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HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

Security Level:

www.huawei.com

WCDMA Fundamentals

2008-10-23
http://www.huawei.com/http://www.huawei.com/

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HUAWEI TECHNOLOGIES CO., LTD. Page 2Huawei Confidential

Contents

n Overview of WCDMA

n Handover Introduction

n Power Control Introduction

n UMTS Channels and Function

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Different Technologies for Different ServicesDifferent Technologies for Different Services

AMPS

TACS

NMT

GSMGSM

CDMACDMA

IS95IS95

TDMATDMA

IS-136IS-136

PDCPDC

1st

generation in 1980sAnalog

2nd

generation in 1990sDigital 3rd

generationIMT-2000

UMTSUMTS

WCDMAWCDMA

cdmacdma

20002000

Driven bydemands

Driven bydemands

Analog

te

chnology

Digitaltechnology

Speec

hservice

Broadba

nd

service

TD-SCDMA

TD-SCDMA

3G provides perfect solutions to integrated services for users and operators.

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UTRAN in UMTS Network

Iu-BC

RNC

RNC

NodeB

NodeB

NodeB

CS

PS

CBC

UE UTRAN CN

Uu Iu

Iu-CS

Iu-PS

Iu-BC

Iur

Iub

Iub

Iub

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Traffic channels: differentusers are assigned uniquecode and transmitted overthe same frequency band,for example, WCDMA andCDMA2000

Traffic channels: different frequency bandsare allocated to different users,for example, AMPS

Traffic channels: different time slotsare allocated to different users,for example, GSM

Multiple Access TechnologyMultiple Access Technology -- DistinguishDistinguish Different UsersDifferent Users

Frequency

Time

TDMATime

Frequency

FDMA

Frequency

Time

CodeCDMA

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Basic Diagram of the WCDMA System

Sourcecoding

Channel

coding andinterleaving

ScramblingSpreading ModulationRF

transmission

Source

decoding

deinterleavingChannel

decoding and

de-interleaving

De-scramblingDe-spreading DemodulationRF

reception

Radio link

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Common Termsl Bit, symbol and chip

[ Bit (bps): the data that is obtained upon source coding and containsinformation.

[ 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

l 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.

For example, for the 12.2 Kbps voice service, its processing gain is as follows:

10*log10 (3.84 Mcps/12.2 Kbps) =10*log10314.75=25 db

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Spreading Factor and Service Rate

l 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.

l 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 9.60 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.

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Source Coding

l 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.

[ The system automatically adjusts the voice rate according to the load & distance

between the user and the NodeB, thus reducing the number of handovers and

call drop.

Channel Coding

l

Channel coding can enhance symbol correlation to recover signals in thecase of interference.

Code type:Voice service: convolutional code (1/2 and 1/3) . The constraint length is9, and 8 tail bits are added.Data service: Turbo code (1/3)

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

caused by fast fading and interference of the channel.

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Procedure of SpreadingProcedure of Spreading

Bit

OVSFCode

ScrambleCode

Chip

1

-11

-11

-1

1

1

-1

-1

Data

OVSFCode

Signal=Data

*code

OVSFCode

Data

Spreading

Despreading

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OVSF Code&Scramble Code

n Scramble Code (Gold Sequence)

l Length:38400 Chip

l Uplink: total 224l Downlink: total 218-1 =262143, only use 0~8191

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)

n OVSF (Orthogonal Variable Spreading Factor) Code

1

-1

1

-1

1

-1

Code1

Code2

Code2_D1

Multi-path will destroythe orthogonality of

OVSF!!!

Multi-path will destroythe orthogonality of

OVSF!!!

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

[ UE1 uses c1 for spreading: UE1 c1[ UE2 uses c2 for spreading: UE2 c2[ UE3 uses c3 for spreading: UE3 c3[ c1, c2 and c3 are mutually orthogonal.

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

Spreading Principle

l UE1 uses c1 for de-spreading.

[ (UE1 c1 + UE2 c2 + UE3 c3) c1

=UE1 (c1 c1) + UE2 (c2 c1) + UE3 (c3 c1)

=UE1 1 + UE2 0 + UE3 0

=UE1

l In the same way, UE2 uses c2 for de-spreading and UE3 uses c3 for de-

spreading to obtain their own signals.

De-spreading Principle

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Frequency spreading overcomes interference

Spreading code

Spreading code

Signalcombination

Spectrum Change in WCDMA

Narrowband signal

f

P(f)

Broadband signal

P(f)

f

Noise + broadband signal

P (f)

f

Separation ofsignals and noise

P (f)

f

Noise+

other user signal

P (f)

f

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Advantages of WCDMA over GSMAdvantages of WCDMA over GSM

q Larger system capacity

q Higher spectrum efficiency

q Higher interference tolerance and security performance

q Higher throughput with multiple services.

q Adapted to mobility speed of up to 500km/h

q Reduce the effects of fading through Rake reception

- Fast fading caused by multi path

- Slow fading caused by shadowing

q Supports soft handover and softer handover

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Contents

q Overview of WCDMA

n Handover Introduction

n Power Control Introduction

n UMTS Channels and Function

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Purpose of handover

Guarantee continuous conversation, it is a necessary

requirement in any mobile communication system. Proper

handover algorithm is propitious to reduce system call dropand increase network capacity.

90% of radio call drop occurs in the process of handover.

WCDMA handover types

1. Soft Handover2. Softer Handover

3. Hard Handover

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Soft Handover (Connection before Disconnection)

RNCNodeB1NodeB2

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Softer Handover (A Special Case of Soft Handover)

RNCNode B

Cell A Cell B

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Hard Handover- (Disconnection before Connection)

RNCNodeB1 NodeB2

Hard Handover- (Disconnection before Connection)

NodeB1 RNC NodeB2

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Rake ReceptionRake Reception

SHO Gain against slow fading= Slow fading margin without SHOSlow fading margin with SHO

SHO Gain against fast fading= FastFadingMargin(without SHO)-FastFadingMargin(with SHO)

Receive set

Correlator 1

Correlator 2

Correlator 3

Searcher correlator Calculate the time

delay and signal

strength

Combiner The combinedsignal

tt

s(t) s(t)

Reduce theeffects of fading

through Rakereception

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Comparison of Soft and Hard Handover

Call drop ratio isrelatively higher

Occupies more resources.Problems occur when the power of soft

handover cells is unbalanced.

Disadvantage

None

Maximum-ratio combining or selective

combining which can reduce the impactof fading and transmission power of theUE.

Handover gain

Intra-frequencyInter-frequency

or

Inter-RAT

Intra-frequencyFrequencies in the cells

before and afterhandover

YesNoInterruption during

handover

OneSeveralNumber of radio links inthe activate set

Hard HandoverSoft Handover (Softer Handover)Item

In a word, some resources are wasted to obtain optimal system performance in soft

handover.

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Contents

q Overview of WCDMA

q Handover Introduction

q Power Control Introduction

q UMTS Channels and Function

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Purposes of Power Control

Solve the near-far effect

Ensure the uplink/downlink quality by adjusting thetransmit power

Overcoming slow fading and fast fading

Decrease interference, and improve system quality andcapacity

In short, the purpose of power control in the WCDMA system isensuring users communication quality with minimum transmit

power

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Near/Far Problem

A B

P()

P()

P()

P()

Power

received

from A.

Power

receivedfrom B.

P()

Output power

of A

Output power

of BTotal receive

Arecoversuccessful

Brecoverfailed

De-spread

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After Power Control

P()

P()

P()

P()

P()

A decreases

its power

A B

Output power

of A

Output power

of B

Arecoversuccessful

Brecoversuccessful

De-spread

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After Power Control

P()

1 2 3 4 5

P()

1

P()

2

P()

3

P()

4

P()

5Total receiveDe-spread

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Interference limit

De-spread

P()

P()

P()

P()

P()

P()

P()

P()

P()

P()

P()

1 2 3 4 5

1 2 3 4

1 2 3 4 5

Total receive

Total receive

De-spread

O C

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Reverse Open Loop Power Control

The transmission power required by the UE is determined by the

following factors:

Distance from the Node B

Load of the cell

Circumstance of the code channels

The transmission power of the UE is relative to its received power.

Node BUE

Reverse Open LoopPower Control

Node B

Node B

Transmitting

Power

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Close Loop Power Control

Node B UE

Sent TPC

SIR measurementand comparing

Inner loop

SIR target setting

BLER measurement

Outer loop

RNC

Comparing

BLER target setting

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Contents

q Overview of WCDMA

q Handover Introduction

q Power Control Introduction

q UMTS Channels and Function

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Control channel

Traffic channel

Dedicated traffic channel (DTCH)

Common traffic channel (CTCH)

Broadcast control channel (BCCH)

Paging control channel (PCCH)

Dedicate control channel (DCCH)

Common control channel (CCCH)

Logical Channel

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Dedicated Channel (DCH)

-DCH is an uplink or downlink channel

Broadcast channel (BCH)Forward access channel (FACH)

Paging channel (PCH)

Random access channel (RACH)

High-speed downlink shared channel

(HS-DSCH)

Common transportchannel

Dedicated transportchannel

Transport Channel

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Physical Channel

A physical channel is defined by a specific carrier frequency,

code (scrambling code, spreading code) and relative phase.

In UMTS system, the different code (scrambling code or

spreading code) can distinguish the channels.

Most channels consist of radio frames and time slots, and each

radio frame consists of 15 time slots.

Two types of physical channel:UL and DL

Physical Channel

Frequency, Code, Phase

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Function of physical channel

Node BUE

P-CCPCH-Primary Common Control Physical Channel

SCH- Synchronisation Channel (Including P-SCH and S-SCH Channel)

P-CCPCH-Primary Common Control Physical Channel

SCH- Synchronisation Channel (Including P-SCH and S-SCH Channel)

P-CPICH-Primary Common Pilot Channel

S-CPICH-Secondary Common Pilot Channel

P-CPICH-Primary Common Pilot ChannelS-CPICH-Secondary Common Pilot Channel

Cell broadcast channels

DPDCH-Dedicated Physical Data ChannelDPDCH-Dedicated Physical Data Channel

DPCCH-Dedicated Physical Control ChannelDPCCH-Dedicated Physical Control Channel

Dedicated channels

Paging channels

PICH-Paging Indicator ChannelPICH-Paging Indicator Channel

S-CCPCH-Secondary Common Control Physical ChannelS-CCPCH-Secondary Common Control Physical Channel

PRACH-Physical Random Access ChannelPRACH-Physical Random Access Channel

AICH-Acquisition Indicator ChannelAICH-Acquisition Indicator Channel

Random access channels

HS-DPCCH-High Speed Dedicated Physical Control ChannelHS-DPCCH-High Speed Dedicated Physical Control Channel

HS-SCCH-High Speed Share Control ChannelHS-SCCH-High Speed Share Control Channel

HS-PDSCH-High Speed Physical Downlink Share ChannelHS-PDSCH-High Speed Physical Downlink Share Channel

High speed downlink share channels

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Thank youwww.huawei.com
http://www.huawei.com/http://www.huawei.com/

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