02 wcdma wireless principle 49

7/27/2019 02 WCDMA Wireless Principle 49

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WR_BT02_E1_1

WCDMA Wireless Principle

ZTE University



Content

The Basic Principles of Wireless

Communication

– Radio Propagation Characteristics

– Spreading Technology

– Channel Coding

– Interleave Technology

– ModulationWCDMA Radio mechanism



Multi-path characteristics of radio channel

Electromagnetic propagation:direct radiation、reflection、diffraction and scattering

Signal attenuation:

Path loss： Loss of electromagnetic waves in large scope

of the spread 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 wavelength ranges

Description of Fast fading distribution

Rayleigh distribution：non line-of –sight(NLOS)

transmission

Rician distribution：line-of –sight(LOS) transmission



Multi-Path Effects

receiving signal

time

strength

0

sending signal



Frequency o ff-set caused by the movement of mobi le ， that

is Dopp ler effect

Sending signal Accepting signal

Interference

0dB

Sending signal

-25dB

Accepting signal

fading

0 +


delay

0 2 3 +


dithering

Characteristics of Radio Propagation



Content


Communication



– Channel Coding





SHANON Formula

C = Blog2(1+S/N)

Spread Spectrum Principles

Where,

C is capacity of channel, b/s

B is signal bandwidth, Hz

S is average power for signal, WN is average power for noise, W

It is the basic principle and theory for spread spectrum

communications.




1.25 MHz

30 KHz

Power is “Spread” Over a Larger Bandwidth



radio channel

Receiver Transmitter

Spreading

Despreading

Noise


User information bits are spread over a widebandwidth by multiplying high speed spreadcode(chip)

Spread signal bandwidth W wider than originalsignal bandwidth Rb

For WCDMA, W=3.84Mchip/s、 Rb(voice)=12kbit/s



f

S（f）

f0

Before spreading

signal

S（f）

ff0

After spreading

signal

S（f）

ff0

After despreading

signal

White noise

f

S（f）

f0

Before despreading

signal

White noise

signal interference White noise




Spreading Mode

Direct sequence spread spectrum（DS-SS）

Base band data is spread by multiplication of pseudo-noisesequence and base-band pulse, the pseudo-noisesequence 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 islimited by power detection accuracy

WCDMA uses DS-SS

Frequency hopping spread spectrum（FH-SS）

Data is transmitted in the random channel by the carrier frequency hopping

Before FH again, data is transmitted using traditionalnarrowband modulation

No near-far effect



DS-SS communication system

A technology of transmission after spreading signalspectrum.

Fast Spreading Sequence

Slow Information

Sent

TX

Slow Information Recovered

RX

Fast Spreading Sequence

WidebandSignal




Many code channels are individually

“spread” and then added together to

create a “composite signal”



Unwanted Power from

Other Resoures


Any Code Channel can be extracted from thereceived composite signal by using the ―right‖

orthogonal code

Energy for transmitting signal can be lower than

interference and noise

Processing Gain

BroadbandInterference



Concept of orthogonal code

Orthogonal—

the result of multiplyingand sum is 0

Code1 +1 -1 +1 +1 -1 +1 -1 -1Code2 -1 +1 +1 -1 -1 +1 +1 -1

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

Sum 0

Orthogonal

Code1 +1 -1 +1 -1 -1 +1 -1 -1Code2 +1 +1 -1 +1 -1 -1 +1 -1

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

Sum -2

Non-orthogonal



-1 1 -11-1 -11 1 -1 -1 11-1 1-1 1MUL-1 1 -11-1 -11 1

1 -1 1 -1

-4 40 0

Judge -1 1

1 -1 1 -1

-1 1 MUL

Integral

1 1 1 1-1 -1 -1 -1

Example of orthogonal code



S1

S2

S1xC1

S2XC2

WSpreading

Despreading

(S1xC1)+(S2xC2)

Air Interface

[S1xC1+S2xC2]xC2

=S2

[S1xC1+S2xC2]xC1

=S1N

S

C1xC2=0,

C1,C2,orthogonal

Direct spread technique



Spreading code =

1 -1 -1 1 -1 1 1 -1

( SF = 8 )

Symbol

Spreading

Despreading

1

-1

1

-1

1-1

1

-1

1-1

Data=010010

Spreading code

Spread signal= Data × code

Data =Spread signal × Spreading code

Chip

Sketch map of Spreading and Despreading



Characteristics of Spreading Communication

High anti-multi-path- interference capability Anti-sudden-pulse

High security

Lower transmitting power

Easy to implement large-capacity Multiple AccessCommunication

Occupy band wide

Complex realization



Content


Communication



– Channel Coding





Purpose of Channel Coding

By adding redundant information in the original datastream, receivers can detect and correct the error

signal, and improve data transmission rates.

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

the communication

Convolutional coding：BER<10-3Can satisfy the

speech communication

Turbo coding： BER<10-6 Can satisfy the

data communication



Principle of Channel Coding

Channel coding

Error-correcting ability obtains by adding redundancy in the

original data

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

widely applied.

Increase noneffective load and transmission time Suitable to correct few non-continuous errors

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 A

T T ? U R R B B O O

S S P P E E A ? K K

Decoding

Encoding



Content


Communication


– Spreading Technology – Channel Coding





Principle of Interleave Technology

advantage

Interleave is to change the sequence of data to random the

unexpected errors

Advance the correcting validity

disadvantage：

Increase the processing delay Especially, Several independent random errors may

intertwined for the 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)

e.g.



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 AA O K A O K

W ? ? C D D M M A ?T ? ? U R ? ? B O O

S ? ? P ? E A A K K

Encoding Interleaving

W T S ? ? ?

? ? ? C U P

D R ? D ? E

M ? A M B A

A O K ? O K

DeinterleavingDecoding

Encoding + Inter leaving can c orrect bo th

cont inuo us and non-con t inuous errors



Content


Communication


– Spreading Technology – Channel Coding





Principle of Modulation

Definition Modulation is the process where the amplitude,

frequency, or phase of an electronic or optical signal

carrier is changed in order to transmit information.

Using symbol stand for one or more bits to improve

communication effectiveness

Classification

Analog Modulation

Digital Modulation

Symbo l b it Modulat ion



Analog Modulation

The purpose of analog modulation is to impressan information-bearing analog waveform onto a

carrier for transmission.

Common analog modulation methods include:

Amplitude modulation (AM)

Frequency modulation (FM)

Phase modulation (PM)



Digital Modulation

The purpose of digital modulation is to convert aninformation-bearing discrete-time symbol sequence

into a continuous-time waveform (perhaps

impressed on a carrier).

Basic analog modulation methods include

Amplitude shift Keying (ASK)

Frequency shift Keying (FSK)

Phase shift Keying (PSK)



Content


Communication

WCDMA Radio mechanism

– WCDMA Data transmission Procedure – Channel Coding of WCDMA

– Spreading Technology of WCDMA

– Modulation of WCDMA



WCDMA Data transmission Procedure

RF ReceivingDemodulationDespreading

Decoding &

De-inteleavingUE Data

UE Data Spreading

RF Transmitting

Modulation

Baseband

demodulation

Baseband

modulation

Encoding &

Interleaving



Content


Communication







Convolutional Code

Characteristics Mainly used in the voice channel and control signal

channel

Coding rate : 1/2 & 1/3

Channel bit error rate is 10-3 magnitude

Easy decoding

Short delay

Suitable for realtime service

e.g. speech and video service.



Turbo Code

Characteristics Used in Data service channel

Code Rate is 1/3

Channel bit error rate is 10-6 magnitude

Can be implemented in the transmission for large block and

long delay services

Complex decoding, needs cycle iterative calculation

Very suitable for non-realtime package service which is

BER sensitive & delay insensitive

e.g. WWW, FTP, E-mail , multimedia transmission .



Content


Communication







Symbol rate × SF = Chip rate=3.84Mcps

For WCDMA，SF of uplink channelization code：4~256

SF of downlink channelization code: 4~512

OVSF: Orthogonal Variable Spreading Factor

OVSF Code Scrambling Code

Data Spread Data

Spreading Process of WCDMA

Symbol Chip

3.84Mcps

3.84Mcps



Channelization Code

Adopt OVSF code Definition: Cch,SF,k, describe channelization code,

where

SF : spread factor ， k : code number, 0 < k<SF-1

SF = 1 SF = 2 SF = 4

C ch,1,0 = (1)

C ch,2,0 = (1,1)

C ch,2,1 = (1,-1)

C ch,4,0 =(1,1,1,1)

C ch,4,1 = (1,1, - 1, - 1)

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

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



Scrambling Code

WCDMA Scrambling code is pseudo random binary

sequence (PN code)

It has similar noise array character, seemingly

random but with regularity.

Can make the user data further random ,

strengthened by scrambling a code to keep secret theuser data, at the same time easy to carry out multiple

access communication.

WCDMA scrambling code is generated from Gold

sequence Gold sequence has excellent self-correlation.

Cross-correlation is very week between two codes.

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



Characteristic of Scrambling code

There are 224 Uplink Scrambling Codes, they are

used to distinguish different users in one cell.

There are 218-1 Downlink Scrambling Codes, used

to distinguish different cells

Scrambling codes usually used are the first 8192

codes, which are code 0，1，……，8191. They are

divided into 512 aggregations，each aggregation has

1 primary scrambling code (PSC) and 15 secondary

scrambling codes (SSC).

The 512 primary scrambling codes are divided further into 64 primary scrambling code groups , with 8

primary scrambling codes in each group.

N b i l f D li k S bli



Numbering rule for Downlink Scrambling

Codes

…

218

-1 Downlink Scrambling Codes in all

(0..262142)

No. 511 Scrambling Code

Group

8176

8177

8191

8176：PSC

8177：SSC

…

8191：SSC


Group

8160

8161

8175

8160：主扰码

8161：辅扰码

…

8175：辅扰码


Group

8064

8065

8079

8064：主扰码

8065：辅扰码 …

8079：辅扰码

…


Group

112

113

127

8176：PSC

8177：辅扰码

…

8191：辅扰码


Group

16

17

31

16：PSC

17：

SSC…

31：SSC


Group

01

15

0：PSC1：SSC

…

15：SSC

No.63 Primary Scrambling Code Group

… …

No.0 Primary Scrambling Code Group



Code Functions

Channelization code ---- for separation of physical

channels in the uplink and separation of users in the

downlink

Scrambling code ---- for separation of

users/terminals in the uplink and cells/sectors in the

downlink.



Air Interface

2chc

3chc

1chc

scrambling c Modulation

Spreading code & scrambling code

Cch：spread code

Relative to service rate，extended to 3.84Mchips/s

A kind of orthogonal code

Cscrambling：scrambling code

Have no effect on signal bandwidth

downlink for identifier cell，uplink identifier terminal

A pseudo-random sequence



f

P

W

Processing

Gain

Rb

Despreading

Processing Gain

PG=Wc/Rb (Wc : Chip rate , Rb : Service bit rate)

Transmitter/receiver can obtain gain after

spread/despread

The narrower original signal bandwidth, the larger Pg ,

the better

The higher PG, the more anti-inter ference capabi l ity system has.

b

c

R

WGainProcessing



Question

What’s the Processing Gain for voice service in

WCDMA system?

Given: Voice data rate = 12.2kbps

PG=10lg(Wc/ Rb) , dB units

Wc: 3.84Mchip/s Rb: 12.2kbps

So for voice service,

PG=10lg(3.84* 106 /12.2* 103)= 25 dB



Despreading procedure

Method of despreading

Input signal

Local PN code

When T=Ts, judge

Output after despreading

integral

0

Ts(*)dt



Content


Communication







Modulation Methods in WCDMA

BPSK (Binary Phase Shift Keying) in Uplink channles

QPSK (Quadrature Phase Shift Keying) in Downlink channels

16QAM (16-state Quadrature Amplitude Modulation) in HSDPA



summary

Principle of WCDMA

All users are simultaneously transmitted in the samefrequency band

Users interfere with each other

Adjacent cells use the same frequency

Cells, users (terminals), and physical channels areseparated by codes

Channel coding

Convolutional code

Turbo code

Codes

Channelization code

Scrambling code Modulation

BPSK

QPSK

16QAM

02 wcdma wireless principle 49

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