02 WCDMA Wireless Principle

8/14/2019 02 WCDMA Wireless Principle

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The Basic Principles of Wireless CommunicationRadio Propagation CharacteristicsSpreading TechnologyChannel CodingInterleave TechnologyModulation

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Multi-path characteristics of radio channel

Electromagnetic propagation:--direct radiation reflection diffraction and scatteringSignal attenuation:

Path loss Loss of electromagnetic waves in large scope of thespread reflects the trend of the received signal in the spreading Slow fading Loss because of being blocked by the building andhill in the propagation pathFast fading Electromagnetic signals rapidly decline in a fewdozens wavelength ranges

Description of Fast fading distributionRayleigh distribution non line-of sight(NLOS) transmissionRician distribution line-of sight(LOS) transmission


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Multi-Path Effects

receiving signal

time

strength

0

sending signal


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Frequency off -se t caused by the mo vement of mo bi le tha t

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


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SHA NON Form ula

C = Blog 2(1+S/N)

Spread Spectrum Principles

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.




5 MHz30 KHz

Power is Spread Over a Larger Bandwidth



radio channel

ReceiverTransmitter

SpreadingDespreading

Noise


User information bits are spread over a widebandwidth by multiplying high speed spreadcode(chip)Spread signal bandwidth W wider than original signalbandwidth RbFor WCDMA, W=3.84Mchip/s Rb(voice)=12kbit/s



f

S f

f0

Before spreading

signal

S f

ff0

After spreading

signal

S f

ff0After 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-noise sequencegenerated by the pseudo-noise generatorBER 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 frequencyhoppingBefore FH again, data is transmitted using traditional narrowbandmodulationNo near-far effect



DS-SS communication system

A technology of transmission after spreading signalspectrum.

FastSpreadingSequence

SlowInformation

Sent

TX

SlowInformat ionRecovered

RX

FastSpreadingSequence

WidebandSignal




Many code channels are individuallyspread and then added together tocreate a composite signal



Unwanted Power fromOther Resoures


Any Code Channel can be extracted from the receivedcomposite signal by using the right orthogonal code Energy for transmitting signal can be lower thaninterference 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 -1Mul -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 -1Mul +1 -1 -1 -1 +1 -1 -1 +1Sum -2

Non-orthogonal



-1 1 -11-1 -11 1 -1 -1 11-1 1-1 1MU

-1 1 -11-1 -11 1

1 -1 1 -1

-4 40 0

Judge -1 1

1 -1 1 -1

-1 1 MU

Integral

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

Example of orthogonal code



S1

S2

S1xC1

S2XC2

W Spreading

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-pulseHigh security

Lower transmitting powerEasy to implement large-capacity Multiple AccessCommunicationOccupy band wideComplex realization




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Principle of Channel Coding

Channel codingError-correcting ability obtains by adding redundancy in theoriginal dataConvolution coding and Turbo coding 1/2 1/3 are widelyapplied.Increase no effective load and transmission timeSuitable 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

Encod ing




Content



Principle of Interleave Technology

advantageInterleave is to change the sequence of data to random theunexpected errors Advance the correcting validity

disadvantage Increase the processing delayEspecially, Several independent random errors may intertwined forthe unexpected error .

x1 x6 x11 x16 x21x2 x7 x22

x3 x8 x23

x4 x9 x24

x5 x1 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

Encod ing + Inter leaving can c orrect bothcont inuo us and non-con t inuous e r rors




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Analog Modulation

The purpose of analog modulation is to impress aninformation-bearing analog waveform onto acarrier 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 acontinuous-time waveform (perhaps impressed on acarrier).

Basic analog modulation methods include Amplitude shift Keying (ASK)Frequency shift Keying (FSK)Phase shift Keying (PSK)


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02 WCDMA Wireless Principle

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