01 Principles of the WCDMA System 20080715 A 1 0

HUAWEI TECHNOLOGIES CO., LTD.

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Huawei Confidential

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Principles of the WCDMA System

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

Preface

Now, the most popular term in the mobile communication field is WCDMA!

What is WCDMA? And what is its benefit? Today, let’s go to know about WCDMA!


Objectives

Know the basic knowledge of the CDMA system.

Master advantages of the CDMA technology comparing with other multiple access technologies.

Know technical features of WCDMA FDD.

After studying this course, you should be able to:


Contents

Chapter 1 WCDMA Principle

Chapter 2 Technical Features of WCDMA FDD


Overview of CDMA Principles

Radio Propagation EnvironmentRadio Propagation Environment

Multiple Access Technology Multiple Access Technology and Duplex Technologyand Duplex Technology

CDMA Principles and Rake CDMA Principles and Rake ReceiverReceiver


Multipath Environment

Time

Strength of the received signal

Transmitted signal


FadingTransmitted data

-40-35-30-25-20-15-10-50

dB

Received data


Fading

Distance (m)

Rx power (dBm)

10 20 30

-20

-40

-60

Slow fadingFast fading


Frequency-Selective Fading

NarrowbandSystem

Fading

Transmit Signal Received Signalff

P(f) P(f)

Fading

Transmit Signal Received Signalff

P(f) P(f)

BroadbandSystem


Classification of Typical Radio Mobile Channels

Static channel

Pedestrian channel in typical urban areas (TU3)

Vehicle mounted channel in typical urban areas (TU30)

Vehicle mounted channel in rural areas (RA50)

Vehicle mounted channel on the highway (HT120)


Overview of CDMA Principles

Radio Propagation EnvironmentRadio Propagation Environment Multiple Access Technology and Duplex Multiple Access Technology and Duplex

TechnologyTechnology

CDMA Principles and Rake CDMA Principles and Rake ReceiverReceiver


Duplex Technology – Distinguish User’s UL and DL Signal – FDD

Frequency division duplex (FDD) : Distinguish the uplink and downlink according to the frequencies. Adopted by the WCDMA, CDMA2000 and GSM Advantage: It can be easily implemented. Disadvantage: The spectrum utilization is low

when the uplink and downlink services (mainly the data services) are asymmetrical.


Duplex Technology – Distinguish User’s UL and DL Signal – TDD Time division duplex (TDD) : Distinguish the uplink and downlink according to the timeslots. Adopted by the TD-SCDMA Advantage: The uplink and downlink can be allocated with

different numbers of timeslots when the uplink and downlink services are asymmetrical. Therefore, the spectrum utilization is high.

Disadvantage:− It cannot be easily implemented and needs precise

synchronization. In the CDMA system, GPS synchronization is needed.

− When it is used with the CDMA technology, it is difficult to control interference between the uplink and the downlink.


Traffic channels: different users are assigned unique code and transmitted over the same frequency band, for example, WCDMA and CDMA2000

Traffic channels: different frequency bands are allocated to different users,for example, AMPS and TACS

Traffic channels: different time slots are allocated to different users, for example, DAMPS and GSM

Multiple Access Technology - Distinguish Different Users

Freque

ncyTime

Power

FDMA

User User User

User User

Freque

ncyTime

Power

TDMA

Power

Time Frequency

CDMA


Characteristics of CDMA System

High Spectral Efficiency Frequency multiplex coefficient is 1.

Soft capacity Quality Coverage Interference

Self-interference system A UE transmission power is interference for another UE.

Wideband system


Overview of WCDMA Principles

Radio Propagation EnvironmentRadio Propagation Environment

Multiple Access Technology Multiple Access Technology and Duplex Technologyand Duplex Technology

CDMA Principles and Rake ReceiverCDMA Principles and Rake Receiver


Questions

Why does the WCDMA system have enhanced anti-interference performance?

Why is the WCDMA system more secure?

Why are the WCDMA handsets more environment protective?


Common Terms Bit, symbol and chip

Bit (bps): the data that is obtained upon source coding and contains information.

Symbol (sps): the data obtained upon channel coding and interleaving.

Chip (cps): the data obtained upon final spreading.− The spreading rate of WCDMA is: 3.84 Mcps

Processing gain It refers to the ratio of the final spreading rate to the

bit rate (cps/bps). In the WCDMA system, the processing gain depends on the

specific service.


Spreading Factor and Service Rate Chip rate = symbol rate spreading factor

For WCDMA, if the chip rate is 3.84 MHz and the spreading factor is 4, the symbol rate is 960 Kbps.

For CDMA2000-1x, if the chip rate is 1.2288 MHz and the spreading factor is 64, the symbol rate is 19.2 Kbps.

Symbol rate = (service rate + check code) × channel code ×repetition or punching rate For WCDMA, if the service rate is 384 Kbps and the channel

code is 1/3 Turbo, the symbol rate is 960 Kbps. For CDMA2000-1x, if the service rate is 9.6 Kbps and the

channel code is 1/3 convolutional code, the symbol rate is 19.2 Kbps.


Basic Diagram of the WCDMA System

Source coding

Channel coding and interleaving

ScramblingSpreading ModulationRF

transmission

Source decoding

deinterleavingChannel decoding and de-

interleaving

De-scramblingDe-spreading Demodulation RF receptio

n

Radio link


Source Coding in WCDMA The WCDMA system adopts the adaptive multi-rate (AMR)

speech coding. A total of eight coding modes are available. The coding rate

ranges from 12.2 Kbps to 4.75 Kbps. Multiple voice rates are compatible with the coding modes

used by current mainstream mobile communication systems. This facilitates the design of multi-mode terminals.

The system automatically adjusts the voice rate according to the distance between the user and the NodeB, thus reducing the number of handovers and call drop.

The system automatically decreases the voice rate of some users according to the cell load, thus saving power and containing more users.

Source coding Interleaving

Channel coding and interleaving

ScramblingSpreading ModulationRF

transmission


Channel Coding in WCDMA Channel coding can enhance symbol correlation to

recover signals in the case of interference.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Code type Voice service: Convolutional code (1/2 and 1/3). Data service: Turbo code (1/3).

Source coding

InterleavingChannel coding interleaving

ScramblingSpreading Modulation RF transmiss

ion


Interleaving Interleaving is used to damage symbol correlation and reduce the impact

caused by fast fading and interference of the channel.

1 2 3 4 5 6 7 8 ... ... 452 453 454 ……

816...456

210...450

614...454

19...449

412...452

715...

455

311...451

513...

453

.... ....

B0 B1 B2 B3 B4 B5 B6 B7

{A4,B0} {A5,B1} {A6,B2} {A7,B3} {B4,C0} {B5,C1} {B6,C2} {B7,C3}

Ist interleaving

2nd interleaving


Self Correlation and Mutual Correlation of Code Words

Different users adopt different spreading code words, such as x1(t) , x2(t) …. Self correlation determines multipath

interference. Mutual correlation determines multiple access

interference.

Self-correlation function R(τ) =<x1(t) ， x1(t+τ) >

Mutual-correlation function V(τ) =<x1(t) ， x2(t+τ) >

Note: <x1(x)， x2(y)> =1, when x1=x2 , and x = y

0, others


Users who need to send information: UE1, UE2 and UE3 UE1 uses c1 for spreading: UE1 x c1 UE2 uses c2 for spreading: UE2 x c2 UE3 uses c3 for spreading: UE3 x c3 c1, c2 and c3 are orthogonal to each other

Information sent: UE1 x c1 + UE2 x c2 + UE3 x c3

Spreading Principle

Source coding

InterleavingChannel coding and interleaving

ScramblingSpreading Modulation RF transmissi

on


UE1 uses c1 for de-spreading. (UE1 x c1 + UE2 x c2 + UE3 x c3) x c1= UE1 x (c1 x c1) + UE2 x (c2 x c1) + UE3 x

(c3 x c1) = UE1 x 1 + UE2 x 0 + UE3 x 0= UE1

In the same way, UE2 uses c2 for de-spreading and UE3 uses c3 for de-spreading to get their own signals.

De-spreading Principle


____________

UE1: +1 -1 1

_____________

UE2: -1 +1

c1: +1 -1 +1 -1 +1 -1 +1 -1

c2: +1 +1 +1 +1 +1 +1 +1 +1

UE1xc1: +1 -1 +1 -1 -1 +1 -1 +1

UE2xc2: -1 -1 -1 -1 +1 +1 +1 +1

UE1xc1 ＋ UE2xc2: 0 -2 0 -2 0 +2 0 +2

Spreading Principle


UE1×c1 ＋ UE2×c2： 0 -2 0 -2 0 +2 0 +2

De-spreading Principle

Question: How to generate those orthogonal codes like c1 and c2?

UE1 de-spreading with c1: +1 -1 +1 -1 +1 -1 +1 -1

De-spreading result: 0 +2 0 +2 0 -2 0 -2

Integral: +4 -4

Decision: +4/4 = +1 -4/4 = -1

UE2 de-spreading with c2: +1 +1 +1 +1 +1 +1 +1 +1

De-spreading result: 0 -2 0 -2 0 +2 0 +2

Integral: -4 +4

Decision : -4/4 = -1 +4/4 = +1


OVSF & Walsh

OVSF codes (Walsh) are completely orthogonal and their mutual correlation is zero.

SF = 1 SF = 2 SF = 4

Cch,1,0 = (1)

Cch,2,0 = (1,1)

Cch,2,1 = (1,-1)

Cch,4,0 =(1,1,1,1)

Cch,4,1 = (1,1,-1,-1)

Cch,4,2 = (1,-1,1,-1)

Cch,4,3 = (1,-1,-1,1)


Why CDMA system is a self interference system?

Since all the users use orthogonal code, where does the self interference come from? Comes from the code error during the transfer. If there are some code error on one user’s information, it misses some orthogonal to others. Then interference comes.


UE1xc1 + UE2xc2： 0 -2 0 -2 0 +2 0 +2

UE1xc1 + UE2xc2 error ： 2 -2 0 -2 1 +2 0 +2

Sample of code error

C2 +1 +1 +1 +1 +1 +1 +1 +1 Result: 2 -2 0 -2 0 +2 0 +2Integral: -2 +4Decision: -2/4=-0.5 +4/4=1

c1: +1 -1 +1 +1 +1 -1 +1 -1 Result: 2 +2 0 +2 0 -2 0 -2Integral: +6 -4Decision: +6/4 = 1.5 -4/4=-1


Scrambling in the WCDMA System Downlink: Different cells have different downlink scrambling

codes. Each cell is configured with a unique downlink scramble. The UE

identifies a cell based on the scramble. The OVSF code is used to distinguish different users in a cell.

Uplink: Scrambles are used to distinguish different users. In one cell, each user is configured with a unique uplink

scrambling code. The OVSF code is used to distinguish the services of a user.

Source coding

InterleavingChannel coding and interleaving

ScramblingSpreading Modulation RF transmissi

on


Spreading and Scrambling

Symbols

OVSF code

Scrambling code

Chips after

spreading and

scrambling

3.84M 3.84Mcps

3.84Mcps

xx sps


Code Generation Technologies in CDMA Random sequence (Bernoulli sequence)

It consists of 0’s and 1’s only, with the number of 0’s equal to that of 1’s.

The probability of continuous 1 or 0 is as follows: 1/2 for one continuous 0 or 1, 1/4 for two continuous 0 or 1, 1/8 for three continuous 0 or 1….

One half of the shift sequence is the same as the original sequence and the other half is different.

m sequence - scrambling code used in the CDMA2000 system It is generated by the shift register. As the longest linear shift register sequence, its period is 2n-1, where

“n” stands for the length of the shift register. When the delay is 0, the self-correlation function has a maximum value.

In other cases, the function value is always -1. It meets the Bernoulli sequence. Its disadvantages are: Only one sequence is available and different

users are distinguished by different phases. So it has a high requirement for synchronization.


Gold Sequence — Scrambling Code in the WCDMA System Gold sequence

It consists of two preferred m sequences on the Exclusive-OR basis.

Its self-correlation function has multiple values, which is worse than the m sequence.

It exceeds the m sequence in quantity.

The Gold sequence is used to distinguish the cells and users in the WCDMA system owing to its good self correlation. Good self correlation determines the Gold sequences

can be used to distinguish users, thus the multiple access function is realized.


Advantages and Disadvantages of the Gold Sequence Advantages: The Gold sequence needs no GPS

synchronization and features high system flexibility and security. The NodeB can work in asynchronous mode. It is easy to realize indoor coverage.

Disadvantages: The Gold sequence has greater inter-code interference than the m sequence.


Allowed maximum interference level of the system

Demodulation threshold

Spreading/De-spreading Principle — Explanations for Frequency Domain

Power spectrum

Power that all the users can share

a2Tbit = Ebit

Gain

Interference signals from other users Echip

Eb / No = Ec / Io gain


The CDMA broadband spreading technology effectively avoids frequency-selective fading of radio channels.

Spreading code

Spreading code

Signal combination

Spectrum Change in CDMA

Narrowband signalf

P(f)

Broadband signal

P(f)

f

Noise

P (f)

f

Noise + broadband signalP (f)

f

Separation of signals and noise

P (f)

f


Rake Receiver

Receive set

Correlator 1

Correlator 2

Correlator 3

Searcher correlator

Calculate the time delay and signal strength

CombinerThe

combined signal

tt

s(t) s(t)

RAKE receiver help to overcome on the multi-path fading and enhance the receive performance of the system


Summary - Advantages of CDMA RAKE receiver is adopted

The time diversity effect generated by channel coherence time is efficiently used.

Frequency diversity Wideband frequency spectrum

Higher interference tolerance and security performance Low signal transmission power

Great flexibility in carrying multiple services with largely different bit rate and QoS requirement. Different spreading factors for different services with different data rates

High spectral efficiency All users can share the same frequency spectrum simultaneously.

Supporting soft handover and softer handover.


Contents

Chapter 1 WCDMA Principle

Chapter 2 Technical Features of WCDMA FDD


Characteristics of WCDMA FDD Channel bandwidth: 5MHz Chip rate: 3.84Mcps Frame length: 10ms Voice coding: AMR (Adaptive Multi-Rate) Uplink and downlink modulation:

QPSK/QPSK Coherence demodulation aided with pilot Fast closed loop power control: 1500Hz Handover: soft/hard handover Support synchronous and asynchronous

NodeB operation


Characteristics of WCDMA FDD Satisfy the minimum performance requirement of

IMT2000 Compatible with GSM-MAP core network Comparatively steady version R99 has been released Support open loop and closed loop transmit

diversity mode Support Common Packet Channel(CPCH) and Downlink

Share Channel, adapt to Internet data access mode Support macro diversity, selection diversity of

NodeB location Support different fast power control algorithms and

open loop, out loop power control Fully support UE locating services


Differences Between the WCDMA and GSM on the Air Interface

WCDMA GSM

Carrier spacing 5 MHz 200 KHz

Frequency reuse coefficient 1 1-18

Power control frequency 1500 Hz 2 Hz or lower

QoS control Through the RRM algorithm

Through network planning (frequency planning)

Frequency diversity

The 3.84 MHz bandwidth enables the air interface to use the rake receiver for multipath diversity.

Frequency hopping

Packet data Load-based packet scheduling

Timeslot-based scheduling in GPRS

Downlink transmit diversity

Supported by the protocol to improve downlink capacity

Not supported by the standard but can be applied.


Conclusion This course describes the WCDMA system. This course first describes some key

technologies. Then, describes the basic principles of CDMA and the WCDMA FDD mode.

After studying this course, we can have a preliminary understanding of WCDMA, thus laying a good foundation for subsequent study.

Thank You !www.huawei.com

01 Principles of the WCDMA System 20080715 A 1 0

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