wcdma

WCDMA Radio Theory

ZTE University TD&W&PCS BSS Course Team

Course Objectives At the end of this course, you will be able to:  Master channel encoding of WCDMA  Master spread spectrum principle of WCDMA  Master modulation of WCDMA

Content The basic principles of wireless communication Radio Propagation Characteristics Multi Access Spread spectrum Technology Channel Coding Interleave Technology

WCDMA wireless technology

Radio propagation charactistics

Characteristic of Radio Propagation 

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 transmission  Rice distribution ： line-of –sight transmission

Radio propagation charactistics

Characteristics of Radio Propagation Interference

dithering 0

2τ

delay

τ

σ

Sending signal

σ+τ

Accepting signal

fading 0dB

0

σ

3τ

Sending signal

Accepting signal

Sending signal

τ

-25dB

σ+τ

Accepting signal

Sending signal

Accepting signal

Frequency Frequencyoff-set off-setcaused causedby bythe the movement movementof ofmobile mobile ， ， that thatis is Doppler Doppler effect effect

Radio propagation charactistics

Multi-Path Effects

sending signal

strength

receiving signal 0

time

Content The basic principles of wireless communication Radio Propagation Characteristics Multi Access Spread spectrum Technology Channel Coding Interleave Technology

WCDMA wireless technology

Multiple access

Multiple Access Frequency division multiple access technology

FDMA

Channels in different frequency are allocated to different users, e.g. TACS 、 AMPS 。

Power

Time division multiple access technology

TDMA

channels in different time are allocated to different users, e.g. GSM 、 DAMPS 。

Power

T im

e

Tim

e

Code division multiple access technology

CDMA

Users distinguished by scramble code, e.g. CDMA

Power Tim e

y nc e u eq Fr

e qu Fre

eq Fr

y nc

y nc e u

Content The basic principles of wireless communication Radio Propagation Characteristics Multi Access Spread spectrum Technology Channel Coding Interleave Technology

WCDMA wireless technology

Spreading technology

Principle of Spreading spectrum 

A technology of transmission technology after spreading frequency of signal.



Theoretical Basis: Shannon theory C=Wlog2(1+S/N) Wideband Signal

Slow Information Sent

Slow Information Recovered

TX

Fast Spreading Sequence

RX

Fast Spreading Sequence

Spreading technology

Sketch Map of Spreading S（f）

S（f） signal

signal f0

f0

f

Before spreading

f

After spreading

S（f）

S（f）

White noise

signal White noise

signal f0

f

Before despreading

signal

interference

f0

f

After despreading

White noise

Spreading technology

Spreading Mode 

Direct sequence spread （ DS － SS ）  Base band data is spreaded 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 （ 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

Spreading technology

Characteristics of Spreading Communication 

High anti-multi-path- interference capability



High security



Lower transmitting power



Easy to implement large-capacity Multiple Access Communication



Occupy band wide



Complex realization

Content The basic principles of wireless communication Radio Propagation Characteristics Multi Access Spread spectrum Technology Channel Coding Interleave Technology

WCDMA wireless technology

Channel coding

Purpose of Channel Coding 

purpose:  By adding redundant information in the original data stream,

receivers can detect and correct the error signal, and improve data transmission rates.  Error-correcting ability obtains by adding redundancy in the

original data

？CCDDMMA

WCDMA

WWCCDDMMAA

W

TURBO

T T UURRBBOO

A

SPEAK

S S PPEEAAKK

T T U

？RRBBO

O S S PPEEA

？KK

Channel coding

Principle of Channel Coding 

Channel coding  Convolutional coding and Turbo coding （ 1/2 ， 1/3 ） are

widely applied.  Increase redundancy and transmission time  Suitable to correct few non-continuous errors No correct coding: BER