01 wr bt1002 e01_1 wcdma wireless principle-49

WCDMA Wireless Principle

ZTE University

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

Electromagnetic propagation:

--direct radiation、reflection、diffraction and scattering

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

Description of Fast fading distribution

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

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

Multi-Path Effects

receiving signal

time

strength

0

sending signal

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

is Doppler effect

Sending signal Accepting signal

Interference

0dB

Sending signal

-25dB

Accepting signal

fading

0 +


delay

0 2 3 +


dithering

Characteristics of Radio Propagation

Content




Channel Coding


Modulation


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.


1.25 MHz

30 KHz

Power is “Spread” Over a Larger Bandwidth

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

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

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

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

DS-SS communication system

A technology of transmission after spreading

signal spectrum.

FastSpreadingSequence

SlowInformation

Sent

TX

SlowInformationRecovered

RX

FastSpreadingSequence

WidebandSignal


Many code channels are individually

“spread” and then added together to

create a “composite signal”

Unwanted Power from

Other Resoures


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

Processing Gain

Broadband

Interference

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

-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 0Judge -1 1

1 -1 1 -1

-1 1MUL

Integral

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

Example of orthogonal code

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

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-pulse

High security

Lower transmitting power

Easy to implement large-capacity Multiple Access

Communication

Occupy band wide

Complex realization

Content




Channel Coding


Modulation


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.

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

the communication

Convolutional coding：BER<10-3Can satisfy the

speech communication

Turbo coding： BER<10-6Can satisfy the

data communication

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

Content




Channel Coding


Modulation


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.

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 ? E

M ? A M B A

A O K ? O K

DeinterleavingDecoding

Encoding + Interleaving can correct both

continuous and non-continuous errors

Content




Channel Coding


Modulation


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 improve

communication effectiveness

Classification

Analog Modulation

Digital Modulation

SymbolbitModulation

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)

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)

Content



WCDMA Data transmission Procedure

Channel Coding of WCDMA

Spreading Technology of WCDMA

Modulation of WCDMA


RF ReceivingDemodulationDespreading

Decoding &

De-inteleavingUE Data

UE Data Spreading

RF Transmitting

Modulation

Baseband

demodulation

Baseband

modulation

Encoding &

Interleaving

Content






Modulation of WCDMA

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.

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 .

Content






Modulation of WCDMA

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 Scrambling Code

Data Spread Data

Spreading Process of WCDMA

Symbol Chip

3.84Mcps

3.84Mcps

Channelization Code

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)

Scrambling Code

WCDMA 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 a code to keep secret the user data, at the same time easy to carry out multiple access communication.

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.

Characteristic of Scrambling code

There are 224 Uplink Scrambling Codes, they are

used 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 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 primary scrambling code groups , with 8 primary

scrambling codes in each group.

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


Group

8160

8161

8175

8160：主扰码

8161：辅扰码

…

8175：辅扰码


Group

8064

8065

8079

8064：主扰码

8065：辅扰码

…

8079：辅扰码

…


Group

112

113

127

8176：PSC

8177：辅扰码

…

8191：辅扰码


Group

16

17

31

16：PSC

17：SSC

…

31：SSC


Group

0

1

15

0：PSC

1：SSC

…

15：SSC

No.63 Primary Scrambling Code Group… …

No.0 Primary Scrambling Code Group

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 the uplink and cells/sectors in

the downlink.

Air Interface

2chc

3chc

1chc

scramblingc Modulation

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

f

P

W

Processing

Gain

Rb

Despreading

Processing Gain

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

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

b

c

R

WGain Processing

Question

What’s the Processing Gain for voice service in

WCDMA system?

Given: Voice data rate = 12.2kbps

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

Wc: 3.84Mchip/s

Rb: 12.2kbps

So for voice service,

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

Despreading procedure

Method of despreading

Input signal

Local PN code

When T=Ts, judge

Output after despreading

integral

0

Ts

(*)dt

Content






Modulation of WCDMA

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

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

01 wr bt1002 e01_1 wcdma wireless principle-49

Technology

spread signal

signal spectrum

spread spectrum communications

transmitting signal

received signal

composite signal

delaysending signal

error signal