UMTS Radio Principles

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1/188UMTS Radio Principles - Page 1All Rights Reserved 2007, Alcatel-Lucent

All rights reserved 2007, Alcatel-Lucent

Alcatel-Lucent W-CDMA - UMTS Radio Principles

Alcatel-Lucent W-CDMAUMTS Radio Principles

TRAINING MANUAL

3FL12543ABAAWBZZA

Edition 1

Copyright 2007 by Alcatel-Lucent - All rights reservedPassing on and copying of this document, use and

communication of its contents not permitted withoutwritten authorization from Alcatel-Lucent


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All Rights Reserved Alcatel-Lucent 2007Alcatel-Lucent W-CDMA

UMTS Radio Principles

3

Table of Contents

Switch to notes view!1. UMTS System Description

Module 1. 3JK10655AAAAWBZZA UMTS System Descritption

2. WCDMA for UMTS

Module 1. 3JK10656AAAAWBZZA WCDMA for UMTS

3. UTRAN scenariosModule 1. 3JK10657AAAAWBZZA UTRAN scenarios

4. HSDPA Description

Module 1. 3JK10658AAAAWBZZA HSDPA Introduction

Module 2. 3JK10659AAAAWBZZA HSDPA Key Concepts

Module 3. 3JK10660AAAAWBZZA HSDPA Channels

Module 4. 3JK10661AAAAWBZZA H-ARQ for Fast Retransmission

Module 5. 3JK10662AAAAWBZZA HSDPA Scheduling Mechanism

Module 6. 3JK10663AAAAWBZZA Adaptative Modulation and Coding with 16-QAM

Module 7. 3JK10664AAAAWBZZA MAC-hs in UTRAN Protocols

Module 8. 3JK10665AAAAWBZZA HSDPA ScenariosModule 9. 3JK10666AAAAWBZZA HSDPA A-L implementation

5. HSUPA Description

Module 1. 3JK10667AAAAWBZZA HSUPA Key Concepts

Module 2. 3JK10668AAAAWBZZA HSUPA Channels

Module 3. 3JK10669AAAAWBZZA HSUPA Scheduling Mechanism

Module 4. 3JK10670AAAAWBZZA H-ARQ for HSUPA

Module 5. 3JK10672AAAAWBZZA MAC-e in UTRAN Protocols

Module 6. 3JK10673AAAAWBZZA HSUPA Scenarios

Module 7. 3JK10674AAAAWBZZA HSUPA A-L implementation

6. APPENDIX

Module 1. 3JK10675AAAAWBZZA Appendix





4

Table of Contents [cont.]

Switch to notes view!

This page is left blank intentionally





5

Course Objectives


Welcome to UMTS Radio Principles

After successful completion of this course, you should understand :

Draw the UTRAN architecture with the protocol stack (radio and Iu) of each network

element and to define the channels generated by these protocols

Define a Radio Resource in 3G.

Build the map of the channels (logical, transport, physical) from a white paper

Describe the HSDPA principles.

Describe the HSUPA principles.





6

Course Objectives [cont.]







7

About this Student Guide

Switch to notes view!Conventions used in this guide

Where you can get further information

If you want further information you can refer to the following:

Technical Practices for the specific product

Technical support page on the Alcatel website: http://www.alcatel-lucent.com

Note

Provides you with additional information about the topic being discussed.

Although this information is not required knowledge, you might find it useful

or interesting.

Technical Reference(1) 24.348.98 Points you to the exact section of Alcatel-Lucent Technical

Practices where you can find more information on the topic being discussed.

Warning

Alerts you to instances where non-compliance could result in equipmentdamage or personal injury.





8

About this Student Guide [cont.]







9

Self-Assessment of Objectives

At the end of each section you will be asked to fill this questionnaire

Please, return this sheet to the trainer at the end of the training


Instructional objectivesYes (orglobally

yes)

No (orglobally

no)Comments

1 To be able to XXX

2

Contract number :

Course title :

Client (Company, Center) :

Language : Dates from : to :

Number of trainees : Location :

Surname, First name :

Did you meet the following objectives ?

Tick the corresponding box

Please, return this sheet to the trainer at the end of the training





10

Self-Assessment of Objectives [cont.]


Instructional objectivesYes (orGlobally

yes)

No (orglobally

no)Comments

Thank you for your answers to this questionnaire

Other comments


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Section 1 Page 1

All rights reserved 2007, Alcatel-Lucent3JK10655AAAAWBZZA Edition 1

Do not delete this graphic elements in here:


Alcatel-Lucent W-CDMA UMTS Radio Principles

1 3JK10655AAAAWBZZA Edition 1Section 1

UMTS System Description


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Section 1 Page 2


All rights reserved 2007, Alcatel-LucentAlcatel-Lucent W-CDMA


UMTS System Description 1 2

Blank Page


Conversion into Alcatel-Lucent templateScholle, Martin2007-06-2103

RemarksAuthorDateEdition

Document History


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Section 1 Page 3





Objectives

To be able to draw the UTRAN architecture with theprotocol stack (radio and Iu) of each network elementand to define the channels generated by these protocols.


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Objectives [cont.]



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Table of Contents

Logical Architecture UTRAN Situation & Core Network in

3GPP R4 UTRAN Logical Architecture Interfaces Network Element Function

Network Protocols Protocols in UTRAN Protocol Stack on the Interfaces General model Iub protocols Iur Protocols

Radio Channels Global Situation RAB Presentation Radio Channels, Protocols &

Network Elements Radio Bearers Logical Channels Why Transport Channels?

Structure of a Transport Channel Transport Channels: Example Transport Channels

Common Transport Channels Dedicated Transport Channels Mapping Logical / Transport Channels Physical Channels Physical Channel List Downlink

Uplink Physical Channels: Structure

UTRAN Radio Protocols Radio protocol stack Radio Resource Control (RRC) PDCP and BMC Protocols Radio Link Control (RLC) Medium Access Control (MAC) The Physical Layer

Exercises MAC protocol

Page

1 Logical Architecture 71.1 UTRAN Situation & Core Network in 3GPP R4 81.2 UTRAN Logical Architecture 91.3 Interfaces 10

1.4 Network Element Function 112 Network Protocols 132.1 Protocols in UTRAN 142.2 Protocol Stack on the Interfaces 152.3 General model 162.4 Iub protocols 172.5 Iur Protocols 18

3 Radio Channels 203.1 Global Situation 213.2 RAB Presentation 223.3 Radio Channels, Protocols & Network Elements 233.4 Radio Bearers 243.5 Logical Channels 253.6 Why Transport Channels? 27

3.7 Structure of a Transport Channel 283.8 Transport Channels: Example 303.9 Transport Channels 313.10 Common Transport Channels 323.11 Dedicated Transport Channels 353.12 Mapping Logical / Transport Channels 363.13 Physical Channels 383.14 Physical Channel List 393.15 Downlink 403.16 Uplink 413.17 Physical Channels: Structure 42

4 UTRAN Radio Protocols 434.1 Radio protocol stack 444.2 Radio Resource Control (RRC) 454.3 PDCP and BMC Protocols 464.4 Radio Link Control (RLC) 474.5 Medium Access Control (MAC) 484.6 The Physical Layer 49

5 Exercises 505.1 MAC protocol 51


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1 Logical Architecture


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1.1 UTRAN Situation & Core Network in 3GPP R4

Core Network

PS-CN

Access Network

Iu-PS

External Networks

HLR

PSTN

IN network

UTRAN

RNCRNC

Node B

PDN

CS Links

PS Links

Gb

Backbone

iGGSiGGSNN

SGSNGSMBSS

BSC

BTSPCU

CS-CN

MSC Server

MGWGMSC

Iu-CS

A Public Land Mobile Network (PLMN) is composed of 2 main parts:

The Access Network (AN) provides the radio interface and radio resource management for mobilecommunications toward the Core Network (CN).

The Core network is in charge of User Equipment (UE) Mobility (MM) and Session (SM) management. Italso deals with the external networks for voice call establishment or data session establishment.

The UMTS Terrestrial Radio Access Network (UTRAN) is the UMTS Access Network; its composed ofNode Bs and Radio Network Controllers (RNCs).

An ATM switch interfaces the UTRAN and the CN:

Iu-CS interface for the Circuit Switched Core Network (CSCN).

Iu-PS interface for the Packet Switched Core Network (PSCN).

The PLMN connects specifically to the Public Switched Telephone Network (PSTN) for voice or to thePacket Data Network (PDN) for data.

The CN includes the Intelligent Network (IN) for value-added services.

Example of services:

For voice:

Voice Call Prepaid Service

SMS service

Call Waiting


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1.2 UTRAN Logical Architecture

Core Network

UTRAN

UE

Iub Iub

Iu-CS Iu-PS

Iur

Uu Interface

RNS

CS-CN PS-CN

RNC RNC

Node B Node B

UEs

CN

2 separated domains: Circuit Switched (CS) and Packet Switched (PS) which reuse the

infrastructure of GSM and GPRS respectively.

UTRAN

new radio interface: CDMA

new transmission technology: ATM

CN independent of AN

The specificity of the access network due to mobile system should be transparent to the core

network, which may potentially use any access technique.

Radio specificity of the access network is hidden to the core network.

UE radio mobility is fully controlled by UTRAN.

Some correspondences with GSM:

CN NSS Uu Um

UTRAN BSS Iub A-bis

RNC BSC Iur no equivalent

Node-B BTS Iu-CS A

UE MS Iu-PS Gb


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1.3 Interfaces

Open Interfaces:

The function of the Network Elements have been clearly specified by the3GPP.

Their internal implementation issues are open for the manufacturer All the interfaces have been defined in such a detailed level that theequipment at the endpoints can be from different manufacturers.

Open Interfaces aim at motivating competition between manufacturers.

Physical implementation of Iu interfaces

Each Iu Interface may be implemented on any physical connection usingany transport technology, mainly on E1 (cable), STM1 (Optic fiber) andmicro-waves.

ATM will be provided in the 3GPP R4 release and IP is foreseen for the3GPP R6

A manufacturer can produce only the Node-B (and not the RNC). This is not possible in GSM (A-bis is a

proprietary interface)

The Iur physical connection can go through the CN using common physical links with Iu-CS and Iu-PS.

However there is a direct logical connection between the 2 RNCs: the Iur information is not handled bythe CN.


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1.4 Network Element Function

RNC: Radio Network Controller

It is the intelligent part of the UTRAN:

- Radio resource management (code allocation, Power Control, congestion

control, admission control)- Call management for the users- Connection to CS and PS Core Network- Radio mobility management

Iub IubIur

RNS

Node B Node B

RNC RNC

An RNS (Radio Network Subsystem) contains one RNC (Radio Network Controller) and at least oneNode-B.

The RNC takes a more important place in UTRAN than the BSC in the GSM BSS. Indeed RNC can perform

soft HO, while in GSM there is no connection between BSCs and only hard HO can be applied.


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1.4 Network Element Function [cont.]

Node-B

A Node-B can be considered, as first approximation, like a transcoderbetween the data received by antennas and the data in the ATM cell on theIub.

- Radio transmission and reception handling- Involved in the mobility management- Involved in the power control

Iub

RNC

Node B

ATM TransportTechnology

An RNS (Radio Network Subsystem) contains one RNC (Radio Network Controller) and at least oneNode-B.

A Node-B is also more complex than the GSM BTS, because it handles softer HO.

Controlling RNC (CRNC): a role an RNC can take with respect to a specific set of Node-Bs (ie those Node-Bs belonging to the same RNS). There is only one CRNC for any Node-B. The CRNC has the overall control

of the logical resources of its Node-Bs


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2 Network Protocols


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2 Network Protocols

2.1 Protocols in UTRAN

Uu Interface

Core Network

RNC RNC

Node B

Iub

Iu

Iur

Iu Protocols

The Iu protocols Used to exchange data (traffic

and signaling) between RNCs,Node Bs and the Core Network.

Radio Protocols

The Radio protocols Used to process the data sent

on the air and for the signalingbetween UTRAN and the UEs

NAS Signaling Signaling between a UE and

the Core Network.

Typically, theAuthentification and the

Location

NAS Signaling

Iu Protocols :

RANAP: Radio Access Network Application Protocol,

RNSAP: Radio Network Sub-system Application Protocol,

NBAP: Node B Application Protocol,

ALCAP is a generic name for the signalling protocols of the Transport Network Control

Plane used to establish/release Data Bearers.

It makes establishment/release of Data Bearers on request of the Application Protocol.

Radio Protocols :

RRC: Radio Resource Control

RLC: Radio Link Control

MAC: Medium Access Control

NAS refers to higher layers (3 to 7). Entities of this part will exchange tele-services and bearer

services


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2 Network Protocols

2.2 Protocol Stack on the Interfaces

Iub

Iub

Iur

Iu- PS

Iu- CS

Node B

RNC

RNC

RNSAP

RANAP

RANAP

Iu UP

Voice

Iur FP

Iu UP

Data

Control plane User plane

Iub

Node B

CS-CN

PS-CN

Radio

Sig Voice

NBAPIub FP

RadioSig Voice Data

AAL5 AAL2

ATM

AAL5 AAL2

ATM

AAL5 AAL2

ATM

AAL5 AAL5

ATM

Data

Node B

AAL5 has been designed to adapt non real time, connectionless oriented data at variable bit rate (eg,

web browsing) to ATM.

AAL2 has been designed to adapt real time, connection oriented data at variable bit rate (eg, voice in

AMR) to ATM.


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The same general protocol model is applied for all Iu interfaces:

Application Protocols:

Radio

Network

Layer

Transport

Network

Layer

Physical Layer

SignalingBearer(s)

SignalingBearer(s)

DataBearer(s)

ALCAP

ApplicationProtocol

DataStream(s)

Transport NetworkControl Plane

Transport NetworkUser Plane


Control

PlaneUser Plane

- NBAP for Iub interface

- RNSAP for Iur interface- RANAP for Iu-CS and Iu-PS interfaces

1. What is thepurpose of theseparation between

the Radio NetworkLayer and theTransport Network

Layer?

2. Why is ALCAPprotocolnecessary?

2 Network Protocols

2.3 General model

The Iu protocols are responsible for exchanges of signalling and user data between two endpoints of anIu interface (e.g. Node-B and RNC over the Iub interface) .

The ALCAP protocol is used to establish the AAL2 connections for the the data stream (user data &

user signaling) of the Radio Network Layer.


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ATM

Radio

Network

Layer

Transport

Network

Layer

Physical Layer

AAL5 AAL2

ALCAP

NBAPFrame

Protocols(IubFP)

Control Plane User Plane

AAL5

RRC ConnectionEstablishment*

Radio LinkEstablishment RABs*

NAS signalling*



Transport Network UserPlane

2 Network Protocols

2.4 Iub protocols

Note: AAL2 and AAL5 are sub-layers of ATM which provide some adaptation between the application

(voice, data, signalling) and the ATM layer.

NBAP

is used to carry signalling (e.g Radio Link Establishment)

Examples of actions of NBAP during Radio Link Establishment:

signalling exchanges over Iub, which permits the RNC to reserve radio resources of Node-B

for the Radio Link

signalling transaction with ALCAP, which will setup a Iub data bearer (on AAL2) to carry the

Radio Link

Frame Protocols

At this stage Data Streams (carrying RABs, NAS signalling, SMS Cell Broadcast service, RRC

connection establishment) have been mapped on transport channels

The Frame Protocols (FP) define the structures of the frame and the basic in-band controlprocedures for every type of transport channels.

ALCAP

is used to set up AAL2 connections for Data Streams.

Bearers

Data Streams are carried on AAL2, which enables better bandwidth efficiency for user packets but

requires its own signalling (ALCAP signalling is used to set up AAL2 connections for Data Streams).

NBAP and ALCAP messages are carried on AAL5.


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ATM

Radio

Network

Layer

Transport

Network

Layer

Physical Layer

...

AAL5 AAL2

ALCAP

RNSAPFrame

Protocols(Iur FP)

Control Plane User Plane

AAL5

RRC ConnectionEstablishment*

Establishment of anadditional radio link

to an UE(for soft HO)

RABs*NAS signalling*



Transport Network UserPlane

2 Network Protocols

2.5 Iur Protocols

Note: AAL2 and AAL5 are sub-layers of ATM which provide some adaptation between the application

(voice, data, signalling) and the ATM layer.

RNSAP

It is used to carry signalling (e.g Radio Link Establishment)

e.g. actions of RNSAP during Radio Link Establishment:

signalling exchanges over Iur: the SRNC request the DRNC to reserve radio resources for the

Radio Link (the DRNC will afterwards reserve these radio resources in the suitable Node-B)

signalling transaction with ALCAP, which will setup a Iur data bearer to carry the Radio Link

Frame Protocols

At this stage Data Streams (carrying RABs, NAS signalling, SMS Cell Broadcast service, RRC

connection establishment) have been mapped on transport channels

The Frame Protocols (FP) define the structures of the frame and the basic in-band control

procedures for every type of transport channels.

ALCAP

It is used to set up AAL2 connections for Data Streams.

Bearers

Data Streams are carried on AAL2, which enables better bandwidth efficiency for user packets but

requires its own signalling (ALCAP signalling is used to set up AAL2 connections for Data Streams).

RNSAP and ALCAP messages are carried on AAL5.


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QUIZ!

A. Put the correct words in the spaces on the figure below

... ... ...

...

...

... ... ... ...

......

...

... ...

CS networks(PSTN, ISDN)

PS networks(internet)

...


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3 Radio Channels


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UTRAN SGSN GGSN PDNInternet

UMTS Bearer Service External BearerService

UMTS Bearer Service

Radio Access Bearer Service(RAB)

CN BearerService

BackboneBearer Service

Iu BearerService

Radio BearerService

Uu Iu

Teleservice

UE

LogicalChannel

TransportChannel

Physical

Channel

3 Radio Channels

3.1 Global Situation

A Radio Bearer is the service provided by a protocol entity (i.e. RLC protocol) for transfer of databetween UE and UTRAN.

Radio bearers are the highest level of bearer services exchanged between UTRAN and UE.

Radio bearers are mapped successively on logical channels, transport channels and physical channels(Radio Physical Bearer Service on the figure)


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The RAB provides confidential transport of signaling and user databetween UE and CN with the appropriate QoS.

UTRAN

UE UMTS Bearer

UMTS Bearers

RABs (mapped on Radio & Iu Bearers)

CN-CS

CN-PS

Radio Bearers Iu Bearers

RAB

RAB

RAB

RAB

UMTS Bearer

UMTS bearerservices

3 Radio Channels

3.2 RAB Presentation

AMR 12.2/12.2, 64/64Conversational(CS)

R2: 64/128, 64/384 64/144, 128/384, 144/384, 32/32, 64/64, 128/128, 144/144Background(PS)

14.4/14.4Streaming (CS)

Example of available RAB in R4

R2: 64/128, 64/384 64/144, 128/384, 144/384, 32/32, 64/64, 128/128, 144/144Interactive (PS)


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RRC

RLC

MAC

BMCPDCP

Physical Layer Physical Layer

NASSignaling

RRCSig.

Voice WebBrowsing

SMS CellBroadcast

RadioBearers

TrafficLogical Ch.

TransportChannels

Uu Interface

RNC Node B UE

Physical Channels

MAC

TransportChannels

3 Radio Channels

3.3 Radio Channels, Protocols & Network Elements

ControlLogical Ch.

The radio protocols are responsible for exchanges of signalling and user data between the UE and the

UTRAN over the Uu interface:

User plane protocols

These are the protocols implementing the actual Radio Access Bearer (RAB) service,

i.e. carrying user data through the access stratum (EXAMPLES 1,2 and 4).

Control plane protocols

These are the protocols for controlling the radio access bearers and the connection

between the UE and the network from different aspects including requesting the service

EXAMPLE 5), controlling different transmission resources, handover & streamlining etc...

Also a mechanism for transparent transfer of Non Access Stratum (NAS) messages is included).

Some principles:

The Radio Protocols are independent of the applied transport layer technology

(ATM in R99): that may be changed in the future while the Radio Protocols remain intact.

The main part of radio protocols are located in the RNC (and in the UE).

The Node-B is mainly a relay between UE and RNC.


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Signaling Radio Bearers (SRB)

SRBs can carry:- layer 3 signaling (e.g. RRC connection establishment)- NAS signaling (e.g location update)

There can be up to 4 SRBs per RRC connection (one UE has one RRCconnection when connected to the UTRAN).

User Plane Radio Bearers

RABs are mapped on user plane RBs.

One RAB can be divided on RAB sub-flows and each sub-flow is mapped on

one user plane RB.

e.g the AMR codec encodes/decodes speech into/from three sub-flows; each

sub-flow can have its own channel coding.

3 Radio Channels

3.4 Radio Bearers

Please note that RAB (Radio Access Bearer) are only provided in the user plane.

What is a RRC connection?

When the UE needs to exchange any information with the network, it must first establish a

signalling link with the UTRAN: it is made through a procedure with the RRC protocol and it iscalled RRC connection establishment.

During this procedure the UE will send an initial access request on CCCH to establish a signalling

link which will be carried on a DCCH.

A given UE can have either zero or one RRC connection.


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Control Channels (CCH)

Broadcast Control Channel (BCCH)

Traffic Channels (TCH)

Paging Control Channel (PCCH)

Dedicated Control Channel (DCCH)

Common Control Channel (CCCH)

Dedicated Traffic Channel (DTCH)

Common Traffic Channel (CTCH)

UTRAN UELogical Channels

3 Radio Channels

3.5 Logical Channels

The logical channels are divided into:

Control channels for the transfer of control plane information

Traffic channels for the transfer of user plane information


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UL ( )/

DL ( )What type of information?

BCCH System control informatione.g cell identity, uplink interference level

PCCH Paging informatione.g CN originated call when the network does not know thelocation cell of the UE

CCCH Control informatione.g initial access (RRC connection request), cell update

DCCH Control information (but the UE must have a RRC connection)e.g radio bearer setup, measurement reports, HO

DTCH Traffic information dedicated to one UEe.g speech, fax, web browsing

CTCH Traffic information to all or a group of UEse.g SMS-Cell Broadcast

3 Radio Channels

3.5 Logical Channels [cont.]


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3 Radio Channels

3.6 Why Transport Channels?

A transport channel offers a flexible pattern to arrange information on anyservice-specific rate, delay or coding before mapping it on a physicalchannel:

it provides flexibility in traffic variation

it enables multiplexing of transport channels on the same physical channel

Transport channels provide an efficient and fast flexibility in radioresource management.

Time

Traffic

Time IntervalTransportChannel

The transport channels provides a flexible pattern to exchange data between UTRAN and the UE at a

variable bit rate for the multimedia services.

The logical channels are mapped on the transport channels by the MAC protocols.

By this way the data are processed according to the QoS required before sending them to the Node B by

the Iub.


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3 Radio Channels

3.7 Structure of a Transport Channel

168

168

168

168

168

168

168 bits

20 ms

Time TransmissionInterval (TTI): periodicityat which a Transport Block

Set is transferred by thephysical layer on the radiointerface

20 ms

Transport Block: basicunit exchanged overtransport channels.

Transport Format (TF): it may be changed every TTI. EachTF must belong to the Transport Format Set (TFS) of thetransport channel

168

168

>> The system delivers one Transport Block Set to the>> The system delivers one Transport Block Set to the

physical layer every TTIphysical layer every TTI: what is the delivery bit rate of the: what is the delivery bit rate of the

transport blocks to the physical layer during the first TTI?transport blocks to the physical layer during the f irst TTI?

20 ms 20 ms

A transport channel is defined by a Transport Format (TF) which may change every Time TransmissionInterval (TTI).

The TF is made of a Transport Block Set. The Transport Block size and the number of Transport Block

inside the set are dynamical parameters.

The TTI is a static parameter and is set typically at 10, 20 or 40 ms.

For example,

For a video-call (CS service at 64 kbps)

TTI = 20 ms

TFS = (640* 0,2)

Turbo coding (coding rate=1/3)

16 CRC bits

For a PS 64 kbps service

TTI=20 ms

TFS = (336* 0,1,2,3,4)

Turbo coding (coding rate=1/3)

16 CRC bits


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3 Radio Channels

3.7 Structure of a Transport Channel [cont.]

Transport Format (TF)

Semi-static part (can be changed, but long process)Transmission Time Interval (TTI),Coding scheme...

Dynamic part (may be changed easily)Size of transport block,Number of transport blocks per TTI

Transport Format Set (TFS)

It is the set of allowed Transport Formats for a transport channel, which isassigned by RRC protocol entity to MAC protocol entity.

MAC chooses TF among TFS.

MAC may choose another TF every TTI without interchanging with RRCprotocol (fast radio resource control).

What is TTI (Transmission Time Interval)?

it is equal to the periodicity at which a Transport Block Set is transferred by the physical layer on

the radio interface

it is always a multiple of the minimum interleaving period (e.g. 10ms, the length of one Radio

Frame)

MAC delivers one Transport Block Set to the physical layer every TTI.

What does the TFS provide ?

The selection at each TTI of a number of transport block among the allowed list provides the

required flexibility for the variable traffic and allows to manages the priority.


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3 Radio Channels

3.8 Transport Channels: Example

576

576

576

576

576

576

576 bits

576

576

40 ms

3. How many Transport Format(s) may be chosen for this transport3. How many Transport Format(s) may be chosen for this transport channel?channel?

4. Can you imagine why the transfer has been interrupted during4. Can you imagine why the transfer has been interrupted during the third TTI?the third TTI?

Static PartTTI ?

Coding scheme Turbo coding, coding rate= 1/ 3

CRC 16 bits

Dynamic PartTransport Block Size ?

Transport Block Size Set 576*B (B= 0,1,2,3,4)

1. Complete the table1. Complete the table

2.2. What is the deliveryWhat is the delivery

bit rate of the transportbit rate of the transport

blocks to the physicalblocks to the physical

layer during the firstlayer during the first

TTI?TTI?


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3 Radio Channels

3.9 Transport Channels

Common Channels

Broadcast Channel (BCH)

Dedicated Channels

Paging Channel (PCH)

Random Access Channel (RACH)

Forward Access Channel (FACH)

Dedicated Channel (DCH)

Common Packet Channel (CPCH)

Downlink Shared Channel (DSCH)

UTRAN Transport Channels UE

The transport channels are divided into:

Common channels: they are divided between all or a group of UEs in a cell. They require in-band

identification of the UEs when addressing particular UEs.

Dedicated channels: it is reserved for a single UE only. In-band identification is not necessary, a given UE

is identified by the physical channel (code and frequency in FDD mode)


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3 Radio Channels

3.10 Common Transport Channels

BCH: Broadcast Channel

A downlink transport channel that is used to carry BCCH. The BCH isalways transmitted with high power over the entire cell with a low fixed bit

rate.

>> The BCH is the only transport channel with a single transport>> The BCH is the only transport channel with a single transport format (noformat (no

flexibility). Can you explain why?flexibility). Can you explain why?

PCH: Paging Channel

A downlink transport channel that is used to carry PCCH. It is alwaystransmitted over the entire cell.

>> Is it possible to carry all types of information on the PCH?>> Is it possible to carry all types of information on the PCH?

BCH

high power to reach all the user and low fixed bit rate so that all terminals can decode the data

rate whatever its ability: only one Transport Format because there is no need for flexibility (fixed

bit rate)

PCH

only two transport channels can NOT carry user information: BCH and PCH.


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3 Radio Channels

3.10 Common Transport Channels [cont.]

FACH: Forward Access Channel

A downlink transport channel that is used to carry control information. It may also

carry short users packets. The FACH is transmitted over the entire cell or over only apart of the cell using beam-forming antennas. The FACH uses open loop power

control (slow power control).

>> In which case is it interesting to use beam>> In which case is it interesting to use beam--forming antennas? would it also beforming antennas? would it also be

relevant to implement this feature for PCH?relevant to implement this feature for PCH?

RACH: Random Access Channel

An uplink transport channel that is used to carry control information from the mobileespecially at the initial access. It may also carry short user packets. The RACH isalways received from the entire cell and is characterized by a limited size data field,a collision risk and by the use of open loop power control (slow power control).

>> Why is it interesting to carry short user packets on RACH in>> Why is it interesting to carry short user packets on RACH in spite of limited dataspite of limited data

field and collision risk (instead of using a dedicated channel)?field and collision risk (instead of using a dedicated channel)?

Note: Beam-forming is also called Inherent addressing of users: it is the possibility of transmission to a

certain part of the cell.

RACH and FACH are mainly used to carry signalling (e.g at the initial access), but they can also carry

small amounts of data.

When a UE sends information on the RACH, it will receive information on FACH.


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3 Radio Channels

3.10 Common Transport Channels [cont.]

DSCH: Downlink Shared Channel

A downlink transport channel shared by several UEs to carry dedicatedcontrol or user information. When a UE is using the DSCH, it always hasan associated DCH, which provides power control.

CPCH: Common Packet Channel

An uplink transport channel that is used to carry long user data packetsand control packets. It is a contention based random access channel. It isalways associated with a dedicated channel on the downlink, whichprovides power control.

Transfer of signalling and traffic on a shared basis

DSCH and CCPH seem to be symmetrical, but:

DSCH is on the DL, so that different user data are synchronised with each other (the information

on whether the UE should receive the DSCH or not is conveyed on the associated DCH)

CPCH is on the UL, so that different user data can NOT be synchronised (the mobile phones are not

synchronised). It may cause big problem of collisions!


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3 Radio Channels

3.11 Dedicated Transport Channels

DCH: Dedicated Channel

A downlink or uplink transport channel that is used to carry user or controlinformation. It is characterized by features such as fast rate change (on a

frame-by-frame basis), fast power control, use of beam-forming andsupport of soft HO.

DCH

It is different from GSM where TCH carries user data (e.g speech frames) and ACCH carries higher

layer signalling (e.g HO commands)

User data and signalling are therefore treated in the same way from the physical layer (although set of

parameters may be different between data and signalling)

wide range of Transport Format Set permits to be very flexible concerning the bit rate, the

interleaving...

Fast Power Control and soft HO are only applied on this transport channel.


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Control Logical Channels

BCCH PCCH CCCH DCCH

Traffic Logical Channels

DTCH CTCH

BCH PCH RACH FACH DSCH CPCH DCH

Common Transport Channels Dedicated

TransportChannels

3 Radio Channels

3.12 Mapping Logical / Transport Channels


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3 Radio Channels

3.12 Mapping Logical / Transport Channels [cont.]

Control Logical Channels

BCCH PCCH CCCH DCCH

Traffic Logical Channels

DTCH CTCH

BCH PCH RACH FACH DSCH CPCH DCH

Common Transport Channels Dedicated

TransportChannels

According to the slide above and the previous one, we can say state that :

Except BCH and PCH, each type of transport channel can be used for the transfer of either control or

traffic logical channels.


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3 Radio Channels

3.13 Physical Channels

RNC

Node B

IubTransportChannels

For the UE point of view, the network is just the physical channels.

There are several kinds of physical channels.

Channel associated with transport channel

UTRAN Signaling (mobility management)

Core Network Signaling (authentication)

User Traffic (voice)

There are common and dedicated channels

Channels not associated with transport channel, the physicalsignaling.

Cell Search Selection

System Information Collection

Connection Request and Paging Surveillance

These channels and resources allowing the UE to share thesechannels with other users are the radio resources

We will see later how data from transport channel are processed to bemapped on the physical channels and how a UE uses these channels.

On a cell, all the physical channels are send on the same frequency and on the same time.

It is due to the radio technology, the WCDMA, really different than the one used with the GSM.

Here the physical channels are separated by codes. We will see this point on the next chapter.


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3 Radio Channels

3.14 Physical Channel List

Not associated with transport channels

CPICH: Common Pilot Channel

PICH: Page Indicator Channel

P-SCH & S-SCH: Primary & Secondary Synchronization Channel

AICH: Acquisition Indicator Channel

Common Physical Channels, associated with transport channels

P-CCPCH & S-CCPCH: Primary & Secondary Common Control Channel

PRACH: Physical Random Access Channel

PDSCH: Physical Downlink Shared Channel

PCPCH: Physical Common Packet Channel

Dedicated Physical Channels, associated with transport channels

DPDCH: Dedicated Physical Data Channel

DPCCH: Dedicated Physical Control Channel


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3 Radio Channels

3.15 Downlink

Logical Ch

Transport Ch

Physical Ch

AICHNot associated withtransport channels PICH CPICH P-SCH

S-SCH

PDSCH S-CCPCH P-CCPCHDPDCH

+DPCCH

DTCH, DCCH CCCH, CTCH

DCH BCHPCHFACHDSCH

Not implemented

yet in Alactel-Lucent

Solution

PCCH BCCH

DPDCH and DPCCH

multiplexed by time

Common Physical ChDedicated

Physical Ch

Some common transport channels are multiplexed on the same physical channels. Like the FACH and the

PCH on the S-CCPCH.

The FACH is a downlink common channel to carry the traffic and the control data.

The PCH is the Paging channel.

By the same principles, several DCH (Dedicated channel) belonging by the same user are mapped

on one physical channel, the DPDCH. The DPCCH is its control channel at the physical level.


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3 Radio Channels

3.16 Uplink

Logical Ch

Transport Ch

Physical Ch

PRACH PCPCHDPDCH+

DPCCH

DTCH, DCCH CCCH

DCH1 RACHDCH2

CCTrCH

CPCH

DPDCH and DPCCH

multiplexed by

modulation

Dedicated Physical Ch Common Physical Ch

There are less channels in uplink. For the physical channels, there are the dedicated channels (DPDCH)

and the common channels (PRACH).

The PCPCH is not implemented in the Alactel-Lucent Solution.


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A physical channel is defined by:

A carrier Some codes (see 4.3 and 4.4 part) A start and stop instant

Physical channels are sent continuously on the air interface between start and stop instants.

3 Radio Channels

3.17 Physical Channels: Structure

15 TimeSlots

Radio Frame =10 ms

N bits(according to the bit rate)

.

1 Time slot =

0.666 ms

After channel coding each transport block is split into radio frames of 10 ms.

The bit rate may be changed for each frame.

Each radio frame is also split into 15 time slots.

But all time slots belong to the same user (this slot structure has nothing to do with the TDMA structure

in GSM).

All time slots of a same TDMA frame have the same bit rate.

Fast power control may be performed for each time slot (1500 Hz).

The number of chips for one bit M is equivalent to the spreading factor. It can easily be computed with

knowledge of N:

In fact the spreading factor must be equal to 4, 8, 16256.

Consequently it may be necessary to add some padding bits to match the adequate value of spreading

factor (rate matching).


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4 UTRAN Radio Protocols


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4.1 Radio protocol stack

Layer 3

Control plane User plane

Layer 2/MAC

Layer 1

Transport Channels

Bearers (calledRAB in user plane)Access Stratum

SAP

Non Access Stratum

control

control

control

PHY

MAC

RRC

Logical Channels

Layer 2/RLC

Radio Bearers

RLC RLCRLC

RLCRLC

RLCRLCRLC

PDCPPDCP

BMCcontrol

control

Layer 2/PDCPLayer 2/BMC

Physical Channels

The radio protocols are responsible for exchanges of signalling and user data between the UE and theUTRAN over the Uu interface

The radio protocols are layered into:

the RRC protocol located in RNC* and UE

the RLC protocol located in RNC* and UE

the MAC protocol located in RNC* and UE

the physical layer (on the air interface) located in Node-B and UE

Two additional service-dependent protocols exists in the user plane in the layer 2: PDCP and BMC.

Each layer provides services to upper layers at Service Access Points (SAP) on a peer-to-peer

communication basis. The SAP are marked with circles. A service is defined by a set of service primitives.

Radio Interface Protocol Architecture is described in 3GPP 25.301.

(*except a part of protocol used for BCH which is terminated in Node-B)


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4.2 Radio Resource Control (RRC)

cont

rol

cont

rol

cont

rol

PHY

MAC

RRC

RLC

BearersCall management

Radio mobility management

Measurement control and reporting

Outer loop power controlRadio Bearers(control plane)

RRC is the brain of the radio interface protocol stack.

Layer 3

control

contr

ol

PDCP

BMC

RRC is a protocol which belongs to control plane.

The RRC functions are:

Call management

RRC connection establishment/release (initial access)

Radio Bearer establishment/release/reconfiguration (in the control plane and in the userplane)

Transport and Physical Channels reconfiguration

Radio mobility management

Handover (soft and hard)

Cell and URA update (see 5.UTRAN/ Mobility Management)

Paging procedure

Measurements control (UTRAN side) and reporting (UE side)

Outer Loop Power Control

Control of radio channel ciphering and deciphering

RRC can control locally the configuration of the lower layers (RLC, MAC...) through ControlSAP. These Control services are not requiring peer-to-peer communication, one or more sub-layers can be bypassed.

See 3GPP 25.331 RRC protocol (over 500 pages!)


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4.3 PDCP and BMC Protocols

PDCP (Packet Data Convergence Protocol)

- in the user plane, only for services from the PS domain

- it contains compression methods

In R99 only a header compression method is mentioned (RFC2507).Why is header compression valuable?

e.g a combined RTP/UDP/IP headers is at least 60 bytes for IPv6, when IPvoice service header can be about 20 bytes or less.

BMC (Broadcast/Multicast Services)

- in the user plane

- to adapt broadcast and multicast services from NAS on the radio interface

In R99 the only service using this protocol is SMS Cell Broadcast Service(directly taken from GSM).

See 3 GPP 25.323 (PDCP protocol) and 25.324 (BMC protocol)


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4.4 Radio Link Control (RLC)

TrafficLogical

Channels

Radio Bearers

(user plane)

Radio Bearers

(control plane)

RLC RLCRLC

RLCRLC

RLCRLCRLC

ControlLogical

Channels

Segmentation

Buffering

Data transfer with 3configuration modes:

- Transparent (TM)

- Unacknowledged (UM)

- Acknowledged (AM)

Ciphering

RLC provides segmentation and (in AM mode) reliable data transfer.

Layer 2/upper part

There is no difference between RLC instances in Control and User planes. There is a single RLC

connection per Radio Bearer.

RLC main functions:

RLC Connection Establishment/Release in 3 configuration modes:

- transparent data transfer (TM): without adding any protocol information

- unacknowledged data transfer (UM): without guaranteeing delivery to the peer entity (but can

detect transmission errors)

acknowledged data transfer (AM): with guaranteeing delivery to the peer entity. The AM mode

provides reliable link (error detection and recovery, in-sequence delivery, duplicate detection,

flow Control, ARQ mechanisms)

ARQ=Automatic Repeat Request (it manages retransmissions)

Transmission/Reception buffer

Segmentation and reassembly (to adjust the radio bearer size to the actual set of transport formats)

Mapping between Radio Bearers and Logical Channels (one to one)

Ciphering for non-transparent RLC data (if not performed in MAC), using the UEA1, Kasumi algorithm

specified in R99

Encryption is performed in accordance with TS 33.102 (radio interface), 25.413, 25.331(RRC signaling

messages) and supports the settings of integrity with CN (CS-domain/PS-domain)

3GPP 25.322 RLC protocol


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4.5 Medium Access Control (MAC)

TransportChannels

(common anddedicated)

Basic data transfer

Multiplexing of logical channels

Priority handling/Scheduling(TFC selection)

Reporting of measurements

Ciphering

MAC can switch a common channel into a dedicated channel if higher bit rateis required (on request of L3-level).

MAC can change dynamically Transport Format (bit rate) of each transportchannel on a frame basis (each 10 ms) without interchanging with L3-level.

MAC provides flexible data transfer.

TrafficLogical

Channels

ControlLogical

Channels

MACLayer 2/lower part

MAC belongs to control plane and to user plane.

MAC main functions:

Data transfer: MAC provides unacknowledged data transfer without segmentation

Multiplexing of logical channels (possible only if they require the same QoS)

Mapping between Logical Channels and Transport Channels

Selection of appropriate Transport Format for each Transport Channel depending on instantaneous

source rate.

Priority handling/Scheduling according to priorities given by upper layers:

- between data flows of one UE

- between different UEs

Priority handling/Scheduling is done through Transport Format Combination (TFC) selection

Reporting of monitoring to RRC

Ciphering for RLC transparent data (if not performed in RLC)

3GPP 25.321 MAC protocol


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4.6 The Physical Layer

DedicatedPhysicalChannels

Multiplexing of transport ch.Spreading/modulation

RF processing

Power control

Measurements

Physical layer

DedicatedTransportChannels

The physical layer provides multiplexing and radio frequencyprocessing with a CDMA method.

Air Interface

CommonTransportChannels

CommonPhysicalChannels

Layer 1

The physical layer belongs to control plane and to user plane.

Physical layer main functions:

Multiplexing/de-multiplexing of transport channels on CCTrCH (Coded Composite TransportChannel) even if the transport channels require different QoS.

Mapping of CCTrCH on physical channels

Spreading/de-spreading and modulation/demodulation of physical channels

RF processing (3 GPP 25.10x)

Frequency and time (chip, bit, slot, frame) synchronization

Measurements and indication to higher layers (e.g. FER, SIR, interference power, transmit power,

etc.)

Open loop and Inner loop power control

Macro-diversity distribution/combining and soft handover execution

3GPP 25.2xx


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5 Exercises


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5 Exercises

5.1 MAC protocol

CCCHPCCH BCCH CTCH DTCHDCCH DTCHBCCH

FACH RACH DSCH

Iur or local

DCH DCH

MAC-d

MAC-c/sh

CPCHFACHPCH

MAC

Control

DSCH

Look at this figure and answer the questions on the following paLook at this figure and answer the questions on the following pages.ges.

MAC-b

BCH


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5 Exercises

5.1 MAC protocol [cont.]

1. On which logical/transport channels will be mapped: system information broadcasting paging telephony speech internet browsing at a high bit rate

internet browsing at a low bit rate

Can you imagine a situation where the UE will use 2 DTCHs (or more) at thesame time?

2. Guess the meaning of MAC-b MAC-c/sh and MAC-d.

3. Why is there one MAC-d entity on the UE side and several MAC-d entities on theUTRAN side?

4. What is the link between MAC-c/sh and MAC-d for?


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5 Exercises

5.1 MAC protocol [cont.]

5. What are the 4 main functions of MAC protocol?

6. MAC can multiplex logical channels only if they require thesame QoS: true or false?

7. Which entity is responsible for TFS selection? TF allocation?

8. Will the physical channel configuration be changed(e.g modification of spreading factor) when MAC selects anew TF inside TFS?

9. MAC makes measurement reports to RRC: why is it necessary?


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Evaluation

Thank you for answeringthe objectives sheet

Objective: To be able to draw the UTRANarchitecture with the protocol stack(radio and Iu) of each network element andto define the channels generated by theseprotocols.


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End of ModuleUMTS System Descritption


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Do not delete this graphic elements in here:


Alcatel-Lucent W-CDMA UMTS Radio Principles

2 3JK10656AAAAWBZZA Edition 1Section 2

WCDMA for UMTS


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WCDMA for UMTS 2 2

Blank Page


Conversion into Alcatel-Lucent templateScholle, Martin2007-06-2003

RemarksAuthorDateEdition

Document History


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WCDMA for UMTS 2 3

Objectives

To be able to define a Radio Resource in 3G


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WCDMA for UMTS 2 4

Objectives [cont.]



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WCDMA for UMTS 2 5

Table of Contents

Context Historical

Advantages & Disadvantages

3GPP

Analogy WCDMA and Restaurant

Spread Spectrum Modulation A Code as a Shell against Noise

Spectrum spreading

Transmission Chain

Code & Spreading factor

Spreading factor & Data Rate

Spreading factor & Error at reception

Exercise: Orthogonal Code

WCDMA, Power Density & Processing Gain

Code Division Multiple Access One-cell reuse

Multiple access

Spreading: Channelization and Scrambling

Channelization Codes (Spreading Codes)

Scrambling codes

Soft Handover Introduction Scenarios: Softer Handover

Scenarios: Soft Handover

Scenarios: Soft Handover inter RNC

Scenarios: SRNC Relocation

Soft Handover & Code Management

Cost & Benefit

Rake Receiver Rake Receiver principle

Rake Receiver and Multi-Service

Rake Receiver and soft handover

Rake Receiver and Path Diversity

Power Control Why ?

Different kinds of Power Control

Open Loop Power Control

Closed Loop Power Control: Principle

Closed Loop Power Control: Power Density

UL Closed Loop PC, in case of Soft Handover

DL Closed Loop PC, in case of Soft Handover

Capacity, Coverage & Quality Links between Coverage, Capacity and Quality

Improvement Ways

Typical Values

Page

1 Context 71.1 Historical 81.2 Advantages & Disadvantages 91.3 3GPP 10

2 Analogy 112.1 WCDMA and Restaurant 123 Spread Spectrum Modulation 15

3.1 A Code as a Shell against Noise 163.2 Spectrum spreading 173.3 Transmission Chain 183.4 Code & Spreading factor 193.5 Spreading factor & Data Rate 203.6 Spreading factor & Error at reception 213.7 Exercise: Orthogonal Code 233.7 WCDMA, Power Density & Processing Gain 24

4 Code Division Multiple Access 264.1 One-cell reuse 274.2 Multiple access 28

4.3 Spreading: Channelization and Scrambling 304.4 Channelization Codes (Spreading Codes) 314.5 Scrambling codes 32

5 Soft Handover 335.1 Introduction 345.2 Scenarios: Softer Handover 355.3 Scenarios: Soft Handover 365.4 Scenarios: Soft Handover inter RNC 375.5 Scenarios: SRNC Relocation 385.6 Soft Handover & Code Management 395.7 Cost & Benefit 40

6 Rake Receiver 426.1 Rake Receiver principle 436.2 Rake Receiver and Multi-Service 456.3 Rake Receiver and soft handover 466.4 Rake Receiver and Path Diversity 47

7 Power Control 497.1 Why ? 507.2 Different kinds of Power Control 517.3 Open Loop Power Control 527.4 Closed Loop Power Control: Principle 537.4 Closed Loop Power Control: Power Density 547.5 UL Closed Loop PC, in case of Soft Handover 557.5 DL Closed Loop PC, in case of Soft Handover 56

8 Capacity, Coverage & Quality 578.1 Links between Coverage, Capacity and Quality 588.2 Improvement Ways 598.3 Typical Values 60


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WCDMA for UMTS 2 6





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WCDMA for UMTS 2 7

1 Context


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WCDMA for UMTS 2 8

1 Context

1.1 Historical

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

1996

CDMA 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)

See http://www.cdg.org for IS-95

In CDMA field, we have experience of IS-95

IS-95 vocabulary:

forward channel=downlink

reverse channel=uplink

handoff=handover


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WCDMA for UMTS 2 9

1 Context

1.2 Advantages & Disadvantages

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

Spectrum efficiency : transmission capacity per spectrum unit (bandwidth), i.e kbit/MHz.

This must not be confused with the traffic capacity.

The spectrum efficiency in UMTS is higher than in GSM (25x200kHz carriers in GSM offering 335 kbps**

while a 5 MHz UMTS carrier offers 400 kbps).

If we factor in densification (frequency reuse pattern), the UMTS traffic capacity is dramatically

increased. According to CDMA Development Group:

Capacity increases by a factor of between 8 to 10 compared to an AMPS

analog system and between 4 to 5 times compared to a GSM system


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WCDMA for UMTS 2 10

1 Context

1.3 3GPP

The 3GPP is the organization in charge of the standardization of theUMTS.

It is made of standardization organization (ETSI in Europe, T1 in USA,ARIB in Japan or CTWS in China ), member of manufacturers and

operators.The UMTS frequency allocations are :

TDD FDD MSS TDD

1900 1980 2010 20251920

MSSFDD

2110 2170 2200

FDD: Frequency Division DuplexTDD: Time Division Duplex

MSS: Mobile Satellite SystemUplink Downlink


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WCDMA for UMTS 2 11

2 Analogy


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WCDMA for UMTS 2 12

Cell

Restaurant room

2 Analogy

2.1 WCDMA and Restaurant

WCDMA Restaurant Room

UE

People at table

Code

Language

Enjoy yourmeal !

Code 1

Code 2

Gutenappetite !

Bonappetit !

Bomapetite !

Ues, like people, sendand receive on thesame time and thesame frequency. Theyare separeted by:

For a table, the conversations of the neighboursare noise, for a UE it is the same principle:

neighbour conversations are interference

The equivalence are:

Restaurant room -> Cell

Table -> UE

Language -> Code

Here the important point is all the UEs send and receive on the same time and on the same frequency.

The WCDMA is really different because with the GSM, the UEs are separated by the time (TS of TDMA)

and the frequency. Here the UEs are separated with codes applied on the signals.

Another important point is for someone the conversation on a neighbour table is considered like noise. It

is the same principle with the WCDMA, for a user the other UEs generates some noises.


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WCDMA for UMTS 2 13

2 Analogy

2.1 WCDMA and Restaurant [cont.]


Node B

Steward

Downlink

Who haveorder this cake

?

????

???Impacts:

Power Control in DL

Control Admission

Very important !

Interference level in DL

problem:

If some UE use too muchpower

If there are too manyusers in the cell

Enjoy yourmeal !

COMOESTAS ?

In downlink,

In the restaurant, the steward want to ask to every table who have order a cake. If some people

speak to loud, the table at the back of the room cant hear the question. It is the same case, if

there are too many users in the room.

In the cell, it is the same principle. If there are too many Ues on the cell or if some Ues use too

much power, the interference level for a UE far from the Node B is too high to allow the UE

decoding the message.


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WCDMA for UMTS 2 14

2 Analogy

2.1 WCDMA and Restaurant [cont.]


It is for me!

Who haveorder this cake

?

QUIERO LA

TARTA!!

Es istmeine

Uplink

Cest lapomme ?

????

At the Node B level:

If a UE, close to the NB,speak too loud

If there are too manyusers

Problem of interferencelevel too high.

The NB cant decode any

users anymore.

Impacts:

Power Control in UL

Admission Control

Very important

In Uplink,

In the restaurant, a steward can understand all the conversation if he knows all the languages.

But if on a table, close to him, some one speak to loud the steward cant understand people on

the other tables. It is the same problem if there are too many people it is too noisy to able to

understand a conversation far from him.

With the WCDMA, there is the same problem. That means if the cell is too load,

the interference level at the Node B is too high to be able to decode the weakest signal.


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WCDMA for UMTS 2 15

3 Spread Spectrum Modulation


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WCDMA for UMTS 2 16


3.1 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 to identify the message .

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 theradio channel.

ReceiverTransmitter

Spreading

Noise

DespreadingRadio Channel


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WCDMA for UMTS 2 17


3.2 Spectrum spreading

At the transmitter the signal is multiplied by a code which spreads thesignal 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.

But the interference level is too high, it is not possible to decode anymessage.

???

f

P

Spreading

Radio channel

Despreading

Interference Level

f

P

f

P

f

P

What is the interference level ?

The interference level is the power received on the UMTS bandwidth used. These interferences are made

of:

the background noise,

the messages of the other users,

the traffic on the neighbouring cells.

Because all the users on a cells use the same bandwidth on the same time, and the users on the other

cells too, the decoding and so the error ratio depend on the interference level.


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WCDMA for UMTS 2 18


3.3 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 (fixed) of this code sequence is much higher than the bit

rate of the data signal: it produces a wideband signal, also called spreadsignal.

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

Code synchronization between the transmitter and the receiver is crucial for de-spreading the wideband

signal successfully.


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WCDMA for UMTS 2 19


3.4 Code & Spreading factor

The code is applied on each bit of the user data.

The Spreading Factor, called SF, is the length of this code.

Example: Data to transmit: 1 0 , SF=8.

1-1

1

-1

Spread data

Code

Coded data

Transmission

Recept

ion

Received data,without error

1

-1

A chip

Chip rate fixed at 3.84 Mchip/s

Code applied

1

-1

1

-1

1

-1

What is the spreading factor?

It is the number of chips per bit (=chip rate/bit rate).

The chip rate is linked with the CDMA carrier bandwidth and has a constant value of 3,84 Mcps.

It is quite easy to match the bit rate of the signal with the CDMA chip rate just by choosing the

adequate spreading factor.

The higher the spreading factor, the more redundancy you add in the signal and the lower theprobability of bit error is by transmitting the signal.

It is also traduced by the processing gain (see below).

Code synchronization?

It is difficult to acquire and to maintain the synchronization of the locally generated code signal

and the received signal.

Indeed synchronization has to be kept within a fraction of the chip time.


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3.5 Spreading factor & Data Rate

The chip rate is fixed, 3.84 Mchip/s.

If the SF is divided by 2, the data rate is multiplied by 2 !


Spread data

Code

Coded data

Transmission

Recept

ion

Received data,without error

Code applied

Receiveddata

Small SF = High data rate

High SF = Small data rate

1-1

1

-1

1

-1

1

-1

1

-1

1

-1

The Spreading Factor available are 4, 8, 16, 32, 64, 128, 256 in uplink, plus 512 in downling

For signaling at very low bit rate.


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3.6 Spreading factor & Error at reception

When an error occurs at the reception, the determination of the bit value is less trivial.


1-1

1

-1

Signal sent onthe air

Signal received

with error

Code

SF=8

Zoomonthe

decoded

signa

l

Decoded data

1

-1

0

The

determination of

the bit value is

based on the area

of the receivedsignal.

Here is 6 areaunits over 8


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3.6 Spreading factor & Error at reception [cont.]

1-1

1

-1

Signal sent onthe air

Signal received

with error

Code

SF=4

Zoom

onthe

decod

edsignal

Decoded data

1

-1

0

The

determination of

the bit value is

based on the area

of the receivedsignal.

Here is 2 areaunits over 4

With a small SF, the signal is more sensitive to errors.

So to have the same error ratio you use more power

If you need a high data rate(video downloading), you

will use a small SF. You willhave more errors on your

message. So if you want to

keep the same error ratio,

you will use more power totransmit your message

To keep in mind

Another way to understand this relation is with the redundancy.

If the SF is small, 4 for example, the useful bit, 0 or 1, is sent just 4 time. The data rate is high.

If the SF is higher, 64 for example, the useful bit is sent 64 time. The data rate is smaller.

So if an error occurs, it is more significant if the SF is 4 than if the SF is 64.


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UMTS Radio Principles

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