01 Wcdma Principles.pdf

01 WCDMA Principles HUAWEI TECHNOLOGIES CO , LTD www huawei com Huawei Confidential Internal Principles of the WCDMA System HUAWEI TECHNOLOGIES CO , LTD Page 2Huawei Confidential Preface � Now, the mo[.]

Internal

Principles of the WCDMA System

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!

Know the basic knowledge of the CDMA system

comparing with other multiple access technologies

After studying this course, you should be able to:

Chapter 1 WCDMA Principle

Chapter 2 Technical Features of WCDMA

FDD

Overview of CDMA Principles

Radio Propagation Environment

Multiple Access Technology and Duplex Technology

CDMA Principles and Rake Receiver

Multipath Environment

Time

Strength of the received signal Transmitted

signal

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 Environment

Multiple Access Technology and Duplex Technology

CDMA Principles and Rake Receiver

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

Frequency division duplex (FDD) : Distinguish the uplink and

downlink according to the frequencies.

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

T ime D ivision D uplex ( TDD ) : Distinguish the uplink and downlink

according to the timeslots.

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

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

Power

Time Frequency

CDMA

Characteristics of CDMA System

High Spectral Efficiency

Frequency multiplex coefficient is 1

Overview of WCDMA Principles

Radio Propagation Environment

Multiple Access Technology and Duplex Technology

CDMA Principles and Rake Receiver

anti-interference performance?

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 specificservice

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 Spreading Scrambling

Modulation

RF transmission

Source

decoding

deinterleavingChannel

decoding and de-interleaving

De-scrambling De-spreading Demodulation RF

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 mode terminals

multi-
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.

Channel

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

Voice service: Convolutional code (1/2 and 1/3)

Data service: Turbo code (1/3)

Source coding

Interleaving

Channel coding interleaving

Scrambling Spreading Modulation transmissionRF

8 16 456

2 10 450

2 10 450

6 14 454

6 14 454

1 9 449

1 9 449

4 12 452

4 12 452

7 15 455

7 15 455

3 11 451

3 11 451

5 13 453

5 13 453

B0 B1 B2 B3 B4 B5 B6 B7

Ist interleaving

2nd interleaving

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 Interleaving

Channel coding and interleaving

Scrambling Spreading Modulation transmissionRF

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

OVSF & Walsh

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

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

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

Channel

RF

Spreading and Scrambling

Symbols

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

Gold Sequence — Scrambling Code in the WCDMA System

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

Eb / No = Ec / Io × gain

Spreading code

Spreading code

Signal combination

Spectrum Change in CDMA

P (f)

f

Rake Receiver

Receive set

Correlator 1 Correlator 2

Correlator 3

Searcher correlator Calculate the

time delay and signal strength

Combiner

The combined signal

t 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

Chapter 1 WCDMA Principle

Chapter 2 Technical Features of WCDMA

FDD

Characteristics of WCDMA FDD

Chip rate: 3.84Mcps

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

Characteristics of WCDMA FDD

Satisfy the minimum performance requirement of IMT2000

Comparatively steady version R99 has been released

Support open loop and closed loop transmit diversity mode

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 Supported by the protocol to

Downlink transmit diversity

Timeslot-based scheduling

in GPRS Load-based packet scheduling

Packet data

Frequency hopping

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

Frequency reuse coefficient

200 KHz

5 MHz

Carrier spacing

GSM WCDMA

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 !

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