Wireless networks - Lecture 21: WCDMA (Part 1)

Wireless networks - Lecture 21: WCDMA (Part 1). The main topics covered in this chapter include: UMTS; service classes in UMTS; UTRAN architecture; radio interface protocol architecture; protocol models for UTRAN; logical channels;...

Wireless Networks

Lecture 21 WCDMA (Part I)

Dr Ghalib A Shah

 Last Lecture review

 UMTS

 Service Classes in UMTS

 UTRAN Architecture

 Radio Interface protocol Architecture

 Protocol Models for UTRAN

 Logical Channels

Last Lecture Review

 Walsh Codes

 IS-95 Reverse Link

 EDGE Introduction

 Modulation and Coding Schemes

 Link Adaptation and Incremental Redundancy

 Capacity Planning

 Dynamic Abis pool

 UMTS networks have predominance of data traffic

unlike GSM networks.

 The data rate will be significantly higher than that

offered by GSM / GPRS / EDGE

 3G networks serve different purpose and thus the

major changes from previous networks are

► Max user data rate up to 384 kbps

► Efficient handover between different operators and

technologies e.g GSM and UMTS

► Ability to deliver at requested bandwidth

► Ability to deliver different services with the required quality

WCDMA Radio Fundamentals

 WCDMA has emerged as most preferred and adopted

technology for 3G air interface

 The major differences between WCDMA and GSM are:

► 5 MHz channel bandwidth as compared to 200 KHz in GSM

► Packet data scheduling is load based unlike time slot based in

GSM

► Theoretically only one f channel, while GSM uses many

channels

► Quality control is done using RRM algorithm, while it was done

by implementing frequency planning techniques in GSM

► Users/cell/channel are separated by codes unlike time or

frequency in GSM

Service classes in UMTS

 In 3G network, ME will be able to establish

multiple connections simultaneously.

 Network allows efficient cooperation between

application with diverse quality of service

requirements.

 The quality can be defined by two main

parameters

► Guaranteed and max bit rate possible (kbps)

► Permissible delay (ms)

 Based on the QoS criteria, multimedia services

has been further classified

► Conversational

• The most delay sensitive, e.g applications video telephony, VoIP

► Streaming

• Flow which is steady and continuous, it is server to user

► Interactive

• Web browsing is an example A user may request timetables of buses, trains or flight schedule

► Background

• Short messages, file transfer, email that has least stringent requirements of QoS

UTRAN and System Architecture

 USIM contains authentication information and

associated algorithms, encryption and

subscriber related information

 ME is user independent

 BS

► Also known as node B in WCDMA and is more

complex than BS in GSM

► Its functions include handover channel management,

baseband conversion, channel encoding and decoding, interfacing to other network elements

Radio Network Controller

 Concerning one connection between UTRAN

and one UE, the following roles of RNCs exist:

► Serving RNC that controls the connections to a UE

► Drift RNC that lends its resources of Serving RNC

for a particular UE

 Each RNC also has the controlling RNC role

towards its Node Bs

Radio Interface protocol architecture

L3 Radio Resource Control (RRC)

L2 Radio Link Control (RLC) L2 Medium Access Control (MAC)

L1 Physical Layer

 Layer 1

► The actual medium of transfer

► The main functions of this layer include RF

processing, modulation/demodulation, multiplexing / demultiplexing of physical channels

► Error detection and correction, rate matching, power

control, synchronization etc

 Layer 2

► It has two main sub-layer

• RLC

► MAC

• Responsible for mapping logical channels to the transport channels

• An interface between L1 & L3 and provides packet

multiplexing / demultiplexing

• Measurement related to traffic volume on logical channels and reporting to layer 3

► RLC

• Segmentation reassembly of variable size data packets

• Error correction by retransmission and ACKed data transfer mode

• Controlling rate flow, concatenation, cyphering and

preservation of higher-order PDUs

• Operates in three mode as in GPRS

 Layer 3

► Contains sub-layers but RRC is the one that interact

with layer 2

► Handles control plane signaling between UE and

network in connected mode

► Responsible for bearer functions like establishment,

release, maintenance and reconfiguration in the user plane and of radio resources in control plane

► Functions of RRC include radio resource

management and mobility management, as well as

 Two other layers

► Packet data convergence protocol (PDCP)

• Major functions being compression of PDU at transmitting end and decompression at receiving end in all of three modes of RLC

► Broadcast – Multicast Control (BMC)

• Functions only in transparent and unACKed modes providing broadcast/multicast scheduling and transmission

of user data

Protocol Model for UTRAN

 UTRAN protocol structure is based this model

Trans Of all user-specific data CS or PS through user plan

For all signaling activities in the network, it includes

RANAP, RNSAP, NBAP protocols

Logical Channels in WCDMA

Broadcast Common 

Control channel 

(DL)

BCCH Transmits the system control information

Common Control 

channel (UL/DL)

CCCH Used (usually by UE) for transmitting info 

related to control between network  and UE

Common Traffic Channel 

(DL)

CTCH Used to transmit dedicated info to a group 

of UEs Dedicated Control 

Channel (UL/DL) DCCH Dedicated channel for control related information between UEs and 

network Dedicated Traffic 

Channel (UL/DL)

DTCH Similar to DCCH except that it is used for 

user information

 UMTS

 Service Classes in UMTS

 UTRAN Architecture

 Radio Interface protocol Architecture

 Protocol Models for UTRAN

 Logical Channels

 Next Lecture

► WCDMA