wcdma explained

7/27/2019 WCDMA Explained

1/27

09-1

WCDMA

power

time

frequency

~5 MHz

09-2

Outline

IMT-2000 Requirements

WCDMA system

Multiservice concepts


2/27

09-3

IMT-2000 requirements Full coverage and mobility for 144 kbps,

and preferably for 384 kbps

Limited coverage and mobility for 2 Mbps

High spectral efficiency

Flexibility to introduce new services

09-4

IMT-2000 user rate vs coverage andmobility

Fixed area / low mobility Wide area / high mobility

User bit rate

2 Mbps

384 kbps

144 kbps

10 kbps Basic 2G

Evolved 2G

GSM EDGE

(Enhanced Data rates using optimised modulation)

IMT-2000


3/27

09-5

JargonFest

IMT-2000 = International Mobile Telephony 2000 ITU (International Telecommunications Union) terminology for 3G

UMTS = Universal Mobile Telecommunication System The UMTS Forum is an international and independent body, uniquely

committed through the building of cross-industry consensus to thesuccessful introduction and development of UMTS/IMT-2000 thirdgeneration mobile communications systems.

UTRA = Universal Terrestrial Radio Access

3GPP = 3rd Generation Partnership Project joint standardisation group

WCDMA is known within 3GPP as UTRA FDD + UTRA TDD

09-6

WCDMA Concepts

WCDMA system specifications

Logical Channels

Physical Channels

Packet Access

Multiservice support

TDD mode


4/27

09-7

WCDMA key characteristics

Multiple access scheme DS-CDMA Duplex scheme FDD/TDD Chip rate 3.84 Mcps Carrier Spacing Flexible 4.4-5.0 MHz (3.84 Mcps) Frame length 10 ms Multi-rate/Variable rate Variable spreading factor (4 to 256)

+ Multi-code Channel coding Convolutional coding (rate 1/2 or 1/3)

Optional outer Reed-Solomoncoding (rate 4/5)

Packet access Dual mode (common channelor dedicated channel)

09-8

Common Control Channels Broadcast control channel (BCCH) Forward Access Channel (FACH) Paging Channel (PCH) Random Access Channel (RACH)

Dedicated Channels Dedicated Control Channel (DCCH)

Dedicated Traffic Channel (DTCH)

Downlink

Uplink

Bidirectional

Uplink and/orDownlink

WCDMA Logical Channel structure


5/27

09-9

Primary Common Control Physical Channel(Primary CCPCH) (full cell coverage)

Secondary Common Control Physical Channel

(Secondary CCPCH)(may be transmittedover only part of a cell, e.g. a lobe)

Physical Random Access Channel (PRACH)

Dedicated Physical Data Channel (DPDCH) Dedicated Physical Control Channel (DPCCH)

The logical channels are mapped intothe above physical channels, (conceptually similarly to GSM).

Common

Dedicated

WCDMA Physical Channel Structure

09-10

Broadcast Control Channel BCCH (DL) Downlink point to multipoint channel Broadcasts system and cell specific information

(including info on available codes at the cell) BCCH is transmitted over entire cell Mapped to Primary CCPCH

Forward Access Channel (DL) Carries control information to mobile

FACH may also carry short user packets FACH may be transmitted over only part of a cell(e.g. smart antennas)

Mapped to Secondary CCPCH

Common Control Channels


6/27

09-11

Paging Channel PCH (DL) Carries control information to mobile when mobile location is

unknown Transmitted over the entire cell Mapped to Secondary CCPCH

Random Access Channel (UL) Carries control information from mobile station RACH may carry short user packets Received from entire cell Mapped to PRACH

Common Control Channels contd

09-12

Dedicated Control Channel DCCH (UL and DL) Bidirectional channel used to carry control information Mapped to DPDCH (together with DTCHs)

Dedicated Traffic Channel DTCH (DL and/or UL) Bidirectional or unidirectional channel Used to carry user information

Mapped to DPDCH(together with DCCH and other DTCHs)

Dedicated Control Channels


7/27

09-13

Common Channels

BCCH Mapped to Primary CCPCHFACH Mapped to Secondary CCPCHPCH Mapped to Secondary CCPCHRACH Mapped to PRACH

Dedicated Channels

DCCH Mapped to DPDCHDTCH Mapped to DPDCH

Summary of Logical Channels

09-14

Dedicated Physical Data Channel DPDCHcarries dedicated data, generated at level 2 and above

Dedicated Physical Control Channel DPCCHcarries control information generated at level 1, i.e.

pilot signals to assist in coherent detection transmit power control signals rate information

Dedicated Physical Channels


8/27

09-15

Superframe, 72 frames, 720 ms

S#1 S#2 S#3 S#4 S#5 S#6 S#7 S#8 S#9 S#10 S#11 S#12 S#13 S#14 S#15 S#16

Frame, 16 slots, 10 ms

RITPCPilot

Slot, 0.625 ms, 2560 chips

Data

Rate InformationTransmit Power Control

Pilot signal

Data Bits

DPCCH DPDCH

WCDMA Frame Structure:

Downlink Dedicated Physical Channels

Slot length is 0.625 ms

with 202kbits , k= 0,1,...,6

SF=256/2k

=>SF from 4 to 256

09-16

Spreading and Modulation for

Downlink Dedicated Physical Channels

cch is the channelisation codecscramb is the scrambling code (cell-specific)p(t) is the pulse shaping filter

For multicode transmission, each DPDCH/DPCCHshould be assigned a distinct channelisation code

Serial

to

Parallelchc scrambc )sin( t

)cos( t

DPDCH/

DPCCH

I

Q

)(tp

)(tp


9/27

09-17

Channelisation CodesOrthogonal Variable Spreading Factor (OVSF) codes defined by code tree:

)1(1,1 =C

)1,1(1,2 =C

)1,1(2,2 =C

)1,1,1,1(1,4 =C

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

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

)1,1,1,1(4,4 =C

SF = 1 SF = 2 SF = 4

a code can only be used iff no other code is usedbetween that code and the root of the code tree

... SF = 256

09-18


S#1 S#2 S#3 S#4 S#5 S#6 S#7 S#8 S#9 S#10 S#11 S#12 S#13 S#14 S #15 S#16



Uplink Dedicated Physical Channels


with 10 2kbits ,k= 0,1,...,6

Pilot TPC RI


Data

DPCCH

DPDCH

Rate Information

Transmit Power ControlPilot signal


10/27

09-19

Spreading and Modulation for

Uplink Dedicated Physical Channels

cC, cD - channelisation codescscramb - primary scrambling code

- a complex code cI+jcQ

cscramb - secondary scrambling code (optional)p(t) is the pulse shaping filter

scrambc'

)sin( t

)cos( t

DPDCH I

Q

)(tp

)(tpDPCCH

Cc

Dc

j*

jQI+(optional)

'' scrambc Real

Imag

09-20

For multicode transmission, each additional DPDCH may be

transmitted on either the I or Q branch,

with a distinct channelisation code

Uplink Dedicated Physical Channels.


11/27

09-21


S#1 S#2 S#3 S#4 S#5 S#6 S#7 S#8 S#9 S#10 S#11 S#12 S#13 S#14 S #15 S#16


Pilot


Data

Pilot signal

Data Bits


with 202kbits ,k = 0,1,...,6

CCPCH hasno power controlconstant rate


Common Control Physical Channels

09-22

CCPCH is modulated and spread as for theDownlink Dedicated Physical Channel

Primary CCPCHhas fixed predefined rate of 32 kbpsis transmitted over an entire cell

Secondary CCPCHhas constant rate, which may be different for different cells,

depending on capacity needed for FACH and PCH

only transmitted when data is available, e.g. in a narrow lobehas the FACH and PCH time multiplexed frame-by-frame.The set of allocated frames is broadcast on the BCCH.

Common Control Physical Channels

(contd)


12/27

09-23

SCH is used for cell searchSCH consists of 2 sub-channels,

the Primary SCH and Secondary SCHSCH is transmitted one codeword per slot

Primary SCH is used to acquire slot synchronisationto the strongest BSSecondary SCH is used to obtain frame synchronisationand identify the code group of the BS.

then the mobile can determine the scrambling code,

then detect the Primary CCPCH,

then acquire superframe synchronisation etc

Synchronisation Channel SCH (DL)

09-24

Primary SCHis

an unmodulated Gold code of length 256 chips, transmitted once per slot, aligned with slot boundary same for every BS

Secondary SCHis a modulated Gold code of length 256 chips

transmitted in parallel with the Primary SCH chosen from a set of 16 different codes,

to match the BS downlink scrambling code

Synchronisation Channel SCH (DL) contd


13/27

09-25

Physical Random Access Channel PRACH

Random access burst contains

a preamble of 16*256 chips (1ms) a variable length data part

Preamble Data

The preamble consists of 16 symbols spread by the preamble codeof length 256 chips (find these from BCCH)

Each symbol is randomly chosen from a set

of 16 orthogonal code words each of length 16 bits Neighbouring BSs use different preamble codes

09-26

CRC

PRACH: Data Part

Data part contains Mobile station ID (16 bits) Required service (3 bits) (e.g short packet, dedicated channel setup) Optional user packet (variable length) CRC (8 bits)

Spreading and modulation as for uplink dedicated physical channels

Preamble DataPreamble ReqSer

MSID

User Packet


14/27

09-27

Scrambling code for data partis based on: the BS specific preamble code plus the randomly chosen preamble sequence plus a randomly chosen time offset

This ensures that random access attempts usingdifferent preamble codes/sequences wont collide

PRACH: Data Part...

09-28

First: obtain chip and frame synchronisation obtain information on available preamble codes

determine transmit power, estimated to achieve target SIRusing open loop power control

Then:transmit the burst with a randomly chosen 2n ms (n= 0,1,2,3,4)time offset relative to the frame boundary

A BS may the receive up to 80 random access attemptswithin one 10 ms frame(80 = 16 preamble sequences, with 5 time offsets)

Random Access procedure


15/27

09-29

Power Control

SIR-based power control, using both open loop andclosed loop power control

Operates similarly on both uplink and downlink

Target SIR is independently adjusted for each connection,based on the estimated quality of the connection.Quality estimate is obtained using a combination ofBER and FER estimates

09-30

WCDMA Concepts

WCDMA system specifications

Logical Channels

Physical Channels

Packet Access

Multiservice support

TDD mode


16/27

09-31

Outerinterleaving

Innerinterleaving

Innerinterleaving

Channel coding/interleaving for QoS

Innercoding

Innercoding

Outercoding

BER=10-3

BER=10-6

Service Specific Coding

09-32

Inner

coding/

interleaving

Outer

coding/

interleaving

Time

Mux

Multiple services belonging to the same connectionare normally time-multiplexed,then mapped to one or more DPDCHs, as necessary

Time

Mux

Time

Mux.

.

.

.

.

.

.

.

.

DPDCH #1

DPDCH #2

DPDCH #NParallelServices

Service Multiplexing


17/27

09-33

Service Multiplexing (contd)

Multiple services belonging to the same connectionmay alternatively be treated completely separately, in multicode fashionThis allows QoS for separate services to be individually controlled,but MS complexity is greater.

Coding/

interleaving

DPDCH #1

Coding/

interleaving

DPDCH #2

Coding/

interleaving

DPDCH #N

.

.

.

Parallel

Services

09-34

Rate Matching

Multiplexed rates can produce almost arbitrary total bit rates

There are a limited set of rates available on a DPDCH

To match the rates: use rate matching repetition coding or

code puncturing


18/27

09-35

Example 8 kbps bearer service

Tail (8 bits)CRC (8 bits)Data (80 bits)

Data (96 x 3 = 288 bits)

Data (288 x 10/9 = 320 bits)

Rate 1/3 convolutional coding

9->10 unequal repetition

DPDCH

32 kbps

Bearer

8 kbps

Coded

channel

28.8 kbps

09-36


Tail (8 bits)

Data (1440 bits)

Data (1440 x 225/180 = 1800 bits)

Data (1808 x 3= 5424 bits)

Rate 180/225 RS coding

Rate 1/3 convolutional code

DPDCH

512 kbps

Bearer

144 kbps

Data (5424x 320/339 = 5120 bits)

339->320 code puncturing

Coded

channel

542.4 kbps


19/27

09-37


Tail (24 bits)

Data (3840 bits)

Data (3840 x 240/192 = 4800 bits)

Data (4824 x 2 = 9648bits)

Rate 192/240 RS coding

Rate 1/2 convolutional code

DPDCH

1024 kbps

Bearer

384 kbps

Data (9648 x 640/603 = 10240bits)

603->640 unequal repetition

Coded

channel

964.8 kbps

09-38

HandoverSoft Handover Active MS receives a priority list from the network MS searches priority list for new BSs

Softer Handover Soft handover between sectors of the same BS Operation as for soft handover

Differences only at network implementation level


20/27

09-39

Handover (contd)

Interfrequency Handover

Needed:

When handover occurs between cells where

a different # of carriers have been allocated

For handover between cell layers using different

carrier frequency (e.g hierarchichal cells)

For interoperator handover

For handover to GSM

09-40

Interfrequency HandoverIdle period is created for measurements of other frequencies,either by reducing the spreading factor by 2,or by code puncturing

Frame

Idle period available for interfrequency measurements

Rate is variable, ~100 ms intervals

Handover (contd)


21/27

09-41

Interfrequency HandoverWhen service allows interleaving over several frames,multiple frames can be compressed to createa 5 ms measurement slot

Frame

Idle period available for interfrequency measurements

Compressed transmissionduring one interleaverspan

Handover (contd)

09-42

WCDMA Packet AccessWCDMA packet access can take place on a common fixed-rate channel on a dedicated channel

Common channel packet transmission Uplink packet is appended directly to a random access burst Limited to short packets that use only a

limited amount of capacity


22/27

09-43

WCDMA Packet AccessDedicated channel packet transmission Single-packet transmission mode, or Multiple-packet transmission mode

Single packet transmission modeSend a random access request, indicating amount of data

to be sentNetwork responds: with an immediate scheduling message OR with a short ACK, followed by a scheduling messageScheduling message indicates when transmission can begin,the bit rate, etc

09-44

WCDMA Packet Access (contd)Randomaccessburst

Userpacket

Randomaccessburst

Userpacket

ArbitraryTime

Packet transmission on common channel

Userpacket

Userpacket

Single packet transmission on dedicated channel

Randomaccessburst

Randomaccessburst

ArbitraryTime

Common Channel

DedicatedChannel


23/27

09-45

WCDMA Packet Access (contd)

Scheduleduser packet

Multi- packet transmission on dedicated channel

Dedicated Channel

Accessrequest

Randomaccessburst Common Channel

Scheduleduser packet

Unscheduleduser packet

Accessrequest

Link maintenance

Multi-packet transmission Random access request is used to set up a dedicated packet channel

Short packets may be sent on dedicated channel without scheduling Long packets require an access request

09-46

TDD Operation TDD mode is based on the same frame structure as FDD mode,

i.e. 10 ms frame split into 16 x 0.625 ms slots Multiplexing and spreading as for FDD mode Each TDD slot can be used either for uplink or downlink

TDD Alternating mode (e.g. outdoor suburban environment)

Rx Rx Rx Rx Rx Rx Rx Rx

Tx Tx Tx Tx Tx Tx Tx Tx

0.625 ms

1.25 ms

10 ms

Coded DataGuard Band

Pilot


24/27

09-47

TDD Operation (contd)

TDD Asymmetric mode (e.g. indoor/low speed outdoor)

0.625 ms

10 ms

ReceivePi G

TransmitPi G

Receive block is a multiple of 0.625 msi.e. allows asymmetry of up to 15:1

09-48

UE UTRAN

UMTS High Level System Architecture

UE:

UserEquipment

CN

UTRAN:

UMTSTerrestrial

Radio Access

Network

CN:

CoreNetwork


25/27

09-49

UE

ME+USIM

UTRAN

Node B + RNC

UTRA High Level System Architecture

ME: Mobile

Equipment

USIM: UMTS

SubscriberIdentity Module

CN

GMSC+

MSC/VLR

+HLR

Node B: Base

Station

RNC: Radio

NetworkController

09-50

RNC

Node B

MSC/

VLR

HLR

MSCN

UTRAN

Uu Interface Iub Interface Iu interface

UTRA: Network Elements

GMSC

UE

USIM

Cu

Interface

External

Network


26/27

09-51

UMTS Terrestrial Radio Access

Network

(UTRAN)

Support of soft handover

Support of the WCDMA-specific radio resource

managementfunctions

Maximisation of commonalities in handling packet-switchedand circuit-switched data

Maximisation of commonalities with GSM

Use ATM transportas the main transport mechanism

09-52

Radio Network Controller (RNC)

Each BS has a Controlling RNC (CRNC)

load and congestion control

admission control

code allocation

Since more than one RNC may be involved (e.g. soft handoff),

each connection may involve:

Serving RNC (SRNC) controls outer loop power control, handoff

decisions. The SRNC may be the same as the CRNC used by someNode B used by the mobile.

Drift RNC (DRNC) controls any other cells used by the mobile. One UEmay have multiple DRNCs


27/27

09-53

ETSI,Wideband Direct Sequence CDMA (WCDMA)

Part 1: System Description and Performance Evaluation,

ETSI Tdoc SMG2 359/97, December 1997

H. Holma and A. Toskala (eds),WCDMA for UMTS: Radio Access for Third Generation Mobile Communications,

Wiley, 2000

R Prasad, T Ojanper,

An Overview of CDMA Evolution toward Wideband CDMA,IEEE Communication Surveys(http://www.comsoc.org/pubs/surveys),

Vol 1, No 1, pp 1-29, Fourth Quarter 1998

References

wcdma explained

Documents