degree programme in computer science and...

DEGREE PROGRAMME IN COMPUTER SCIENCE AND ENGINEERING

Ville Pukari

LTE EVOLUTION TOWARDS 5G

Master’s Thesis

Degree Programme in Computer Science and Engineering

2016

Pukari V. (2016) LTE evolution towards 5G. University of Oulu, Degree

Programme in Computer Science and Engineering. Master’s Thesis, 64p.

ABSTRACT

The development of mobile telecommunication systems is a constant process

and there is a high demand to add new features and further enhance the long

term evolution advanced (LTE-A), also known as 4G. The development of

telecommunication systems will continue with new, 5th

generation (5G) radio

technology. The latest enhancements and added features of the LTE will be

inherited by the 5G. 5G technology is likely to satisfy different wireless

communication user requirements concerning higher data rates, greater

reliability, mobility, energy efficiency and security. This thesis will present the

5G requirements set by 3rd

Generation Partnership Project (3GPP), as well as

the most important enhancements and new features for the LTE which aim to

partially fulfill these requirements. The key feature concepts shall be examined

and their impacts on protocol layers 1 and 2 shall be analyzed briefly.

One of the biggest challenges for mobile telecommunication system is to

minimize power consumption. 3GPP has introduced several methods to address

this issue e.g. Discontinuous Reception (DRX). In this thesis, the power saving

mode (PSM) feature implementation is presented based on the technology of

3GPP Release 12. The basic idea of this feature is to allow the user equipment

(UE) to enter a power saving mode when there is no need for network

communications. This expands total battery life and opens new use cases for

similar LTE based devices, e.g. weather stations. The completed feature was

validated with unit tests. The power consumption of the UE was measured with

and without the PSM and the results were evaluated accordingly. UE can

achieve even lower power consumption levels in PSM, than in normal idle mode

and with appropriate PSM timer values standby time can stretch to several

weeks or even years.

Keywords: 3GPP Release 12, power saving mode, unit testing

Pukari V. (2016) LTE:n evoluutio kohti 5G:tä. Oulun yliopisto, tietotekniikan

tutkinto. Diplomityö, 64s.

TIIVISTELMÄ

Mobiilien telekommunikaatiojärjestelmien kehitys on jatkuva prosessi ja tänä

päivänä on paljon kysyntää lisätä uusia ominaisuuksia ja parannuksia

kehittyneeseen pitkän aikavälin evoluutioon (Long Term Evolution Advanced,

LTE-A), toisinsanoen 4G:hen. Telekommunikaatiojärjestelmien kehitys jatkuu

uuden, viidennen sukupolven (5G) radioteknologialla ja uusimmat parannukset

periytyvät LTE:stä osaksi 5G:tä. 5G-teknologian nähdään täyttävän monen eri

langattoman viestinnän käyttäjäryhmän tarpeet esimerkiksi suurempien

datanopeuksien, paremman luotettavuuden, liikkuvuuden, energiatehokkuuden

ja turvallisuuden suhteen. Tämä työ esittelee 3rd Generation Partnership

Projektin (3GPP) asettamat vaatimukset 5G:lle sekä tärkeimmät LTE-

parannukset ja uudet ominaisuudet, joilla pyritään osittain täyttämään nämä

vaatimukset. Tärkeimpien ominaisuuksien periaatteet selvitetään ja vaikutukset

protokollatasoille 1 ja 2 analysoidaan lyhyesti.

Yksi suurimmista mobiilin tietoliikennejärjestelmäkehityksen haasteista

on virrankulutuksen minimoiminen. 3GPP on esitellyt useita menetelmiä

ongelman ratkaisemiseksi, kuten esimerkiksi epäjatkuvan vastaanoton

(Discontinuous Reception, DRX) mekanismin. Tämä työ esittelee

virransäästötilan (PSM) toteutuksen 3GPP release 12:sta perustuvalla LTE-

mobiililaitteen prototyypillä. Tämän ominaisuuden perusideana on

mahdollistaa mobililaitteen meneminen valmiustilaan silloin kun ei ole

tarpeellista kommunikoida verkon kanssa. Tämä lisää akunkestoa ja avaa uusia

käyttötapauksia, kuten esimerkiksi LTE-sääasemat. Valmis ominaisuus

varmennettiin yksikkötesteillä. Virrankulutus mitattiin virransäästötila päällä

sekä pois päältä ja tulokset arvioitiin. Virrankulutuksen huomattiin laskeavan

virransäästötilassa alemmalle tasolle kuin tilanteessa, jossa verkkoa ei

kuunnella ja sopivilla PSM-ajastinarvoilla valmiustilan kestoa voidaan pidentää

viikoilla tai jopa vuosilla.

Avainsanat: 3GPP Release 12, virransäästötila, yksikkötestaus

TABLE OF CONTENTS

ABSTRACT

TIIVISTELMÄ

TABLE OF CONTENTS

FOREWORD

ABBREVIATIONS

1. INTRODUCTION ................................................................................................ 9 2. STANDARDIZATION ...................................................................................... 10

2.1. 3GPP Organization ................................................................................. 10 2.2. Specification process .............................................................................. 11

2.2.1. Specification numbering ........................................................... 12 2.2.2. Change control .......................................................................... 12

3. EVOLUTIONARY OVERVIEW OF LTE ........................................................ 14 3.1. Releases .................................................................................................. 14

3.1.1. 3GPP Release 8 – Freeze Date 2008 ......................................... 15 3.1.2. 3GPP Release 9 – Freeze Date 2010 ......................................... 15

3.1.3. 3GPP Release 10 – Freeze Date 2011 ....................................... 15 3.1.4. 3GPP Release 11 – Freeze Date 2012 ....................................... 15 3.1.5. 3GPP Release 12 – Freeze Date 2015 ....................................... 16

3.1.6. 3GPP Release 13 - Freeze date 2016 ........................................ 17 3.2. Summary and relevance for future work ................................................ 18

4. E-UTRAN ARCHITECTURE ........................................................................... 19 4.1. Layer 3 – Radio Resource Control (RRC) ............................................. 20 4.2. Layer 2 – Medium Access Control (MAC) ............................................ 21

4.3. Layer 1 – Physical Layer ........................................................................ 22

5. 5G REQUIREMENTS AND LTE EVOLUTION ............................................. 23 5.1. Timeline for 5G ...................................................................................... 25 5.2. Enhanced Mobile Broadband (eMBB) ................................................... 25

5.2.1. Higher cell density (small cells) ................................................ 26 5.2.2. cmWaves and mmWaves .......................................................... 28

5.2.3. Beamforming and massive MIMO ............................................ 29 5.2.4. LTE in unlicensed spectrum ...................................................... 31 5.2.5. Carrier Aggregation enhancements ........................................... 36

5.3. Reliability and latency improvements .................................................... 38 5.3.1. Enhancements for device-to-device (D2D) framework ............ 39

5.3.2. Mission Critical Push To Talk (MCPTT) ................................. 41 5.3.3. Single-cell Point-to-Multipoint (SC-PTM) ............................... 46 5.3.4. V2X ........................................................................................... 47

5.4. Massive Machine Type Communication MMTC .................................. 50

5.4.1. LTE enhancements for low cost MTC ...................................... 50 6. RELEASE 12 – POWER SAVING MODE....................................................... 52

6.1. Concept ................................................................................................... 52

6.2. Impact ..................................................................................................... 52 6.2.1. NAS design ............................................................................... 53 6.2.2. RRC design ............................................................................... 54

6.3. Unit testing ............................................................................................. 54

6.4. Test setup ................................................................................................ 55

6.5. Power saving evaluation ......................................................................... 56 6.6. Future work ............................................................................................ 58

7. CONCLUSIONS ................................................................................................ 59

8. REFERENCES ................................................................................................... 60 9. APPENDICES .................................................................................................... 64

FOREWORD

The work for this thesis was carried out for Mediatek Inc. in Oulu, Finland. I would

like to thank everyone at Mediatek who has provided technical guidance and assisted

with the work along the way. I would like to especially thank my technical

instructors Antti Suronen and Antti Kangas for giving me valuable advice and

support whenever needed. I wish to express my gratitude for giving me an

opportunity to share their knowledge and the best available information. My thanks

also go to my supervisor Prof. Juha Röning and the second inspector Prof. Matti

Latva-Aho. And finally, I would like to thank my beautiful girlfriend Tuuli and my

whole family for being understanding and supportive during this thesis and

throughout my studies.

Oulu, Finland March 29, 2016

Ville Pukari

ABBREVIATIONS

3GPP 3rd

Generation Partnership Project

5G 5th

Generation

ACK Acknowledge

AS Access Stratum

BER Bit-error Ratio

CCA Clear Channel Assessment

CDMA Code Division Multiple Access

CGI Cell Global Identifier

CIoT Cellular Internet of Things

CN Core Network

CR Change Request

CRS Cell-specific Reference Signal

DMRS Demodulation Reference Signal

DMTC Discovery Measurement Timing Configuration

DRS Discovery Reference Signal

DRX Discontinuous Reception

eMBB Enhanced Mobile Broadband

eMBMS Evolved Multimedia Broadcast and Multicast Service

EMM EPS Mobility Management

eNB E-UTRAN Node B

EPS Evolved Packet System

ETSI European Telecommunications Standards Institute

E-UTRAN Enhanced Universal Terrestrial Radio Access Network

ePDCCH Enhanced Physical Downlink Control Channel

FDD Frequency Division Duplex

GCSE Group Communication System Enablers

HARQ Hybrid Automatic Repeat Request

HetNet Heterogeneous Network

Hz Hertz

ICIC Inter-Cell Interface Coordination

IP Internet Protocol

ITS Intelligent Transportation System

ITU International Telecommunications Union

LBT Listen-before-talk

LCID Logical Channel ID

LTE Long Term Evolution

LTE-A Long Term Evolution Advanced

MBSFN Multicast Broadcast Single Frequency Network

MCCH Multicast Control Channel

MCE Multicast Coordination Entity

MeNB Master E-UTRAN Node B

MIMO Multiple-In Multiple-Out

MME Mobility Management Entity

MMTC Massive Machine Type Communications

MTC Machine Type Communications

MCPTT Mission Critical Push To Talk

NACK Negative-Acknowledge

NAS Non-access Stratum

OFDMA Orthogonal Frequency Domain Multiple Access

PER Packet Error Rate

PHR Power Headroom Report

PHY Physical Layer

ProSe Proximity Services

PS Public Safety

PBCH Physical Broadcast Channel

PCDICH Physical Control Format Indicator Channel

PCell Primary Cell

PDCCH Physical Downlink Control Channel

PDN Packet Data Network

PDSCH Physical Downlink Shared Channel

PHICH Physical Hybrid ARQ Indicator Channel

PMCH Physical Multicast Channel

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

PRACH Physical Random Access Channel

PSS Primary Synchronization Signal

QAM Quadrature Amplitude Modulation

QoS Quality of Services

RA Random Access

RAN Radio Access Network

RAT Radio Access Technology

RNTI Radio Network Temporary Identifier

RSU Roadside Unit

RX Reception

SAE System Architecture Evolution

SCell Secondary Cell

SeNB Secondary E-UTRAN Node B

SIP Session Initiation Protocol

SC Service Centre

SNR Signal to Noise Ratio

SRS Sounding Reference Signal

SSS Secondary Synchronization Signal

TCP Transmission Control Protocol

TDD Time Division Duplex

TDMA Time-Division Multiple Access

TSG Technical Specification Groups

TTI Transmission Time Interval

TX Transmission

UDP User Datagram Protocol

UTRAN Universal Terrestrial Radio Access Network

V2I Vehicle-to-infrastructure

V2P Vehicle-to-pedestrian

V2V Vehicle-to-vehicle

V2X Vehicle-to-X

WG Working Group

http://www.3gpp.org/Specification-Groups

1. INTRODUCTION

Mobile devices are more capable than ever and the increased performance goes

hand-in-hand with increase in power usage. Currently the battery industry cannot

keep up with the progress and the embedded system developers have to come up

with more power efficient solutions and algorithms. Creating these power saving

mechanisms is crucial for use cases where long battery life is the main marketing

aspect, such as for Cellular Internet of Things (CIoT) devices, but also in everyday

usage of mobile devices such as smart phones. 3GPP aims to push LTE-enabled

CIoT with its new releases and power efficiency play a significant part in it. These

enhancements are part of 3GPPs plan to move towards a new fifth generation radio

access technology which will be standardized in parallel with LTE standardization

work. Requirements for 5G have already been drafted and the new 5G RAT is

expected to enter consumer markets by 2020.

The goal of this thesis is to present the most important LTE-A features in 5G

scope and implement the power saving mode (PSM) feature on a real LTE hand-held

device prototype, based on 3GPP release 12. Public studies with actual power saving

measurements on a live device using this feature are still uncommon and was the

driving force for this thesis. The feature is validated with unit tests and power saving

measurements are executed in a test environment where a network base station is

emulated with a RF tester. Test results are analyzed and related future work is

drafted.

Chapter 2 is a brief look into the history of mobile telecommunication

standardization and how the LTE standardization work is conducted today by 3GPP.

Chapter 3 presents the 3GPP LTE standard release features and discusses their

relevance in 5G scope. Chapter 4 gives an overview on LTE focusing on the radio

interface. Chapter 5 presents 5G requirements and introduces key features for each

requirement category by analyzing their impacts on current protocol implementation.

Chapter 6 introduces the power saving mode feature design and testing activities, as

well as the results of power saving measurements. Chapter 6.6 is reserved for the

discussion of the results and of the future work. Chapter 7 gives the conclusions of

the thesis.

10

2. STANDARDIZATION

The first commercial cellular network (first generation) based on the Nordisk Mobile

Telephone (NMT) standard was developed in the north European countries in the

70’s. The 2nd generation (2G) cellular network standardization started in 1987 when

Global system for mobile communications (GSM) was founded. GSM made a

transition from analog to digital and improved signal modulation, voice codecs and

security service as compared to first generation analog systems. In order to serve

multiple subscribers, the GSM system adopted time-division multiple access

(TDMA) [1]. The first GSM-functionality phases were specified by the European

Telecommunications Standards Institute (ETSI) which was founded in 1988. These

phases introduced system requirements and items that would evolve GSM towards

3rd

generation (3G).

The first four major releases (Releases 96, 97, 98, and 99) were released during

years 1996-2000 and they cover nearly entire GSM Phase 2+ program [1]. Compared

to previous 2G technology, these releases added new services such as General Packet

Radio Service (GPRS) and Enhanced Data Rates for Global Evolution (EDGE).

Today, mobile telecommunications development continues under the 3rd Generation

Partnership Project (3GPP). 3GPP LTE standardization work is done in co-operation

with global telecommunication standardization organizations such as ETSI and

International Telecommunications Union (ITU) who set requirements for future

3GPP releases.

2.1. 3GPP Organization

The 3rd Generation Partnership Project (3GPP) was founded in 1998 and it is a

global organization whose goal is to produce technical specifications for the global

cellular telecommunications network technologies. Formed from groups of

telecommunication associations, 3GPP aims to develop the 3rd generation (3G)

cellular network standard based on Code Division Multiple Access (CDMA)

technology. The standardization produced radio access technology (RAT) called

Wideband CDMA (WCDMA). 3GPP release 99 was released in 2000 and it was the

first version of the standard also known as Universal Mobile Telecommunication

System (UMTS). As demand for wireless data traffic increased and CDMA

capability reached its limit, 3GPP decided to develop a new standard to respond to

the demand. This standard based on a new access technology, called long term

evolution (LTE). Instead of CDMA, LTE adopted orthogonal frequency division

multiplexing (OFDM) as multiple access technology, in order to efficiently support

wideband transmission. In addition, spectral efficiency was hugely improved with

the use of multiple-input multiple-output (MIMO) techniques. The LTE standard was

finalized in 2010 with release 9 as its final version. The highest theoretical downlink

peak data rate for LTE depends on spatial multiplexing. With spatial multiplexing,

downlink peak data rate can be as high as 300 Mbps and without it 75 Mbps. For the

uplink, peak data rate is 75 Mbps. The International Mobile Telecommunications

(IMT)-Advanced requirements were defined by ITU for the fourth generation (4G)

evolution and 3GPP began to work on LTE enhancements to fulfill these

11

requirements after release 9 [2]. LTE releases from 10 to 12 are called LTE-

Advanced.

2.2. Specification process

The Third-Generation Partnership Project produces standards that specify the

LTE/LTE-Advanced, 3G UTRA and 2G GSM systems. 3GPP member companies

participate in specifications and studies in Working Groups and at the Technical

Specification Group level – see Figure 1 [3].

PCG(Project Coordination Group)

TSG GERAN(GSM EDGE Radio Access

Network)

TSG RAN(Radio Access Network)

TSG SA(Services & System Aspects)

TSG CT(Core Network & Terminals)

WG1Radio Aspects

WG1Radio Layer 1 (L1)

WG1Services

WG1MM/CC/SM (lu)

WG2Protocol Aspects

WG2Radio Layer 2 & Layer 3

RR

WG2Architecture

WG2Interworking with external networks

WG3Terminal Testing

WG3Lub, luc, lur & UTRAN

GSM requirements

WG3Security

WG3MAP/GTP/BCH/SS

WG4Radio performance &

Protocol aspects

WG4Codec

WG4Smart Card Application

Aspects

WG5Mobile Terminal

Conformance Testing

WG5Telecom Management

WG6Mission-critical

application

Figure 1. 3GPP Organization.

There are four Technical Specification Groups (TSG) in 3GPP;

GSM EDGE Radio Access Networks (GERAN)

Radio Access Networks (RAN)

Service & Systems Aspects (SA)

Core Network & Terminals (CT)

12

The main responsibility of TSGs is to approve the documents and coordinate the

overall work. The Working Groups meet regularly and their work is presented for

information, discussion and approval in quarterly TSG Plenary meetings. The TSGs

work on the reports and specifications by following their own Terms of Reference

(TR) for their dedicated responsibility area [3].

The standardization is done by forming releases. Each release can be used to

build a complete system and each release contains added functionality compared to

the previous release. These functionalities are a result of ongoing specification work.

System backwards and forwards compatibility is the main area of concern as well as

ensuring the operation of user equipment. For example backward compatibility

between LTE and LTE-Advanced was a huge concern when starting the work on the

IMT-Advanced requirements. LTE-A terminal had to work in an LTE cell and an

LTE terminal had to work in the LTE-A cell.

2.2.1. Specification numbering

The version number of each 3GPP Technical Specification document and Technical

Report change as the document evolves from the early drafting stages, through

progressively more stable versions, to being brought under change control. Each

version has a numeric value consisting of 3 digits, starting with 1.0.0. The

specifications are stored on 3GPP’s file server as zipped MS-Word files and the

filenames of each specification consists of different fields [4]. The filename structure

and different fields are described in Table 1.

Table 1. 3GPP specification filename structure

SM[-P[-Q]]-V.zip

S = Series number

M= Mantissa

P = Optional part number

Q = Optional sub-part number

V = Version number in hexadecimal

For example, a specification 36.833.6.42 v.13.0.0 would be stored to a file named

36833-6-42-d00, where the series number is 36 for LTE-A, mantissa is 833 for inter-

band carrier aggregation (CA), part number 6 is for non-contiguous, sub-part number

42 for band 42 and version is d00 for Release 13 (in hex), 0 for baseline and last 0

for editorial number.

2.2.2. Change control

A Change Request (CR) defines proposed changes to the specification in detail. A

CR describes why a change is needed on its coversheet and summarizes how the

change is proposed to be made. Any 3GPP member organization can propose a CR

and which is submitted for discussion to the responsible Working Group (WG).

When a Release is under change control, the major field indicates which

13

specification applies to the Release. The second number of version number,

the technical version field, is incremented each time a technical change is made as a

result of the drafting process or as a result of the incorporation of one or more

approved CR. Each time a non-technical correction is made to the specification, the

editorial version number field is incremented by one. An example of an editorial

change could be a correction of typographical errors. The Release status is changed

to frozen, when the specification is considered complete. After the status has been

changed to frozen, new functionalities are not allowed into the same Release. Only

error corrections to severe errors can be done through CR.

14

3. EVOLUTIONARY OVERVIEW OF LTE

After deployment of 3G, the rapid evolution of technology used in

telecommunication systems and user equipments (UE) increased the pressure to

come up with a new radio access technology. There was also a demand for more

spectrum resources to expand the system capabilities and this demand also led to

more competition between an increasing the number of mobile operators. During the

development of LTE, there was also competition between alternative, more

unpopular technologies such as WiMax and CDMA2000 to provide mobile

broadband services. Some of these alternative technologies are still used to this day,

even though 3G and 4G systems along with several other mobile broadband are

deployed with evolved 3G HSPA and 4G LTE-Advanced systems standardized in

3GPP[5]. The Long Term Evolution (LTE) project started in 2004 and its main goal

was to increase the cellular network capabilities by optimizing the radio access

architecture and enhancing the Universal Terrestrial Radio Access Network

(UTRAN). Standardization work is an iterative and cumulative process as new

releases will build on top of earlier releases and might include bug fixes. Preserving

backwards compatibility with earlier releases is the most important task of the

standardization work. Therefore, interpreting earlier releases is always relevant when

developing new features.

3.1. Releases

Following chapters present the 3GPP Releases from 2008 up to 2015 and their most

important features in 5G scope. Many of these relevant features, such as MIMO were

already presented in the first release (Rel-8) of LTE and were enhanced by later

releases. Figure 2 specifies the timeline of releases of notable 3GPP technologies and

specification releases. The main focus will be on releases 12 and 13, as they are the

most recent ones and release 12 is already frozen and ready for full stack system

development. The most recent technology release from 3GPP is LTE-Advanced Pro,

which was approved and released at their meeting in Vancouver in October 2015.

With the completion of Release 13, LTE-Advanced Pro will add several

functionalities to better address new markets, and improve system efficiently.

2008 20162009 2010 2011 2012 2013 2014 2015

2008 - 2010

Release 9

2009 - 2011

Release 10

2010 - 2013

Release 11

2011 - 2015

Release 12

LTE

LTE-Advanced (4G)

LTE-Advanced Pro

2012 - 2016

Release 13 (open)

2008Release 8

Figure 2. Timeline of 3GPP specification releases.

15

3.1.1. 3GPP Release 8 – Freeze Date 2008

LTE was introduced for the first time, improving data rates with a completely new

radio interface and core network based totally on internet protocol (IP). Unlike GSM

base station deployments, the LTE uses flat radio network architecture, where the

functionalities were distributed among the base stations (eNBs). Key features were

the OFDMA downlink, multiple input multiple output (MIMO) and enhanced

package core (EPC)[6]. The bandwidth allocation depends on the amount of

spectrum acquired by the LTE network operators in the target country. With use of

spatial multiplexing the peak data rate increased to 300Mbit/s for downlink and

75Mbit/s for uplink. Also, with this release the latency for setup and handover was

decreased down to 10ms and support for variable bandwidths was added.


Release 9 can be seen as evolution from LTE to LTE-Advanced. Release 9

introduced changes to the network architecture and several new service features [7].

The LTE femtocells were introduced for the first time in the form of the Home

eNodeB (HeNB). Self organizing network (SON) features, e.g. optimization of the

random access channel were added along side with Evolved Multimedia Broadcast

and Multicast Service (eMBMS). The SON features focus on improving the network

configurations dynamically e.g. by configuring S1 and X2 interfaces according to

channel measurements. Release 9 also added location services (LCS) to enable the

use of location based applications.


Release 10 improved the capacity and throughput of the LTE system by increasing

peak data rates for downlink up to 3Gbps and 1.5Gbps for the uplink.l. TR 36.912 [8]

is 3GPP's submission to the ITU for LTE-Advanced and is a useful summary of the

new features of the system [8]. The most notable features were the introduction of

carrier aggregation (CA), 8x8 DL and 4x4 UL MIMO configurations and

Heterogeneous Networks (HetNet). With CA, the total bandwidth was increased up

to 100 MHz by allowing connection up to five different carriers. Release 10 also

improved the system performance on the cell edges by introducing enhanced Inter-

Cell Interface Coordination (eICIC).


Release 11 added enhancements to Carrier Aggregation, MIMO, relay nodes, Wi-Fi

integration and eICIC [9]. It also introduced new frequency bands, Enhanced

Physical Downlink Control Channel (ePDCCH) and a new feature called

Coordinated Multi-Point (CoMP) to enable beamforming and scheduling of multiple

carriers. EPDCCH added an ability to support increased downlink capacity, inter-cell

interference coordination and beamforming.

16


The rapid increase in mobile data usage set high capacity requirements for release 12

along with demand for high quality user experience and support of new applications.

Key features of release 12 include [10]:

New antenna techniques and advanced receivers to maximize the system capacity

New features to improve the support of HetNets such as dual connectivity and

small cell on/off feature

Intra-band non-contiguous carrier aggregation

Enhancing interworking between LTE and WiFi

256 Quadrature Amplitude Modulation (QAM) for DL

Machine-Type Communication (MTC) features to allow devices to benefit from

LTE services; new UE categories, support for low data rates by means of single

receive antenna, narrowband data channel and half duplex operation.

3.1.5.1. Release 12 UE Capabilities

As part of Release 12 finalization, several additional UE categories were introduced,

along with the new category 0 with lower networking capacity for MTC. To address

the need for high performance capable UE categories, categories 13-16 were

described with higher peak data rates and support for more advanced modulation and

MIMO procedures. These new categories are indicated with separate ue-categoryDL

and ue-categoryUL fields [10]. All supported UL/DL-category combinations and

maximum number of DL-SCH/UL-SCH transport block bits received within a

Transmission Time Interval (TTI) are listed in 3GPP TS36.306 – see Table 2 [11].

17

Table 2. Supported DL/UL Category combinations.

UE DL Category UE UL

Category

Maximum number

of DL-SCH

transport block bits

received within a

TTI

Maximum number

of UL-SCH

transport block bits

transmitted within a

TTI

Total layer 2

buffer size

[bytes]

DL Category 0 UL Category 0 1000 1000 20 000

DL Category 6 UL Category 5 301504 75376 3 500 000











DL Category 15 UL Category 3 749856-798800 1 51024 8 000 000




DL Category 16 UL Category 3 978960 -1051360 1 51024 10 000 000




3.1.6. 3GPP Release 13 - Freeze date 2016

The newest 3GPP Release will be frozen in March 2016 and it will be the first

release for LTE-Advanced Pro. Release 13 will bring various new features and

enhancements to already existing features, introduced in previous releases. Some of

expected Release 13 key features are:

Public safety features such as D2D and Proximity-Services (ProSe)

Further enhancing MTC features and indoor positioning

Completing CA enhancements

Small cell dual-connectivity and interworking with Wi-Fi

Licensed Assisted Access (LAA) at 5GHz

Beamforming and massive MIMO

Single cell-point-to-multipoint (SC-PTM)

Latency reduction

1 The required value shall be determined by UE based on its capabilities (i.e. CA band combination,

MIMO, Modulation scheme).

18

3.2. Summary and relevance for future work

Figure 3 shows a summary of main features in releases from 8 to 12. Standardization

work for release 13 and beyond will build on top of already existing mechanisms or

further enhance them e.g. by developing new aggregation methods. Target is to

achieve higher data transfer rates for the whole network as well as for single UE.

One good example is the beamforming mechanism which was already introduced in

release 8 but only for horizontal axis and one layer. In release 9 this functionality

was expanded to support two layers and release 13 will add support for vertical axis

as well - see chapter 5.2.3.

REL-82008

- First LTE release

- All IP core

network, the System

Architecture

Evolution (SAE).

REL-92010

- LTE HeNB

- Self organizing

network (SON)

- Location

Services (LCS)

- eMBMS support

- Multi-standard

BS

REL-102011

- ”LTE-A”, 3Gb/s

DL/ 1.5 Gb/s UL

- Carrier

aggregation

- Enhanced MIMO

- Relay nodes

(HetNet)

- Enhanced eICIC

REL-112013

- Enhancements

for MIMO, eICIC

and relay nodes

- CoMP

- New frequency

bands

- Advanced

receivers

REL-122015

- Small cell

enhancements

- Intra-band non-

contiguous carrier

aggragation

- Multi-antenna

enhancements

- Device-to-device

-Machine-Type

Communications

(MTC)

Figure 3. Main features of 3GPP releases 8-12 in 5G scope.

19

4. E-UTRAN ARCHITECTURE

The E-UTRAN is the first point of entry for a UE to the LTE network. The E-

UTRAN protocols cover the communication process between the UE and the

network over the wireless link. E-UTRAN is responsible for the

transmission/reception (TX/RX) of radio signals to and from a given UE and the

associated digital signal processing. E-UTRAN also includes the medium access

control mechanisms by which multiple UEs share the common wireless channel.

Other functions of E-UTRAN are to ensure link level reliability, segmentation, and

reassembly of higher-layer Protocol Data Units (PDUs) and IP header compression

[12]. These protocols between the UE and the E-UTRAN are collectively referred to

as Access Stratum (AS) protocols. The enhanced Node B (eNodeB or eNB) is the

single logical node in the E-UTRAN. The job of the eNB is to implement the AS

protocols.

Figure 4. LTE-Advanced E-UTRAN architecture.

20

Figure 4 presents the architecture of E-UTRAN for LTE-A. The air interface towards

the UE is provided by the base station, which is the eNB in the E-UTRAN

architecture. The interface connecting the eNBs is called the X2 interface and each

eNB serve one or multiple E-UTRAN cells [13].

The user plane side consists of the Radio Link Control (RLC) protocol, the

Packet Data Convergence Protocol (PDCP), the Medium Access Control (MAC)

protocol and the Physical Layer (PHY) [13]. The control plane consists of the same

four sub-layers with addition of the Non-Access Stratum layer (NAS) and the radio

resource control (RRC) protocol. The information from the user plane and control

plane is processed by PDCP, RLC and the MAC, before being passed to the physical

layer for transmission.

NAS

RRC

PDCP

RLC

MAC

PHY

RRC

PDCP

RLC

MAC

PHY

S1-AP

SCTP

IP

L2

PHY

S1-AP

SCTP

IP

L2

PHY

NAS

LTE-Uu S1-MME

UE eNode B MME

RELAY

Figure 5. Evolved Packet System (EPS) control plane for U-EUTRAN access.

Figure 5 gives a graphical overview of control plane between the UE and MME. The

MME and the UE are connected an interface created by the NAS layer, through

which the NAS can handle its main responsibilities, which are authentication, UE

mobility management and bearer management between the UE and MME.

4.1. Layer 3 – Radio Resource Control (RRC)

The Radio Resource Control is responsible for the control of information exchange

between the UE and E-UTRAN [13]. RRC is in charge of Quality of Service (QoS)

management, NAS direct messaging, information broadcasting, paging, connection

handling and UE measurement reporting. Information is passed down from E-

21

UTRAN to UE through data blocks known as the Master Information Block (MIB),

and number of System Information Blocks (SIBs). There can be up to 16 different

system information blocks, each containing information about network capabilities,

but MIB and SIB1 are the most important since these blocks contain system frame

number (SFN), system bandwidth, scheduling information and cell access related

information [14].

The RRC connection handling is done with only two states: RRC_IDLE and

RRC_CONNECTED. In RRC_IDLE state, RRC performs cell (re)selection and

neighbor cell measurements and acquires the system information [14]. It also

monitors a paging channel for incoming calls and possible public warning system

(such as ETWS and CMAS) messages. When the UE is in RRC_CONNECTED

state, the UE performs bi-direction transferring of data in uplink and downlink, e.g.,

for ongoing call or internet access. At its lower layers UE may be configured with

UE-specific discontinuous Reception (DRX) [14]. System information changes are

informed through a paging message, which needs to be monitored also while in

RRC_CONNECTED state. In connected state, RRC performs all necessary

procedures requested or triggered by network activities. These procedures include

connection management, configuration management, paging control, security

management, broadcasting to multiple bearers, measurement control/ reporting,

mobility procedures, handovers and inter radio technology operations.

4.2. Layer 2 – Medium Access Control (MAC)

The MAC sub-layer is responsible for handling uplink/downlink scheduling, data

transferring, mapping of logical channels to transport channels, hybrid automatic

repeat request (HARQ) retransmissions and random access procedure. In case carrier

aggregation is configured, MAC will take care of multiplexing/demultiplexing data

across the configured component carriers. A MAC PDU, illustrated in Figure 6 [15],

consists of a MAC header, zero or more Service Data Units (SDU), zero or more

MAC Control Elements (CE) and optional padding. The MAC header consists of one

or more subheaders which have six header fields [15]. The different fields contain

important information about the PDU such as the logical channel ID and the length

of corresponding MAC SDU. MAC CEs are always before the SDUs and the

optional PDU padding and they hold control information for different MAC

processes. For example, the power headroom MAC CE has a 6 bit PH field that

indicates the power headroom level.

22

MAC Control

element 1...

R/R/E/LCID

sub-header

MAC header

MAC payload

R/R/E/LCID

sub-header

R/R/E/LCID/F/L

sub-header

R/R/E/LCID/F/L

sub-header... R/R/E/LCID/F/L

sub-header

R/R/E/LCID padding

sub-header

MAC Control

element 2MAC SDU MAC SDU

Padding

(opt)

Figure 6. Example of MAC PDU.

4.3. Layer 1 – Physical Layer

The physical layer offers transport channels for higher layers. Different transport

channels are described in Table 3 [16]. The transport channel is defined by how and

for which purpose the information is transferred over the radio interface. As

mentioned in previous chapter, MAC provides different logical channels for the

Radio Link Control (RLC). The main tasks for the physical layer are error detection

on the transport channels, mapping of the coded transport channel onto physical

channels, forward error encoding/decoding of the transport channel, rate matching of

the coded transport channel to physical channels, Hybrid Automatic Repeat Request

(HARQ) soft-combining, power weighting of physical channels, modulation and

demodulation of physical channels, frequency and time synchronization, radio

characteristics measurements, MIMO antenna processing, TX diversity,

beamforming and RF processing [16].

Table 3. Physical layer transport channels

Uplink channels

PUSCH Physical Uplink Shared Channel – UL user data

PUCCH Physical Uplink Control Channel – UL control

PRACH Physical Random Access Channel – Initial synchronization between

UE and eNB

Downlink channels

PDSCH Physical Downlink Shared Channel – DL user data

PDCCH Physical Downlink Control Channel – DL control

PHICH Physical Hybrid ARQ Indicator Channel – HARQ status reporting

PMCH Physical Multicast Channel – Multicast information

PBCH Physical Broadcast Channel – System information for UE requiring

access to the network

PCFICH Physical Control Format Indicator Channel – Information for UE to

decode PDSCH

23

5. 5G REQUIREMENTS AND LTE EVOLUTION

The use of LTE-A networks has increased excessively in recent years and demand of

new application services is constantly growing. The evolution of mobile broadband

will continue with new, fifth generation (5G) radio access technology. 5G will inherit

all that has been added to LTE-A and further improve upon new capability

requirements. The major goal for 5G is to create a unified platform which is scalable

for new applications, services and use cases. This will open new deployment and

business opportunities, but also require development of a new scalable and adaptable

air interface for all spectrum types and various services. 5G aims to address the

expanded connectivity and capacity needs of the next decade and beyond. The

demanded new services and use cases, such as vehicle communication can also be

provided on top of LTE-A networks, which will be a high performance and yet more

cost-effective solution. Evolved LTE-A will pave the way towards 5G era and

provide networking framework to fulfill the needs of new markets, such as Cellular

Internet of Things (CIoT).

International Telecommunications Union (ITU) IMT-2020 defines 3 types of use

case scenarios for 5G [17]. These are:

1. Enhanced Mobile Broadband (eMBB) - e.g. Smart phones

2. Ultra-reliable and low latency communications - e.g. for self-driving car

3. Massive MTC -e.g. for massive sensor nodes

Figure 7. 5G Applications and requirements.

Figure 7 shows how these use case scenarios set different requirements for the

network and the network must adapt to these requirements. The new radio access

network (RAN) has to be very versatile to support all these use cases. The target for

EMBB is to improve peak data rates by 10-fold and increase user-experienced

throughput by 100-fold (1Gbps) everywhere. In addition to providing higher data

24

rates, 5G also has to serve a massive number of devices simultaneously and provide

user-plane latency of less than 1ms over the RAN. However, depending on the use

case, only some- but not all- of these requirements need to be met simultaneously.

Table 4 shows the new requirements in numbers compared to earlier key

performance indicator values [18] and Figure 8 compares them with current LTE-A

capabilities [19]. As can be seen, LTE enhancements alone cannot fulfill all

requirements and a new RAT is needed for 5G. The companies participating in the

standardization progress have suggested that one of the best solution candidates

would be to slice the RAN into multiple serving segments. Each service segment

would have a dedicated carrier(s), which would operate independently of other

services [20]. This ensures service reliability which is highly important especially for

the low latency communications.

Table 4. IMT-2020 requirements in numbers

Key performance

Indicators

LTE performance ITU value for 5G Difference

Peak data rate 1 Gbps 20 Gbps ~20x

User experienced

data rate

0.01 Gbps 0.1-1Gbps 10-100x

Traffic density 0.1 Tbps/Km² 10 Tbps/Km² 100x

Connection density 60 million/Km² 100 million/Km² 1,6x

Latency 60 ms (over the

air)

1 ms (over the air) 60x

Mobility 300 Km/h 500 Km/h 1,6x

Energy efficiency 1 (network side) 100x (network side) 100x

Spectral efficiency 3-5x 1 3-5x

Figure 8. ITU top level requirements for 5G.

25

5.1. Timeline for 5G

The commercial 5G era is expected to start by 2020. Before that, there will be

numerous 3GPP TSG meetings and workshops to specify requirements of the 5G

network. 3GPP and ITU have made preliminary timelines for these events and they

are shown in Figure 9[21].

2015

A M J J A S O N D

2016

J F M A M J J A S O N D

2017


2018


2019


2020

J F M A M J

#22 WRC-15 #23 #24 #25 #26 #27

Wo

rksh

op

#28 #29 #30 #31 WRC-19 #32 #33 #34

#68 #70 #71

Wo

rksh

op

#72

RA

N w

ork

sho

p

#69

Technology trendsM.2320

IMT Feasibilityabove 6GHz

Vision of IMTbeyond 2020

Rel-13

Rel-15

Rel-16

Technical performance and requirements

Evaluation criteria and method

Requirements, evaluation criteria and submission templates

New spectrum below 6GHz unlocked Spectrum above 6GHz unlocked

#73 #74 #75 #76 #77 #78 #79 #80 #81 #82 #83 #84 #85 #86 #87 #88

Proposals IMT-2020

Evaluation

IMT-2020 Specifications

Outcome and decision

Rel-14

Figure 9. ITU and 3GPP timelines for 5G standardization.

ITU timeline for IMT-2020 calls for initial submissions of IMT-2020 technology by

Work Package 5D meeting #32 (June 2019) and final specification submission by

meeting #36 (October 2020) [22]. 3GPP is planning the 5G standardization to have

two phases for the normative work. Phase 1 is to be completed by 2018 and shall

include LTE-A Pro releases 14 and 15 to address the most demanded commercial

needs such as eMBB. Phase 2 consists of finalization of Rel-16 and it is expected to

be complete by the end of 2019 for the IMT 2020 specification.

5.2. Enhanced Mobile Broadband (eMBB)

The rapid increase of broadband usage and demand for higher data rates forces 3GPP

to seek new techniques to fulfill these needs. eMBB will enable new services and

markets, such as broadcasting ultra-high definition content over air. 5G will most

likely be based on very dense network deployment of small cells, using current radio

access networks. In addition to current cellular access bands below 6GHz, 5G is

expected to exploit the spectrum range between 6Hz and 100GHz. In order to do so,

a new radio access for centimeter and millimeter sized radio waves is needed.

26

5.2.1. Higher cell density (small cells)

Development of multi-operator small cells is important as it will have a significant

role in addressing future high capacity demand for LTE- and upcoming 5G networks.

Densification of the network by using smaller cells can enable a more flexible system

where the network is optimized for cell sizes below 200m. Small cells can cover a

number of different options from relatively high power outdoor cells to indoor pico

cells and very low power femto cells. Higher user rata rates and QoS are achieved

due to improved coverage and higher data throughput. In addition to flexibility,

another major advantage of small cells is easy deployment as the small cell products

have become more compact and therefore it is easier to optimize the cell

performance and get the best end-user experience by selecting optimal placement for

the access point.

5.2.1.1. Concept

Small cells have been supported by the LTE specifications since the beginning of

LTE with Release 8. This functionality was enabled using frequency-domain Inter-

Cell Interference Coordination (ICIC) which was further enhanced by adding time-

domain ICIC in Release 10. This additional time-domain ICIC enabled co-channel

deployment of small cells by using so called almost blank subframes for semi-static

resource partitioning. The 3GPP started the work for the small cell-related

improvements following the workshop held in June 2012 on LTE-Advanced

evolution, which concluded the need for evolution for the small cell operation. The

scenario of importance was especially the use of small cells with a dedicated small

cell frequency, as shown in Figure 10 (first scenario 1A).

Figure 10. Dual connectivity scenarios.

27

For this type of co-channel scenario, Release 11 specified solutions such as

Coordinated Multi-Point operation (CoMP) and further enhanced ICIC. Dual

connectivity or inter-site carrier aggregation was introduced in Release 12 and it was

intended to enable UE to be connected to both macro eNB and small eNB at the

same time. With this method, it is possible to aggregate maximum data rate and

maintain connection by using macro cell as primary cell even if the small cell layer

does not offer enough coverage [23]. In dual connectivity, UE is configured with one

master eNB (MeNB) and at least one secondary eNB (SeNB). Since there can be

multiple possible cells to be connected to, different cells are organized into master

cell group (MCG) and secondary cell group (SCG).

5.2.1.2. Layer 2 impact

Dual connectivity requires changes to control- and user plane architectures. The split

between control plane and user plane architectures can reduce handover failure rate

and avoid frequent handovers. S1-MME connection is closed by the MeNB only

when it is necessary to reduce radio resource management- (RRM) and signaling

complexity. The purpose of the new control plane architecture is to reduce signaling

overhead towards the core network in multiple SeNB handovers and configuration

changes [24]. There is no RRC entity in the SeNB, therefore RRC configurations are

only transmitted to the MeNB as a RRC container. The connection to MeNB is

always maintained by the UE as long as it is under coverage of MeNB.

Figure 11. User plane traffic split options.

28

There are a couple of options for division of the user plane architecture. There can be

traffic split at the MeNB or service gateway (S-GW). S1-U connection between the

UE and S-GW can be established by both eNBs. 3GPP Release 12 describes user

plane architecture of bearer split at the S-GW and PDCP PDUs level split at the

MeNB. If the split takes place at the MeNB, and only one S1-U interface via the

MeNB is needed, both options are possible. For the bearer level split, all user data is

routed to UE via the SeNB and the UE (see Figure 11 1A). In packet level split the

data can be routed to UE via the MeNB or SeNB (Figure 11 1B). It is more difficult

to make this split due to non-ideal backhaul and that MAC PDUs are generated in

real time according to radio conditions within current TTI.


Dual connectivity does not allow sending PUCCH exclusively on the PCell, but

instead it demands sending PUCCH also to primary SCell (PSCell). PSCell has a

similar role as PCell and UE does radio link monitoring also for PSCell to avoid

excess UL interference. If there is a radio link failure on PSCell, UE continues

measuring SeNB, but terminates RX and TX procedures on the SeNB and indicates

radio link failure for the MeNB.

Scheduling decisions in the SeNB and MeNB cannot be immediately

coordinated and might lead to a situation where combined UL grants from SeNB and

MeNB exceed transmission power resources of the UE. To avoid this situation, UE

configures MCG and SCG with Pcmax information in the power headroom report

(PHR). Type 2 PH of PSCell also needs to be configured, because there is additional

PUCCH in the SeNB. Type 2 PH includes information about power consumed by the

PUCCH and PUSCH. Different PHR parameters can be configured for MeNB and

SeNB to better suit radio conditions and path loss variation characteristics for each

cell [25].

In case of random access procedures, both contention-based and non-

contention-based procedures are supported in the SCG. A contention-base Random

Access (RA) procedure might be ongoing when an eNB initiates non-contention-

based RA procedure. Before initiation of non-synchronized physical layer random

access procedure, Layer 1 shall receive PRACH configuration and frequency

position from the higher layers. In Release 12 dual connectivity, parallel RA

procedure is only supported in case preamble transmissions do not collide.

5.2.2. cmWaves and mmWaves

Currently cellular networks allocate frequencies below 6GHz since low frequencies

have better wide area coverage due to lower path loss. 5G is expected to exploit the

large portion of spectrum between 6GHz and 100GHz. The spectrum between 6 and

100GHz can be split into two parts, centimeter and millimeter waves, based on

frequency. Frequencies below 30GHz are seen as centimeter-sized radio waves

(cmWaves) and frequencies greater than 30GHz are seen as millimeter-sized radio

waves (mmWave). Recent developments in radio technology enable the use of

mmWaves in small form-factor devices such as smart phones. Using mmWaves

unlocks a large amount of spectrum from 30GHz up to 100GHz. This is essential for

very high data rates and capacity which both are key requirements for eMBB.

29

Challenges of mmWaves are higher path-loss, increased RF unit cost and need for

robust beam search and tracking. These challenges can be tackled by developing

smart beam search, tracking and beamforming. LTE-A must support adapting

mmWave frequencies for all potential applications such as virtual reality services.

Deployment of variety of innovative antenna arrays is needed as well as duplexing,

modulation, and multiple access schemes.

5.2.2.1. Concept

Key elements of future 5G mmWave systems are antenna array, printed circuit board

(PCB), mmWave front-end (MFE) and the radio frequency integrated circuit (RFIC).

The most popular design choice for antenna array implementation would be to patch

antenna arrays on PCB, because they would be easy to manufacture at low cost.

Unfortunately, this type of PCBs are still under designing phase and not yet

available. Another alternative is to use antenna array packages where the antennas

are embedded on the package that encapsulates the MFE chip. RFICs are small and

can be dynamically reconfigured, therefore reducing the power consumption and

system cost. The higher path losses of mmWaves can be overcome with use of

antenna arrays with multiple elements and by amplifying the TX signals[26].

MmWaves enable using more antenna elements with the same form factor. The most

straightforward way to increase the transmission power in order to compensate for

path losses would be to use more powerful analog RF amplifiers. However, this

would increase the unit cost significantly and a more cost-efficient way is to use

more advanced digital signal processing methods.


Impacts will mostly affect the physical layer as the connectivity has to be expanded

up and beyond 6GHz. Extremely compact Radio Frequency Integrated Circuit

(RFIC) solutions with complete transmitter and receiver chains are wanted to meet

the size, cost and power consumption needs of future generations of mmWave radio

products. MmWave bands can already be utilized and the semiconductors are under

development to provide necessary performance. Combining cm- and mmWaves with

MIMO and beamforming means that the physical layer has to change from cell

specific measurements to radio beam-specific measurements and configurations.

5.2.3. Beamforming and massive MIMO

Beamforming and massive MIMO will improve spectral efficiency, which translates

to higher data rates and overall network capacity, which both are key requirements

for the eMBB. The basic idea of beamforming is to direct radio signals straight

towards the UEs connected to the cell and focus radio energy to improve

performance and energy efficiency. As a result, signal strength is increased and

interference is reduced. MIMO provides the ability to transmit and receive multiple

spatial streams, which multiply the throughput (and therefore spectral efficiency)

delivered in the same part of spectrum. MIMO techniques have been part of LTE

30

from the beginning and enhancements have been introduced with every standard

release.

5.2.3.1. Concept

mmWave frequencies rely on antenna arrays and analog beamforming to achieve the

desired cell radius of 100m. The WiGig/11ad standard has proven beamforming

effective in a short-range and low-mobility environment. However, 5G will require a

new design to support beamforming in a mobility environment with much larger

coverage. Adding vertical dimension for beamforming and expanding antenna port

support from 8 to 64 at the eNB will be necessary when considering future

frequencies above 3GHz. With beamforming, the performance is significantly gained

as the transmission energy can be focused towards the user. 3GPP RAN1 is currently

studying how and with which parameter combinations the two-dimensional antenna

arrays can improve the LTE spectral efficiency.

Currently, 3GPP has considered beamforming only by using the horizontal

antenna arrays in the azimuth dimension. However the vertical antenna arrays would

bring considerable performance potential especially in dense urban areas as

presented in Figure 12. With support for vertical beamforming it is possible to direct

a beam to a certain floor of a building. From technology perspective, vertical

sectorization that may exploit the elevation domain is needed.

Figure 12. Beamforming and MIMO.

UE-specific elevation beamforming, on the other hand, may be used to point the

vertical antenna pattern in the direction of the UE, while spraying less interference.

In addition, if a 2D array is used, the UE-specific elevation beamforming can be

combined with UE-specific beamforming. The first phase objective for RAN1 is to

find most ideal antenna configuration by studying and performing multiple

measurements with different antenna element spacing and varying the number of

antennas per transceiver unit. Multi-user MIMO (MU-MIMO) can be applied in

31

addition to single-user MIMO (SU-MIMO) in both azimuth and elevation

dimensions.

5.2.3.2. Impacts

Expanding number of currently supported antenna ports from 8 to 64 will have an

impact on the physical layer as the Channel State Information (CSI) feedback must

correspond to the number of antenna ports. The eNB adapts its antenna array

parameters (signal phase and amplitude) according to received CSI feedback from

the UE. Adding support for vertical beamforming can be implemented by

configuring a subset of antenna ports for each vertical sector.

Another approach, called reciprocity-based approach does not use CSI

feedback but instead uses UL transmission measurement data to control the antenna

array parameters. With this approach, the number of antenna ports is not fixed.

Therefore the antenna configuration can for example consists of only one RX

antenna and multiple TX antennas. The challenge with this approach is estimating

other transmission parameters as the RF chain pair at the eNB end might not

correspond to the UE antenna configuration.

5.2.4. LTE in unlicensed spectrum

To meet rapidly growing traffic demand, the use of unlicensed spectrum is becoming

a more important technological advancement. In licensed spectrum, operators have

exclusive licenses for certain frequency ranges and they can control the interference

situations in the network. This is essential for quality of service (QoS) and for

performance. Unlicensed spectrum is “free for all” and therefore it is much more

unpredictable, as there can be uncoordinated interference situations. Licensed-

Assisted Access (LAA) aims to handle these interference situations and offers the

full benefits of unlicensed spectrum for the operators. In addition to a more usable

spectrum, these benefits include better operational cost and better user experience.

5.2.4.1. Concept

The basic principle of LAA is presented in Figure 13. LAA will target 5GHz band

and use small cells; e.g. in shopping malls, office buildings, universities and similar

places where there is lots of network traffic. The first phase for the LAA is to support

downlink traffic and later extend support to handle uplink traffic [27]. Concept of

LAA in Release 13 is as follows; the PCell will operate in licensed spectrum in order

to deliver critical information and guarantee QoS, while the SCell will potentially

increase data rate by operating in unlicensed spectrum. Main focus is to ensure

coexistence with Wi-Fi. Luckily there is a simple mechanism to enable this called

Clear Channel Assessment (CCA). CCA means that LAA node tries to find an

unlicensed spectrum with least users by applying Listen-Before-Talk (LBT)

mechanism, included in release 13. In LBT, the transmitter ensures there are no

ongoing transmissions on the carrier frequency by measuring received energy from

the channel. Europe and Japan prohibit continuous transmission and impose limits on

32

the maximum duration of a transmission burst in the unlicensed spectrum [28].

Hence, discontinuous transmission with limited maximum transmission duration is a

required functionality for LAA. Next sub-chapters will present the impact that the

LAA will have on the UE side. The impact of regulatory requirements of unlicensed

spectrum deployment will be ignored in this thesis.

Figure 13. LAA Carrier Aggregation Framework.


There are several requirements for LAA which have an impact on layer 1. This

chapter describes those requirements and recommended solutions.

Listen-before-talk

As mentioned earlier, the coexistence of LAA with other radio technologies requires

LBT mechanism to be applied. LBT procedures require the node to perform a CCA

by using energy detection to determine if the channel is being used. It is

recommended that LAA supports a mechanism to adaptively lower the energy

detection threshold because different regions have different energy threshold

requirements and this ensures co-existence with other RATs including Wi-Fi which

has energy detection threshold of -62dBm [27]. The channel is considered as used if

the received energy is greater than the threshold value. Another thing to take into

considerations is that LAA for nodes belonging to same operator can lead to

asynchronous transmission on the channel.

Discontinuous transmission

As mentioned earlier, one of the required functionalities for LAA is discontinuous

transmission. This will have an impact on LTE functionalities that can be supported

by signaling them at the beginning of an LAA DL transmission. One example would

be channel reservation, where LAA node gains channel access via successful LBT

operation. For time and frequency synchronization of DL transmission burst in LAA,

33

it is recommended to use Discovery Reference Signals (DRS) for RRM

measurements.

Channel State Information (CSI) measurements and reporting

Due to LBT mechanism there can be silent periods when the serving cell is not

transmitting and during those periods, the interference measurements are not valid.

To make sure all interface measurements are valid, UE should not allow interference

measurements for CSI when the serving cell is not transmitting.

RRM measurements and reporting

LAA support will require changes to Discovery Reference Signal (DRS) procedures

introduced in release 12. If UE is configured with discovery measurement timing

configuration (DMTC), UE can expect DRS to occur in periods of 40, 80 or 160 ms.

Since short control transmission without LBT is not allowed in some regions, DRS

design should apply DRS transmission to be transmitted with LBT. LBT limits DRS

transmissions so that UE cannot expect periodically transmitted DRS in a particular

time slot. Therefore, a method to detect DRS presence is needed to only include

successfully detected DRS signals into RRM measurements and guarantee the

quality of measurements.

Current DRS design does not ensure DRS transmission to be contiguous in

time and there can be periods when some OFDM symbols are not transmitted and the

channel seems silent. Other nodes listening to the same channel could potentially

interpret from these periods that channel is free. This can lead to transmission

collisions between coexisting nodes and the ongoing DRS transmissions. This can be

avoided by using contiguous OFDMA symbols to form DRS signals. Another

unwanted scenario is when there are two operators on the same carrier and UE is

receiving signals from two different cells. Therefore DRS signal should also indicate

the operator to differentiate multiple DRS signals from one another.

DL transmissions

Currently downlink transmission schemes for PDSCH base their demodulation on

either Cell-specific Reference Signals (CRS) or Demodulation Reference Signal

(DMRS). If CRS is present in an LAA SCell, UE cannot assume CRS signals to be

present in every subframe, therefore the demodulation and CSI measurements might

be imperfect. It might be best to not support CRS-based demodulation for PDSCH in

LAA and only use DMRS based demodulation. Another PDSCH DL transmission

related design decision to be made is if a DL transmission block should be

transmitted on a subset or all of the OFDM symbols in the subframe.

Scheduling

There are two scheduling approaches, cross-carrier scheduling and self-scheduling.

The difference between these approaches is that in cross-carrier scheduling, the

scheduling command and data is sent on different cells and in self-scheduling they

are sent on the same cell. The LTE design in Release 12 supports DL/UL cross-

carrier scheduling from the same scheduling carrier or self-scheduling on both DL

and UL. In addition, 3GPP study has identified that for the case with uplink self-

scheduling where the UE applies a LBT procedure before transmitting on the UL,

two successful LBT operations are required before the UE transmits on the UL. This

is because the first eNB performs an LBT procedure for an LAA SCell to send the

34

scheduling command, and if this is successfully received by the UE, the UE performs

an LBT procedure before transmitting in UL. Therefore, it is recommended to

support self-scheduling on DL and cross-carrier scheduling on UL.

HARQ

Due to discontinuous transmission from LBT in both DL and UL directions,

synchronous UL HARQ process retransmission may not be guaranteed. Therefore,

3GPP has proposed to base the UL operation of LTE LAA on asynchronous HARQ

which may require additional information on HARQ information to be transmitted as

part of the UL scheduling grant. This additional information indicates the HARQ

process number and redundancy version to the UE, so that the UE can correctly

associate each retransmission with the corresponding initial transmission. With

asynchronous HARQ on LAA UL, the UE would depend on the UL grant for UL

(re)transmissions and therefore the use of PHICH is not necessary.

For LAA DL HARQ, an asynchronous and adaptive protocol can be applied,

similar to DL HARQ for carriers in licensed spectrum. The DL HARQ-ACK timing

rules from Rel-12 CA can be reused at least for DL-only LAA transmissions, i.e., the

timing between the subframe in which a LAA PDSCH transmission ends and the

subframe in which the corresponding HARQ-ACK feedback is transmitted follows

the DL HARQ-ACK timing based on Rel-12 FDD-FDD and TDD-FDD CA

specifications assuming that the LAA SCell is an FDD SCell.

UL transmissions

To achieve the throughput requirements set for LAA, a new UL waveform is needed.

One candidate waveform would be to extend current single and dual cluster

allocation. To find the most efficient waveform every possible combination of

waveform characteristics has to be studied carefully. These characteristics are; the

number of clusters, the size of clusters and the spacing between the clusters.

The release 12 design allows transmitting Sounding Reference Signals (SRS)

with a PUSCH transmission or transmitted separately from a PUSCH transmission. It

is recommended that SRS transmissions are supported for an LAA SCell at least

along with a PUSCH transmission. In addition, it is recommended that LAA should

support UL multiplexing of multiple UEs in one subframe by multiplexing in the

frequency domain using MU-MIMO.

5.2.4.3. Layer 2/3 impact

LAA impacts also multiple layer 2 processes and in this section presents those

impacts and possible solutions.

In-device coexistence (IDC)

Modern UEs often combine multiple RATs and the very close proximity of the RF

components causes IDC interference. 3GPP release 11 introduced several solutions

for handling this interference and these existing solutions can be used to detect

WLAN networks during LAA operation. The basic principle is that UE indicates

IDC interference to eNB and the eNB resolves this by configuring the UE with DRX,

performing a handover of the UE to another cell or completely releasing one or more

SCells.

35

Random Access

Only non-contention random access is supported on LAA cells. If LBT is required

before UL transmission, dropping from LAA carriers due to LBT failure is done

similarity as in release 12 dual connectivity.

Quality of service control

The QoS of some radio bearers might suffer in LAA due to support of LBT and as

there can be various interference sources in the unlicensed spectrum, such as other

RATs and LAA nodes of other operators. To improve QoS, the characteristics of an

LAA cell should be considered when mapping traffic from radio bearers to carrier(s).

For example, it is better not to send critical control information, delay critical data or

guaranteed bit rate (GBR) bearers through LAA cells if the LBT operation is

required.

HARQ operation

Due to LBT mechanism in LAA, the cell might be uncertain of its availability for DL

HARQ retransmissions. For example, the LBT operation may need to acquire the

channel or the maximum transmission duration of an LAA cell has been reached

before HARQ operation has been fully performed. There are at least two design

alternatives to solve this issue. The first option is to keep HARQ retransmissions on

the same cell, start HARQ process when LBT operation acquires the channel and

complete the HARQ process before maximum LAA cell transmission duration is

exceeded. If HARQ doesn’t complete successfully, RLC retransmission may be

invoked and the HARQ retransmission is delayed until LAA cell acquires the

channel again. The second alternative is to move HARQ retransmissions to another

cell, for example, another SCell. This is a more complex option as it requires a

change in current HARQ process modeling and for the sake of simplicity the first

design option is recommended.

It is also recommended to use asynchronous UL HARQ for LAA. To enable

this, the eNB needs to indicate in the UL grant which HARQ process the grant is

intended to. Otherwise eNB would not know which HARQ process is ongoing and

which soft-buffer should be combined with the received transmission. The number of

UL HARQ processes is not explicitly specified as it depends on the HARQ timing

but the maximum number may need to be specified during the implementation.

When DRX is used together with asynchronous UL HARQ, the UE can expect to

receive UL grants as the HARQ process is following a fixed pattern.

Discontinuous Reception (DRX)

Due to LBT in LAA, there is no guarantee that a channel is obtained for scheduling

the UE at the exact moment when desired by the eNB. LBT also limits the duration

when the channel can be occupied, therefore the DRX timers should be adjusted to

be long enough or the DRX cycles should be short enough to allow time for

obtaining the channel access.

RRM measurements and reporting

As already mentioned in previous section about layer 1 impacts, release 12 DRS

works by configuring the UE with a DMTC which includes subframes on which the

36

UE may perform RRM measurements. From an RRC protocol point of view, it is

considered feasible to perform the RRM measurement and reporting for LAA.

Similar to configuring and activating SCells on licensed carriers, RRM

measurements on LAA cells can be used to configure and activate LAA cells. For

each configured LAA SCell, there is a single DRS configuration configured by the

eNB. The UE’s physical layer will only report valid RRM measurement samples to

RRC (invalid measurements due to LBT are discarded). It is recommended for UE to

report RSSI measurements to the eNB as it enables detecting hidden node in channel

selection.

Physical Cell Identity (PCI) confusion

3GPP has identified an ‘PCI collision’ scenario in which there can be multiple

operators operating in the same frequency using the same PCI value. The probability

of this occurring depends on the number of LAA cells under same coverage as UE’s

primary cell and whether the operators of these cells have not coordinated the PCI

values for their cells. The PCI confusion can be detected by the eNB for example if it

discovers that the UE is not able to receive or transmit data even though it is

reporting good signal quality for the cell. The PCI confusion can be resolved by the

eNB by changing PCI value of the LAA cell(s) in case. In some cases when the

nodes are not hidden, the network can detect PCI collision by listening to carriers and

resolve it by changing the PCI values of their cells. In current EUTRAN architecture,

PCI collisions are avoided by using a unique cell group identifier (CGI) values for

each cell, transmitted via system information broadcast. A similar mechanism has

been considered unnecessary, since PCI confusion is expected to happen only rarely

with LAA.

5.2.5. Carrier Aggregation enhancements

As mentioned in an earlier chapter 3.1.3, the LTE CA framework was first

introduced in Release 10 [29] and enabled UE to receive and transmit data from/to 5

different Component Carriers (CC). With this feature, LTE downlink data rate was

boosted up to maximum of 150Mbps with only 10MHz frequency bands for each

carrier. In phase 2 CA, the downlink data rate was doubled to 300Mbps with the use

of 20MHz bands. Bandwidths up to 100MHz are supported but 5GHz bands

considered for LAA would make room for even larger bandwidths. As demand for

more carriers has increased from the operator side, expanding the CA framework to

aggregate more than 5 CCs has become necessary with addition of TDD-FDD carrier

aggregation support.

5.2.5.1. Concept

Currently LTE-Advanced supports CA transmission and reception on maximum

bandwidth of 20 MHz for each of five possible CCs. There are three CA types,

shown in Figure 14. In inter-band aggregation (type 1), the component carriers are

located in different frequency bands which are usually in case of LTE spaced by 100

kHz. In non-contiguous intra-band aggregation (type 2), the carriers are in the same

band, while in contiguous intra-band aggregation the carriers are in the same band

and are next to each other. In the last CA type, the carriers are separated by a

37

multiple of 300 kHz. The sub-carriers do not interfere as they are orthogonal to each

other.

Figure 14. Carrier Aggregation types.

The SCell cannot be configured for UL usage only and the number of downlink

component carriers is always greater than or equal to the number used on the uplink.

In TDD mode, each component carrier had to have the same TDD configuration in

Release 10, but that restriction was removed as part of Release 11. However, UL/DL

configuration in aggregated carriers can be different only in case of inter-band TDD

carrier aggregation. Up to Release 11, the component carriers had to have the same

mode of operation (FDD or TDD), but that restriction was removed in Release 12.

FDD-TDD aggregation enables operators to use such band combinations which mix

the two duplex modes together such as Band 8 (900 MHz FDD) and Band 40 (2300

MHz) [30]. This inter-band CA band combination was introduced in release 12 as an

example two carrier TDD-FDD pair and release 13 is adding even more

combinations. The component carriers are organized into one PCell and up to

four SCells. Secondary cells are only used by UEs in RRC_CONNECTED and are

added or removed by means of mobile-specific signalling messages. In case of FDD

or TDD carrier aggregation, UE can be configured to support either modes or just

one of them (e.g. FDD only). The goal in Release 13 is to improve achievable data

rates for LTE-A by expanding possible number of supported CCs from 8 to 32. In

addition to improved data rates, enabling aggregation of large numbers of carriers in

different bands also provides more frequency diversity. There is no RLC or PDCP

impact. Carrier aggregation only affects the physical layer, the MAC protocol on the

air interface and RRC protocol. The next two sub-chapters will present the impacts

on layer 1 and 2 as well as recommended solutions.

38

5.2.5.2. Layer 2/3 impacts

In terms of FDD-TDD aggregation, most of current CA procedures are already

supported with both duplex modes, but the handling of Acknowledge (Ack) and

Negative-Acknowledge (Nack) signaling has to be changed as there can be situation

where the UE is camped on TDD PCell and it does not have UL resources available

for sending Ack/Nack. RRC has to read CA band combinations and duplex mode

support for PCell from the physical layer. RCC will signal in UE-EUTRA-Capability

messages’ information element for PhyLayerParameters-v1250 its support for FDD-

TDD carrier aggregation. This is done by setting field tdd-FDD-CA-PCellDuplex-

r12 to a bit value with length of 2 according to the duplex mode received from the

physical layer. The first bit is set to 1 if UE supports the TDD PCell. The second bit

is set to 1 if UE supports FDD PCell. This field is added only if the UE supports

band combination containing at least one FDD band and at least one TDD band.

In addition to signaling TDD-FDD CA support for E-UTRAN, the RRC has

to set the HARQ Re-Transmission Time (RTT) timer value according to which

duplex mode the serving cell is using. In case of FDD, the timer value is 8 subframes

and in case of TDD, the value has to be the interval between the DL TX and the

transmission of associated HARQ feedback + 4 subframes. Adding new carriers only

affects the MAC layer as the scheduler has to decide which of the possible CCs has

the most favorable physical resource blocks for the transmission.

5.2.5.3. Layer 1 impacts

TDD-FDD CA impact on the physical layer involves signaling PCell duplex mode

(FDD/TDD) to RRC and expanding already existing band combination tables. In

total there are three new intra-band contiguous CA operation bands (5, 8, 66) and 41

new TDD-FDD CA operation band combinations in Release 13 (TS 36.101) - see

Appendix 1 [30] for detailed list of added combinations. The increased number of

CCs will also increase the payload size of the PUCCH as there are more CCs to

aggregate. Reporting CSI for multiple CCs requires multiplexing all reports together

as they are needed for UL/DL signaling control.

5.3. Reliability and latency improvements

Latency reduction is key requirement for ultra-reliable communication e.g. multiple

public service applications that are relying on almost instant communication with the

UE. Current LTE-A network has latency of 60ms and the 5G will require scalable

options for over the air communications with medium latency (2-6ms) and high

latency (10-30ms). In order to support such low latencies, 3GPP has specified several

new features and service frameworks. These improvements will be carried out for

LTE-A Pro and will function as foundations for future enhancements. Lower latency

will enable support for new applications, such as industry processes, virtual reality

services and traffic control.

39

5.3.1. Enhancements for device-to-device (D2D) framework

The D2D/Proximity Services (ProSe) framework was standardized in Release 12.

The D2D feature enables a UE to directly communicate with another UE. D2D

communication reduces cellular traffic congestion and therefore benefits the whole

cellular network infrastructure. Benefits of D2D communication also include higher

data rates, resource-efficiency and low end-to-end delay which is crucial e.g. when

considering public safety applications. As the D2D communication doesn’t have to

route its messages through the base station, the D2D can also be seen as more energy

efficient communication procedure compared to normal cellular communication. The

direct UE to UE D2D channels are called sidelink channels in order to distinguish

them from the uplink and downlink. For public safety purposes D2D must be

efficient and reliable for in-coverage and out-of-coverage situations. In release 12 the

D2D out-of-coverage communication is planned only for public safety, but the 3GPP

plans to add support for more advanced proximity services for Public Safety and

consumer use cases in the release 13. This chapter presents release 12 D2D

framework use cases, methods and general impacts.

5.3.1.1. Concept

Communication between two UEs using sidelink channels is not as straightforward

as between E-UTRAN and UE. ProSe Discovery is the key enabler procedure where

a UE identifies itself for the base station (E-UTRA) as ProSe-capable device and that

it is in proximity of another UE. Methods for device-based synchronization signaling

had to be developed, since another UE can be out-of-coverage or the two UEs can be

attached to different base stations that are asynchronous. The different D2D

communication use cases are illustrated and numbered in Figure 15. The first use

case is the most common use case where both UEs are connected to same primary

cell eNB. The second case is when two devices, 3 and 4, are connected to different

eNBs. The third use case is a scenario where one UE is in-coverage and another one

is out-of-coverage. In the last use case there are two or more devices out-of-coverage

of eNBs. In terms of synchronization, the first use case is the least challenging as

both UEs are connected to same eNB and can use the base station as synchronization

source for D2D discovery and D2D communication. In other use cases (2, 3 and 4),

the sidelink synchronization signal has to be used [31].

40

Figure 15. D2D communication use cases.

5.3.1.2. Impact

Connectivity and relaying

In a situation where some of the Public Safety -enabled UEs are within network

coverage and some are not, those Public Safety -enabled UEs within network

coverage may relay the radio resource management control to the Public Safety -

enabled UEs not within network coverage.

Duplexing

D2D operates in downlink spectrum in the case of Frequency Division Duplex

(FDD) operation and in the uplink subframes in the case of Time Division Duplex

(TDD) operation. In addition to regulatory and licensing restrictions in some

countries, this design choice reduces implementation costs since transmission on

downlink would require additional effort. Also, with this design the interference with

other UEs is easier to control on uplink resources.

Control modes

Telecommunications architecture consists of three main components; the control-

plane, the data-plane and the management plane. The data-plane enables data transfer

from client to another. The control-plane carries signaling traffic and is responsible

for routing. The management plane carries administrative traffic and together with

control-plane serves the data-plane. In direct D2D communications, two devices are

in proximity of each other and there is no need for network control for D2D pairs and

therefore control-plane can be split between the two UE and the network.

In public safety use cases, when there is no network coverage available, the

control path can be established directly between the UEs. In this option pre-

configured radio resources are available. Radio resources for public safety ProSe

Communication can be managed using Public Safety Radio Resource Management

Function within a Public Safety - enabled UE.

41

Device-based synchronization

Synchronization is needed when the D2D pair is in-coverage or out-of-coverage. The

eNB uses a Primary D2D Synchronization Signal (PD2DSS) to synchronize UEs

timing, frequency adjustment and channel estimation during cell search. Secondary

SD2D Synchronization Signal (SD2DSS) is used for timing synchronization but also

to transmit cell group identification during cell search [32]. One crucial aspect to

take into account is the out-of-coverage frequency error. The error may be twice

greater than in standard cellular use. To estimate frequency errors it is recommended

that the symbols are repeated and the primary- and secondary synchronization signal

symbols are separated.

Future work

3GPP will continue enhancing D2D in Release-13 and it will include such

enhancements as prioritization of different groups and sidelink discovery

enhancements. The target is to support Type 1 discovery, meaning that radio

resources for Physical Sidelink Discovery Channel are allocated on non-UE specific

basis.

5.3.2. Mission Critical Push To Talk (MCPTT)

In order to provide mission critical Public Safety (PS) services, 3GPP is working on

MCPTT to allow communication between two or more users with and without

connection with the EPS. One major benefit of large scale MCPTT deployment is

emergency communication e.g. in case of a natural disaster when the network is

down. MCPTT is ongoing project to complete LTE support of PS services in Release

13. Rel-13 MCPTT will only support audio transferring. The impact on voice codecs

is not in scope of this thesis.

5.3.2.1. Concept

MCPTT users may request permission to transmit (e.g., traditionally by means of a

press of a button). The MCPTT over LTE service supports an enhanced PTT service,

suitable for mission critical scenarios, based upon 3GPP EPS services. When

multiple requests occur, the determination of which user's request is accepted and

which users' requests are rejected or queued is based upon a number of

characteristics (including the respective priorities of the users in contention). MCPTT

Service provides a means for a user with higher priority (e.g., MCPTT Emergency

condition) to interrupt the current talker. MCPTT Service also supports a mechanism

to limit the time a user talks (holds the floor) in order to permit users of the same or

lower priority a chance to gain the permission to talk [33].

With MCPTT Service it is possible to set up a group call where every client

has equal chance to gain the permission to talk. In addition, Private Calls between

two clients is also supported. The MCPTT Service builds on the existing 3GPP

transport communication mechanisms provided by the EPS architectures to establish,

maintain, and terminate the actual communication path(s) among the users. The

MCPTT Service also builds upon service enablers: MBMS and ProSe. As mentioned

before, ProSe enables off-network communication as MCPTT capable UEs create

42

communication chains to deliver point-to-point messages. As the messages can travel

via several UEs to the recipient, the messages must be encrypted so that only

recipient can decrypt the message. The end user's experience is expected to be

similar regardless if the MCPTT Service is used under coverage of an EPC network

or based on ProSe without network coverage.

On-network architectural model

The architectural model is shown in Figure 16 [34]. The MCPTT Application Service

provides the service for the MCPTT client using only one PLMN node, while the

Session Initiation Protocol (SIP) core takes care of service control. The EPS provides

bearer services for the UE B. UE A represents one or more UEs that use ProSe UE-

to-Network relaying with UE B to support MCPTT applications.

Figure 16. On-network architectural model.

Off-network architectural model

The architectural model for off-network is shown in Figure 17 [34]. The UE B uses

Prose to handle inter-UE communications with other MCPTT capable UEs (UE A).

Even though UE B does not have EPS connection, it can use another IP Connectivity

Access Network to connect to an offline common services server. The servers’

responsibility is to support configuration management and MCPTT group

management such as provide a group id.

Figure 17. Off-network architectural model.

5.3.2.2. Impact

MCPTT service will have architectural impact on both network and terminal side.

Multiple new processes will be added to support private- and group calls in both on-

43

network and off-network scenarios. Following subchapters introduce basic scenarios

for each category.

On-network private calls

When an automatic commencement mode is supported, a MCPTT client can initiate

an MCPTT private call for communicating with another MCPTT user, with or

without floor control enabled. Figure 18 [34] illustrates a setup process of a private

on-network MCPTT call. After registration of MCPTT clients, client 1 sends a

private call request to MCPTT server. If floor control is wanted, it can be indicated to

the server in this message. Next, MCPTT server sends a private call request to

recipient client, which accepts the call. Response is sent back to the server and then

to the original client. The final step is to establish media plane and floor control if

one was requested during the private call request.

MCPTT client1

MCPTT client2

MCPTT server

3. initiate private call

4. MCPTT private call request

5. Authorize request

7. Accept call

8. MCPTT private call response

10. Media plane established and floor control established (OPTIONAL)

6. MCPTT private call request

9. MCPTT private call response

1. Register as MCPTT service client

2. Register as MCPTT service client

Floor control request (OPTIONAL)

Figure 18. On-network private call setup.

On-network Group calls

The most basic on-network group call scenario is called a pre-arranged group call.

Pre-arrangement means that the group has already been assigned a unique group id

and each group call participant belongs to same MCPTT system and is already

registered for the service. An example scenario is illustrated in Figure 19 [34].

MTCPTT client 1 initiates the group call by sending a group call request to the

MCPTT server. The server then resolves a group id and sends request to associated

clients. The other MCPTT clients send group call responses to MCPTT server which

then sends a response back to the first client and establishes data connection and

floor control.

44

MCPTT client 1 MCPTT server MCPTT client 2 MCPTT Client 3

1. Initiate group call

2. Group call request

3. Resolve group id

4a.Group call request

4a. Accept group call

4b. Group call request

4b. Accept group call

5.Group call response

5.Group call response6. Group call response

8. Media plane and floor control establishment

7.Group call notify

Figure 19. On-network group call setup.

Off-network private calls

In order to communicate with a specific MCPTT user with ProSe mechanism, the

MCPTT client shall first requests the ProSe layer to provide the layer 2 ID and IP

address for the target MCPTT UE. The ProSe layer has a list of all ProSe-enabled

UEs and it can provide User Info Id of the target MCPTT user. Figure 20 [34] shows

how a MCPTT private call setup is done, using ProSe in off-network scenario. The

private call initiator sends a call setup request to the other MCPTT client, who then

accepts the call and send a response back.

45

MCPTT client 2

2. Call setup request

4. Call setup response

MCPTT client 1

1. Initiate private call

3.Accept call

5. Media plane is established with floor control

Figure 20. Off-network private call setup.

Off-network Group calls

Off-network group calls can use pre-defined configuration information provided to

MCPTT clients prior to the off-network group call or configuration information that

is transmitted to MCPTT clients during group call setup or late entry procedures.

Figure 21 [34] shows how a group call is initiated between three MCPTT clients via

ProSe communication. ProSe layer ensures that the messages are only sent to the

corresponding MCPTT group members by using the ProSe layer 2 Group ID

mapping with the MCPTT group ID.

1. Group call announcement

3. Response

4. checking participants

MCPTT client 1 MCPTT client 2 MCPTT client 3

3. Response

2. Setting parameters for media plane

2. Setting parameters for media plane

Figure 21. Off-network group call setup.

46

5.3.3. Single-cell Point-to-Multipoint (SC-PTM)

To position LTE as technology for critical communications, 3GPP presented Group

Communication System Enablers (GCSE) for LTE in release 12. GCSE is based on

evolved Multimedia Broadcast and Multicast Service (eMBMS) which enables

efficient multicast services on multi-cell areas. Multicasting services over a single

cell could also have multiple applications such as an earthquake warning system.

However, multiplexing unicast together with eMBMS in the same subframe is not

allowed even though not all the radio resources in frequency domain are utilized.

Multicast Broadcast Single Frequency Network (MBSFN) subframe configuration

cannot be dynamically adjusted according to the number of active groups and the

traffic load of active groups. Using the physical channels for group communications

in release 12 is challenging as it would require modifying SIB2 frequently to change

PDSCH and PMCH subframe portions. This is unwanted as SIB2 modification

requires unnecessary signaling, i.e. effort on both UE and eNB side. To address this

issue, 3GPP has started a new specification item for SC-PTM in release 13, which

will enable new type of radio access method dedicated to multicast through a single

cell PDSCH.

5.3.3.1. Concept

Single-cell PTM transmission in E-UTRAN uses the existing eMBMS system

architecture and focuses on radio efficiency improvement. The target is to reuse

existing standardized functionalities when possible and justified. In MBSFN, a cell

could belong to up to 8 MBSFN areas and each MBSFN area carries its own

Multicast Control Channel (MCCH) [35]. For SC-PTM, the area of all PTM

transmissions is the cell, so it is sufficient to only have one Single Cell-MCCH. For

an SC-PTM transmission, the group data is sent via PDSCH to the UEs in a group.

This way the resource usage is more efficient as the group data can be provided in a

single PDSCH subframe by multiplexing group data together with normal unicast

data. Data queuing on the eNB side is reduced as there is no need to duplicate

transmissions for the SC-PTM even if there are numerous UEs per group. In terms of

latency reduction, as the SC-PTM group communications queuing delay will not

occur, the overall end-to-end delay is reduced compared to normal unicast PDSCH

transmissions. Also the queuing delay is reduced due to the fact that MCE scheduling

will not occur as the eNBs perform scheduling per a subframe.

5.3.3.2. Impact

SC-PTM will have impact on high level procedures and architecture. High level

procedure is illustrated in Figure 22. First, CN establishes eMBMS and provides

target area information to the Multicast Coordination Entities (MCE). Within this

establish request, the MCE will receive a cell list containing identification and QoS

information for each eNB. Next, MCE makes a decision whether to use SC-PTM or

not based on the eNB capabilities, operations and maintenance configuration. If the

SC-PTM is used, MCE sends eMBMS Session Start Request message to

corresponding eNBs trough PDSCH and includes target area information and QoS

information. eNB will transmit downlink control information through PMCH and the

47

group data through PDSCH simultaneously using the group RNTI. Using the unique

group RNTI acquired from an SC-PTM configuration message, UEs can decode the

received downlink control information as well as the group data.

CN(Core Network)

MCE (Multicast Coordination Entity)

eNB (E-UTRAN Node B)

UE (User Equipment)

M3 M2 Uu

1. MBMS Session Start Request (Cell list, QoS)

2. MBMS Session Start Respose

3. Decide to use SC-PTM for the MBMS bearer

4. MBMS Session Start Request (Cell list, Qos)

5. MBMS Session Start Response

6. Trigger SC-PTM (Configuration)

MBMS user data

Figure 22. SC-PTM High level procedure for bearer setup.

5.3.4. V2X

Ultra reliable and low latency communications will enable a totally new market for

enhanced LTE and future 5G networks. One of the biggest markets to enter is the

smart-driving market and 3GPP has started a new specification item for a service

called V2X in release 14. The term V2X covers three different LTE communication

scenarios; vehicle-to-vehicle (V2V), vehicle-to-pedestrian (V2P) and vehicle-to-

infrastructure (V2I). There are two main reasons why connected vehicle technologies

are needed. One reason is safety, as V2X communication will significantly reduce

the number of accidents. Another reason is travel efficiency, as V2X aims to enable

end-users to reduce travel delays and therefore V2X will also give tools to make

environmentally friendly decisions based on real time information.

5.3.4.1. Concept

Vehicle-to-vehicle

Vehicle manufacturers and cellular operators have strong interests on V2X and they

are pushing the development of LTE-based V2X. There are ongoing research

projects and field tests, such as self driving car and road safety related studies. V2X

requires ultra-reliable communications and low latency from the network. IMT-2020

requirement for latency is 1ms over the air. This means shorter Transmission Time

48

Interval (TTI). Figure 23 shows three V2X application examples where low

communication latency is crucial. In scenario number 2, a vehicle indicates a

collision ahead via Forward Collision Warning (FCW) application service [36]. The

purpose of FCW is to avoid rear-end vehicle collisions by enabling V2V

communication where each vehicle broadcasts periodically its current location,

speed, acceleration and trajectory. Based on received messages from other vehicles, a

vehicle can determine if corrective actions are needed and alert the driver to take

these actions.

Figure 23. V2X scenario examples.

Exchange of V2V-related information between UEs using E-UTRAN is allowed

when permission, authorization and proximity criteria are fulfilled. As in case of the

previous example, the information exchange can be configured to happen

periodically. The configuration of proximity criteria and periodical broadcasting is

done by the mobile network operator. It should be noted that even though the

operator does the configuration, the information can be exchanged even if the UE is

not served by E-UTRAN. The payload has to be flexible in order to enable periodical

transmissions and various information contents.

Vehicle-to-pedestrian

V2P is similar in case of communication configuration and criterias. Also, UEs

supporting V2P Service can exchange such information even when not served by E-

UTRAN. The UE supporting V2P applications transmits application layer

information and the information can be transmitted either by a vehicle or by a

pedestrian with UE supporting V2P Service. In the example scenario 3 (Figure 23)

49

the driver does not see the approaching pedestrian around the corner and the V2P

service alerts the driver. The exchange of V2P-related application information

between distinct UEs can be direct, but if UEs are out of direct communication

range, the application information between distinct UEs can be done via

infrastructure, for example, roadside units (RSU). [36]

Vehicle-to-infrastructure

With V2I support it is possible for UE to send application layer information to any

infrastructure supporting V2I. For example a vehicle can indicate its location for

RSU. RSU broadcasts application layer information to a UE supporting V2I

applications. One possible use case is deployment of Intelligent Transportation

System (ITS) which could guide drivers to make more efficient decisions by

suggesting shortest routes and appropriate driving speed [37]. The ITS would also

increase road safety as it could inform the driver about constructions or other out of

the ordinary situations ahead. In the example scenario 1 Figure 23 the vehicle

communicates with the Road Side Unit (RS) and gets information of upcoming

construction site on the left. The driver can use this information and take appropriate

actions by e.g. using alternative route suggested by the ITS system.

5.3.4.2. Impact

The LTE V2X impact on layer 2 will be similar to D2D communication impact. D2D

communication development could work as a foundation for out of coverage

situations for V2X. In general, high speed over air communication is a field full of

challenges to overcome. Providing robust connection and even decent QoS is

difficult due to dependency on e.g. vehicle speeds, Doppler effect and traffic load. To

overcome these issues that decrease physical layer performance, it is necessary to

specify mechanisms to enable UEs to readjust themselves to adapt to unfavorable

radio conditions. The physical layer performance can be evaluated with parameters

such as Packet Error Rate (PER) vs. SNR and Bit-error Ratio (BER) vs. Signal to

Noise Ratio (SNR). As studies show [38], 256QAM modulation support added in

Rel-12 demands better SNR in order to achieve acceptable BER in high velocity

scenarios. This means the current modulation schemes of LTE-A are suitable for

V2X deployment, but the transmit power must be configured according to selected

signal modulation type.

50

5.4. Massive Machine Type Communication MMTC

LARGE COVERAGE

Power spectral Density (PSD) boosting Channel repetition Longer TTI

LOW COST

Narrower bandwidth Smaller transport block size

(TBS)

LONG BATTERY LIFE

Longer DRX/PSM Functionality simplification

MASSIVE CONNECTION

Scheduling overhead reduction New multiple access scheme Signaling procedure optimization

MTC

Figure 24. Massive MTC trends.

MMTC is seen as one of main use case scenarios for evolving 4G and future 5G

networks. MMTC has to improve network capacity to support a huge amount of

connections e.g. smart lighting systems with over 1000 nodes. 5G workshop

requirements were set at RAN WS [17]. In Figure 24 [19] these requirements are

divided into four main trends; large coverage, low cost, long battery life and massive

connection. Large coverage can be achieved by using longer transmission time

intervals (TTI), channel repetition and boosting power spectral density (PSD).

Massive amount of connections could be handled by reducing scheduling overhead,

using new multiple access schemes and optimizing signaling procedure. User

equipment (UE) manufacturers are always interested in costs per unit. The cost of

one UE can be reduced by using narrower bandwidths and smaller transport block

size which enables manufactures to use cheaper RF components. Long battery life is

a crucial requirement for MTC, since many of its applications require up to years of

operating time. To improve battery consumption, 3GPP will further improve DRX

and increase standby time for Power Saving Mode (PSM), which was introduced in

release 12 (see chapter 6).

5.4.1. LTE enhancements for low cost MTC

Extended access barring, extended wait time and delay tolerant access were

introduced in Release 11 and they are seen as first MTC features introduced for LTE.

3GPP keeps enhancing MTC by enabling categorization of UEs as low complexity

devices. The low complexity support means sacrificing capacity to improve power

consumption and reduce unit costs. The sacrifice is justified as the MTC devices are

expected to have low data rates and the cheap manufacturing has the highest priority.

51

5.4.1.1. Concept

Release 12 introduced a new UE category 0 to address the need for smaller transport

block size. Category 0 devices support 1Mbit transport block size for DL and UL and

have conditional access to cell; access is only allowed if the network explicitly

permits it. An optional feature, called ‘LTE FDD Half duplex’ was also specified to

be used together with Category 0 in order to reduce RF cost. FDD Half duplex was

already introduced at the beginning of LTE (Release 8), but until this point, there has

not been a real use for it. In half duplex, TX and RX are alternated. TS 36.306 [11]

specifies that category 0 should use half duplex FDD operation, i.e. there are guard

periods between TX and RX that are created by UE by not receiving DL subframe

immediately before or after UL subframe. The unit cost can be further reduced by

using only one reception antenna, which lowers the complexity of the RF parts.

Release 13 will define new low complexity UE category types that support

reduced downlink transmission modes and bandwidths of 1.4 MHz in downlink and

uplink. Rel-13 will also achieve extended coverage operation and ultra-long battery

life via power consumption reduction techniques such as enhanced DRX which

allows exceeding current DRX limit of 2.56 seconds. Maximum transmission power

is reduced from 23dBm to 20dBm and this will reduce unit cost as less powerful

power amplifiers enable integrated power amplifier implementation. The coverage of

delay-tolerant MTC devices is expected to be increased by 15dB for 1.4 MHz FDD

by combining signal repetition and retransmission of data packets with PSD

boosting. Extended coverage will also require discarding unneeded PDCCH,

PCFICH and PHICH and using only EPDCCH as a control channel for downlink

[39]. Increased coverage will allow more versatile placement options for MTC

devices such as wireless humidity- and temperature sensors in underground parking

lots. LTE MTC enhancement specifications for Release 14 are ongoing and will

reduce supported bandwidth down to 200 kHz in downlink and uplink.


For bandwidth redundancy, the guideline is to enable operation of MTC services on

reduced bandwidth of 1.4 MHz at the terminal within any LTE system bandwidth

multiplexed together with regular LTE UEs. Currently, all LTE UEs support

bandwidth up to 20MHz and typically support multiple bandwidths, which provide

flexibility to exploit the full performance of the bandwidth deployed. Table 5 shows

how many resource blocks and subcarriers are required in each bandwidth. 1.4MHz

bandwidth can be realized by restricting the downlink transmission to six 180-kHz

LTE physical resource blocks (PRB) for DL instead of 100 PRBs.

Table 5. LTE Bandwidths and PRBs

Bandwidth Resource Blocks DL subcarriers UL Subcarriers

1.4 MHz 6 73 72

3 MHz 15 181 180

5 MHz 25 301 300

10 MHz 50 601 600

15 MHz 75 901 900

20 MHz 100 1201 1200

52

6. RELEASE 12 – POWER SAVING MODE

In addition to lowering unit cost on RF side, the target is to use cheaper and smaller

batteries or at least maximize the power efficiency. Multiple MTC use cases rely on

wireless sensors that can be installed in hard-to-reach places, outside the power grid

and the batteries of these devices may be expensive to charge. These devices might

transmit data only once a week or even once a month and otherwise be in idle mode.

To enable more effective power saving during idle connection phases, Rel-12

standardized a new UE Power Saving Mode (PSM) [10] for Machine Type

Communications (MTC). Intelligent solutions to better control UE power

consumption will be key enabler for LTE MTC and support for devices that are

expected to have a standby time up to 10 years. Power consumption must be scalable

according to current access needs (e.g. D2D/MTC vs. regular mobile broadband use-

cases). This chapter will introduce one design approach to implement power saving

mode for a real LTE-A device. Testing activities and test results shall be analyzed

and future work shall be discussed.

6.1. Concept

First, the UE needs to decide how often it is required to be active in order to enter

PSM between transmitting and receiving data. PSM is activated by UE by proposing

two timer values, T3324 and T3412, in the Attach request or Tracking Area Update

(TAU). The network will provide the actual values of the T3324 and T3412 to be

utilized in the Attach Accept message if it allows UE to enter PSM between

transmissions. After this the network releases the RRC connection and the timers

T3324 and T3412 are started by the NAS.

Timer value of T3324 determines how long the UE needs to stay in idle mode

following the Attach or TAU procedure. This is called the Active Time and this is

the opportunity to contact the UE. If there is no downlink data pending, the T3324

can be shorter. According to 3GPP specification TS 23.682[40], the minimum

recommended length for the Active Time is the time it takes for Mobility

Management Entity (MME) to trigger the Service Centre (SC) to deliver a Short

Message Service (SMS) to the MME, which is 2 DRX cycles plus 10 seconds.

After T3324 expires, the UE will enter PSM for the duration of T3412 which

can be up to 12.1 days [41]. In PSM mode, the UE should enter its lowest power

mode and prevent all signaling procedures such as paging and cell search. While the

UE is in PSM, the MME should not try to locate the UE with paging. Any data that

arrives for the UE is held by the eNodeB. During PSM the UE and eNodeB shall

maintain all existing AS configurations such as states and temporary identities.

Sending a TAU to the EMM without the PSM timers will cancel the PSM mode.

This can happen anytime during PSM.

6.2. Impact

Implementing the feature on Release 12-based LTE system requires changes on NAS

and AS layer. No changes are needed for the physical layer. NAS will control PSM

states and the biggest impact is the implementation of a new ‘PSM state’ for NAS

53

and handling transitions between different states and communication between

different modules. In addition, RRC must enter a special PSM state where it behaves

like in RRC_IDLE state but does not perform any neighbor cell measurements, cell

selection or monitoring of paging channel.

6.2.1. NAS design

Timers

In UE initialization, timers T3324 and T3412 are initialized to ‘null’ value. PSM

timer configuration interface towards EPC is implemented through Attach/TAU

request procedures. T3324 and T3412 values are acquired from the EPC through

Attach/TAU request. T3412 extended value may be requested only if T3324 is

requested. T3324 and T3412 shall be requested only if UE is in PSM_IDLE.

Received T3324 and T3412 extended values are stored and used for PSM activation.

NAS-AS interface

According to 3GPP NAS specification [41], NAS needs an interface message to

deactivate AS. A new message ‘PSM_ACTIVE_IND’ must be added to NAS-AS

interface to set AS to PSM state. The message does not need any informational

content inside it and receiving this message initiates state change on AS. Activation

of AS layer is already supported by the interface since it can be done any time during

PSM by requesting a new connection for mobile oriented data or user data.

PSM state control

At least three states are needed for PSM; PSM-IDLE, PSM-WAIT and PSM-

ACTIVE. These states are controlled by the EMM connection module and the state

machine is presented in Figure 25. Timer T3324 will be activated when EMM enters

PSM-IDLE state, and timer value is not null. Activation is executed by EMM

connection module when RRC is released and EMM enters PSM-WAIT virtual state.

PSM will be activated checking first if PLMN selection is ongoing, if not, then when

T3324 expires, EMM will enter PSM-ACTIVE state where it will stay until T3412

expires. After that, EMM will deactivate PSM.

PSM-ACTIVE

PSM-IDLEPSM-WAIT

T3324

expire

sT3412

expires

Attach/TAU

Figure 25. PSM states.

54

PSM activation/deactivation

Before PSM can be activated, EMM must check if higher priority operations are

ongoing. UE must not be attached or have packet data network (PDN) connection for

emergency bearer services and it has to be in EMM-IDLE mode and in a state other

than EMM-REGISTERED. Before PSM activation, the network performs a RRC

connection release. Timers 3324 and T3412 are started when NAS receives an RRC

connection release indication message from RRC. If all conditions mentioned above

are fulfilled, then the PSM activation can be executed when T3324 expires,

otherwise the activation event is suspended and executed later. Excluding T3346,

T3412 and T3396, all other NAS timers are stopped and related procedures are

aborted [40].

PSM deactivation is triggered by requesting mobile originated or user data

transmission. UE can also wake up after T3412 expires or when periodic TAU timer

expires. In PSM deactivation, EMM will execute connection establishment

procedure. This will trigger RRC to exit PSM and handle connection establishment.

EMM will continue with normal operation after connection is established. PSM is

also deactivated when the SIM card is removed or the device is shut down.

6.2.2. RRC design

PSM activation/deactivation

NAS can indicate PSM start to ERRC during an attachment or TAU procedure. Since

eNB will release the RRC connection or NAS will request a connection release

before entering PSM, RRC will be in IDLE mode when PSM activation indication

message arrives. When ERRC receives PSM_ACTIVE_IND message from NAS,

ERRC shall keep all its timers running but it will not perform any idle mode

activities (e.g. PLMN selection or cell selection and reselection) [14]. During PSM,

UE will not monitor paging channel or perform cell measurements for the serving- or

neighboring cells. RRC shall not remove any existing AS configurations, meaning

that the same configurations can be used when PSM ends. NAS can deactivate PSM

at any time (e.g. for the transfer of mobile originated signalling or user data) and

indicate PSM end to RRC using RRC connection establish request. There is no need

for additional ‘PSM_END’ message. After this, ERRC shall perform all idle mode

activities normally.

6.3. Unit testing

The completed feature can be validated with unit tests. The purpose of unit testing is

to verify that all implemented functions and modules are working as expected. The

focus of the testing should be on the functional part of the code. In addition to basic

functionalities, the unit tests should also cover more rare exception cases and most

common failure- or exception cases. As an unit test example, Figure 26 presents an

interface unit test where the NAS configures the PSM timers with values acquired

from Attach Accept and after T3324 expires, indicates PSM for AS and RRC. Only

relevant messages for PSM activation are shown. Hence, messages such as NAS

authentication requests, UE capability signalling and security mode signalling are

55

ignored. Also, initial connection activation messages between NAS and RRC was not

shown as well as the reception of information blocks (MIB and SIB1-5).

UE-NASeNode B

Attach Request (Suggest T3324, T3412 values)

Attach Request Accept [T3324,T3412]

T3324 expires

PSM_IDLE

PSM_WAIT

UE-RRC

RRC IDLE

RRC PSM

RRC CONNECTED

PSM_ACTIVE

PSM_ACTIVATION

RRCConnectionRelease

Timer start: T3324, T3412

RRCConnectionRequest

RRCConnectionSetup

ConnectionEstablishCNF

RRCConnectionSetupComplete

AttachComplete

Timer set for T3324, T3412

ConnectionEstablishRequest

ReleaseIND

PSM_ACTIVATION_CNF

Figure 26. NAS-RRC interface unit test example; PSM activation.

6.4. Test setup

The PSM feature was also tested with a real system setup by simulating real-life

network conditions using RF tester to mimic the behavior of an eNodeB. Figure 27

shows how the UE, two PCs, a multimeter and this base station simulator can be set

up. One PC was connected to the tester to configure the tester and create test cases.

Another PC was connected to the multimeter and the UE and its purpose was to

control the UE if needed and to store all measurement data locally. The multimeter

probes were placed between the UE and its battery in order to measure the battery

56

drain during the test. Anritsu Signalling Tester MD8430A [42] was selected to

support technology beyond LTE-A release 12 and especially the new UE categories.

The tester was configured with following parameters; 1.4 MHz bandwidth, support

for category 0 LTE UEs (indicated in SIB1). These parameters were chosen to match

real deployment of a low priority UE targeted for CIoT use cases. A cell indicating

support for category 0 UEs must support half duplex FDD and usage of only one RX

antenna as well as reduced MAC PDU size of 1000 bits per TTI. The following test

scenario was created and executed using software tool called Rapid Test Designer.

RF tester simulating eNBMultimeter UE

RF

Data PC Control PC

Figure 27. Test environment.

Test scenario:

1. UE attaches to network. Attach request contains T3324 and T3412

2. Tester sends Attach Accept with T3324 (10 seconds) / T3412 (2 mins)

3. RRC Connection released by NAS

4. UE enters PSM after 10 seconds as instructed by T3324

5. NAS indicates PSM for RRC and RRC enters PSM

6. Poll UE after 1 minute (no answer expected)

7. Send periodic TAU after 2min

8. NAS sends a cell selection request to RRC which enters IDLE state

9. NW deactivates T3324 in TAU Accept

10. Send data after 1 minute

6.5. Power saving evaluation

The measurement results are shown in Figure 28. As the used platform is not

optimized for low-power CIoT devices, real current drain values are not displayed

and instead the results are analyzed using percentages. Measurements show that UE

the power drain is reduced during PSM compared to normal idle mode. Higher

current spikes in idle mode are result of idle mode activities such as neighboring cell

measurements and paging channel monitoring. These idle mode activities appear as

periodic spikes in the graph. With PSM, there are only few current spikes and these

57

are due to operating system (OS) activities. The amplitude of these spikes is

significantly lower and they are less frequent.

Figure 28. PSM power drain measurements.

Figure 29. Power saving with Rel-12 PSM.

The impact on power saving can be illustrated by collecting current data and drafting

a cumulative current chart as seen in Figure 29. The red line represents normal idle

mode current accumulation and the blue is the current accumulation in PSM.

Comparing these lines reveals that even though they both are linear lines, the blue

has smaller ascending angle due to lack of current spikes in PSM. This means energy

is saved for each clock tick. Green line illustrates the saved energy and by calculating

median difference between the red and the green lines’ medians resulted energy

saving of roughly 40%.

58

6.6. Future work

All the measurements were performed in lab conditions. Hence the next step would

be to recreate the test within live network. As the current base stations are not yet

compatible with the feature, PSM development could continue with other

improvement activities, e.g. adding support for special scenarios such as emergency

calls during PSM. With this feature the UE is capable of dozing its layer 2 and layer

3 to sleep. Battery consumption is reduced significantly as the RF parts can be

turned off between the transmissions. In addition, compared to full registration

signalling, the only necessary signaling during reconnection is TAU for a UE with

mobility.

Future work can also include enabling power saving mode for physical layer.

The current implementation does not optimize power consumption on physical layer.

Simply powering off the whole UE is out of the question as the UE would need to do

full connection setup as it would lose existing cell measurement data and AS

configurations. A promising design option would be to create a mechanism to take a

snapshot of existing cell configurations and store them on non-volatile memory. This

way the data can be retrieved even after full power off and wake up from PSM could

continue with a simple reconnection to the cell instead of full connection setup

procedure. In-depth study is needed to map how the stored configurations can be

routed back to the NAS-AS and applied after start up. As the power on procedure

consumes more energy and takes more time, it is important to study what is the

threshold value for T3412 on which the full power off is actually more efficient.

Durability and reliability of the memory components must also be considered as

corrupted data can paralyze the whole system.

59

7. CONCLUSIONS

At this point one can only theorize what the 5G network will look like in 2020. The

standardization work is already ongoing and some development directions and

candidate solutions have been suggested. LTE-A Pro standardization work will

continue in parallel with the new RAT standardization work and fulfill some of

requirements set for 5G. This thesis listed these requirements and analyzed their

impacts on the UE side by analyzing 3GPP specifications, studies and change

requests considering releases 12 and 13. The specification process of the release 13

items is still ongoing and had an impact on this thesis as the existing information was

not yet complete. Most of the presented features will have various impacts on the

protocol specification. An example feature design and implementation of release 12

power saving mode in chapter 6 shows that with these new features it is possible to

enhance current protocols. The overall test results clearly showed the power

efficiency improvement with the PSM turned on. Minimizing UE activities during

PSM reduced the total power drain almost by half.

The PSM feature was proof of concept implemented on a real LTE device and

the measurements performed in this work will provide reference data for future use.

The feature was tested in collaboration with a test vendor and it will be part of a real

future product based on this prototype product. Collecting power measurement data

was valuable for the target company as good power efficiency results could give a

leading edge and differentiate the company’s product from otherwise similar product

competitors. Further development of the feature will require more study on

possibilities to turn physical layer parts off during PSM.

60

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64

9. APPENDICES

Appendix 1. TDD-FDD CA operation band combinations

Table 6. New TDD-FDD inter-band CA band combinations for two bands in Rel-13

E-UTRA

CA Band

E-

UTRA

Band

Uplink (UL) operating band Downlink (DL) operating band Duplex

Mode BS receive / UE transmit BS transmit / UE receive

FUL_low – FUL_high FDL_low – FDL_high

CA_1-40 1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz FDD

40 2300 MHz – 2400 MHz 2300 MHz – 2400 MHz TDD

































CA_20-

42-42

20 832 MHz – 862 MHz 791 MHz – 821 MHz FDD


CA_21-42

21 1447.9

MHz –

1462.9

MHz

1495.9

MHz –

1510.9 MHz FDD








65

Table 7 New TDD-FDD inter-band CA band combinations for three bands in Rel-13

E-

UTRA

CA

Band

E-

UTRA

Band




CA_1-

3-40


3 1710 MHz – 1785 MHz 1805 MHz – 1880 MHz


CA_1-

3-42


3 1710 MHz – 1785 MHz 1805 MHz – 1880 MHz


CA_1-

5-40


5 824 MHz – 849 MHz 869 MHz – 894 MHz


CA_1-

8-40


8 880 MHz – 915 MHz 925 MHz – 960 MHz


CA_1-

19-42


19 830 MHz – 845 MHz 875 MHz – 890 MHz


CA_1-

21-42

1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz

FDD 21 1447.9

MHz –

1462.9 MHz 1495.9

MHz –

1510.9 MHz


CA_3-

5-40


5 824 MHz – 849 MHz 869 MHz – 894 MHz


CA_3-

8-40


8 880 MHz – 915 MHz 925 MHz – 960 MHz


CA_3-

19-42


19 830 MHz – 845 MHz 875 MHz – 890 MHz


CA_3-

7-38


7 N/A 2620 MHz – 2690 MHz

38 N/A 2570 MHz – 2620 MHz TDD

CA_3-

28-40


28 703 MHz – 748 MHz 758 MHz – 803 MHz


CA_3-

41-42



42 3400 MHz – 3600 MHz 3400 MHz – 3600 MHz

CA_7-

20-38

7 N/A 2620 MHz – 2690 MHz FDD

20 832 MHz – 862 MHz 791 MHz – 821 MHz

38 N/A 2570 MHz – 2620 MHz TDD

CA_19-

21-42


21 1447.9

MHz – 1462.9 MHz

1495.9

MHz – 1510.9 MHz

TDD

42 3400 MHz – 3600 MHz 3400 MHz – 3600 MHz

66

Table 8 New TDD-FDD inter-band CA band combinations for four bands in Rel-13

E-

UTRA

CA

Band

E-

UTR

A

Band




1-3-5-

40

1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz

FDD 3 1710 MHz – 1785 MHz 1805 MHz – 1880 MHz

5 824 MHz – 849 MHz 869 MHz – 894 MHz


1-3-8-

40

1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz


8 880 MHz – 915 MHz 925 MHz – 960 MHz


1-3-19-

42

1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz


19 830 MHz – 845 MHz 875 MHz – 890 MHz


1-19-

21-42

1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz


21 1447.9 MHz – 1462.9 MHz 1495.9 MHz – 1510.9 MHz


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