Wireless networks - Lecture 21: WCDMA (Part 1)

Wireless Networks

Lecture 21
WCDMA (Part I)
Dr. Ghalib A. Shah

1


Outlines








Last Lecture review
UMTS
Service Classes in UMTS
UTRAN Architecture
Radio Interface protocol Architecture
Protocol Models for UTRAN
Logical Channels

2


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

3


UMTS
 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

4


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
5


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)

6


 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
7


UTRAN and System Architecture

8


 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
9


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

10


Radio Interface protocol architecture

L3

L2
L2

L1

Radio Resource Control (RRC)

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

Physical Layer

11


 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
12


► 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
13


 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
power control, routing and paging
14

 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.

15


Protocol Model for UTRAN
 UTRAN protocol structure is based this model
For all signaling activities in the network, it includes
RANAP, RNSAP, NBAP protocols

Trans. Of all userspecific data CS or PS
through user plan

16


Logical Channels in WCDMA
Channel

Abb.

Functionality

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  CTCH
(DL)

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

Paging Control channel 
(DL)

PCCH

Used to page info the UE
17


Summary








UMTS
Service Classes in UMTS
UTRAN Architecture
Radio Interface protocol Architecture
Protocol Models for UTRAN
Logical Channels
Next Lecture
► WCDMA

18