01 wr_bt1002_e01_1 wcdma wireless principle-49

8/13/2019 01 WR_BT1002_E01_1 WCDMA Wireless Principle-49

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WCDMA Wireless Principle

ZTE University


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Content

The Basic Principles of Wireless Communication Radio Propagation Characteristics

Spreading Technology

Channel Coding

Interleave Technology

Modulation

WCDMA Radio mechanism


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Multi-path characteristics of radio channel

Electromagnetic propagation:

--direct radiationreflectiondiffraction and scattering

Signal attenuation:

Path lossLoss of electromagnetic waves in large scope of the spreadreflects the trend of the received signal in the spreading

Slow fadingLoss because of being blocked by the building and hill in thepropagation path

Fast fadingElectromagnetic signals rapidly decline in a few dozenswavelength ranges

Description of Fast fading distribution

Rayleigh distributionnon line-ofsight(NLOS) transmission

Rician distributionline-ofsight(LOS) transmission


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Multi-Path Effects

eceiving signal

time

strength

0

sending signal


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Frequency of f -set caused by the mo vement of mobi le that

is Dopp ler effect

Sending signal Acceptingsignal

Interference

0dB

Sendingsignal

-25dB

Acceptingsignal

fading

0 +

Sendingsignal Acceptingsignal

delay

0 2 3 +

Sendingsignal Acceptingsignal

dithering

Characteristics of Radio Propagation


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Content



Channel Coding


Modulation



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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, W

N is average power for noise, W

It is the basic principle and theory for spread spectrum

communications.


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1.25 MHz

30 KHz

Power is Spread Over a Larger Bandwidth


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radio channel

ReceiverTransmitter

Spreading

Despreading

Noise


User information bits are spread over a wide bandwidth by

multiplying high speed spread code(chip) Spread signal bandwidth W wider than original signal

bandwidth Rb

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


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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



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Spreading Mode

Direct sequence spread spectrumDS-SS Base band data is spread by multiplication of pseudo-noisesequence and base-band pulse, the pseudo-noise sequencegenerated 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 bypower detection accuracy

WCDMA uses DS-SS

Frequency hopping spread spectrumFH-SS

Data is transmitted in the random channel by the carrier frequencyhopping

Before FH again, data is transmitted using traditional narrowbandmodulation

No near-far effect


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DS-SS communication system

A technology of transmission after spreadingsignal spectrum.

FastSpreadingSequence

SlowInformation

Sent

TX

SlowInformat ionRecovered

RX

FastSpreadingSequence

WidebandSignal


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Many code channels are individually

spreadand then added together to

create a composite signal


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Unwanted Power from

Other Resoures


Any Code Channel can be extracted from the receivedcomposite signal by using the right orthogonal code

Energy for transmitting signal can be lower than

interference and noise

Processing Gain

BroadbandInterference


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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

Sum0

Orthogonal

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

Sum -2

Non-orthogonal


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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


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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= Datacode

Data =Spread signalSpreading code

Chip

Sketch map of Spreading and Despreading


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Characteristics of Spreading Communication

High anti-multi-path- interference capabilityAnti-sudden-pulse

High security

Lower transmitting power Easy to implement large-capacity Multiple Access

Communication

Occupy band wide

Complex realization


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Content



Channel Coding


Modulation



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Purpose of Channel Coding

By adding redundant information in the originaldata stream, receivers can detect and correct the

error signal, and improve data transmission rates.

No correct coding: BER


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Principle of Channel Coding

Channel coding Error-correcting ability obtains by adding redundancy in the

original data

Convolutional coding and Turbo coding 1/21/3arewidely 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 AT 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

Encod ing


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Content



Channel Coding


Modulation



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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 x21x2 x7 x22x3 x8 x23x4 x9 x24x5 x1 x25

ata inputA = (x1 x2 x3 x4 x5 x25)

Data outputA= (x1 x6 x11 x16 x25)

e.g.


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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

Encod ing + Inter leaving can c orrect bo th

cont inuo us and non -cont inuo us errors


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Content



Channel Coding


Modulation



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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 improvecommunication effectiveness

Classification

Analog Modulation

Digital Modulation

Symbolbi tModulat ion


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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)


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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)


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WCDMA Data transmission Procedure

RF ReceivingDemodulationDespreading

Decoding &

De-inteleavingUE Data

UE Data Spreading

RF Transmitting

Modulation

Baseband

demodulation

Baseband

modulation

Encoding &

Interleaving


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Content

The Basic Principles of Wireless Communication WCDMA Radio mechanism


Channel Coding of WCDMA Spreading Technology of WCDMA

Modulation of WCDMA


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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.


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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 blockand 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 .


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Content



Channel Coding of WCDMA

Spreading Technology of WCDMA

Modulation of WCDMA


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Symbol rate SF = Chip rate=3.84Mcps

For 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


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Channelization Code

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

SF : spread factork : code number, 0 < k


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Scrambling Code

WCDMA Scrambling code is pseudo randombinary sequence (PN code) It has similar noise array character, seemingly random

but with regularity.

Can make the user data further random , strengthenedby scrambling a code to keep secret the user data, atthe same time easy to carry out multiple accesscommunication.

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.


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Characteristic of Scrambling code

There are 224 Uplink Scrambling Codes, they areused 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 018191. They are dividedinto 512 aggregationseach aggregation has 1 primaryscrambling 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


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Numbering rule for Downlink Scrambling

Codes

218-1 Downlink Scrambling Codes in all0..262142)

No. 511 Scrambling Code

Group

8176

8177

8191

8176PSC

8177SSC

8191SSC


Group

8160

8161

8175

8160

8161

8175


Group

8064

8065

8079

8064

8065

8079


Group

112

113

127

8176PSC

8177

8191


Group

16

17

31

16PSC

17SSC

31SSC


Group

01

15

0PSC1SSC

15SSC

No.63 Primary Scrambling ode Group

No.0 Primary Scrambling ode Group


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Code Functions

Channelization code ---- for separation of physicalchannels in the uplink and separation of users in

the downlink

Scrambling code ---- for separation ofusers/terminals in the uplink and cells/sectors in

the downlink.


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Despreading procedure

Method of despreading

Inputsignal

Local PN code

When T=Ts, judge

Outputafterdespreading

integral

0

Ts(*)dt


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Content



Channel Coding of WCDMA

Spreading Technology of WCDMA

Modulation of WCDMA


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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


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summary

Principle of WCDMA

All users are simultaneously transmitted in the same frequency band

Users interfere with each other

Adjacent cells use the same frequency

Cells, users (terminals), and physical channels are separated by codes

Channel coding

Convolutional code Turbo code

Codes

Channelization code

Scrambling code

Modulation BPSK

QPSK

16QAM


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01 wr_bt1002_e01_1 wcdma wireless principle-49

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