WR_BT02_E1_1 WCDMA Wireless Principle 49

8/6/2019 WR_BT02_E1_1 WCDMA Wireless Principle 49

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WR_BT02_E1_1

WCDMA Wireless Principle

ZTE University

TD&W&PCS BSS Course Team


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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 radiation reflection diffraction and scattering

Signal attenuation:

Path loss Loss of electromagnetic waves caused because of distance Slow fading Loss because of being blocked by some objects 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



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Multi-Path Effects

receiving signalreceiving signal

timetime

strengthstrength

00

sending signalsending signal



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FrequencyFrequencyoff-setoff-setcaused by the movement of mobilecaused by the movement of mobile

that is Doppler effectthat is Doppler effect

FrequencyFrequencyoff-setoff-setcaused by the movement of mobilecaused by the movement of mobile

that is Doppler effectthat is Doppler effect

Sending signal Acceptingsignal

InterferenceInterference

0dB

Sendingsignal

-25dB

Acceptingsignal

fadingfading

0 +

Sendingsignal Acceptingsignal

delaydelay

0 2 3 +

Sendingsignal Acceptingsignal

ditheringdithering

Characteristics of Radio Propagation



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Contents




Channel Coding


Modulation



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SHANON Formula

C = Blog2(1+S/N)

Where,C is capacity of channel, b/sB is signal bandwidth, HzS is average power for signal, WN is average power for noise, W

It is the basic principle and theory for spread spectrumcommunications.

Spread Spectrum Principles



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5 MHz

30 KHz

Power is Spread Over a Larger Bandwidth

MATHHAMMER

MATH

HAMMER



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radio channel

ReceiverTransmitter

Spreading

Despreading

Noise

User information bits are spread over a wide bandwidth bymultiplying high speed spread code(chip)

Spread signal bandwidth W wider than original signal

bandwidth Rb

For WCDMA, W=3.84Mchip/s Rb(voice)=12.2kbit/s




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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




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Spreading Mode

Direct sequence spread spectrum DS-SS Base band data is spread by multiplication of pseudo-noisesequence 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 bypower 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 traditional narrowband

modulation

No near-far effect

The Basic Principles of Wireless Communication v


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DS-SS communication system

A technology of transmission after spreading signal

spectrum.

FastSpreadingSequence

SlowInformation

Sent

TX

SlowInformationRecovered

RX

FastSpreadingSequence

WidebandSignal



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Many code channels are individually

spread and then added together to

create a composite signal



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Unwanted Power from

Other Resoures


Processing Gain

Broadband

Interference

Any Code Channel can be extracted from the received composite signal byusing the rightorthogonal code

Energy for transmitting signal can be lower than interference and noise


Th B i P i i l f Wi l C i i


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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

Sum 0

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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Th B i P i i l f Wi l C i ti


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S1S1

S2S2

S1xC1S1xC1

S2XC2S2XC2

WWSpreading

Despreading

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

Air InterfaceAir Interface

[S1xC1+S2xC2]x[S1xC1+S2xC2]x

C2C2

==S2S2

[S1xC1+S2xC2]xC[S1xC1+S2xC2]xC

11

==S1S1NN

SS

C1xC2=0,C1,C2,orthogonal

Direct spread technique


Th B i P i i l f Wi l C i ti


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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= Data code

Data =Spread signal Spreading code

Chip

Sketch map of Spreading and Despreading



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Contents




Channel Coding


Modulation




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Purpose of Channel Coding

By adding redundant information in the original data

stream, receivers can detect and correct the error signal,

and improve data transmission rates. Ensure the integrality

of DATA.

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 1/2 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



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Contents




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 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.




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Encoding and Interleaving

W C D M AT 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 SC 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 OS ? ? 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+ Interleaving can correct bothcontinuous and non-continuous errors



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Contents




Channel Coding


Modulation




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Principle of Modulation

Definition

Modulation is the process where the amplitude, frequency, orphase 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

SymbolbitModulation




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Analog Modulation

The purpose of analog modulation is to impress an

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 an

information-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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Contents



WCDMA Data transmission Procedure

Channel Coding of WCDMA

Spreading Technology of WCDMA

Modulation of WCDMA



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RF ReceivingDemodulationDespreading

Decoding &

De-

inteleaving

UE Data

UE Data Spreading

RF Transmitting

Modulation

Baseband

demodulation

Baseband

modulation

Encoding &

Interleaving



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Contents






Modulation of WCDMA



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Convolutional Code

Characteristics

Mainly used in the voice channel and control signal

channel

Coding rate : 1/2 & 1/3Channel 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 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 .


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Contents






Modulation of WCDMA



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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 ScramblingCode

Data Spread Data

Spreading Process of WCDMA

SymbolChip

3.84Mcps

3.84Mcps



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Channelization Code

Adopt OVSF code

Definition: Cch,SF,k, describe channelization code, whereSF : spread factor k : code number, 0 < k


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WCDMA Scrambling code is pseudo random binarysequence (PN code)

It has similar noise array character, seemingly randombut with regularity.

Can make the user data further random ,strengthened by scrambling a code to keep secret the

user data, at the same time easy to carry out multiple

access communication.

Scrambling Code

WCDMA scrambling code is generated from Gold

sequence

Gold sequence has excellent self-correlation.

Cross-correlation is very weak between two

codes.

It is used to identify cell and user for multipleaccess.



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Characteristic of Scrambling code

There are 224

Uplink Scrambling Codes, they are used to distinguishdifferent users in one cell.

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

different cells

Scrambling codes usually used are the first8192 codes, whichare code 0 1 8191. They are divided into 512

aggregations each aggregation has 1 primary scrambling code

(PSC) and15 secondary scrambling codes (SSC).

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

in each group.



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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

No. 510 Scrambling CodeGroup

8160

8161

8175

8160

8161

8175

No. 504 Scrambling Code

Group

80648065

8079

8064

8065

8079

No. 7 Scrambling Code Group

112

113

127

8176 PSC

8177

8191


16

17

31

16 PSC

17 SSC

31 SSC


0

1

15

0 PSC

1 SSC

15 SSC

No.63 Primary ScramblingCode Group

No.0 Primary Scrambling CodeGroup


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AirInterface

2chc

3chc

1chc

scramblingc Modulatio

n

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



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f

P

W

ProcessingGain

Rb

Despreading

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

Transmitter/receiver can obtain gain after spread/despreadThe narrower original signal bandwidth, the larger Pg , the better

Processing Gain

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

b

c

R

WGainProcessing =


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Despreading procedure

Method of dispreading

Inputsignal

Local PN code

When T=Ts, judge

Outputafterdespreading

integral

0

Ts(*)dt


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Contents






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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WR_BT02_E1_1 WCDMA Wireless Principle 49

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