1-2 wcdma wireless principle 49

8/6/2019 1-2 WCDMA Wireless Principle 49

1/49

WCDMA Wireless Principle

ZTE University

PDF created with pdfFactory Pro trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/


2/49


3/49

Multi-path characteristics of radio channel

n Electromagnetic propagation:--direct radiationreflectiondiffraction and scattering

n Signal attenuation:

l Path loss Loss of electromagnetic waves in large scope

of the spread reflects the trend of the received signal in the

spreading

l Slow fadingLoss because of being blocked by the

building and hill in the propagation path

l Fast fadingElectromagnetic signals rapidly decline in a

few dozens wavelength ranges

n Description of Fast fading distribution

l Rayleigh distributionnon line-of sight(NLOS)transmission

l Rician distributionline-of sight(LOS) transmission



4/49

Multi-Path Effects

receiving signaleceiving signaltimetime

strengthstrength

00

sending signalending signal



5/49

Frequency off-set caused by the movement of mobilethat is Doppler effect

FrequencyFrequencyoffoff--setsetcaused by the movement of mobilecaused by the movement of mobilethat is Doppler effectthat is Doppler effect

Sending signal Accepting signal

InterferenceInterference

0dB

Sending signal

-25dB

Accepting signal

fadingfading

0 +


delaydelay

0 2 3 +


ditheringdithering

Characteristics of Radio Propagation



6/49

Content

The Basic Principles of WirelessCommunication

Radio Propagation Characteristics

Spreading Technology

Channel Coding

Interleave Technology

Modulation

WCDMA Radio mechanism



7/49

SHANON Formula

C = Blog2(1+S/N)C = Blog2(1+S/N)

Spread Spectrum Principles

n Where,

C is capacity of channel, b/s

B is signal bandwidth, Hz

S is average power for signal, W

N is average power for noise, W

n It is the basic principle and theory for spread spectrum

communications.



8/49


1.25 MHz

30 KHz

Power is Spread Over a Larger Bandwidth

MATHHAMMER

MATHHAMMER



9/49

radio channel

ReceiverTransmitter

Spreading

Despreading

Noise


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

n Spread signal bandwidth W wider than originalsignal bandwidth Rb

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



10/49

f

Sf

f0

Before spreading

signal

Sf

ff0

After spreading

signal

Sf

ff0

After despreading

signal

White noise

f

Sf

f0

Before despreading

signal

White noise

signal interference White noise




11/49

Spreading Mode

n

Direct sequence spread spectrum

DS-SS

l Base band data is spread by multiplication of pseudo-noisesequence and base-band pulse, the pseudo-noisesequence generated by the pseudo-noise generator

l BER subject to Multiple Access Interference and near-fareffect

l Power control can overcome the near-far effect, but it islimited by power detection accuracy

l WCDMA uses DS-SS

n Frequency hopping spread spectrumFH-SS

l Data is transmitted in the random channel by the carrierfrequency hopping

l Before FH again, data is transmitted using traditionalnarrowband modulation

l No near-far effect



12/49

DS-SS communication system

n A technology of transmission after spreading signalspectrum.

FastSpreadingSequence

Slow

InformationSent

TX

Slow

InformationRecovered

RX

FastSpreadingSequence

WidebandSignal



13/49


Many code channels are individuallyspread and then added together to

create a composite signal



14/49

Unwanted Power fromOther Resoures


n Any Code Channel can be extracted from thereceived composite signal by using the rightorthogonal code

n Energy for transmitting signal can be lower than

interference and noise

Processing Gain

BroadbandInterference



15/49

Concept of orthogonal code

n Orthogonal

the result of multiplying

and sum is 0

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

0Sum

Orthogonal

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

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

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

-2Sum

Non-orthogonal

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

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



16/49

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

-1 1 -11-1 -11 1

1 -1 1 -1

-4 4

0 0J u d g e

-1 1

1 -1 1 -1

-1 1MUL

Integral

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

Example of orthogonal code



17/49

S1S1

S2S2

S1xC1S1xC1

S2XC2S2XC2

WWSpreading

Despreading

(S1xC1)+(S2xC2)(S1xC1)+(S2xC2)

Air InterfaceAir Interface

[S1xC1+S2xC2]xC2[S1xC1+S2xC2]xC2

==S2S2

[S1xC1+S2xC2]xC1[S1xC1+S2xC2]xC1

==S1S1NN

SS

C1xC2=0,C1,C2,orthogonal

Direct spread technique



18/49

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 signalSpreading code

Chip

Sketch map of Spreading and Despreading



19/49

Characteristics of Spreading Communication

n

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

n High security

n Lower transmitting power

n Easy to implement large-capacity Multiple Access

Communication

n Occupy band wide

n Complex realization



20/49

Content




Channel Coding


Modulation




21/49

Purpose of Channel Coding

n

By adding redundant information in the original datastream, receivers can detect and correct the errorsignal, and improve data transmission rates.

No correct coding: BER


22/49

Principle of Channel Coding

n Channel coding

l Error-correcting ability obtains by adding redundancy in the

original data

l Convolutional coding and Turbo coding1/21/3 arewidely applied.

l Increase noneffective load and transmission time

l 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



23/49

Content




Channel Coding


Modulation




24/49

Principle of Interleave Technology

n advantage

l Interleave is to change the sequence of data to random the

unexpected errors

l Advance the correcting validity

n disadvantage

l Increase the processing delay

l Especially, Several independent random errors mayintertwined for the unexpected error .

x1 x6 x11 x16 x21x2 x7 x22x3 x8 x23x4 x9 x24x5 x10 x25

Data inputA = (x1 x2 x3 x4 x5 x25)

Data outputA= (x1 x6 x11 x16 x25)

e.g.



25/49

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 ?

T ? ? U R ? ? B O O

S ? ? P ? E A A K K

Encoding Interleaving

W T S ? ? ?

? ? ? C U P

D R ? D ? EM ? A M B A

A O K ? O K

DeinterleavingDecoding

Encoding+ Interleaving can correct both

continuous and non-continuous errors



26/49

Content




Channel Coding


Modulation




27/49

Principle of Modulation

n

Definitionl Modulation is the process where the amplitude,

frequency, or phase of an electronic or optical signalcarrier is changed in order to transmit information.

l Using symbol stand for one or more bits to improvecommunication effectiveness

n Classification

l Analog Modulation

l Digital Modulation

SymbolbitModulation



28/49

Analog Modulation

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

carrier for transmission.

l Common analog modulation methods include:

n Amplitude modulation (AM)

n Frequency modulation (FM)

n Phase modulation (PM)



29/49

Digital Modulation

n

The purpose of digital modulation is to convert aninformation-bearing discrete-time symbol sequenceinto a continuous-time waveform (perhapsimpressed on a carrier).

l Basic analog modulation methods include

n

Amplitude shift Keying (ASK)n Frequency shift Keying (FSK)

n Phase shift Keying (PSK)



30/49

Content



WCDMA Data transmission Procedure

Channel Coding of WCDMA

Spreading Technology of WCDMA

Modulation of WCDMA



31/49


RF ReceivingDemodulationDespreading

Decoding &De-inteleaving

UE Data

UE Data Spreading

RF Transmitting

Modulation

Basebanddemodulation

Baseband

modulation

Encoding &

Interleaving



32/49

Content






Modulation of WCDMA



33/49

Convolutional Code

n Characteristics

l Mainly used in the voice channel and control signalchannel

l Coding rate : 1/2 & 1/3

l Channel bit error rate is 10-3 magnitude

l

Easy decodingl Short delay

l Suitable for realtime service

n e.g. speech and video service.



34/49

Turbo Code

n Characteristicsl Used in Data service channel

l Code Rate is 1/3

l Channel bit error rate is 10-6 magnitude

l Can be implemented in the transmission for large block and

long delay servicesl Complex decoding, needs cycle iterative calculation

l Very suitable for non-realtime package service which is

BER sensitive & delay insensitive

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



35/49

Content






Modulation of WCDMA



36/49

Symbol rate SF = Chip rate=3.84McpsFor WCDMASF of uplink channelization code4~256

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



37/49

Channelization Code

n Adopt OVSF code

l Definition: Cch,SF,k, describe channelization code,where

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


38/49

Scrambling Code

n WCDMA Scrambling code is pseudo random binary

sequence (PN code)

l It has similar noise array character, seeminglyrandom but with regularity.

l 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 multipleaccess communication.

n WCDMA scrambling code is generated from Goldsequence

l Gold sequence has excellent self-correlation.

l Cross-correlation is very week between two codes.

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



39/49

Characteristic of Scrambling code

n There are 224 Uplink Scrambling Codes, they are

used to distinguish different users in one cell.

n There are 218-1 Downlink Scrambling Codes, usedto distinguish different cells

l Scrambling codes usually used are the first 8192

codes, which are code 0

1

8191. They aredivided into 512 aggregationseach aggregation has1 primary scrambling code (PSC) and 15 secondaryscrambling codes (SSC).

l The 512 primary scrambling codes are divided furtherinto 64 primary scrambling code groups , with 8

primary scrambling codes in each group.


N mbering r le for Do nlink Scrambling


40/49

Numbering rule for Downlink ScramblingCodes

21 8

- 1 Do wn l i n k Sc r a mb l i n g Co d e s i n a l l( 0 . . 2 6 2 1 4 2 )

8176PSC

8177SSC

8191SSC

8176

8177

8191

No. 511 Scrambling CodeGroup

8160

8161

8175

8160

8161

8175


8064

8065

8079

8064

8065

8079


8176PSC

8177

8191

112

113

127


16PSC

17SSC

31SSC

16

17

31


0PSC

1SSC

15SSC

0

1

15


No . 6 3 P r i ma r y S c r a mb l i n g Co d e Gr o u p

No . 0 P r i ma r y S c r a mb l i n g Co d e Gr o u p



41/49

Code Functions

n Channelization code ---- for separation of physical

channels in the uplink and separation of users in thedownlink

n Scrambling code ---- for separation of

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



42/49

Air Interface

2chc

3chc

1chc

scramblingc

Modulation

Spreading code & scrambling code

l Cchspread code

n Relative to service rateextended to 3.84Mchips/sn A kind of orthogonal code

l Cscramblingscrambling code

n Have no effect on signal bandwidth

n downlink for identifier celluplink identifier terminaln A pseudo-random sequence



43/49

f

P

W

ProcessingGain

Rb

Despreading

Processing Gain

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

l Transmitter/receiver can obtain gain afterspread/despread

l The narrower original signal bandwidth, the larger Pg ,the better

The higher PG, the more anti-interference capability system has.

b

c

R

WGainProcessing =



44/49

Question

n Whats the Processing Gain for voice service in

WCDMA system?

n Given: Voice data rate = 12.2kbps

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

l Wc: 3.84Mchip/s

l Rb: 12.2kbpsn So for voice service,

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



45/49

Despreading procedure

n Method of despreading

Input signal

Local PN code

When T=Ts, judge

Output after despreading

integral

0

Ts

(*)dt



46/49

Content






Modulation of WCDMA



47/49

Modulation Methods in WCDMA

n BPSK (Binary Phase Shift Keying) in Uplink channles

n QPSK (Quadrature Phase Shift Keying) in Downlink channels

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



48/49

summary

n Principle of WCDMA

l All users are simultaneously transmitted in the samefrequency band

l Users interfere with each other

l Adjacent cells use the same frequency

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

n Channel coding

l Convolutional code

l Turbo coden Codes

l Channelization code

l Scrambling coden Modulation

l BPSKl QPSK

l 16QAM



49/49


1-2 wcdma wireless principle 49

Documents