curs 2-umts network

UMTS/UTRAN Introduction

1.Introduction Definition

Universal

Mobile

Telecommunication

System

“UMTS is one of the major new third generation mobile communications systems being developed within the framework which has been defined by the ITU and known as IMT-2000”

UMTS Forum

1. Introduction

1.11.1 ContextContext

1.21.2 StandardizationStandardization

1.31.3 UMTS goalsUMTS goals

1.41.4 UMTS technical overview UMTS technical overview

1.Introduction/1.1 Context

Past mobile systems (1)

First Generation (1G)

In the early 80’s, analog systemse.g Radiocom 2000, C-Netz…

Service:speech

Limitations of 1G:•poor spectrum efficiency•expensive and heavy user equipment•mobility only in a small area •no security of communications


Past mobile systems (2)

Second Generation (2G)In the early 90’s, digital systemsEurope : GSMUS : IS-95 (also called cdmaOne), IS-136 (TDMA system) Japan : PDC

Services: Speech and low data rate

Limitations of 2G:• Congestionmore than 300 million wireless subscribers worldwide -->need to increase system capacity

• Limited mobility around the world -->need for a global standardisation

• Limited offer of servicesmore than 200 million internet users--> Need for new multimedia services and applications (video telephony, e-commerce...)

1.Introduction/1.1 Context Technical solutions

Two types of solutions were possible :

• enhancement of 2G system --> 2,5Glow cost but short terme.g.: HSCSD, GPRS, EDGE for GSM evolution

• design of a complete new standard --> 3Ghigh cost, long term, but great amount of new potential servicese.g: UMTS


GSM evolution (1)

HSCSD (High Speed Circuit Switched Data)Principle: to enhance channel coding scheme and to bundle GSM time slots on a circuit-switched basis.

Performance: up to 115,2 kbps

Already implemented but not all operators/manufacturers have made this choice.

GPRS (General Packet Radio Service)

Principle: to enhance channel coding scheme and to bundle GSM time slots on a packet-switched basis (the allocation of time slots is performed dynamically at the initialisation and during the connection)

Performance: up to 171,2 kbps

1999/2000 : deployment phase2002 : service offers for most operators


GSM evolution (2)

EDGE (Enhancement Data rates for GSM evolution)

Principle: new modulation scheme (8PSK instead of GMSK)

Performance: up to 384 kbps

Implementation is yet to come (foreseen for 2003)

EDGE might be a good alternative to 3G systems in certain areas or for operators who do not have 3G licences, although the 3G brings more in terms of new multimedia services.

1.Introduction/1.1 Context Let’s take some examples!

A 2 1/2 minutes MP3 music file (2.4 MBytes)

GSM 34 mnGPRS 7 mnEDGE 128 s UMTS 10 s

Audio and Video streaming

Streaming with all technologies

except with GSM

Downloading a map (50 KBytes)

GSM 42 sGPRS 8 sEDGE 3 sUMTS 0.2 s

Downloading a Word document (500 KBytes)

GSM 7 mnGPRS 82 sEDGE 27 sUMTS 2 s

1.Introduction



1.31.3 UMTS GoalsUMTS Goals


1.Introduction/1.2 Standardization IMT-2000: definition

IMT-2000 is a framework for third generation mobile systems (3G) which is scheduled to start service worldwide around the year 2000 subject to market considerations.

IMT-2000 should use the frequencies around 2 GHz all over the world.

IMT-2000 is defined by a set of interdependent ITU Recommendations*.

IMT-2000 main requirements are :- wide range of high quality services- capability for multimedia applications - worldwide roaming capability - compatibility of services within IMT-2000 and with the fixed networks

1.Introduction/1.2 Standardization

IMT-2000: terrestrial radio interfaces

IMT-TC (Time Code)TD-CDMAUMTS TDD

IMT-DS (Direct Spread)W-CDMAUMTS FDD

IMT-MC (Multi Carrier)CDMA2000FDD MC

IMT-SC (Single Carrier)TDMA Single CarrierUWC-136EDGE/ERAN

IMT-FT (Frequency Time)TDMA Multi-CarrierDECT

Radio/Network Connection

Evolved IS-41 Core Network

Evolved GSM Core Network

1.Introduction/1.2 Standardization

UMTS Roadmap

EDGEEDGECommercialCommercialintroduction introduction

UMTS R4/R5UMTS R4/R5

UMTS R99UMTS R99Field TrialsField Trials

2000 2001 20032002

GPRSGPRSimplementationimplementation

UMTS R99UMTS R99commercialcommercial

SystemSystem

1.Introduction





1.Introduction/1.3 UMTS goals

Why UMTS?

“UMTS will be a mobile communication system that offers significant user benefits including high-quality wireless multimedia services to a convergent network of fixed, cellular and satellite components.”

It will deliver information directly to users and provide them with access to new and innovative services and applications.

It will offer mobile personalized communications to the mass market regardless of location, network and terminal used.”

UMTS Forum 1997

1.Introduction





1.Introduction/1.4 UMTS technical overview

UMTS general architecture

Core network (CN)it provides support for the network features and telecommunication services. It is connected to external CS networks or PS networks.

Radio Access network (RAN)it comprises roughly the functions specific to the access technique.3 different RANs are foreseen:•UTRAN (UMTS Terrestrial RAN)•MSS (Mobile Satellite component)•BRAN (Broadband RAN)

User Equipment (UE)It is the mobile phone.

Iu

RAN

UEUu

CN Core NetworkRAN Radio Access NetworkUE User Equipment

CN

CS networks (PSTN, ISDN..)

PS networks(Internet…)


UMTS Cellular System

UMTS consists of a set of hierarchical cells, but the multiple access technique is completely different from GSM.

GSMUsers are separated in frequency

(FDMA) and in time (TDMA)

UMTSUsers are separated with codes

(CDMA)


UMTS duplex modes

Downlink

UplinkFDD modeCode and Frequency

orthogonality

f1

f2

5 MHz channel

15TS

5 MHz channel

TDD modeCode and Time orthogonality

Uplink & Downlink ......


UMTS Frequency allocations

TDD FDD MSS TDD1900 1980 2010 20251920

MSSFDD2110 2170 2200

FDD: Frequency Division DuplexTDD: Time Division DuplexMSS: Mobile Satellite System

Uplink Downlink

3.

UMTS System Description

3. UMTS System Description 3 views of the system

Entities

Bearers

Protocolstacks

Logical architecture Protocol architecture

Call scenario

3. UMTS System Description

3.1 Logical architecture

3.2 Protocol architecture

3.3 Call scenario

Entities

Bearers

Protocolstacks

3. UMTS System Descript./3.1 UMTS logical architecture

UMTS logical Architecture

RNS

RNC

RNS

RNC

Core Network

Node B

Iu-CS Iu-PS

Iur

Iub IubIub Iub

CS-ServiceDomain

PS-ServiceDomain

Iu-referencepoint

Iu-PS Iu-CS

Node_B Node B Node B Node B

UU

CN

IU

UTRA N

UE

Uu-referencepoint

3. UMTS System Descript./3.1 UMTS logical architecture

CN logical architecture

UMTS Core Network for Release 99PLMN

PSTN / ISDN

ExternalIP Network

2G/3GSGSN

HLR VHE

GSM BSSBSC

Iu (PS)

Iu (CS)

2G/3GMSC

RNC IP Backbone 2G/3GGGSN

A

Gb

UTRAN

2G/3GGMSC

EIR AuC

3. UMTS System Descript./3.1 UMTS logical architecture UTRAN logical

Architecture

RNCIt is the intelligent part of the UTRAN:- radio resource management (code allocation, congestion control, admission control)- radio mobility management- macro-diversity handling (soft HO)- control of Node-Bs

Node-BA Node-B can be composed of several cells and performs:- radio transmission handling- macro-diversity handling (softer HO)

RNS

RNC

RNS

RNC

Node B

Iur

Iub IubIub Iub

Node_B Node B Node B Node B

5

DS

621

3. UMTS System Descript./3.1 UMTS logical architecture Soft Handover (1)

Core Network

IubIub

Iu

Iub

Iur

Iu

Iub

RNC1 RNC2

NodeB1 NodeB2 NodeB3 NodeB4

3 4

S

3. UMTS System Descript./3.1 UMTS logical architecture Soft Handover (2)

The role of an RNC (Serving or Drift) is on a per connection basis between a UE and the UTRAN:Serving RNC: provide Iu UE-CN connection

Drift RNC: supports Serving RNC by providing radio resources

The recombination of the signal is performed in Serving RNC (in Node B for softer HO) and in UE using a RAKE receiver.

Soft HO is highly recommended in UMTS system: about 30 to 40% of mobiles are in macro-diversity mode in IS-95.

3. UMTS System Descript./3.1 UMTS logical architecture UMTS logical Interfaces

Open InterfacesThe functional split for the UMTS components (UE, Node-B, RNC...) are clearly specified, but the internal architecture and implementation issues are left open (it is up to the manufacturer).

However all the interfaces (Cu, Uu, Iub, Iur, Iu-CS, Iu-Ps) have been defined in such a detailed level that the equipment at the endpoints can be from different manufacturers.

“Open Interfaces” aim at motivating competition between manufacturers.

Physical implementation of Iu interfacesEach Iu Interface may be implemented on any physical connection using any transport technology.

ATM will be provided in the R99 release and IP is foreseen in further releases

4.

WCDMA for UMTS

4. WCDMA for UMTS

4.14.1 Context Context

4.24.2 Spread Spectrum modulationSpread Spectrum modulation

4.34.3 Code Division Multiple AccessCode Division Multiple Access

4.44.4 Rake ReceiverRake Receiver

4.54.5 Power ControlPower Control

4.64.6 Soft HandoverSoft Handover

4.74.7 Typical coverage and capacity valuesTypical coverage and capacity values

4. WCDMA for UMTS/ 4.1 Context

From military to civil modern radio-communications

Early 70’sCDMA developed for military field for its great qualities of privacy (low probability interception, interference rejection)

1996CDMA commercial launch in the USThis system called IS-95 or cdmaOne was developed by Qualcomm and has reached 50 million subscribers worldwide

2000IMT-2000 has selected three CDMA radio interfaces:- WCDMA (UTRA FDD)- TD-CDMA (UTRA TDD)- CDMA 2000

In the following material we will only refer to WCDMA (UTRA FDD)

4. WCDMA for UMTS/ 4.1 Context

Why CDMA?

CDMA is very attractive:

• Better spectrum efficiency than 2G systems

• Suitable for all type of services (circuit, packet) and for multi-services

• Enhanced privacy

• Evolutionary (linked with progress in signal processing field)

BUT:

• Complex system: not easy to configure and to manage

• Unstable in case of congestion








4. WCDMA for UMTS

4. WCDMA for UMTS/ 4.2 Spread Spectrum Modulation

A code as a shell against noise

The letter ‘A’ represents the signal to transmit over the radio interface.

At the transmitter the height (ie the power) of ‘A’ is spread, while a color (i.e a code) is added to ‘A’.

At the receiver ‘A’ can be retrieved with knowledge of the code, even if the power of the received signal is below the power of noise due to the radio channel.

Radio channel

ReceiverTransmitter

Spreading

Noise

Despreading

4. WCDMA for UMTS/ 4.2 Spread Spectrum Modulation Spectrum spreading

At the transmitter the signal is multiplied by a code which spreads the signal over a wide bandwidth while decreasing the power (per unit of spectrum).

At the receiver it is possible to retrieve the wanted signal by multiplying the received signal by the same code: you get a peak of correlation, while the noise level due to the radio channel remains the same, because this is not correlated with the code.

The spectrum spreading permits transmission of a signal below the noise level and makes the signal very hard to detect.

Spectrum spreading makes CDMA very secure.

f

P

f

P

f

P

f

P

Noise level

Radio channel

Spreading De-spreading

4. WCDMA for UMTS/ 4.2 Spread Spectrum Modulation Transmission Chain

Air Interface

The narrowband data signal is multiplied bit per bit by a code sequence: it is known as “chipping”.

The chip rate of this code sequence is much higher than the bit rate of the data signal: it produces a wideband signal, also called spread signal.

At the receiver the same code sequence in phase should be used to retrieve the original data signal.

Modulator Demodulator

Code Sequence

Data Data

Code sequence

NB- Signal WB- Signal NB- SignalWB- Signal

4. WCDMA for UMTS/ 4.2 Spread Spectrum Modulation Spreading factor

Signal 1 0 0 (bits)Spreading 1111 0000 0000 (chips)Code 0101 0101 0101Tx signal 0101 1010 1010

Rx signal 0101 1010 1010Code 0101 0101 0101Despreading 1111 0000 0000Signal 1 0 0

(In this case, each bit of the signal is spread over 4 chips. The spreading factor is 4)

Spreading makes CDMA adequate for services with variable bit rates.

Radio channel

4. WCDMA for UMTS/ 4.2 Spread Spectrum Modulation Processing Gain

The Processing Gain is the gain you have at the receiver by the despreading of the signal (peak of correlation). It enables transmission of the signal below the noise level.

A high bit rate signal needs more power to cross the noise level by de-spreading.

f

P

W

Processing Gain

Rb

De-spreading

bRWLog1010Gain Processing








4. WCDMA for UMTS

4. WCDMA for UMTS/ 4.3 Code Division Multiple Access One-cell reuse

The area is divided into cells, but the entire bandwidth is reused in each cell (frequency reuse of one)

> Inter-cell interference

> Cell orthogonality is achieved by codes

The entire bandwidth is used by each user at the same time

> Intra-cell interference

> User orthogonality is achieved by codes

4. WCDMA for UMTS/ 4.3 Code Division Multiple Access Multiple access (1)

All the users transmit on the same 5 MHz carrier at the same time and interfere with each over.

At the receiver the users can be separated by means of (quasi-)orthogonal codes.

Transmitter 2

Spreading 1

Spreading1

Spreading 2 Receiver

Radio ChannelTransmitter 1

The receiver aims at receiving Transmitter 1 only.

4. WCDMA for UMTS/ 4.3 Code Division Multiple Access

Multiple access (2)

If a user transmits with a very high power, it will be impossible for the receiver to decode the wanted signal (despite use of quasi-orthogonal codes)

CDMA is unstable by nature and requires accurate power control.

Transmitter 2

Receiver

Radio ChannelTransmitter 1

The receiver aims at receiving Transmitter 1 only.

Spreading 1

Spreading1

Spreading 2


Spreading: Channelization and scrambling

2chc

3chc

1chc

scramblingc

The channelization code (or spreading code) is signal-specific: the code length is chosen according to the bit rate of the signal.

The scrambling code is equipment-specific.

air interface

Modulator


Channelization codes (spreading codes)

The channelization codes are OVSF (Orthogonal Variable Spreading Factor) codes: • their length is equal to the spreading factor of the signal: they can match variable bit rates on a frame-by-frame basis.• orthogonality enables to separate physical channels:Uplink: separation of physical channels from the same terminalDownlink: separation of physical channels to different users within one cell

SF = 1

C ch,1,0 = (1)

C ch,2,0 = (1,1)

C ch,2,1 = (1,-1)

C ch,4,0 =(1,1,1,1)

C ch,4,1 = (1,1,-1,-1)

C ch,4,2 = (1,-1,1,-1)

C ch,4,3 = (1,-1,-1,1)

SF = 4SF = 2 SF = 8

The code tree is shared by several users (usually one code tree per cell)


Scrambling codes

The scrambling codes provide separation between equipment:• Uplink: separation of terminals No need for code planning (millions of codes!) There are 214 long and 214 short scrambling codes in uplink

• Downlink: separation of cells Need for code planning between cells (but trivial task) There are only long scrambling codes in downlink (512 to limit the code identification during cell search procedure)

The long scrambling codes are truncated to the 10 ms frame length.

Only one downlink scrambling code should be used within a cell.Another scrambling code may be introduced in one cell if necessary (example : shortage of channelization code), but orthogonality between users will be degraded.

4. WCDMA for UMTS








4. WCDMA for UMTS/ 4.4 Rake Receiver Rake Receiver principle (1)

In a CDMA system there is a single carrier which contains all user signals.

Decoding of all these signals by one receiver is only a question of signal processing capacity.

A Rake receiver is capable to decode several signals simultaneously in the so called “fingers” and to combine them in order to improve the quality of the signal or to get several services at the same time.

A Rake receiver is implemented in mobile phones and in base stations.

A Rake receiver can provide:- multi-service (via handling of multiple physical channels that are carrying the services)- soft handover - path diversity

4. WCDMA for UMTS/ 4.4 Rake Receiver

Rake receiver principle (2)

The components of the multi-code signal are demodulated in parallel each in one “finger” of the Rake Receiver.

The outputs of the fingers:• can provide independent data signals• can be combined to provide a better data signal(s)

Delay 1Code Sequence 1

Code Sequence 2 or 3

Code Sequence 2Delay 2

Delay 3

Data 2

1stFinger

2ndFinger

3rdFinger

Data 1

Multi-code signal

Delay Adjustment


Rake receiver and multi-service

As a first approach, we can say:

One service, one code! (*)

Multimedia receiverTransmitter

Spreading 1 Despreading 1

Radio ChannelSpreading 2

Despreading 2

>> Which codes make it possible to >> Which codes make it possible to separate the two signals at the receiver?separate the two signals at the receiver?


Rake Receiver and soft handover

Soft handover is possible, because the two mobile stations use the same frequency band. The mobile phone need only one transmission chain to decode both simultaneously.

Base Station 2

Spreading 1

Despreading 1&2

Spreading 2 Mobile phone

Radio ChannelBase station 1

>> Which codes make it possible to >> Which codes make it possible to separate the two signals at the separate the two signals at the receiver?receiver?


Rake Receiver and path diversity (1)

Natural obstacles (buildings, hills…) cause reflections, diffractions and scattering and consequently multipath propagation.

The delay dispersion depends on the environment and is typically:

• 1 µs (300 m) in urban areas • 20 µs (6000 m) in hilly areas

The delay dispersion should be compared with the chip duration 0,26 µs (78 m) of the CDMA system.

If the delay dispersion is greater than the chip duration, the multipath components of the signal can be separated by a Rake Receiver.

In this case, CDMA can take advantage of multipath propagation.


Rake Receiver and path diversity (2)

Dispersion > Chip durationThe Rake Receiver can provide path diversity to improve the quality of the signal.

ReceiverTransmitter

Spreading Despreading

Direct path

Reflected path

ReceiverTransmitter

Spreading Despreading

Direct path

Reflected path

Dispersion <Chip durationThe Rake Receiver cannot provide path diversity. >> Which codes make it >> Which codes make it

possible to separate the two possible to separate the two signals at the receiver?signals at the receiver?

4. WCDMA for UMTS








4. WCDMA for UMTS/ 4.5 Power Control

Why Power Control?

> Need for very efficient and very fast Power Control on UL

> Power Control is also used in DL to reduce interference and consequently to increase the system capacity.

NodeB

MS2

MS1

Near-Far Problemon the uplink way an overpowered mobile phone near the base station can jam any other mobile phones far from the base station.


Open Loop

If UE receives a STRONG DL signal,then UE will speak low.

NodeB

NodeB

1

2

1

2

If UE receives a weak DL signal,then UE will speak LOUD.

Problem:fading is not correlated on UL and DL due to separation of UL and DL band.

Open loop Power Control is inaccurate.

Open loop power control


Closed Loop

The Node-B controls the power of the UE (and vice versa) by performing a SIR estimation (inner loop).

The RNC controls parameters of the SIR estimation (outer loop).

This SIR estimation is performed each 0,66 ms (1500 Hz command rate).

Closed loop Power Control is very fast.

NodeB

Closed loop power control

...

”Power down”

”Power up”

”Power down”

”Power ...”

SIR estimation

SIR estimation

SIR estimation

SIR estimationRNC SIR

target








4. WCDMA for UMTS

4. WCDMA for UMTS/ 4.6 Soft Handover Soft Handover (1)

NodeB

NodeB

Soft HO

Softer HO

RNC

NodeB

4. WCDMA for UMTS/ 4.6 Soft Handover

Soft Handover (2)

Why do we need soft HO?Imagine that a UE penetrates from one cell deeply into an adjacent cell: > it may cause near-far problem> hard HO is not a good solution, because of the need for the hysteresis mechanism

Additional resources due to soft HO:- Additional rake receiver in Node-B- Additional Rake Fingers in UE- Additional transmission links between Node-Bs and RNCs

Soft HO provides Diversity (also called Macro-Diversity), but requires more network resource.

4. WCDMA for UMTS/ 4.6 Soft Handover

Soft Handover (3)

Soft Handover execution: Soft Handover is executed by means of the following procedures

Radio Link Addition (FDD soft-add); Radio Link Removal (FDD soft-drop); Combined Radio Link Addition and Removal.

The cell to be added to the active set needs to have information forwarded by the RNC: Connection parameters (coding scheme, layer 2 information, …) UE ID and uplink scrambling code, Timing information from UE

The UE needs to get the following information Channelization & scrambling codes to be used Relative timing information (Timing offset based on CPICH synchro)

4. WCDMA for UMTS








4. WCDMA for UMTS/ 4.7 Typical coverage and capacity values

Radio dimensioning process: What’s new?

Market perspectiveMobile data market forecastMarketing inputs

Multi-service environmentVoice+dataVariable bit rateDifferent QoSAsymmetric traffic

New radio technologyW-CDMA Capacity

Coverage Quality


Concentric coverage

Service Speech 12 kbit/s

Packet data144 kbit/s

Packet data384 kbit/s

Cell radius(uplink limited)

The coverage is determined by the uplink range, because the transmission power of the terminal is much lower than that of the base station.

UE Transmit Power21 dBm (126 mW)24 dBm (251 mW)

3 km 2 km 1,5 km

in suburban area


Ways of improving coverage

AMR speech Codecit enables to switch to a lower bit rate if the mobile is moving out of the cell coverage area: it is a trade-off between quality and coverage.Multipath diversityit consists of combining the different paths of a signal (due to reflections, diffractions or scattering) by using a Rake Receiver.Multipath diversity is very efficient with W-CDMA.Soft(er) handoverthe transmission from the mobile is received by two or more base stations.Receive antenna diversitythe base station collects the signal on two uncorrelated branches. It can be obtained by space or polarization diversity.Base stations algorithmse.g. accuracy of SIR estimation in power control process


Soft capacity

The capacity is determined by the downlink direction, because:- better receiver techniques can be used in the base station than in the mobile station (but requiring more CPU power).- the downlink capacity is expected to be more important than the uplink capacity because of asymmetric traffic.

The downlink capacity has two limitations:- the amount of interference in the air interfaceAdjacent cells share part of the same interference: there is an additional capacity in a cell, if the number of users in the neighboring cells is smaller. - the loss of code orthogonalityThe downlink codes originate from a single point and can be synchronized.But, after transmission over multipath channel, part of orthogonality is lost.

It is a soft capacity, because it is not limited by the hardware equipment.


Parameters influencing capacity

The capacity depends on:- the radio environment (rural, suburban, indoor)- the terminal speeds - the distribution of the terminals- the load of the cell: trade-off capacity/coverage (breathing cells)

High loaded cellHigh DL interference levelDL data throughput 660 kbps(per carrier per sector)

High loaded cellLow DL interference levelDL data throughput 1440 kbps(per carrier per sector)

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