wcdma

WCDMA Radio Theory

ZTE University

TD&W&PCS BSS Course Team

Course Objectives

At the end of this course, you will be able to:

Master channel encoding of WCDMA

Master spread spectrum principle of WCDMA

Master modulation of WCDMA

Content

The basic principles of wireless communication

Radio Propagation CharacteristicsRadio Propagation Characteristics

Multi AccessMulti Access

Spread spSpread spectrum ectrum TechnologyTechnology

Channel CodingChannel Coding

InterleavInterleavee Technology Technology

WCDMA wireless technology

Characteristic of Radio Propagation

Electromagnetic propagation: direct radiation 、 reflection 、 diffracti

on and scattering

Signal attenuation:

Path loss ： Loss of electromagnetic waves in large scope of the spre

ad reflects the trend of the received signal in the spreading 。 Slow fading ： Loss because of being blocked by the building and hill in

the propagation path

Fast fading ： Electromagnetic signals rapidly decline in a few dozens w

avelength ranges

Description of Fast fading distribution

Rayleigh distribution ： non line-of –sight transmission

Rice distribution ： line-of –sight transmission

Radio propagation charactistics

Frequency Frequency off-setoff-set caused by the movement of mobile caused by the movement of mobile ，， thatha

t is Doppler effectt is Doppler effect

Frequency Frequency off-setoff-set caused by the movement of mobile caused by the movement of mobile ，， thatha

t is Doppler effectt is Doppler effect

Sending signal Accepting signal

Interference Interference

Sending signal

Accepting signal

fadingfading

0 + Sending signal Accepting signal

delaydelay

0 2 3 + Sending signal Accepting signal

ditheringdithering

Characteristics of Radio Propagation

Multi-Path Effects

receiving signalreceiving signal

timetime

strengthstrength

sending signalsending signal

Content

SpreadSpread spectrum spectrum Technology Technology

Interleave TechnologyInterleave Technology

FrequencyTime

Frequency division multiple access technology Channels in different frequency are allocated to different users, e.g. TACS 、 AMPS 。

Time division multiple access technologychannels in different time are allocated to different users, e.g. GSM 、 DAMPS 。

Code division multiple access technology

Users distinguished by scramble code, e.g. CDMA

Code division multiple access technology

Users distinguished by scramble code, e.g. CDMA

Multiple Access

Multiple access

Content

Principle of Spreading spectrum

A technology of transmission technology after spreading freque

ncy of signal.

Theoretical Basis: Shannon theory C=Wlog2(1+S/N)

FastSpreadingSequence

SlowInformation

SlowInformationRecovered

FastSpreadingSequence

WidebandSignal

Spreading technology

S （ f ）

Before spreading

signal

S （ f ）

After spreading

signal

S （ f ）

After despreading

signal

White noise

S （ f ）

Before despreading

signal

White noise

signal interference White noise

Sketch Map of Spreading

Spreading Mode

Direct sequence spread （ DS － SS ） Base band data is spreaded by multiplication of pseudo-noise sequ

ence and base-band pulse, the pseudo-noise sequence generated by the pseudo-noise generator

BER subject to Multiple Access Interference and near-far effect Power control can overcome the near-far effect, but it is limited by

power detection accuracy WCDMA uses DS-SS

Frequency hopping spread （ FH-SS ） Data is transmitted in the random channel by the carrier frequency

hopping Before FH again, data is transmitted using traditional narrowband m

odulation No near-far effect

Characteristics of Spreading Communication

High anti-multi-path- interference capability

High security

Lower transmitting power

Easy to implement large-capacity Multiple Access Communicati

Occupy band wide

Complex realization

Content

Spread spectrum TechnologySpread spectrum Technology

Purpose of Channel Coding

purpose:

By adding redundant information in the original data stream,

receivers can detect and correct the error signal, and improv

e data transmission rates.

Error-correcting ability obtains by adding redundancy in the o

riginal data

Channel coding

W C D M A

T U R B O

S P E A K

W W C C D D M M A A

T T U U R R B B O O

S S P P E E A A K K

W ？ C C D D M M A

T T U ？ R R B B O

S S P P E E A ？ K K

Principle of Channel Coding

Channel coding

Convolutional coding and Turbo coding （ 1/2 ， 1/3 ） are

widely applied.

Increase redundancy and transmission time

Suitable to correct few non-continuous errors

Channel coding

No correct coding: BER<10-1 ~ 10-2Can not satisfy

the communication

Convolutional coding ： BER<10-3Can satisfy the

speech communication

Turbo coding ： BER<10-6Can satisfy the

data communication

Content

Principle of Interleave Technology

advantage

Interleave is to change the sequence of data to discretize the burst

continuous errors

Advance the correcting validity

disadvantage ： Increase the processing delay

Especially, Several independent random errors may intertwined for t

he unexpected error .

x1 x6 x11 x16 x21

x2 x7 … x22

x3 x8 … x23

x4 x9 … x24

x5 x10 … x25

Data input

A = (x1 x2 x3 x4 x5 … x25)

Data output

A’= (x1 x6 x11 x16… x25)

Interleaving technology

Encoding and Interleaving

W C D M A

T U R B O

S P E A K

W W C C D D M M A A

T T U U R R B B O O

S S P P E E A A K K

W T S W T S

C U P C U P

D R E D R E

M B A M B A

A O K A O K

W ? ? C D D M M A A

T ? ? U R R B B O O

S ? ? P E E A A K K

Encoding Interleaving

W T S ? ? ?

? ? ? C U P

D R E D R E

M B A M B A

A O K A O K

DeinterleavingDecoding

Interleaving technology

Content

UE DataEncoding & Interleaving

Spreading&Scrambling

RF Transmission

RF ReceivingDemodulationDespreading&Descrambling

Decoding & Deinteleaving

UE Data

Data transmission Procedure

Modulation

Baseband

demodulation

Convolutional Code

Mainly used in the voice channel and control signal channel

Coding rate is ½ and 1/3 。

Output 0 G0 = 557 (octal)

Input D D D D D D D D

Rate 1/3 convolutional coder

Characteristics of Convolutional code

Easy decode

Short delay

Generally use the Viterbi Algorithm

Channel bit error rate is 10 － 3 magnitude

Suitable to realtime service

e.g. speech and video service.

Turbo Code

Used in Data service channel

Code Rate is 1/3

Can be implemented in the transmission for large block and long delay services

Turbo coding structure is based on two or more weak error control code combinations. Turbo coding structure is based on two or more weak error control code combinations.

The information bits are interleaved in the two Encoder, and generate two information The information bits are interleaved in the two Encoder, and generate two information

flow. At last, this information can be multiplexed and puncturedflow. At last, this information can be multiplexed and punctured

Decoding needs cycle iterative calculationDecoding needs cycle iterative calculation

InterleaverEncoder 1

Encoder 2

inputoutput

Characteristics of Turbo Codes

Complex decoding

Use the LOG-MAP arithmetic

Channel bit error rate is 10 － 6 magnitude

Very suitable to non-realtime package service which is BER sen

sitive & delay insensitive ,

e.g. WWW, FTP, E_mail , multimedia transmission .

Interleaving Technology of WCDMA

Intra-frame interleave

Bits transform in the internal frame

Inter-frame interleave

Data transform among the frames

Intra-Turbo codes interleave

Complex nesting of intra-frame and inter-frame interleave

Spreading&Scrambling Modulation

RF Transmission

UE Data

Symbol rate × SF = 3.84McpsSymbol rate × SF = 3.84Mcps

WCDMAWCDMA ，， SF of uplink channelized codeSF of uplink channelized code ：： 4~2564~256

SF of downlink channelized code:4~512SF of downlink channelized code:4~512

OVSF: Orthogonal Variable Spreading Factor OVSF: Orthogonal Variable Spreading Factor

Symbol rate × SF = 3.84McpsSymbol rate × SF = 3.84Mcps

WCDMAWCDMA ，， SF of uplink channelized codeSF of uplink channelized code ：： 4~2564~256

SF of downlink channelized code:4~512SF of downlink channelized code:4~512

OVSF: Orthogonal Variable Spreading Factor OVSF: Orthogonal Variable Spreading Factor

OVSF Code Scramble Code

Data bitChip after Spreadin

Spreading of WCDMA

Despreading of WCDMA

Method of despreading

Input signal

Local PN code

When T=Ts, judge

Output after despreading

integral

Symbol

Spreading

Despreading

Data = 010010

Spreading code

Spread signal= Data × code

Spreading code =1 -1 -1 1 -1 1 1 -1 ( SF = 8 )

Data = Spread signal × Spread code

Spreading and Despreading

Concept of orthogonal code

Orthogonal—

the result of multiplying and sum is 0

Code1 +1-1+1+1-1+1-1-1

Code2 -1+1+1-1-1+1+1-1

Mul -1-1+1-1+1+1-1+1

OrthogonalCode1 +1-1+1-1-1+1-1-1

Code2 +1+1-1+1-1-1+1-1

Mul +1-1-1-1+1-1-1+1

Sum -2

Non-orthogonal

Code Resource Allocation

Channelization code:

Channelization codes are based on the orthogonal variable

spreading factor (OVSF) technology. Transmission from a

single source are separated by channelization codes.

Scrambling code:

Scrambling codes are used after spreading, which will not

change the signal bandwidth. They are only used to

differentiate different UEs or Node Bs.

In WCDMA, code resources are mainly divided into channelization codes and scrambling codes.

Channelization Code

Adopt OVSF code

C ch,SF,k： describe channelization code,

SF ： spread factor ，

k ： code number, 0 < k<SF-1

Characteristic of channelization code

Premise of code allocation: ensure not occupied for the code in the root direction and d

ownwards subtree

Result of code allocation: block all low rate SC in subtree and high rate in upwards ro

ot direction

Example

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

(a) (b)

(c) (d)

Allocated

Blocked

OVSF Code Scramble Code

Data bitChip after Spreadin

Scrambling code

In addition to spreading, part of the process in the transmitter is the sc

rambling operation. This is needed to separate terminals or base statio

ns from each other. Scrambling is used on top of spreading, so it does

not change the signal bandwidth but only makes the signals from differ

ent sources separable from each other.

Scrambling code of WCDMA

WCDMA scrambling code is generated from Gold sequence Gold has excellent self_correlation,

Mutual_correlation is very small between subsection serial.

It is used to identify cell and user for multiple address.

WCDMA scrambling code is generated from Gold sequence Gold has excellent self_correlation,

Mutual_correlation is very small between subsection serial.

It is used to identify cell and user for multiple address.

WCDMA Scrambling code is pseudo random binary sequence (PN code)

It has similar noise array character , is that one kind is seemingly random bu

t cyclicity binary system array. Can make the user data a further randomizati

on , strengthened by scrambling a code to keep secret the function, at the s

ame time easy to carry out multiple access communication.

WCDMA Scrambling code is pseudo random binary sequence (PN code)

It has similar noise array character , is that one kind is seemingly random bu

t cyclicity binary system array. Can make the user data a further randomizati

on , strengthened by scrambling a code to keep secret the function, at the s

ame time easy to carry out multiple access communication.

Characteristic of Scrambling code

There are 224 Uplink Scrambling Codes, they are used to distinguish differe

nt users in one cell.

Uplink Scrambling codes include long scrambling codes and short scramblin

g codes. The Short Scrambling codes are used for multi-user detecting

There are 218-1 Downlink Scrambling Codes, used to distinguish different c

Scrambling codes in common use are 0 ， 1 ，……， 8191 ， they are divided i

nto 512 aggregations ， each aggregation has 1primary scrambling code and 15

secondary scrambling codes.

512 primary scrambling codes can be divided into 64 scrambling code groups ,th

ere is 8 primary scrambling in each group.

Spreading&Scrambling Modulation

RF Transmission

UE Data

WCDMA Modulation

UL: BPSK

DL:QPSK （ HSDPA introduce 16QAM ）

Exercise

multiple access technolog include ?

pls describe the channel coding purpose and interleaving techn

ology purpose.

WCDMA adopts( ) and( )channel coding technology. th

e coding rate is( ) ( )

the spreading code of WCDMA is ( ), the sf of ul channelize

code is ( ), and the dl is ( )

There are ( ) Uplink Scrambling Codes, they are used to dist

inguish different( ) in one cell.

There are ( ) Downlink Scrambling Codes, used to distingui

WCDMA modulation technology include ( ) and ( )

wcdma

technology characteristics

frequency of signal

technology principle

error signal

signal strength

received signal

propagation path

turbo coding

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