01 WCDMA Principles

HUAWEI TECHNOLOGIES CO., LTD.

www.huawei.com

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 and Multiple Access Technology and Duplex TechnologyDuplex Technology

�� CDMA Principles and Rake ReceiverCDMA Principles and Rake Receiver


Multipath Environment

Time

Strength of the received signal

Transmitted signal


FadingTransmitted data

-40

-35

-30

-25

-20

-15

-10

-5

0

dB

Received data


Fading

Distance (m)

Rx power (dBm)

10 20 30

-20

-40

-60

Slow fading

Fast fading


Frequency-Selective Fading

NarrowbandSystem

NarrowbandSystem

Fading

Transmit Signal Received Signalff

P(f) P(f)

Fading

Transmit Signal Received Signalff

P(f) P(f)

BroadbandSystem

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





Duplex Technology (Distinguish UL and DL for one User) –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 UL and DL for one User) –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: differentusers 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

FrequencyTime

Power

FDMA

User

User

User User

User

FrequencyTime

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





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 DemodulationRF

reception

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

InterleavingChannel coding and interleaving


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


transmission


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

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.... ....

B0 B1 B2 B3 B4 B5 B6 B7

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

Ist interleaving

2nd interleaving


� Users who need to send information: UE1, UE2 and UE3

� UE1 uses c1 for spreading: UE1 x c1



� c1, c2 and c3 are orthogonal to each other

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

Spreading Principle

Source coding



transmission


� 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 +2

Integral: -2 +4

Decision: -2/4=-0.5 +4/4=1

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

Result: 2 +2 0 +2 0 -2 0 -2

Integral: +6 -4

Decision: +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



transmission


Spreading and Scrambling

Symbols

OVSF code Scrambling code

Chips after spreading

and scrambling

3.84M3.84Mcps

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 ra dio channels.

Spreading code

Spreading code

Signal combination

Spectrum Change in CDMA

Narrowband signal

f

P(f)

Broadband signal

P(f)

f

Noise

P (f)

f

Noise + broadband signal

P (f)

f

Separation of signals and noise

P (f)

f


Rake ReceiverRake 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 fa ding 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 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

Not supported by the standard but can be applied.

Supported by the protocol to improve downlink capacity

Downlink transmit diversity

Timeslot-based scheduling in GPRS

Load-based packet scheduling Packet data

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

Frequency diversity

Through network planning (frequency planning)

Through the RRM algorithmQoS control

2 Hz or lower1500 HzPower control frequency

1-181Frequency reuse coefficient

200 KHz5 MHzCarrier spacing

GSMWCDMA


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 WCDMA Principles

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