1_WCDMA Wireless Principle 49

8/8/2019 1_WCDMA Wireless Principle 49

http://slidepdf.com/reader/full/1wcdma-wireless-principle-49 1/49

WR_BT02_E1_1WCDMA Wireless Principle

ZTE University

PDF created with pdfFactory Pro trial version www.pdffactory.com

http://www.pdffactory.com/




Content

The Basic Principles of Wireless Communication

» Radio Propagation Characteristics

» Spreading Technology

» Channel Coding

» Interleave Technology

» Modulation

WCDMA Radio Mechanism






Multi-path characteristics of radio channel

n Electromagnetic propagation:

--direct radiation, reflection, diffraction and scattering

n 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

n Description of Fast fading distribution

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

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







Multi-Path Effects

receiving signaleceiving signal

timetime

strengthstrength

00

sending signalending signal







Frequency off-set caused by the movement of mobile ，

that is Doppler effect

Frequency Frequency off off - - set set caused by the movement of mobile caused by the movement of mobile ，

that is Doppler effect that is Doppler effect

Sending signal Accepting signal

InterferenceInterference

0dB

Sending signal

-25dB

Accepting signal

fadingfading

0 τ σ σ+ τ


delaydelay

0 τ 2τ 3τ σ σ+ τ


ditheringdithering

Characteristics of Radio Propagation







Contents




» Channel Coding


» Modulation

WCDMA Radio mechanism






SHANON Formula

C = B*log2(1+S/N)C = B*log2(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 spectrum

communications.

Spread Spectrum Principles








1.25 MHz30 KHz

Power is “Spread” Over a Larger Bandwidth

M AT H H AM M E R

MATHHAMMER







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/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

n Direct sequence spread spectrum（DS-SS）„ Base band data is spread by multiplication of pseudo-noise (PN)

sequence 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 by

power detection accuracy

„ WCDMA uses DS-SS

n 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






DS-SS communication system

n A technology of transmission after spreading signal

spectrum.

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 fromOther Resources


Processing Gain

BroadbandInterference

„ Any Code Channel can be extracted from the received composite

signal by using the “ right ” orthogonal code

„ Energy for transmitting signal can be lower than interference and

noise







Eb =Signal Power

Bit Rate=

S

R

E / t

B / t= N0 =

Noise Power

Bandwidth=

N

W

Eb

N0

=

S

R

N

W

=S

RX

W

N=

S

NX

W

R

Signal to Noise

Processing Gain

The relation between Eb/N0 and PG

扩频通信原理






f

P

W

ProcessingGain

Rb

Despreading

n 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

Processing Gain

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

b

c

R

WGainProcessing =







Question

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

„ Wc: 3.84Mchip/s

„ Rb: 12.2kbps

n So for voice service,

„ PG=10lg(3.84*106 /12.2*103)= 25 dB

What’s the Processing Gain for voice service in WCDMA

system?

Given: Voice data rate = 12.2kbps







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







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

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

Example of orthogonal code


1 1 1 1






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







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

n High anti-multi-path interference capability

n 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







Contents




» Channel Coding


» Modulation







Purpose of Channel Coding

n

By adding redundant information in the original data stream,receivers can detect and correct the error signal, and

improve data transmission rates.

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

Convolutional coding：BER<10-3Can satisfy the

speech communication

Turbo coding： BER<10-6

Can satisfy the

data communication



C





Principle of Channel Coding

n 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







Contents




» Channel Coding


» Modulation



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





Principle of Interleave Technology

n advantage

„ Interleave is to change the sequence of data to random the unexpected

errors

„ Advance the correcting validity

n disadvantage：

„

Increase the processing delay

„ Especially, Several independent random errors may intertwined for the

unexpected error .

x1 x6 x11 x16 x21

x2 x7 … x22x3 x8 … x23

x4 x9 … x24

x5 x10 … x25

Data inputA = (x1 x2 x3 x4 x5 … x25)

Data outputA’= (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 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







Contents




» Channel Coding» Interleave Technology

» Modulation








Principle of Modulation

n 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

n Classification

„ Analog Modulation

„ Digital Modulation

Symbol bit Modulation








Analog Modulation

n The purpose of analog modulation is to impress an

information-bearing analog waveform onto a carrier

for transmission.

„ Common analog modulation methods include:

Ÿ Amplitude modulation (AM)

Ÿ Frequency modulation (FM)

Ÿ Phase modulation (PM)








Digital Modulation

n 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 modulation methods include

Ÿ Amplitude shift Keying (ASK)

Ÿ Frequency shift Keying (FSK)

Ÿ Phase shift Keying (PSK)







Contents



» WCDMA Data Transmission Procedure

» Channel Coding of WCDMA» Spreading Technology of WCDMA

» Modulation of WCDMA







WCDMA Data transmission Procedure

RF ReceivingDemodulationDespreading

Decoding &De-inteleaving

UE Data

UE Data Spreading

RF Transmitting

Modulation

Basebanddemodulation

Baseband

modulation

Encoding &

Interleaving

C ad o ec a s






Contents



» WCDMA Data transmission Procedure









Convolutional Code

n 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

Ÿ e.g. speech and video service.







Turbo Code

n 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

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






Contents












Symbol rate× SF = Chip rate=3.84Mcps

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

SF of downlink channelization code: 4~512OVSF: Orthogonal Variable Spreading Factor

OVSF Code Scrambling Code

Data Spread Data

Spreading Process of WCDMA

Symbol Chip

3.84Mcps

3.84Mcps







Channelization Code

n 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)







nWCDMA 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 code

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

access communication.

Scrambling Code

n 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 multiple access.







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, 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 primaryscrambling code groups , with 8 primary scrambling codes in each group.







Numbering rule for Downlink Scrambling

Codes

…

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 )

8176：

PSC8177：SSC

…

8191：SSC

81768177

8191

No. 511 Scrambling Code

Group

8160：主扰码

8161：辅扰码

…

8175：辅扰码

8160

8161

8175


Group

8064：主扰码

8065：辅扰码

…

8079：辅扰码

8064

8065

8079


Group …

8176：PSC

8177：辅扰码

…

8191：辅扰码

112

113

127


Group

16：PSC

17：SSC

…

31：SSC

16

17

31


Group

0：PSC

1：SSC

…

15：SSC

0

1

15


Group

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 Pr i ma r y S c r a mb l i n g Co d e Gr o u p







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 theuplink and cells/sectors in the downlink.







Air Interface

2chc

3chc

1chc

scramblingc

Modulation

Spreading code & scrambling code

„ Cch：spread code

Ÿ Relative to service rate，extended to 3.84Mchips/s

Ÿ A kind of orthogonal code

„ Cscrambling：scrambling code

Ÿ Have no effect on signal bandwidth

Ÿ downlink for identifier cell，uplink identifier terminal

Ÿ A pseudo-random sequence







Despreading procedure

n Method of despreading

Input signal

Local PN code

When T=Ts, judge

Output after despreading

integral

0

Ts

(*)dt






Contents




»Channel Coding of WCDMA

» Spreading Technology of WCDMA








Modulation Methods in WCDMA

n BPSK (Binary Phase Shift Keying) in Uplink channels

n QPSK (Quadrature Phase Shift Keying) in Downlink channels

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







Summary

n 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

n Channel coding

„ Convolutional code

„ Turbo code

n Codes

„ Channelization code

„ Scrambling code

n Modulation

„

BPSK„ QPSK

„ 16QAM




Documents

1_WCDMA Wireless Principle 49