCto UE).

There are two kinds of RRC connections. One kind is related to service access, the otherkind is not related to service, such as related to location update, cell update, networkregistration etc.

As we know, Radio Resource Control (RRC) is the name of control plane protocolbetween UE and RNC. Therefore, an ‘RRC Connection’ is a connection that carries controlsignalling between these two entities. RRC connection is always point-to-point betweenRRC entities on the UE and the RNC sides. It is always bi-directional in nature. UE hasat least zero and at most one RRC connection1.

• When UE has zero RRC connections, it is said to be in RRC IDLE Mode.In this state, RNC has no information about the subscriber.

• When UE has one RRC connection, it is in RRC Connected Mode. In RRCconnected mode, UE can be in either CELL DCH, CELL FACH, CELL PCH orURA PCH states.

1Note: Even in soft-handover or Inter-RNC Soft-handover case, there is only one RRC connec-tion.

9.1. BUILDING BLOCKS OF 3G SIGNALLING 297

Figure 9.1: RRC Connection Establishment & Idle to Connected Mode Transition

The transition from Idle to Connected mode takes place on RRC Connection Establish-ment. Request to setup an RRC connection is always initiated by UE. RNC’s admissioncontrol has the authority to setup or reject the RRC connection request. The signallingflow is illustrated in figure 9.1.

1. The UE initiates set-up of an RRC connection by sending RRC CONNECTIONREQUEST message on RACH.

2. Based on a look-up table which shows mapping between the establishment cause andtransport channel type (e.g., for voice calls: DCH/DCH and for SMS: RACH/FACH),the SRNC decides to use either RACH/FACH or DCH/DCH for this RRC connec-tion. Later, RNC checks for the availability of radio resources, hardware resources,transmission resources and if all these checks are successful, RRC CONNECTIONSETUP message is sent on FACH.

3. UE sends RRC CONNECTION SETUP COMPLETE on a DCCH logical chan-nel mapped on the DCH transport channel or RACH transport channel asdecided by RNC and indicated to UE by RRC CONNECTION SETUP message.

In this section, we are trying to define ‘RRC Connection’ as a signalling building blockonly. A more detailed description of RRC Connection establishment is available in section9.2.


9.1.2 Radio Access Bearer (RAB)

According to 3GPP TR 21.905 which contains a vocabulary for 3GPP Speci-fications, “Radio Access Bearer (RAB) is a service provided by access stra-tum to the non-access stratum for transfer of user data between UserEquipment (UE) and Core Network (CN)”.

In order to establish a RAB between UE and CN, we require

1. Radio Bearer (between UE and RNC), and

2. Iu Bearer (between RNC and CN)

As a first step, we can consider RAB as the same as service. There are many types ofRABs, e.g., CS Voice RAB, CS Streaming RAB, CS Video RAB, PS Interactive RAB,PS Background RAB, etc. In case of multiple services, we can define a multi-RAB as acombination of two or more RABs. A CS RAB is established between UE and MSC anda PS RAB is between UE and SGSN. Radio Access Bearer is a logical connection betweenUE and Core Network(MSC or SGSN). But in order to guarantee the QoS, RAB uses theservices of Radio Bearer and Iu Bearer.

Figure 9.2 illustrates the sequence of messages exchanged between UE, RNC and CN forestablishing a RAB.

1. The process of RAB establishment starts after RNC gets a RANAP: RAB ASSIGN-MENT REQUEST message from Core Network.

2. RNC has the authority to either accept or reject this request. In both the cases,RNC sends a RANAP: RAB ASSIGNMENT RESPONSE message to CN whichindicates either positive outcome or negative outcome of the RAB establishmentprocedure.

9.1.3 Radio Bearer

Radio Bearer is a bearer service which defines the quality of service for theuser data stream between UE and RNC. If we study the Radio Bearer care-fully, we can find the configuration of all protocol layers of radio protocols e.g.,PDCP, RLC, MAC and Physical layers.

According to 3GPP TR 21.905, Radio Bearer is defined as, “the service provided by theLayer 2 for transfer of user data between User Equipment and UTRAN”. Radio Bearer isa building block and pre-requisite for RAB. Therefore, when core network requests RNCfor RAB establishment, the Radio Bearer setup procedure gets automatically triggered.


Figure 9.2: Radio Access Bearer

The same situation has been illustrated in figure 9.3. Since radio bearer is establishedbetween UE and RNC, the RRC protocol plays an important role in the setup procedure.

After successful decision to establish Radio Bearer, RNC informs UE about the configu-ration of Physical, MAC, RLC and PDCP layer using RRC: RADIO BEARER SETUPmessage. During the connection, if RNC decides to modify the current configuration, itsends RRC: RADIO BEARER RECONFIGURATION message to UE. As shown in figure9.3, UE acknowledges the receipt and compatibility by sending a RRC: RADIO BEARERSETUP COMPLETE or RRC: RADIO BEARER RECONFIGURATION COMPLETEmessage.

Figure 9.3: Radio Bearer Establishment/Modification

9.1.4 Radio Link

By definition, “Radio Link is the logical name given to the association betweena single user and single Node B”. During soft-handover, UE can maintain


several radio links (one radio link for each active set cell). Radio links areadded to or deleted from the active set. Even in softer-handover, UE hasmultiple radio links.

A Radio Link is simply a bunch of UL & DL physical channels between one UE andone Node B. The decision about the codes used on the physical channels is made by RNC.Therefore, RNC informs Node B about the codes, timing, Transport Format Set, TTI andother essential information using NBAP: RADIO LINK SETUP REQUEST message. Thedetails of NBAP protocol are available in 3GPP TS 25.433.

As shown in the figure 9.4, RNC initiates the setup of radio link by sending NBAP: RADIOLINK SETUP REQUEST message to Node B. This message instructs Node B about the‘CRC communication Context id’, which acts like a nickname for this particular radiolink whenever Node wants to address RNC regarding this radio link. This process getscompleted when Node B replies with NBAP: RADIO LINK SETUP RESPONSE message,which includes a ‘Node B Communication Context id’. For any future NBAP transactions,reference will be made using these 2 context ids.

Figure 9.4: Radio Link Setup or Reconfiguration

An example of this is shown in the right sub-figure in figure 9.4. In this figure, theprocedure of ‘Synchronised Radio Link Reconfiguration’ is illustrated. There can be severalRadio Links between the UE and the Node B but with the help of Node B CommunicationContext ID and CRNC Communication context id, we can uniquely identify the radio linkwhose configuration must be modified. This procedure gets completed in three messages:

1. Radio Link Reconfiguration Prepare

2. Radio Link Reconfiguration Ready


3. Radio Link Reconfiguration Commit

9.1.5 Non-Access Stratum (NAS) Signalling Connection

NAS Signalling connection (UE � CN) is a control plane logical connection.NAS connection is realized using a combination of RRC Connection (UE �RNC) and Iu Connection (RNC � CN).

Figure 9.5: Non-Access Stratum (NAS) Signalling Connection

Non-Access Stratum is a combined name for a group of control plane protocols that areused in 2G & 3G. These set of protocols are access-agnostic which means that their defini-tions do not depend on the underlying Access Stratum technology. Access stratum is usedto carry the NAS messages. Transfer of NAS messages between RNC and Core networkhappens by RANAP signalling protocol. Similarly, between UE and RNC, RRC protocolis used to transfer NAS messages. The example described in the following paragraph andfigure 9.5 elaborate this concept.

For example, CM: Service Request is a message which UE sends to MSC in order to requestfor a specific circuit switched service. Therefore, CM: Service Request is a NAS messagewhich gets transported by RRC:Initial Direct Transfer from UE to RNC and by RANAP:Initial UE message from RNC to CN. The RRC layer and RANAP layer do not decodethe NAS message because Node B and RNC do not have NAS entities. NAS entities areonly in UE and Core Network.

After learning about these building blocks, now we will focus on few commonly discussedsignalling scenarios and analyze how these building blocks are used.


9.2 RRC Connection Establishment

As explained in section 9.1.1, RRC connection is a dedicated signalling connection be-tween UE and RNC. The transport channels used for these signalling messages can beeither dedicated channels (DCH(↑↓) ) or common channels (FACH (↓) /RACH(↑)). Inthe following sections, we will investigate both the options.

Option 1: ‘Signalling Radio Bearers on dedicated channels’ (see section 9.2.1).

1. UE sends RRC CONNECTION REQUEST on CCCH logical channel mappedon the RACH transport channel.

2. RNC sends RRC CONNECTION SETUP on CCCH logical channel mappedon the FACH transport channel.

3. UE sends RRC CONNECTION SETUP COMPLETE on a DCCH logicalchannel mapped on the DCH transport channel.

4. All further DCCH messages are exchanged on DCH.

Option 2: ‘Signalling Radio Bearers on common channels’ (see section 9.2.2)

1. UE sends RRC CONNECTION REQUEST on CCCH logical channel mappedon the RACH transport channel (same as option 1).

2. RNC sends RRC CONNECTION SETUP on CCCH logical channel mappedon the FACH transport channel (same as option 1).

3. UE sends RRC CONNECTION SETUP COMPLETE on a DCCH logicalchannel mapped on the RACH transport channel.

4. All further DCCH messages are exchanged on RACH/FACH.

9.2.1 RRC Connection on Dedicated Channels - DCH

1. The UE initiates the set-up of an RRC connection by sending RRC CONNECTIONREQUEST message on RACH. The main parameters in this message are Initial UEIdentity (e.g., IMSI or TMSI+LAI), Establishment cause (e.g., Originating conver-sation call), measurement result about DL coverage quality. The quantity used forthis reporting is broadcasted in SIB 11 of system information under the IE ‘Intra-frequency reporting quantity for RACH reporting’.

From Rel-5 onwards, the new devices must also indicate whether they support HS-DPA or HSPA2. All the possible values for establishment cause are listed in 3GPPTS 25.331.

2Not the exact device category and radio access capabilities.

9.2. RRC CONNECTION ESTABLISHMENT 303

Figure 9.6: RRC Connection Establishment - DCH Establishment.

2. Based on a look-up table, the SRNC decides to use either RACH/FACH or DCH/DCHfor this RRC connection. Operators can tune this table by RNC parameters for eachestablishment cause. At this moment, RNC allocates both U-RNTI and C-RNTIidentifiers to address the UEs within UTRAN.

In this example, the SRNC decides to use a DCH for this RRC connec-tion, allocates U-RNTI and radio resources for the RRC connection.

Step 2a. Radio Link Setup: When a DCH is to be setup, NBAP: RADIO LINKSETUP REQUEST message is sent to Node B. In this message, RNC informsNode B about the Cell id, Transport Format Set (TFS), Transport FormatCombination Set (TFCS), frequency, UL Scrambling code, DL channelizationcode, Power control information etc. Node B allocates resources, starts phys-


ical layer reception, and responds with NBAP: RADIO LINK SETUP RE-SPONSE message. The main parameters in this message are: signalling linktermination, transport layer addressing information (AAL2 address, AAL2Binding Identity) for the Iub Data Transport Bearer.

As indicated in section 9.1.4, Node B and RNC negotiate two context ids forthis particular radio link for future NBAP transactions related to this radiolink.

Step 2b. Iub Transport Bearer Setup: RNC initiates setup of Iub Data Trans-port bearer using ALCAP protocol using ALCAP: ESTABLISHMENT RE-QUEST (ERQ) message. This request contains the AAL2 Binding Identity tobind the Iub Data Transport Bearer to the DCH. The request for setup of IubData Transport bearer is acknowledged by Node B by sending an ALCAP:ESTABLISHMENT CONFIRM message.

Step 2c. DCH Frame Synchronization: The Node B and SRNC establish syn-chronization for the Iub Data Transport Bearer by means of exchange of the ap-propriate DCH Frame Protocol frames ‘DOWNLINK SYNCHRONIZATION’and ‘UPLINK SYNCHRONIZATION’. Then Node B starts DL transmission.

3. If all these procedures are successful, theRRC CONNECTION SETUPmessageis sent on FACH from RNC to UE. Using this message, RNC informs UE aboutseveral parameters, such as, Initial UE Identity, U-RNTI, Transport Format Set(TFS), Transport Format Combination Set (TFCS), DL channelization code, ULScrambling code, Power control information, etc. RRC CONNECTION SETUPmessage informs UE about the ‘Capability update Requirement’. It is expectedthat UE will include the details about its capabilities in the next message. If RRCredirection to another frequency is used, RRC CONNECTION SETUP message alsoincludes the target frequency where the redirection must take place.

4. Node B achieves uplink sync and notifies SRNC with NBAP: RADIO LINK RE-STORE INDICATION message.

5. Message RRC Connection Setup Complete is sent on DCCH logical channel from UEto SRNC. This message includes parameters like integrity protection and cipheringalgorithms supported by UE information and UE radio access capability. If thedevice supports HSDPA and/or HSUPA, the device category number must also bespecified here. Additionally, if smart features like MIMO, A-GPS, DC-HSDPA,16-QAM etc. are supported, UE must include these details in this message.

9.2.2 RRC Connection on Common Channels - FACH/RACH

Figure 9.7 shows the establishment of an RRC connection on the RACH/FACH commontransport channel. In comparison to the previous example, we can observe that there is nosignalling to setup the Iub Data Transport bearer. Therefore, it is required that transportbearer for the RACH/FACH is established prior to this procedure.

9.2. RRC CONNECTION ESTABLISHMENT 305

Figure 9.7: RRC Connection on Common Channels - FACH/RACH

Advantages:The use of Common Channel for carrying DCCH is very beneficial for theoperator because it brings resource efficiency in various ways. The connectionsetup signaling and user dedicated resource requirements are reduced at theBTS, the Iub, and the RNC.

At the Iub interface also, the common channels are carried in a resource-efficient way. In the Node B, less processing capacity (channel element) isconsumed for signalling radio bearers, and the hardware load caused by sig-nalling is decreased. In the RNC, the number of users in the Cell DCH state,as well as the load of the connection setup signaling, is reduced.

At the radio interface, less channelization codes are required for signaling.

Typically, RRC connection setup on common channels is faster than using DCH, becausedelays for setting up dedicated channels and synchronous reconfiguration can be avoided.

When RNC feels the need of setting up an DCH, HS-DSCH or E-DCH channel for UE, itcan instruct the user to perform Cell FACH to Cell DCH transition.

Disadvantages:Since RACH and FACH are common transport channels, they can experiencecongestion if a large number of UEs are using them simultaneously. Therefore,the quality of service offered by RRC connection on common channels is lessthan the same on dedicated channels.

Operators have to consider an upgrade in L1 capacity of RACH and FACHbefore allowing RRC connection on common channels.


9.3 Mobile Originated Voice Call Establishment

Source:

• Chris Johnson, ‘Radio Access Networks For UMTS ; Principles And

Practice’ , John Wiley & Sons.

3G has improved the end-user experience of high bit rate data services but voice is still themost important service offered by mobile operators. In this section, we will understandthe signalling flow of a ‘Mobile Originated CS conversational voice call’ setup. If thereaders are familiar with the call flow of GSM, they should compare the GSM call flowwith UMTS CS call flow and find out the similarities and differences. In short, we canmake 2 statements in advance.

1. RRC connection and RAB are new concepts that were introduced in 3G. Therefore,RRC Connection establishment and RAB setup phase are different in comparisonto 2G call flow.

2. The signalling between UE and Core Network is exactly the same as used in GSM.

In order to simplify the understanding, we will divide the whole procedure into phases 4phases:

1. Phase 1: RRC Connection Establishment

2. Phase 2: Signalling between UE & CN

3. Phase 3: RAB Setup


Phase 1: RRC Connection Establishment: In order to establish any CS service, UEmust contact MSC and request for the same. But in order to reach MSC, UE needsdedicated signalling resources (DCCH). UE uses the common signalling resources(CCCH mapped on RACH/FACH) to obtain dedicated signalling resources. Thisprocedure was explained in full detail in section 9.2.

Phase 2: Signalling between UE & CN: Using the signalling resources obtained inphase 1, UE performs negotiations with MSC.

1. The first NAS message is CM: Service Request. This NAS message iscarried by two access stratum (AS) protocols RRC and RANAP, as shown infigure9.8. When the first NAS message arrives at RNC, it encapsulates it intoan SCCP: CONNECTION REQUEST message. SCCP signalling is used toestablish an Iu-CS signalling connection. The CS core network confirms the

9.3. MOBILE ORIGINATED VOICE CALL ESTABLISHMENT 307

Figure 9.8: Mobile Originated Voice Call Establishment; Source: ‘Radio AccessNetworks For UMTS; Principles And Practice’ by Chris Johnson


setup of an Iu-CS connection by sending SCCP: CONNECTION CONFIRMmessage. SCCP connection is identified by 2 numbers ‘source local reference’and ‘destination local reference’.

2. Serving MSC sends AUTHENTICATION REQUEST message with 2 pa-rameters: Authentication Token (AUTN) and Random Number (RAND). Us-ing RAND and a secret key (stored in SIM card), UE calculates the AUTN,Signed Response (SRES), Integrity key (IK) and ciphering key (CK). UE com-pares the calculated AUTN with received AUTN. If they match, UE sendsAUTHENTICATION RESPONSE message to MSC including SRES.

3. The RANAP: SECURITY MODE COMMAND message informs RNCabout the list of integrity protection and ciphering algorithms that are per-mitted by the core network. RNC chooses the algorithms according to its owncapability and UE’s capability. This message also includes the reference start-ing point of ciphering. UE acknowledges by responding with SECURITYMODE COMPLETE and RNC forwards this message to core network.

4. The next message in the sequence is aCM: SETUPmessage from UE to MSCwhich informs MSC about the bearer capability (supported codecs), the binarycoded decimal (BCD) number of called party and call control capabilities.

Phase 3: RAB Setup: Procedure of RAB setup begins when core network requestsRNC for setting up a CS conversational class RAB with some requested QoS. Atthis moment, RNC’s admission control checks for UL interference, DL transmissionpower and DL channelization codes. If these radio resources are available, RNCstarts hunting for logical and physical resources. This mechanism is briefly summa-rized as:

(3.a) Radio Link: A radio link between UE and Node B was established at thetime of RRC connection establishment. But that radio link was purely forsignalling. In order to setup the radio bearer for user plane voice traffic, radiolink must be reconfigured. The procedure has been illustrated in figure 9.4 andexplained in section 9.1.4. Using this proedure, RNC informs Node B aboutthe transport format set, DL channelization code, UL scrambling code, DPCHoffset etc. At this point, RNC informs Node B about the Connection FrameNumber (CFN) where the modified radio link will become active.

(3.b) Transport Bearer: Using ALCAP signalling, data transport bearer on Iuband Iu-CS is established. RNC initiates the setup of the transport bearerbetween RNC and Node B and between RNC and MSC.

(3.c) Radio Bearer: UsingRRC: Radio Bearer Setupmessage, RNC instructsUE about the configuration of various protocol layers and channel mapping.Information about all the transport channel parameters e.g. Transport For-mat Set, TTI, CRC size etc. and all physical layer parameters e.g., codes,frequency band, slot format, power control information and CFN are carried

9.3. MOBILE ORIGINATED VOICE CALL ESTABLISHMENT 309

by this message3. UE acknowledges the reception by sending RRC: RADIOBEARER SETUP COMPLETE message.

Phase 4: Signalling between UE & CN: 1. After getting response from the serv-ing MSC of the called party, MSC of the calling party sends an ALERTINGmessage to UE which indicates that the other party’s phone is ringing.

2. After the called party accepts the call, this information is transported to thecalling party using CONNECT message.

3. UE responds with a CONNECT ACKNOWLEDGE message to CN.

From this point onwards, a CS voice call is established between the calling and the calledparty.

3This step can be compared to TCH ASSIGNMENT in GSM call flow because up to this point,UE is assigned resources for only DCCH and after this point, DTCH can also be sent/received byUE.


9.4 Mobile Terminated Voice Call Establishment

Source:



When we compare the figure 9.9 showing the call flow for ‘Mobile Terminated CS con-versational voice call’ setup with figure 9.8 showing the same for mobile originated callflow, it is obvious that there are a lot of similarities but there are some differences too.In this section, we will investigate the signalling for an incoming call by focussing on theserving-MSC, SRNC and the called party4.

Similar to the example of mobile-originated-call, we will divide the whole procedure intophases to simplify the learning:

1. Phase 1: Paging



4. Phase 4: RAB Setup


The first difference between the MTC and MOC is already visible at this point. There isan additional signalling phase called Paging for MTC case.

Phase 1: Paging: In idle mode, UE keeps on reporting5 its Location Area (LA) toMSC/VLR and about its Routing Area (RA) to the SGSN of the visited-PLMN(VPLMN). In other words, the location of an idle mode UE is known to the networkat LA level or RA level. Therefore, if there is any incoming call for him, the networkmust page him by ‘shouting’ his name in the relevant area.

In the case of Mobile Terminated Call (MTC), when MSC receives a request tosetup a call, it sends a RANAP: PAGING message to all the RNCs in that LocationArea. This message contains the subscriber’s identity (e.g., IMSI or TMSI+LAI,etc.) and the paging cause. In case of incoming voice call, it will be ‘TerminatedConversation Call.’ RNCs forward the paging message to all the cells in their

4often called as subscriber ‘B’ or ‘B Party’5

1. At Switch On/OFF,

2. after moving to a new LA/RA,

3. and periodically based on timers

9.4. MOBILE TERMINATED VOICE CALL ESTABLISHMENT 311

Figure 9.9: Mobile Terminated Voice Call Establishment; Source: ‘Radio AccessNetworks For UMTS; Principles And Practice’ by Chris Johnson


respective controlling areas using RRC: PAGING TYPE 1 message (PCCH → PCH→ S-CCPCH).

Phase 2: RRC Connection Establishment: When UE in idle mode reads its ownidentity on the paging message, it tries to contact the network by using initialaccess. This triggers the setup of an RRC Connection. This mechanism is the sameas in Mobile Originated Call (MOC) except the establishment cause parameter.The cause specified in paging message is echoed by UE while requesting for an RRCConnection.

Phase 3: Signalling between UE & CN: Using the signalling resources obtained inphase 1, UE performs negotiations with MSC.

1. The first NAS message is CM: PAGING RESPONSE. This NAS messageis carried by two access stratum (AS) protocols: RRC and RANAP, as shownin figure 9.9.

Similar to the MOC case, when the first NAS message arrives at RNC, a SCCPconnection is setup between CN and RNC.

2. Authentication procedure is optional but if it is used, there is no differencecompared to the MOC case.

3. SECURITY MODE COMMAND and SECURITY MODE COM-PLETE procedures are also exactly the same as in MOC example.

4. In MTC case, the CM: SETUP message is sent from MSC to UE whichinforms UE about the bearer capability (supported codecs) and the binarycoded decimal (BCD) number of the calling party. This number is used to flashon the UE’s display so that the called subscriber can identify the calling party.The UE acknowledges the setup message by sending aCALL CONFIRMEDmessage.

Phase 4: RAB Setup: RAB setup phase has no difference compared to the MOC ex-ample. Therefore, the description of this phase will not be repeated. This phaseincludes following procedures:

(4.a) Radio Link setup

(4.b) Transport Bearer setup

(4.c) Radio Bearer setup

Phase 5: Signalling between UE & CN: After the Radio Access Bearer (RAB) hasbeen established, the signalling to connect the two parties takes place.

1. The UE of called party sends an ALERTING message to the core network.This message will be forwarded to the serving core network of the calling partyand finally delivered to the calling subscriber. The calling subscriber will beintimated by playing the ring-back tone or by playing the caller tune. Thisaction will not stop until the called party answers the call or a timer expires.

9.4. MOBILE TERMINATED VOICE CALL ESTABLISHMENT 313

2. Once the ‘called’ subscriber (human being) answers the call, a CONNECTmessage is forwarded from Called Party to → CN of called party to → CN ofcalling party to → the calling party.

3. The CN of the called party responds with a CONNECT ACKNOWL-EDGE message to the calling UE.

With this CONNECT ACKNOWLEDGE message, we can say that the call has beenestablished and voice traffic can be transported in both directions.


9.5 PS Data Session Setup

Source:



The packet session setup is also similar to voice call setup up to some extent. Butthere are some significant differences which must be discussed now.

• In CS-domain, UE performs IMSI attach to get registered with MSC/VLR. In PS-domain, UE must perform ‘GPRS ATTACH’ and register with SGSN. While learn-ing about the PS session setup, we must differentiate the 2 cases:

1. UE is not yet registered with SGSN and it performs PS data session setup.

2. UE is already registered with SGSN and it performs PS data session setup.

• In CS-domain, UE can make and receive calls as soon as it is attached to MSC/VLR.But in PS-domain, data transfer is possible only after getting an IP-address.

The signalling shown in this section is valid for UMTS PS sessions, HSDPAPS sessions and also for HSUPA PS data sessions.

Figure 9.10: Initial NAS message from a registered and non-registered user

There are 4 phases in the session setup signalling and they are listed below:

9.5. PS DATA SESSION SETUP 315


2. Phase 2: Signalling between UE and PS Core Network: GPRS ATTACH

3. Phase 3: Signalling between UE and PS Core Network: PDP Context Activation

4. Phase 4: RAB Setup (during PDP activation phase)

Phase 1: RRC Connection Establishment: As discussed in the earlier signalling ex-amples and in the beginning of chapter, RRC connection is established betweenUE and RNC to setup a signalling connection for the transfer of signalling radiobearers. This mechanism is the same as explained earlier except the establishmentcause parameter. These causes are defined in 3GPP TS 25.331 specification. Theterminology used by core network specifications and radio specification is slightlydifferent. Fortunately, in Table L.1.2 of 3GPP TS 24.008 the mapping of PS NASprocedure to establishment cause in RRC connection request is explained. In short,the establishment cause used in this case will be:

• ‘REGISTRATION’ if UE has not already registered with SGSN,

• Otherwise ‘ORIGINATING INTERACTIVE CALL’ or

• ORIGINATING ‘BACKGROUND CALL’ or

• ORIGINATING ‘HIGH-PRIORITY SIGNALLING’.

Similarly, when the UE is registered with SGSN (or ATTACHED), there can bepaging with paging causes ‘TERMINATING INTERACTIVE CALL’, ‘TERMI-NATING BACKGROUND CALL’ or ‘TERMINATING HIGH-PRIORITY SIG-NALLING’. In that case, UE uses the same establishment cause while requestingan RRC connection.

Phase 2: UE � Core Network signalling: GPRS ATTACH: In order to ATTACHitself to the packet core network, UE sends a GMM: ATTACH REQUEST mes-sage towards SGSN. This NAS message is carried by the RRC and RANAP protocolsin access stratum. As soon as the first NAS message arrives at RNC, it triggers thesetup of an SCCP connection between RNC and SGSN. Figure 9.10 shows twodifferent scenarios.

1. In the left sub-figure, the UE is not yet registered in SGSN and it performsPS data session setup.

2. In the right sub-figure, the UE is already registered in SGSN and it performsPS data session setup.

Phase 3: UE � Core Network signalling: PDP Context Activation: After reg-istering in SGSN, a mobility management context exists at SGSN and UE side,but UE does not have an IP address. In order to acquire an IP address and negoti-ate the QoS, UE requests activation of PDP context.


The NAS message ‘ACTIVATE PDP CONTEXT REQUEST’ arrives at SGSN andit chooses the desired GGSN based on Access Point Name (APN) requested inthis message. If UE does not explicitly ask for some particular QoS, then theQoS profile from HLR should be used. SGSN obtains this data from HLR whileperforming ATTACH in the previous step. UE assigns a Network Service AccessPoint Indicator (NSAPI) to this PDP context. Optionally, UE can also specify theprotocol configuration information for external network protocols.

If GGSN agrees on the QoS requested, it sends its response to SGSN. SGSN caninform the UE about the successful PDP context activation but before that RABmust be established.

Phase 4: RAB Setup (during PDP activation phase): Depending on the strategieschosen by equipment vendors, packet session in UMTS and HSPA can be establishedin 2 different ways.

Option 1: Direct Resource Allocation: One strategy is to directly allocate somenominal bit rate on DCH or HSPA resources at the time of RAB setup (seefigure 9.11). This scheme reduces the connection establishment delay. In thisstrategy, RNC makes the decision about using DPH, HSDPA or HSPA config-uration during RAB establishment itself.

Option 2: First ‘Zero Bitrate’ bearer and later resource allocation: Anotherstrategy is establish a RAB with radio bearer of only DCH ‘0 kbps’ in UL &DL and allocate the real resources only if RNC’s packet scheduler receives a‘capacity request’ from UE or from MAC layer within RNC. This scheme hasan advantage that the resources are allocated only when there is actual needto send or receive data.

It depends on the equipment vendors to support either one or both the schemes.Some vendors support both schemes and operators can choose the one, suitable totheir own preference, by RNC level parameters.

Phase 4; Option 1: Direct Resource Allocation

In Direct Resource Allocation (DRA) strategy, the UE will be allocated some nominal bitrate at the time of RAB setup.

1. The SGSN sends a RAB ASSIGNMENT REQUEST message to RNC. In thisrequest, a particular RAB is identified by a RAB-id which is exactly the same asNSAPI used in the PDP context phase. Other important parameters in this messageare:

• Traffic class,


Figure 9.11: PS session setup with direct resource allocation; Source: ‘RadioAccess Networks For UMTS; Principles And Practice’ by Chris Johnson


• Symmetrical or asymmetrical,

• maximum6 UL & DL bit rate,

• Acceptable error ratios,

• Traffic Handling Priority, (THP) (only for Interactive traffic class, value 1, 2or 3; 1 = highest priority).

• Allocation Retention Priority (ARP), which can range from 1 to 15 ; 1 =highest priority).

• Pre-emption Vulnerability and capability, etc.

2. At this moment, the admission control of RNC decides whether the RAB can beestablished or not. Packet scheduler decides the transport channel type selection.HSDPA & HSUPA, HSDPA & DCH or DCH & DCH could be selected for thisparticular bearer. The initial bit rates should be decided by the RNC’s parameters.

3. NBAP signalling between Node B and RNC takes place to reconfigure the radio linkat the Node B.

4. ALCAP signalling between Node B and RNC takes place to establish a user planeIub data transport bearer.

5. RRC: RADIO BEARER SETUP message informs the UE about the selectedradio bearer configuration for the particular RAB and the activation time. If the HS-DSCH transport channel has been selected in DL, the HSDPA-specific user identityH-RNTI is allocated to user. Similarly, if E-DCH transport channel has been selectedin UL, HSUPA specific E-RNTI is also allocated.

6. UE acknowledges by sending an RRC: RADIO BEARER SETUP COMPLETEmessage to RNC.

7. Finally, the RAB setup phase is completed when RNC informs SGSN about thepositive outcome of the RAB establishment procedure by sending RANAP: RABASSIGNMENT RESPONSE.

At this moment, a PS data connection exists all the way between UE and some externalserver using GGSN as the gateway router. Now, UE can send and receive packets fromthe external network to which it just got connected via a specific GGSN. The conceptsabout secondary PDP contexts and multiple PDP contexts are not explained further inthis book.

6‘Maximum’ word plays an important role in this message. UE might ask for maximum bit rateof several Mbps but allocated only few kbps depending on cell load situation and radio conditions.


Phase 4; Option 2: First ‘Zero Bit rate’ bearer and laterresource allocation

As explained earlier, RNC of some equipment vendors act differently when the RABASSIGNMENT REQUEST message arrives at RNC. In the strategy explained below,following procedures are postponed until there is a demand for actual resource allocationfrom UE or/and from RNC.

1. Postpone bit rate allocation (allocate 0 bit rate)

2. Postpone transport channel type selection (always choose DCH)

3. Postpone radio link reconfiguration at Node B (use same radio link as used for RRCconnection)

4. Postpone Iub transport bearer setup (use same bearer as used for RRC connection)

It is illustrated in figure 9.12, RNC immediately sends a RRC: RADIO BEARER SETUPmessage to UE without performing any checks on the resource availability. The actualbit rate allocated in this message is only ‘0’ kbps. Therefore, this radio bearer is only oflogical value. The transport channel selected for this configuration is always dedicatedchannel (DCH).

Afterwards, UE is informed about the minimum threshold of traffic volume that mustbe crossed before it can actually request for the resources. Whenever that threshold iscrossed UE informs RNC by sending RRC: MEASUREMENT REPORT. At this momentthe transport channel type selection can take place. RNC can select one of the followingoptions:

• HSUPA & HSDPA; If both cell & UE support HSPA

• or DCH & HSDPA; If Either cell or UE does not support HSUPA

• or DCH & DCH; If Either cell or UE does not support HSDPA

• or RACH & FACH

If there is no ‘Capacity Request’ in uplink or downlink, RNC will wait some timer expiry.When this timer expires, UE is shifted from CELL DCH state to CELL FACH state. InCELL FACH state, UE can send uplink data on RACH and receive DL data on FACH.


Figure 9.12: PS Call setup with ‘Zero bit rate’ and later resource allocation;Source: ‘Radio Access Networks For UMTS; Principles And Practice’ by Chris John-son

9.6 Soft Handover

Soft handover is a category of handover procedures where the radio links are added anddeleted in such a manner that the UE always keeps at least one radio link to the UTRAN.Soft handover is only possible when the source cell and target cell both operate at the samefrequency. Therefore, soft handovers are always intra-frequency handovers. According tothe network topology, we can identify various scenarios. The source cell and the targetcell can:

1. belong to the same Node B (special case of Soft handover, called Softer Handover).

2. belong to two different Node Bs but controlled by the same RNC.

9.6. SOFT HANDOVER 321

3. belong to two different Node Bs and different RNCs & with Iur interface betweenthe two RNCs.

4. belong to two different Node Bs and different RNCs but without Iur interface be-tween the two RNCs.

A more detailed description can be found in 3GPP TR 25.832. From the four optionslisted above, in the first three cases, a Soft Handover is possible but for the option # 4,only a Hard Handover is possible.

Figure 9.13: Schematic description of Intra-RNC soft handover: Source 3GPP TR25.832

Figure 9.13 shows the schematic description of an Intra-RNC Inter-Node B soft handover.The signalling flow for the same example is illustrated in figure 9.14.

The UE connected to Primary-Scrambling code ‘A’ reports to RNC that it is able to detecta new cell with scrambling code ‘B’ with acceptable CPICH Ec/No strength. According toTS 25.331, this situation is called Event 1A7. The signalling scenario is briefly explainedin the following paragraph.

1. If UE is able to detect a neighboring cell with acceptable signal strength (CPICHEc/No), it informs RNC by sending RRC: MEASUREMENT REPORT mes-sage. The main parameters in this message are scrambling codes and signal strengthof both active set cells and strong monitored cells.

2. Based on the current load in the target cell, RNC’s admission control decideswhether the new ‘radio link’ can be ‘added’ to the active set or not.

7Definition of event 1A: “P-CPICH of a neighbour cell enters the reporting range.”


Figure 9.14: Intra-RNC soft handover - Radio Link Branch Addition; Source:‘Radio Access Networks For UMTS; Principles And Practice’ by Chris Johnson

In this example, the SRNC decides to add the radio link from a neigh-boring cell to the active set. But before that, it needs to do the necessaryarrangements with the new Node B.

2a. Radio Link Setup: When a new DCH is to be set-up, NBAP: RADIO LINKSETUP REQUEST message is sent to Node B and it responds with the NBAP:RADIO LINK SETUP RESPONSE message. The new Node B starts ULreception after this point.

9.7. INTER-RNC HANDOVER WITH IUR INTERFACE 323

2b. Iub Transport Bearer Setup: RNC initiates set-up of Iub Data Transportbearer using ALCAP protocol using ALCAP: ESTABLISHMENT REQUEST(ERQ) message. The request for set-up of Iub Data Transport bearer is ac-knowledged by Node B by sending an ALCAP: ESTABLISHMENT CONFIRMmessage.

2c. DCH Frame Synchronization: The Node B and SRNC establish synchro-nization for the Iub Data Transport Bearer by means of exchange of the ap-propriate DCH Frame Protocol frames DOWNLINK SYNCHRONIZATIONand UPLINK SYNCHRONIZATION. Then Node B starts DL transmission.

3. New Node B achieves uplink synchronization and notifies SRNC with NBAP: RA-DIO LINK RESTORE INDICATION message.

4. Finally, SRNC sends an RRC:ACTIVE SET UPDATE message to UE. Usingthis message, RNC informs UE about the DL primary scrambling code, DL DPCHchannelization code and the DL DPCH frame offset. This message is sent from theoriginal active set as well as via the recently added radio link although the UE willonly receive it from the original active set cell.

5. UE concludes the soft handover procedure by sending RRC: Active Set UpdateComplete message in UL.

9.7 Inter-RNC Handover with Iur Interface

Figure 9.15: Schematic description of Inter-RNC soft handover: Source 3GPP TR25.832


Figure 9.15 describes the behaviour of an Inter-RNC Soft Handover. The new radio linkadded to the active set belongs to a cell which is controlled by another RNC. In thisscenario, soft handover can take place only if there is an Iur interface between the 2 RNCswhich is capable of carrying user plane data frames. The signalling messages exchangedbetween various UTRAN network elements and between UE and UTRAN are shown infigure 9.16.

Figure 9.16: Inter-RNC soft handover - Radio Link Branch Addition

1. UE transmits RRC: MEASUREMENT REPORT message and informs RNC thatevent 1A has triggered. SRNC decides to setup a radio link via a new cell controlledby another RNC.

9.7. INTER-RNC HANDOVER WITH IUR INTERFACE 325

Radio Link Setup: SRNC requests DRNC for radio resources by sending RN-SAP: RADIO LINK SETUP REQUEST message. The main parametersin this message are Cell id, Transport Format Set per DCH, Transport FormatCombination Set, frequency, UL Scrambling code etc. DRNC forwards therequest to the target Node B using NBAP: RADIO LINK SETUP RE-QUEST message. Then Node B starts the UL reception. Node B allocatesrequested resources and informs DRNC about the result in the form of NBAP:RADIO LINK SETUP RESPONSE message. DRNC, in turn, forwardsRNSAP: RADIO LINK SETUP RESPONSE message to SRNC.

Iub Transport Bearer Setup: Using ALCAP protocol, Iub and Iur data trans-port bearers are established between the new Node B and DRNC; and betweenSRNC and DRNC.

DCH Frame Synchronization: After achieving UL synchronization, Node B no-tifies DRNC and DRNC informs SRNC about it by sending NBAP/RNSAP:RADIO LINK RESTORE INDICATION message respectively. SRNC andnew Node B exchange control frames of DCH-Frame Protocol (DCH-FP) andestablish DCH frame synchronization. Then Node B starts DL transmission.

2. After successful co-ordination with Node B and DRNC, the SRNC signals RRC:ACTIVE SET UPDATE message for Radio Link Addition to UE.

3. UE acknowledges with RRC message RRC:ACTIVE SET UPDATE COM-PLETE.


9.8 Inter-RNC Handover without Iur Interface

Figure 9.17 shows the schematic description of an Inter-RNC hard handover where thesource cell and the target cell belong to two different RNCs and there is no Iur interfacebetween them. As we can see, there is a hard switching from ‘Source cell’ to ‘Target cell’.Even in the area of overlapping between the two cells, UE is connected to only one cell.

Along with handover, the functionality of ‘Serving’ RNC is shifted from source RNC totarget RNC. This procedure is known as SRNS relocation.

Figure 9.17: Schematic description of Inter-RNC Hard handover: Source 3GPPTR 25.832

The signalling between UE, source RNC, core network and the target RNC is shown infigure 9.18. In order to simplify the picture, Node Bs and Iub signalling is not shown inthis figure. Let’s break down this procedure in several steps.

STEP 1: For UE, it’s the business as usual. UE detects a neighbouring cell with goodCPICH quality and informs this event to RNC in the form of RRC: MEASURE-MENT REPORT. In this special case, RNC cannot add the new radio link to theactive set because there is no Iur between the CRNC of source cell and the CRNCof target cell. Meanwhile, UE keeps on reporting measurement report at regularperiods.

When the target cell’s Ec/No becomes better than the E/No of the source cell by apredefined margin, RNC decides to perform Hard Handover and SRNS relocation.

Step 2: Since, the 2 RNC’s are not directly connected via Iur, they must communicatevia core network. Source RNC informs core network by sending RANAP: RE-LOCATION REQUIRED message. Core network forwards this message in the

9.8. INTER-RNC HANDOVER WITHOUT IUR INTERFACE 327

Figure 9.18: Inter-RNC Hard Handover and SRNS Relocation

form of RANAP: RELOCATION REQUEST to the target RNC. These stepsare quite clearly shown in figure 9.18.

Finally, the source RNC receives a RANAP: RELOCATION COMMANDfrom the core network, which shows that the target RNC has prepared itself andthe target Node B for the hard handover procedure.


Step 3: Source RNC sends a RRC message PHYSICAL CHANNEL RECONFIG-URATION to the UE.

For illustration, this step can be considered as if RNC is giving a ‘hard handovercommand’ to UE.

Step 4: In response, UE changes the configuration of physical layer and automaticallystarts communicating with the target cell. Target Node B achieves uplink synchro-nization on the radio interface and informs target RNC about it. At this point, targetRNC informs the core network by sending RANAP: RELOCATION DETECTmessage.

Step 5: After establishing the RRC connection with the target RNC and allocation of thenecessary radio resources, UE sends the RRC message PHYSICAL CHANNELRECONFIGURATION COMPLETE to the target RNC.

Step 6: As expected, the target RNC informs Core network about the successful handoverand core network, in turn, asks the source RNC to release the Iu Connection for theUE.

9.9. CS INTER-SYSTEM HANDOVER (3G TO 2G) 329

9.9 CS Inter-System Handover (3G to 2G)

Source:

• 3GPP TR 25.931 ver. 8.0.0 ;‘UTRAN functions, examples on signalling

procedures’



This section is also inspired from the book ‘Radio Access Networks For UMTS ;Principles And Practice’ by Chris Johnson, where various signalling scenariosare illustrated with the help of diagrams, signalling traces and elaborative text.In ‘Let’s Learn 3G in 10 Days’, the author has tried to explain the sameand skipping some details. The advanced readers should refer to the abovementioned reference to get more details.

Voice is the most important and most popular circuit switched service. It is quite normalthat while using voice service, subscribers will run into geographical areas where 3G cov-erage is not strong. But fortunately, GSM coverage can be used to avoid this 3G call dropby carefully planning for a 3G to 2G handover for CS services. 3G to 2G CS ISHO successrate is a very important key performance indicator of any 3G network. The signalling flowof this procedure is broken down into two parts shown in figure 9.19 and figure 9.20.

Let us break down the procedure into several phases and discuss them step-by-step.

1. Phase 1: ISHO triggers

2. Phase 2: Compressed Mode measurements for BCCH RSSI


4. Phase 4: Compressed Mode measurements for BSIC verification


6. Phase 6: HO decision

7. Phase 7: Signalling between SRNC & BSC

8. Phase 8: Communication between UE and GERAN

9. Phase 9: Confirmation about successful HO to RNC

Phase 1: ISHO triggers: There could be several reasons (or triggers) for starting inter-system measurements e.g., poor P-CPICH RSCP, poor P-CPICH Ec/No, high ULtx power, high DL radio link power, poor UL quality (or high UL BLER), poor DL


Figure 9.19: Inter System HO Signalling - UTRAN Part; Source: ‘Radio AccessNetworks For UMTS; Principles And Practice’ by Chris Johnson

quality etc. Other than these critical reasons, there are some non-critical reasonsas well. For example, service-based handover and load-based handover. Opera-tors can control the reporting due to each mechanism by RNC parameters. Theseparameters are given to user either by SYSTEM INFORMATION (BCCH) or byRRC: MEASUREMENT CONTROL MESSAGE. In chapter 5, we defined “event1F which gets triggered whenever the P-CPICH of an active set cell falls below a


certain threshold”. Please refer to section 5.8.3 and figure 5.21.

Whenever a P-CPICH of an active set falls below the parameter defined by RRC:MEASUREMENT CONTROL, UE sends a RRC: MEASUREMENT REPORTmessage to RNC. If there are more cells in the active set, then RNC does not takeany action. When event 1F is triggered for the last active set cell, RNC decides toprepare UE and Node B for inter-system measurements.

Phase 2: Compressed Mode measurements for BCCH RSSI: It is RNC’s duty toprepare both Node B and UE for compressed mode measurements in the scheduledgaps. The compressed mode will not be further explained in this section.

Between Node B & RNC: Using RADIO LINK RECONFIGURATION proce-dure RNC prepares Node B for compressed mode measurements. This proce-dure has 3 signalling messages as shown in figure 9.19.

1. NBAP: RADIO LINK RECONFIGURATION PREPARE message con-tains important parameters related to compressed mode configurationsuch as compressed mode method (SF/2, Higher Layer Scheduling orpuncturing), gap length (# slots), gap starting point within a radio frame,gap pattern etc. With this message up to 3 Transmission Gap PatternSequence (TGPS) can be configured, one for UMTS inter-frequency mea-surements, one for GSM RSSI measurements and one for GSM BSIC ver-ification. Each sequence contains its own set of CM parameters.

2. Node B acknowledges the compressed mode parameters by respondingwith NBAP: RADIO LINK RECONFIGURATION READY message.

3. Finally, RNC sends NBAP: RADIO LINK RECONFIGURATION COM-MIT and informs Node B about the Connection Frame Number (CFN),from which the CM parameters should apply.

Between UE & RNC: The communication between UE an RNC takes place in 2steps. First, RNC informs the CM parameters and then the parameters relatedto GSM RSSI measurements.

1. RRC: PHYSICAL CHANNEL RECONFIGURATION messageis used to inform UE about the compressed mode configuration and therelated parameters. It also contains information about the activation time.This activation time is exactly the same as RNC sent to Node B in NBAP:RL Reconfiguration Commit message.

2. RRC: MEASUREMENT CONTROL message is used to configureGSM RSSI measurements. In this message, RNC specifies whether BSICverification is required at this stage or not. In our signalling example,BSIC verification is not performed at this stage. Each neighbour is identi-fied using a combination of its Absolute Radio Frequency Channel Number(ARFCN) and its Base Station Identity Code (BSIC)8.

8BSIC = Network Colour Code (NCC) and the Base station Colour Code (BCC).


3. UE acknowledges by sending RRC: PHYSICAL CHANNEL RECONFIG-URATION message.

Phase 3: Measurement Reports (UE to RNC): After performing measurements onGSM RAT, UE reports the condition to RNC in the form of RRC: MeasurementReport messages. In our example, we are using periodic measurement reportsat predefined interval. Each report contains information about BCCH RSSI andnon-verified BSIC of 6 strongest GSM neighbours.

Phase 4: Compressed Mode measurements for BSIC verification: There needs tobe some modification in the compressed mode configuration for BSIC verificationwhich Node B should be aware of.

Between Node B & RNC: Using NBAP: COMPRESSED MODE COM-MAND RNC instructs Node B to switch from one Transmission Gap PatternSequence (TGPS) to another one. This message has two important parame-ters:

1. The ‘Compressed Mode Configuration Change CFN’ : This parameter de-fines the radio frame during which the Node B stops using the activeTGPS.

2. The ‘Transmission Gap CFN’ : This parameter defines the radio framein which the new TGPS will become active. ‘New’ means the sequencedefined in this message itself.

Between UE & RNC Well known RRC: Measurement Control massage is usedto switch the compressed mode methods and pattern sequences. RNC may se-lect the best RF carrier or several RF carriers. In this message, RNC instructsUE to verify the BSIC of those remaining neighbours which are not explicitlyremoved by this message.

Phase 5: Measurement Reports (UE to RNC): After performing measurements onGSM RAT and verifying the BSIC, UE reports back to SRNC using the same mes-sage RRC: Measurement Report. Each report contains information about BCCHRSSI and verified BSIC of the GSM neighbours defined in measurement controlmessage.

Phase 6: HO decision in SRNC: If a GSM cell is reported by UE whose BSIC hasbeen verified and whose RSSI level is acceptable, it is considered as a suitable targetcell for inter-system handover.

Phase 7: Signalling between SRNC & BSC: This phase of signalling is illustratedin figure 9.20. It involves signaling between UTRAN radio controller (RNC) andGERAN radio controller (BSC). Typically, these 2 are not connected by some directinterface. Therefore, the communication takes place with the help of core network.

(SRNC � 3G-MSC � 2G-MSC � BSC)


Figure 9.20: UTRAN to GSM HO Signalling - UTRAN & Core Network Part(source 3GPP TR 25.931)

1. SRNC contacts 3G-MSC by sending RANAP:RELOCATION REQUIREDmessage. 3G-MSC forwards this request to 2G-MSC and 2G-MSC in turninforms BSC.

2. BSC allocates the radio resources in 2G cell and acknowledges the request forhandover by sending BSSMAP: HANDOVER REQUEST ACKNOWLEDGEmessage to 2G MSC. 2G-MSC forwards this message to 3G-MSC. 3G-MSCsends a RANAP: RELOCATION COMMAND and informs RNC about the2G radio resources (TCH) allocated for this user.

3. RRC: HANDOVER FROM UTRAN COMMAND message allows the userto leave 3G resources and start accessing 2G radio resources. This messageprovides the UE with sufficient information to continue its speech connectionon GSM, such as

• BSIC (BCC & NCC) and BCCH Carrier’s ARFCN

• Time slot #, hopping information, channel configuration, training se-quence code

• Handver reference number

Phase 8: Communication between UE and GERAN: In the process of synchro-nizing with the 2G base station, UE transmits ‘Handover Access burst’. In thisburst, UE signals the same handover reference number which was given in the RRC:HANDOVER FROM UTRAN COMMAND. After this, BSC sends a ‘Handover De-tect’ message to the 2G-MSC. Finally, UE transmits a Handover Complete messageto 2G-MSC, which then informs the 3G-MSC.


Phase 9: Confirmation about successful HO to SRNC: 3G-MSC sends an RANAP:Iu Release Command to SRNC to release the radio resources, hardware resources,Iub and Iu-cs transport resources. These resources are released only after UE hassuccessfully accessed the 2G resources and call is continuing on GSM.

9.10. PS INTER-SYSTEM HANDOVER (3G TO 2G) 335

9.10 PS Inter-System Handover (3G to 2G)

Source:

• 3GPP TS 23.060 ver. 6.0.0 ;‘General Packet Radio Service (GPRS);

Service description’

CS UTRAN to GERAN handover is commonly called CS ISHO or CS IRAT HO. Similarlyfor Packet switched services too, UTRAN to GERAN handover is called PS ISHO or PSIRAT HO. The signalling for this procedure is quite complicated and a simplified versionof that is illustrated in 9.21. A more detailed description can be found in 3GPP TS 23.060.According to 3GPP, this mechanism is called“Iu mode to A/Gb mode Inter-SGSNChange.” Although some vendors support functionality of 2G and 3G SGSN in the samenetwork element, in our example, it is assumed that 2G SGSN and 3G SGSN are twodifferent nodes. As we have done with the previous scenarios, we will divide the wholeprocedure into several phases. In this discussion, we have 7 phases:

1. Phase 1: 2G Measurement & HO decision by SRNC(UE � SRNC)

2. Phase 2: Routing Area Update (UE � 2G-SGSN)

3. Phase 3: Core Network Signalling (2G SGSN � 3G-SGSN � HLR)

4. Phase 4: Updating PDP Context (2G SGSN � GGSN)

5. Phase 5: Informing Home PLMN (2G SGSN � HLR)

6. Phase 6: Releasing 3G resources ( HLR � 3G SGSN � RNC)

7. Phase 7: Informing UE about the successful ‘handover’ (2G SGSN � UE)

Phase 1: 2G Measurement & HO decision by SRNC(UE � SRNC): Just like cir-cuit switched ISHO, RNC instructs UE to perform the Inter-RAT measurements onGSM neighbouring cells. UE reports the BCCH RSSI in RRC: MEASUREMENTREPORT message. In the example shown, periodic measurement is used. Alter-natively, event triggered measurement could also be used. After finding a suitablecell, RNC decides for UTRAN to GERAN cell change and informs UE using RRC:CELL CHANGE ORDER FROM UTRAN message. The purpose of thismessage is to transfer a connection between the UE and UTRAN to another radioaccess technology (e.g. GSM). This message contains BSIC of the target 2G celland the activation time9.

9Activation time is optional parameter, default is “now”


Figure 9.21: PS IRAT (Source: 3GPP TS 23.060)

Phase 2: Routing Area Update (UE � 2G-SGSN): UE informs 2G-SGSN aboutits presence by sending a ROUTING AREA UPDATE REQUEST message.In this message, UE includes parameters like old RAI, old P-TMSI, Update Type,MS Network Capability etc. The BSS shall add the Cell Global Identity includingthe RAC and LAC of the cell where the message was received before passing themessage to the new 2G-SGSN.

Phase 3: Core Network Signalling (2G-SGSN � 3G-SGSN � HLR) The 2G-SGSNhas no information about the UE’s MM context and PDP context. Therefore, itrequests for the same from 3G-SGSN. 3G-SGSN requests SRNS Context from theSRNC. After receiving this message, the SRNC stops sending downlink PDUs to the

9.10. PS INTER-SYSTEM HANDOVER (3G TO 2G) 337

UE and starts buffering. SRNC replies with an SRNS CONTEXT RESPONSEmessage. The 3G-SGSN responds with an SGSN Context Response (MM Context,PDP Contexts) message (optionally, security procedure may be used to authenticateUE by 2G-SGSN).

Phase 4: Updating PDP Context (2G-SGSN � GGSN): The new 2G-SGSN in-forms GGSN about the changes that have taken place using an UPDATE PDPCONTEXT REQUEST message. This message contains parameters like newSGSN Address, TEID, QoS Negotiated, etc.

Phase 5: Informing Home PLMN (2G SGSN � HLR): The HLR in the Home-PLMN is informed about the routing area update when it receives an UPDATEGPRS LOCATION message from 2G-SGSN. This message contains the IMSI ofsubscriber, SGSN address and SGSN number.

Phase 6: Releasing 3G resources ( HLR � 3G SGSN � RNC): HLR informs theold 3G-SGSN to delete the subscriber’s data from its register because the userhas been successfully registered in 2G-SGSN. 3G-SGSN instructs SRNC to releasethe UTRAN resources reserved for this subscriber by RANAP: IU RELEASECOMMAND message. When the buffered data has been successfully forwarded,the SRNS responds with an RANAP: IU RELEASE COMPLETE message.

Phase 7: Informing UE (2G SGSN � UE): The new 2G-SGSN responds to the MSwith a ROUTING AREA UPDATE ACCEPT message.


9.11 HSDPA Mobility

Figure 9.22: Inter-Node B serving HS-DSCH cell change (Source 3GPP TS 25.308)

According to 3GPP TS 25.308, “a serving HS-DSCH cell change facili-tates the transfer of the role of ‘serving HS-DSCH radio link’ from one radiolink belonging to the source HS-DSCH cell to a radio link belonging to thetarget HS-DSCH cell”.

This concept has already been discussed in Chapter 7 but we did not analyze the signallingassociated with these procedure. Let’s do it now.

9.11.1 Serving HS-DSCH Cell Change

During an active HSDPA session, the UE can move from one cell to another. It is alsopossible that due to other reasons, the Ec/No of a neighbouring cell becomes better thanthat of the serving cell. According to design implementation, the serving cell change canhappen in two methods.

HS-DSCH via DCH Channel: In figure 9.23, ‘Option 1’ shows a simple mechanismwhere the HSDPA channels are released for the mobility purpose. In the transitionarea between ‘A’ and ‘B’, the UE performs a HS-DSCH to DCH channel switching.The handover takes place between source cell ‘A’ and target cell ‘B’ just like a R99DCH handover (via soft handover mechanism). After reaching the target cell ‘B’, aHS-DSCH can be re-allocated to UE from the target cell.

9.11. HSDPA MOBILITY 339

Figure 9.23: Two Methods for HS-DSCH Serving Cell Change

Direct HS-DSCH Serving Cell Change: As depicted in ‘Option 2’ of figure 9.23, dur-ing the transition period, UE keeps on receiving HSDPA data from source cell ‘A’but the associated-DCH (A-DCH) channels perform soft handover with a radio linkof target cell ‘B’. The HS-DSCH channel is still scheduled by the Node B whichcontrols the source cell. This scheme is more efficient than the one explained as‘Option 1’.

As readers might have guessed, the option 1 is not the most optimized solution. It hasbeen implemented by infrastructure vendors as an interim solution if their equipmentsdo not yet support option 2. Now-a-days, almost all networks support direct HS-DSCHtransition. The source and target cells may or may not belong to the same Node B whichgives rise to two separate discussions:

Intra-Node B serving HS-DSCH cell change: In this scenario, the source and thetarget cells are two adjacent sectors of the same site (Node B). Therefore, the


unacknowledged data which is buffered at Node B can be transmitted to the userusing new radio link. There is no need to flush the data in MAC-hs buffer. Intra-Node B SCC has less interruption in service. An example of Intra-Node B SCC isillustrated in figure 9.24.

Inter-Node B serving HS-DSCH cell change: In contrast to the earlier case, in thiscase, the source and the target cells are controlled by two different Node Bs. There-fore, when the user moves into the new cell, the unacknowledged MAC-hs bufferdata at the old Node B must be flushed and the new Node B must get the samefrom RNC. As expected, this causes delay and increases the service interruptiontime. This mechanism is depicted in figure 9.25.

1. Intra-Node B Synchronized Serving HS-DSCH Cell Change

Figure 9.24: Intra-Node B Intra RNC Serving HS-DSCH Cell Change

Figure 9.24 illustrates an intra-Node B serving HS-DSCH cell change while keep-ing the dedicated physical channel configuration and the active set, using thePHYSICAL CHANNEL RECONFIGURATION procedure. The transition from source totarget HS-DSCH cell is performed in a synchronized manner, i.e. at a given activation time.This activation time is decided by RNC and informed to Node B using ‘NBAP: RADIOLINK RECONFIGURATION COMMIT’ and ‘RRC: PHYSICAL CHANNEL RECON-FIGURATION’.


In this example, it is assumed that HS-DSCH transport channel and radio bearer param-eters do not change. If transport channel or radio bearer parameters shall be changed,the serving HS-DSCH cell change would need to be executed by a TRANSPORT CHAN-NEL RECONFIGURATION procedure or a RADIO BEARER RECONFIGURATIONprocedure, respectively.

2. Inter-Node B Synchronized Serving HS-DSCH Cell Change

Figure 9.25: Inter-Node B Intra RNC Serving HS-DSCH Cell Change

In comparison with the intra-Node B case, the major difference is that the sourceand the target HS-DSCH cells are controlled by two different Node Bs, MAC-hs in sourceand target Node B need to be released and setup, respectively.

The procedure can be studied in the following steps:

Step 1: SRNC establishes a new radio link in the target Node B. This process is completedusing the classical signalling of DCH soft-handover mechanism. As usual, NBAPand RRC protocols are used by RNC to communicate with Node B and UE.


Step 2: The target Node B starts transmission and reception on associated-dedicatedchannels (A-DCH).

Step 3: UE sends a measurement report to SRNC and indicates the ‘change of best cellor Event 1d’.

Step 4: RNC prepares the source-Node B for a synchronized reconfiguration to be exe-cuted at a given activation time (using a sequence of 3 NBAP messages).

Step 5: RNC prepares the target-Node B for a synchronized reconfiguration to be exe-cuted at a given activation time.

Step 6: Finally, SRNC sends a PHYSICAL CHANNEL RECONFIGURATION messageto the UE which indicates the target HS-DSCH cell and the activation time.

Step 7: To conclude, the UE responds with a PHYSICAL CHANNEL RECONFIGU-RATION COMPLETE message.

If the source cell and the target cell are under the control of 2 different RNCs then thesituation becomes even more complex and more interesting. The implementation verymuch depends on the vendor’s support for these advanced procedures.

• If ‘HS-DSCH over Iur ’ is supported and ‘soft HO for A-DCH over Iur ’is also supported, it is possible to perform a serving HS-DSCH Cell Change to thecells controlled by DRNC. From UE perspective, there is no difference betweenIntra-RNC and Inter-RNC cell change. Since there are 2 RNCs involved, plannersshould take extra care while planning the parameters related to neighbouring cells.

• On the contrary, if ‘HS-DSCH over Iur ’ is not supported or not enabled,then the A-DCH will perform SHO with the target cell of DRNC. After receivingan RRC: Measurement Report of event 1D, normally SRNC will perform servingcell change but due to the lack of HS-DSCH support on Iur, a reconfiguration fromHS-DSCH to DCH is performed, and in the target cell UE maintains service on R99DCH channel.

9.11.2 HS-DSCH Channel Type Switch

In this discussion, our main focus will be on the DL transport channel switch from DCHto HS-DSCH and vice-versa. Uplink radio bearers can be configured on DCH or E-DCHtransport channels.

DCH to HS-DSCH Switch

A radio bearer reconfiguration from DCH to HS-DSCH can be triggered by various reasons.Some of them are listed below:


• If a cell that supports HSDPA and allows current RAB combination on HSDPA isadded to active set.

• If the compressed mode measurements triggered a switch from HS-DSCH to DCHand the handover was not successful, DCH can again be reconfigured to HS-DSCH.

• If earlier HSDPA allocation was not successful due to temporary reasons (e.g., maxnumber of HSDPA users), and now those reasons are resolved.

• If earlier HSDPA allocation was not successful because Guard Timer was running.These guard times are used to avoid too frequent channel type switch. When theguard timer expires, RNC tries to switch DCH to HS-DSCH.

When one of the reasons listed above triggers DCH → HS-DSCH switch then RNC startslooking for a suitable HS-DSCH target cell. After finding a suitable cell, the RNC reservestransport resources and RNC internal hardware resources for HS-DSCH. Later radio links,transport channel and radio bearer are reconfigured. Radio bearer is mapped to HS-DSCH.After successful reconfiguration, the DCH resources are released and HS-DSCH-specificmeasurements are configured in the UE.

HS-DSCH to DCH Switch

A radio bearer reconfiguration from HS-DSCH to DCH can be triggered by various reasons.Some of them are listed below:

• UE enters a new cell where HSDPA is not enabled.

• If the HSDPA resources in target cell can not be allocated.

• If a new RAB is established and new RAB configuration is not supported on HS-DSCH.

• If compressed mode measurements are triggered for Inter-frequency and Inter-systemmeasurements & system does not support CM measurements on HS-DSCH.

HS-DSCH → DCH switch procedure also takes place in 2 phases. First, the RNC andtransport resources are reserved for DCH, radio links, transport channel & radio bearerare reconfigured and Radio bearer is mapped to DCH. In the second phase, resources forHS-DSCH are released & DCH-specific measurements are configured to the UE.

9.11.3 HS-DSCH IFHO and ISHO

The triggers for Inter-frequency handover and Inter-system handover are the same as forR99 DCH channels. HSDPA does not bring any new triggers for the IFHO or ISHO. Fora quick reminder, some of them are listed below:


• CPICH RSCP becomes weaker than an absolute threshold (Event 1F).

• CPICH Ec/No becomes weaker than an absolute threshold (Event 1F).

• UE transmission power is higher than an absolute threshold (Event 6A).

• UL quality is very poor.

• DL DPCH Radio link power is very high.

• other load based and service based triggers.

The functionality of Inter-frequency handover and Inter-system handover strongly dependson the 2 following implementation alternatives.

If Compressed Mode for IFHO /ISHO not supported: If RNC features do not al-low compressed mode measurements during the HS-DSCH session, HS-DSCH chan-nel will be switched to DCH and IF-measurements/IS-measurements take place justlike in the Rel-99 case.

This method will certainly reduce the HSDPA throughput during measurementphase. It will also cause extra delay due to unnecessary channel switching.

If Compressed Mode for IFHO/ISHO is supported: If RNC supports compressedmode measurements during HS-DSCH configuration, it orders compressed mode onHSDPA so that IF/IS-measurements can be performed on HSDPA without channeltype switching to DCH.

As expected, this alternative does not reduce the user throughput and it causes lessdelays which speeds up the handover execution time.

9.12. HSUPA MOBILITY 345

9.12 HSUPA Mobility

9.12.1 E-DCH Soft Handover

When an E-DCH transport channel is configured for a user, its mobility is supported bysoft-handover. The measurement events related to R99 DCH soft handover signalling,e.g., Event 1A, 1B, 1C, etc. are also valid for HSUPA. In special circumstances, it ispossible to have different E-DCH active set and DCH active set. Although the conceptof handover is same but it should be possible to keep different parameter sets for intra-frequency measurements for DCH and E-DCH soft handover. Operators define differentparameter sets and assign one set each for various service. For example, operators cankeep different set of parameters to control soft handover procedure for real time (RT)services, for non-real time (NRT) services, for HSDPA services, and for HSPA services.

In E-DCH active set there is one ‘Serving’ E-DCH active set and (one or more) ‘non-serving’ E-DCH cell(s). A detailed description of these terms is available in Chapter8.

Serving E-DCH RLS: The serving E-DCH Radio Link Set contains a serving E-DCHcell and non-serving E-DCH cell(s) under the same Node B.

Non-serving E-DCH RLS: The non-serving Radio Link Set contains those non-servingactive set cells that belong to another Node B.

9.12.2 E-DCH Serving Cell Change

E-DCH serving cell is always the same as HS-DSCH cell change. The triggering of HS-DSCH serving cell change and the selection of HS-DSCH serving cell described in theprevious section are also valid if the UL MAC-d flows are configured on E-DCH.

9.12.3 E-DCH Channel Type Switch

In this discussion, our main focus will be on UL transport channel switch from E-DCH toDCH and vice-versa.

• If UL radio bearers are configured on E-DCH, DL must be HS-DSCH.

• If the UL is on DCH, then DL can be configured on either HS-DSCH or DCHtransport channels.


DCH to E-DCH Switch

The mechanism of channel type switch from DCH to E-DCH is a tool by which E-DCHcan be allocated if it was not possible in the initial channel allocation. There are severaltriggers for this transition. Some of them are listed below:

• Channel type switching if the UE enters an HSPA cell.

• When DL DCH is reconfigured to HS-DSCH then RNC tries of the usage of E-DCHis possible. If possible, then E-DCH is preferred and a transition from DCH →E-DCH is started.

• When a DCH/HS-DSCH is configured and UE performs HS-DSCH serving cellchange, the RNC checks whether a DCH to E-DCH channel type switch is needed.

• Whenever an E-DCH → DCH channel type switch is performed, a guard timer isset. When this timer expires, it triggers a DCH → E-DCH channel type switch.

• If at the initial allocation, DCH is selected because E-DCH-capable cell is veryweak compared to a non-E-DCH capable cell. An E-DCH active set can change toacceptable if the cell not in E-DCH active set becomes ‘weak enough’ or is removedfrom the DCH active set. Weak enough is defined relative to the serving HS-DSCHcell.

• If initial E-DCH allocation fails, RNC can also periodically check if the usage ofE-DCH transport channel has become possible now. This is possible due to varyingcell load conditions.

There are several possibilities for UL/DL combinations for DCH → E-DCH.

1. DCH/DCH → HS-DSCH/E-DCH

2. HS-DSCH/DCH → HS-DSCH/E-DCH

E-DCH to DCH Switch

Channel type switch from E-DCH → DCH is required when E-DCH channel cannot bemaintained or its usage become inefficient. There are several triggers for this switch. Someof them are:

• When the DL HS-DSCH is switched to DCH, it becomes impossible to maintainE-DCH in UL. Therefore, a switch from E-DCH rightarrow DCH is required.

• When a HS-DSCH serving cell change is triggered, RNC checks whether the targetHS-DSCH serving cell supports E-DCH and whether the proposed E-DCH activeset is acceptable. If any of these 2 checks fails, the channel type switch from E-DCHto DCH cannot be avoided.


• If E-DCH is used and DCH active set contains some cell(s) which are not in E-DCHactive set. If any DCH active set cell becomes stronger than the serving E-DCH cellby a predefined margin, the E-DCH active set becomes unacceptable and a switchfrom E-DCH to DCH is necessary.

• During HS-DSCH/E-DCH operation if UE moves to a cell where HSDPA or HSUPAis not supported, the following channel switch are possible.

1. HS-DSCH/E-DCH → HS-DSCH/DCH

2. HS-DSCH/E-DCH → DCH/DCH

9.12.4 E-DCH IFHO and ISHO

The discussion about E-DCH inter-frequency handover and inter-system handover is verysimilar to the one for HSDPA IF/IS HO (see section 9.11.3). Once again, the sameintra-frequency measurement events are used to trigger these hard handovers. The mea-surements are performed in compressed mode which gives rise to 3 possibilities.

Compressed Mode not supported for HSDPA & HSUPA: If RNC features do notallow compressed mode measurements during HS-DSCH/E-DCH session HS-DSCH/E-DCH will be switched to DCH/DCH and IF-measurements/IS-measurements takeplace just like in R99 case.

Compressed Mode for HSDPA is supported but not for HSUPA: A channel typeswitch from HS-DSCH/E-DCH → HS-DSCH/DCH is performed and then com-pressed mode measurements are carried out as usual.

Compressed Mode is supported for both HSDPA & HSUPA: If RNC supportscompressed mode measurements during HS-DSCH/E-DCH configuration, measure-ments can be performed without channel type switching to DCH.


Copyright Notices



Figure 9.21 on page 336 Figure 54 of 3GPP TS 23.060 v 6.0.0.Text in section 9.10 on page 335 Section 6.13.2 of 3GPP TS 23.060 v 6.0.0.c⃝2003. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

Figure 9.22 on page 338 Figure 9.1-1 of 3GPP TS 25.308 v 6.3.0.Figure 9.24 on page 340 Figure 9.3-1 of 3GPP TS 25.308 v 6.3.0.Figure 9.25 on page 341 Figure 9.5-1 of 3GPP TS 25.308 v 6.3.0.c⃝2004. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

Figure 9.1 on page 297 Figure 8.1.3-1 of 3GPP TS 25.331 v 6.9.0.Figure 9.3 on page 299 Figure 8.2.2-1 of 3GPP TS 25.331 v 6.9.0.Figure 9.3 on page 299 Figure 8.2.2.3 of 3GPP TS 25.331 v 6.9.0.Figure 9.4 on page 300 Figure 24 of 3GPP TS 25.433 v 7.0.0.c⃝2006. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.


Text in section RRC Connectionon Dedicated Channels on page302

Section 7.3.1 of 3GPP TR 25.931 v 8.0.0.

Figure 9.5 on page 301 Figure 7 of 3GPP TR 25.931 v 8.0.0.Figure 9.6 on page 303 Figure 8 of 3GPP TR 25.931 v 8.0.0.Figure 9.7 on page 305 Figure 8b of 3GPP TR 25.931 v 8.0.0.Figure 9.20 on page 333 Figure 36 of 3GPP TR 25.931 v 8.0.0.c⃝2008. 3GPPTM TSs and TRs are the property of ARIB, ATIS, ETSI, CCSA,TTA, and TTC who jointly own the copyright for them. They are subject tofurther modifications and are therefore provided to you “as is” for informationpurposes only. Further use is strictly prohibited.

BIBLIOGRAPHY

[1] 3GPP TR 21.905 ver. 8.0.0 ;‘Vocabulary for 3GPP Specifications’

[2] 3GPP TS 23.060 ver. 6.0.0 ;‘General Packet Radio Service (GPRS); Service descrip-tion’


[4] 3GPP TS 25.308 ver. 7.0.0 ;‘High Speed Downlink Packet Access (HSDPA); Overalldescription;’

[5] 3GPP TS 25.319 ver. 7.0.0 ;‘High Speed Uplink Packet Access (HSUPA); Overalldescription’






[11] 3GPP TS 25.308 ver. 7.0.0 ;‘High Speed Downlink Packet Access (HSDPA); Overalldescription;’





350

CHAPTER

10

SELF TEST

In the 9 modules of this book, we learnt the essential concepts about UMTS and HSPA.In this final module, we should put ourself to a self-test and examine our understanding.Therefore, I request the readers to try and independently answer these questions and solvethe exercises given in this module. You are free to refer back to the previous modules butthe only condition is ‘do it yourself ’.

10.1 Module 1

Question 1.1: Arrange the following technologies in the chronological order oftheir releases.

1. IMS

2. HSCSD

3. HSUPA

4. TD-SCDMA

5. GPRS

Correct Answer:

1.

351

352 CHAPTER 10. SELF TEST

2.

3.

4.

5.

Question 1.2: In one or two words, explain the highlights of each 3GPP re-lease. Write your answers in Table 10.1.

3GPP Release Main Features or Improvements

R99REL-4REL-5 1.

2.REL-6REL-8

Table 10.1: Exercise 1.2: Highlights of few 3GPP releases

Question 1.3: Which of the following SDOs1 are 3GPP Organizational Part-ners?

• GSMA

• ETSI

• TIA (USA)

• TTC (JAPAN)

• ATM Forum

• WiMAX Forum

• CCSA (China)

• ARIB (Japan)

• ATIS (USA)

• NGMN Alliance

Correct Answer:

1.

2.

3.

1Standards Development Organizations

10.1. MODULE 1 353

4.

5.

6.

Question 1.4: According to REL-6, the peak bitrates of HSDPA and HSUPAare:

• DL 2 Mbps and UL 2 Mbps

• DL 7.2 Mbps and UL 2 Mbps

• DL 14.4 Mbps and UL 2 Mbps

• DL 14.4 Mbps and UL 5.8 Mbps

• DL 21 Mbps and UL 5.8 Mbps

• DL 42 Mbps and UL 11 Mbps

Correct Answer:

•

Question 1.5: “All-IP” solution means that we do not need to depend on thelegacy circuit switched nodes, e.g., MSC. In history, which was the firsttechnology & 3GPP release allowed this scheme?

Technology: Pick one from the following options

• GPRS

• UMTS

• HSPA

• IMS

• HSPA+

3GPP release: Pick one from the following options

• R4

• R5

• R6

• R7

• R99

Correct Answer:

• Technology:

• Release:


10.2 Module 2

Question 2.1: According to the original GSM network architecture, the fol-lowing subsystems are defined.

Identify the wrong options from the list of subsystems mentioned below.

• Mobile station

• External networks

• Circuit Switched Core Network (Switching Subsystem)

• Base Station Subsystem

• Packet Switched Core Network (Packet Core)

Correct Answer:

•

Question 2.2: While in roaming, which network elements are always locatedin Home PLMN?

Choose 2 options from the following list

• MSC

• BSC

• GMSC

• Transcoding Unit (TRAU)

• Home Location Register (HLR)

Correct Answer:

•

•

Question 2.3: While in roaming, which network elements are always locatedin Visited PLMN?

Choose 3 options from the following list

• MSC

• BSC

• GMSC

• Visitor Location Register

• Home Location Register (HLR)

10.2. MODULE 2 355

Correct Answer:

•

•

•

Question 2.4: In GPRS roaming scenario, the SGSN of Visited PLMN andGGSN of Home PLMN are connected via an IP backbone network knownas:

Correct Answer:

•

Question 2.5: In 2G and 3G, the following interfaces can be considered as“equivalent” interfaces for understanding the 3G network.

Name of 2G interface Equivalent Interfacein 3G

1. A

2. Abis

3. Gb

i. Iu-PS

ii. Iu-CS

iii. Iub

Table 10.2: Exercise 2.5: Match the 2G & 3G interfaces

Correct Answer:

• A:

• Abis:

• Gb:

Question 2.6: An IMS subscriber of PLMN ‘A’ is roaming in the PLMN ‘B’.While inviting another IMS subscriber for a multimedia session, the ‘SIPINVITE’ message will be sent to which SIP server first?

• Interrogating-CSCF of PLMN ‘A’

• Interrogating-CSCF of PLMN ‘B’

• Proxy-CSCF of PLMN ‘A’

• Proxy-CSCF of PLMN ‘B’

• Serving-CSCF of PLMN ‘A’


• Serving-CSCF of PLMN ‘B’

Correct Answer:

•

10.3. MODULE 3 357

10.3 Module 3

Question 3.1: Identify the UL & DL frequency range used in UTRAN FDDband I.

Use table 10.3 and choose the right frequency ranges.

Uplink Freq. Downlink Freq.

832 - 862 MHz 791 - 821 MHz1710-1785 MHz 1805-1880 MHz1920-1980 MHz 2110 -2170 MHz1710-1755 MHz 2110-2155 MHz1850 -1910 MHz 1930 -1990 MHz1710-1770 MHz 2110-2170 MHz

Table 10.3: Exercise 3.1: Identify UTRAN FDD Band I

Correct Answer:

•

Question 3.2: The code which provides processing gain is called:

• Gold Code

• Long Code

• Pseudo-Random Noise

• Channelization code

• Scrambling Code

Correct Answer:

•

Question 3.3: The spreading principle allows us to get variable bit rate byusing variable spreading factors.

Choose the 2 correct statements from the following list:

1. As SF increases, the required transmission power decreases.

2. As SF increases, the required transmission power also increases.

3. As SF increases, the service bit rate decreases.

4. As SF increases, the service bit rate also increases.

Correct Answer:


••

Question 3.4: How many scrambling codes are available?

Choose the correct answer from the following list:

1. Millions of codes in UL & DL

2. 256 codes in UL & DL

3. 512 in UL & DL

4. Millions in UL and 512 in DL

Correct Answer:

•

Question 3.5: 512 DL scrambling codes are organized into 64 SC groups of 8codes. If two WCDMA cells belong to the same group, which channelwill broadcast the identical information in the 2 cells:

Choose the correct answer from the following list

1. DL DPCH

2. P-CCPCH ( Broadcast channel)

3. P-SCH & S-SCH (Pri- & Sec-Synchronization channel)

4. P-CPICH (Primary Common Pilot channel)

Correct Answer:

•

Question 3.6: Two Voice users in the same WCDMA cells must use differentcombination of channelization and scrambling codes.

From the list below, select the two codes that must be different?

1. Channelization Codes in UL

2. Channelization Codes in DL

3. Scrambling Codes in UL

4. Scrambling Codes in DL

Correct Answer:

••

10.3. MODULE 3 359

Question 3.7: The physical layer process which tries to convert a ‘burst oferrors’ into ‘random errors’ is called:

1. Segmentation

2. CRC attachment

3. Interleaving

4. Turbo decoding

Correct Answer:

•


10.4 Module 4

Question 4.1: The mapping of logical channels onto transport channels isperformed by:

1. RLC layer in Node B

2. MAC layer in Node B

3. RLC layer in RNC

4. MAC layer in RNC

5. RRC layer in RNC

Correct Answer:

•

Question 4.2: Non-real time (NRT) service with very small bit rate can betransported on the following channels:

Choose the 2 options.

1. P-CCPCH (BCH)

2. PRACH (RACH)

3. DPCH (DCH)

4. PCCH (PCH)

5. S-CCPCH (FACH)

Correct Answer:

••

Question 4.3: Some channels are unidirectional (either in UL or in DL but notboth) and some channels are bidirectional.

Identify the transport channel which is bidirectional.

1. BCH

2. PCH

3. FACH

4. RACH

5. DCH

Correct Answer:

10.4. MODULE 4 361

•

Question 4.4: Just before decoding S-CCPCH and reading the paging request,UE must read following physical channel.

Select one answer from the following list:

1. RACH

2. DPCH

3. PICH

4. FACH

5. CPICH

Correct Answer:

•

Question 4.5: For the same Spreading Factor (SF), the UL and DL bit ratesare different.

What is the reason for it?

1. Channel coding rate is different in UL & DL

2. Modulation Scheme is different in UL & DL

3. UL & DL use two different types of Spreading codes

4. The rate difference is due to scrambling code

Correct Answer:

•

Question 4.6: In Cell Search procedure, select the order in which the followingphysical channels are used by UE.

1. P-CPICH

2. P-SCH

3. S-CCPCH

4. P-CCPCH

5. S-SCH

6. E-HICH

7. DPCH

Correct Answer:


1.

2.

3.

4.

10.5. MODULE 5 363

10.5 Module 5

Question 5.1: Which RRM algorithms makes sure that the interference in thecell remains under controllable limits?

Choose 2 answers:

1. Code Allocation

2. BTS Site Manager

3. Admission Control

4. Congestion Control

5. Handover Control

6. Power Control

Correct Answer:

•

•

Question 5.2: In CDMA networks, the UL cell load is measured in referenceto the:

1. Max. UL Power of UE

2. Max. DL power of Node B

3. UL noise floor when the cell is unloaded

4. Power received at the receiver of UE

5. UE receiver’s sensitivity

Correct Answer:

•

Question 5.3: When does the admission control algorithm in UMTS get in-voked?

Name any 3 scenarios.

Correct Answer:

•

•

•


Question 5.4: In RF optimization, we often hear about the code congestionor code blocking.

Which codes are scarce resources and often cause blocking?

1. DL Scrambling Code

2. DL Channelization Code

3. UL Scrambling code

4. UL Channelization Code

Correct Answer:

•

Question 5.5: Which RRC Connected mode states are the power saving “standby” states?

Choose only one answer.

1. CELL DCH

2. CELL FACH

3. CELL PCH only

4. CELL PCH & URA PCH

Correct Answer:

•

Question 5.6: Which statements about Open Loop Power Control (OLPC) aretrue?

Choose only two correct statements.

1. Open Loop Power Control (OLPC) works on PRACH channel.

2. Node B sends feedback so that UE can adjust its power of RACH preambles.

3. OLPC is also used on DL physical channels.

4. OLPC suggests that initial preamble transmit power should be directly pro-portional to the path-loss.

5. OLPC takes place 1500 times in one second.

Correct Answer:

•

10.5. MODULE 5 365

•

Question 5.7: Which statements about Inner Loop & Outer Loop Power Con-trol are true?

Choose 5 correct statements.

1. Inner Loop & Outer Loop PC work in parallel.

2. Inner Loop PC tries to adjust the Tx power in order to reach the desired SIR(Target SIR).

3. Outer loop PC tries to adjust the Target SIR in order to reach the desiredBLER (Target BLER).

4. Inner loop takes place between UE and RNC.

5. Outer loop takes place between Node B and UE.

6. Inner loop takes place between Node B and UE.

7. Outer loop takes place between Node B and RNC.

Correct Answer:

•••••

Question 5.8: In response to a PRACH preamble, if UE received no positiveor negative acquisition indicator (AI ̸= +1 nor -1), UE will send the nextpreamble with higher power. Will the signature used in next preamblebe the same as original?

Choose 1 correct statements.

1. Same signature will be used.

2. A new signature will be randomly selected.

Correct Answer:

•

Question 5.9: Which of the following events will trigger an Inter-frequency orInter-System HO from an UTRAN cell?

Choose only 1 correct option.


1. Event 1A

2. Event 1B

3. Event 1C

4. Event 1D

5. Event 1E

6. Event 1F

Correct Answer:

•

Question 5.10: Which event is used to inform RNC that compressed modemeasurements can be aborted because UE is again in suitable 3G cover-age?


1. Event 1A

2. Event 1B

3. Event 1C

4. Event 1D

5. Event 1E

6. Event 1F

Correct Answer:

•

Question 5.11: Which compressed mode method suits the requirements ofreal-time services like Voice call?


1. SF-halving (SF/2) method

2. Higher Layer Scheduling Method (HLS)

3. Puncturing

Correct Answer:

•

10.6. MODULE 6 367

10.6 Module 6

Question 6.1: Access Stratum Protocol for the signalling between UE andRNC is known as:

Choose 1 answer:

1. NBAP

2. RANAP

3. RRC

4. ATM

5. SS7

6. GTP

Correct Answer:

•

Question 6.2: Access Stratum Protocol for the signalling between RNC andCore Network is known as

Choose 1 answer:

1. NBAP

2. RANAP

3. RRC

4. ATM

5. SS7

6. GTP

Correct Answer:

•

Question 6.3: Scope of Radio Access Bearer (RAB) is to define the Quality ofService between:

Choose 1 answer:

1. UE & Node B

2. UE & RNC

3. UE & Core Network

4. UE & External Server


Correct Answer:

•

Question 6.4: Which protocols can be described as NAS protocols:

Choose 1 answer:

1. NBAP

2. RANAP

3. RRC

4. Mobility Management

5. SS7

6. GTP

Correct Answer:

•

Question 6.5: Which radio protocol is used in IP-based user plane and per-forms IP header compression?

Choose 1 answer:

1. NBAP

2. RANAP

3. RRC

4. Mobility Management

5. PDCP

6. BMC

Correct Answer:

•

Question 6.6: RRC is perhaps the most important protocol in UTRAN.

List at least 4 functions of RRC protocol.

Correct Answer:

1.

2.

3.

4.

10.7. MODULE 7 369

10.7 Module 7

Question 7.1: According to Release 6, the following modulations can be usedfor DL HSDPA transmission.

Choose only 1 answer:

1. QPSK only

2. QPSK & BPSK

3. QPSK & 16QAM

4. QPSK, 16QAM & 64QAM

Correct Answer:

•

Question 7.2: RNC forwards the buffered MAC-d PDUs to Node B in a con-trolled manner. This procedure is called:

1. Transmission Control

2. Data Stream Control

3. Overload Control

4. Flow Control

Correct Answer:

•

Question 7.3: According to the CQI tables ‘A’ and ‘G’, at which CQI, themodulation is switched to a better modulation scheme?

1. 10 & 18

2. 15 & 23

3. 16 & 26

4. 16 & 21

Correct Answer:

•

Question 7.4: From network operations viewpoint, which re-transmissions aremore expensive?

1. MAC layer retransmission


2. RLC layer retransmission

3. RRC layer retransmission

Correct Answer:

•

Question 7.5: Very smart re-transmission techniques are used in HSDPA (&HSUPA):

Name the two H-ARQ schemes defined for HSDPA.

Correct Answer:

•

•

Question 7.6: Match the name of HSDPA-specific physical channel with theirspreading factor.

Name of PhysicalChannel

Spreading Factor

1. HS-DPCCH

2. HS-SCCH

3. HS-PDSCH

i. 16

ii. 256

iii. 128

Table 10.4: Exercise 7.6: Match the SF to the channel name

Correct Answer:

1. HS-DPCCH:

2. HS-SCCH:

3. HS-PDSCH:

Question 7.7: In Rel-6 onwards, why 3GPP recommends using F-DPCH in-stead of DL A-DCH?

Choose only 1 correct answer:

1. F-DPCH uses smart power control.

2. F-DPCH uses 64QAM modulation and improves the bit rates of associatedchannels.

10.7. MODULE 7 371

3. F-DPCH allows multiplexing several HSDPA users on one code and solves codecongestion.

4. F-DPCH has no benefit compared to DL A-DCH.

Correct Answer:

•

Question 7.8: Arrange the following HSDPA UEs according to their peak bitrate capabilities.

1. 10

2. 12

3. 6

4. 14

5. 16

Correct Answer:

1.

2.

3.

4.

5.


10.8 Module 8

Question 8.1: A HSUPA-capable device can use the following combinationsof UL & DL transport channels for sending & receiving user data.

Fill your answers in table 10.5:

Correct Answer:

# UL Transport Channel DL Transport Channel

1.2.3.4.

Table 10.5: Exercise 8.1: Transport channel for carrying DTCH logical channel inUL & DL

Question 8.2: In an HSUPA-capable UE, the user data is processed by threeMAC layers before being delivered to the physical layer.

Choose the correct sequence. (Note! The question is based on the processing on theUE side).

1. MAC-e → MAC-es → MAC-d

2. MAC-d → MAC-es → MAC-e

3. MAC-d → MAC-e → MAC-es

Correct Answer:

1.

Question 8.3: In Table 10.6, match the transport channel with their corre-sponding TTI lengths.

Transport Channel TTI length

1. DCH

2. E-DCH

3. HS-PDSCH

i. 2 ms

ii. 10 to 80 ms

iii. 2 ms & 10 ms

Table 10.6: Exercise 8.3: Match the TTI length to the channel name

Correct Answer:

10.8. MODULE 8 373

1. DCH

2. E-DCH

3. HS-PDSCH

Question 8.4: The set of those cells which are in E-DCH Active Set but notcontrolled by the same Node B as the serving E-DCH serving cell arecalled:

1. Secondary Cells

2. Interfering Cells

3. Non-serving Radio Link Set Cells

4. E-DCH Diversity Cells

Correct Answer:

•

Question 8.5: How many E-DCH users can be present in a cell where onlyone channelization code is reserved for E-RGCH & E-HICH channels?

Hint! There are only 40 Signature sequences defined by 3GPP.

1. 10

2. 20

3. 40

4. 72

Correct Answer:

•

Question 8.6: How many E-DPDCH physical channels must be transmittedfrom a UE to achieve the peak bit rate of 5.76 Mbps?

1. 2

2. 4

3. 6

4. 8

5. 16

Correct Answer:

•


Question 8.7: The Absolute Grant channel carries a Grant value which de-scribes the power of E-DPDCH in reference to:

1. DPCCH Power

2. DPDCH Power

3. HS-DPCCH power

4. E-DPCCH Power

5. Thermal Noise Power

Correct Answer:

•

Question 8.8: In a cell, the E-DCH Relative Granch Channel (E-RGCH) oc-cupies a single 2 ms sub-frame:

Choose one correct statement from the following options:

1. This cell belongs to Serving E-DCH Radio Link Set

2. This cell belongs to Non-serving E-DCH Radio Link Set

3. Cannot be answered because information provided is not enough

4. None of the above

Correct Answer:

•

Question 8.9: In a cell, the E-DCH Relative Granch Channel (E-RGCH) oc-cupies four consecutive sub-frames:


1. This cell belongs to Serving E-DCH Radio Link Set

2. This cell belongs to Non-serving E-DCH Radio Link Set

3. Cannot be answered because information provided is not enough

4. None of the above

Correct Answer:

•

Question 8.10: In a cell, the E-DCH Relative Granch Channel (E-RGCH)occupies a five consecutive sub-frames:


10.8. MODULE 8 375

1. This cell belongs to Serving E-DCH Radio Link Set & E-DCH TTI =2ms.

2. This cell belongs to Non-serving E-DCH Radio Link Set & E-DCH TTI= 10 ms.

3. This cell belongs to Non-serving E-DCH Radio Link Set & but TTIcannot be determined from the information provided.

4. This cell belongs to Serving E-DCH Radio Link Set & but TTI cannot bedetermined from the information provided.

Correct Answer:

•

Question 8.11: In a cell, for E-DCH H-ARQ Indication Channel (E-HICH)Negative Acknowledgement (NACK) is coded as ‘-1’:


1. This cell belongs to Serving E-DCH Radio Link Set.

2. This cell belongs to Non-serving E-DCH Radio Link Set.

3. It cannot be determined from the information provided.

4. None of above.

Correct Answer:

•


10.9 Module 9

Question 9.1: An NAS signalling connection between UE and Core Networkis composed of 2 parts.

Choose the two items from the following list which constitute an NAS signallingConnection.

1. RRC Connection

2. Radio Access Bearer

3. Iu Connection

4. GTP tunnel

5. Active Set

Correct Answer:

••

Question 9.2: RRC Connection Establishment pushes a UE from RRC IDLEmode to RRC Connected Mode. From IDLE Mode, UE can enter the followingstates of connected mode.(Choose 2 answers):

1. CELL PCH

2. CELL DCH

3. CELL FACH

4. URA PCH

Correct Answer:

••

Question 9.3: The procedure of getting a UE registered in SGSN is known as:


1. PS REGISTRATION

2. PS SIGNUP

3. GPRS ATTACH

4. PDP Context Setup

Correct Answer:

10.9. MODULE 9 377

•

Question 9.4: The procedure by which a UE establishes a connection to someexternal packet data network is known as:


1. PS CONNECT

2. IP packet forwarding

3. PDP Context Activation

4. Cell Reselection

5. DIAMETER Routing

Correct Answer:

•

Question 9.5: Which statement is true for HSDPA and HSUPA mobility:

Choose only 2 answers:

1. HSDPA supports Soft Handover but HSUPA does not.

2. Both HSDPA & HSUPA support Soft Handover.

3. HSDPA supports Hard Handover known as Serving Cell Change.

4. HSUPA supports Soft Handover.

5. In HSUPA, when a user moves to a new cell, it performs cell reselection.

Correct Answer:

••

INDEX

16QAM, 21, 207, 214, 231, 232, 2473GPP Releases, 18, 20, 22

R99 to REL-10, 193rd Generation Partnership Project (3GPP),

143rd Generation Partnership Project 2 (3GPP2),

154 Pulse Amplitude Modulation (4PAM, 253,

261, 26264QAM, 21, 22, 207, 214, 230–232, 237

, 20, 39

Absolute grant, 264, 268Acquisition indication channel (AICH), 76,

99, 102, 146Adaptive Modulation and Coding, 211, 247Admission control, 45, 118, 119, 126, 129,

130, 159ALCAP, 172, 174, 304, 323AMPS, 4Authentication Center, 31

Background class, 178Base Station Subsystem, 26BCCH, 84, 85, 87, 99Binary Phase Shift Keying (BPSK), 79, 247,

253, 261, 262, 264

BSS, 27

BTS, 28

Call State Control Function (CSCF), 55

Interrogating - , 56

Proxy - , 56

Serving - , 56

CAMEL, 33

CCCH, 85, 93, 197, 302

Cell search, 109

CELL DCH, 138

Cell DCH, 139

CELL FACH, 138

Cell FACH, 139–143

CELL PCH, 138

Cell PCH, 139, 142, 143

Channel Quality Indicator (CQI), 137, 206,207, 213–216, 224, 226, 228

Channelization code, 72, 73, 88, 98, 117,133, 134, 232, 234, 262, 267, 291,292, 303

compressed mode, 166

Conversational class, 177

Core Network, 26

CTCH, 85

DCCH, 85, 250, 251, 297, 302, 304, 309

378

INDEX 379

DECT, 17

Dedicated physical channel for HSDPA, 134,226, 290

DTCH, 85, 86, 93, 135, 250, 251, 309

Dual-Carrier HSDPA, 212

Dual-Carrier HSUPA, 22, 253

E-DCH Absolute Grant Channel (E-AGCH),264, 268, 277, 292

E-DCH Hybrid-ARQ Indication Channel (E-HICH), 267, 268, 270, 274, 281, 282,292

E-DCH Relative Grant Channel (E-RGCH),266–268, 274, 277, 292

E-DCH Transport Format Combination In-dicator (E-TFCI), 263

EIR, 31

Enhanced Cell FACH, 21

Enhanced Data rates for GSM Evolution (EDGE),9

Event

1A, 158

1B, 159

1C, 160

1E, 163

1F, 162

2A-2F, 164

3A-3D, 165

First Generation (1G), 4

Frame synchronization, 109

Gateway GPRS Support Node, 39, 41, 58

General Packet Radio Service (GPRS), 9

GMSC, 29

GSM, 5

Handover, 28, 118, 154

Hard, 47, 155

Inter-frequency, 156

Inter-System, 156

Intra-frequency, 155

Soft, 48, 155

Softer, 155

High Speed Circuit Switched Data (HSCSD),8

High Speed Downlink Shared Channel, 232High Speed-Physical Downlink Shared Chan-

nel, 228, 229, 232, 292HSDPA, 19–22, 54, 68, 83, 111, 118, 134,

135, 137, 204, 205, 209, 211, 213,221, 224–226, 245–248, 251, 273, 292

HSPA, 295HSUPA, 21, 83, 113, 118, 137, 206, 207, 245,

247, 248, 251, 253, 254, 292

IMEI, 27, 31IMSI, 27IMT-2000, 66Interactive class, 178IP Multimedia Subsystem (IMS), 55IS-95, 6

Macro Diversity Combining, 157MC-CDMA or CDMA2000, 17MDC, 157Medium Access Control (MAC), 86Mobile Station, 26MSISDN, 27

Open Loop Power Control, 93

P-CPICH, 90PCCH, 85, 88Physical Channels, 88Physical layer, 89Pilot bits, 154Primary Synchronization Codes (PSC), 95

Radio Access Bearer, 296Radio Bearer, 296Radio Link, 296Radio Network Temporary Identity

Cell, C-RNTI, 303E-DCH, E-RNTI, 264HS-DSCH, H-RNTI, 231UTRAN, U-RNTI, 303

Radio Resource Management (RRM), 117RRC Connection, 296

380 INDEX

RRM, 118, 121–123, 126, 133, 134, 144, 155,259

Scrambling code, 73, 75, 76, 79, 88, 96, 98,109, 110, 117, 125, 132–134, 289,303, 304, 325

scrambling code, 79Scrambling Code Group, 96Scrambling code group, 76Second Generation (2G), 5Secondary Synchronization Codes (SSC), 96Serving GPRS Support Node, 37, 38, 41, 58serving HS-DSCH cell, 239Shared Control Channel for HSDPA, 225,

227, 230–232, 292SIB, 99SIM, 27Slot synchronization, 109Streaming class, 178Switching Subsystem, 26

TFCI, 106Third generation (3G), 11Traffic Class, 177Transport Format Combination Indicator (TFCI),

107

UE CategoriesE-DCH, 251, 252HS-DSCH, 206, 214

URA PCH, 138, 140, 141UTRA FDD, 17UTRA TDD, 17UTRAN, 82

VLR, 29

WiMAX, 17WRC-92, 66

Zeroth Generation (0G), 4

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