WCDMA Radio Theory

ZTE UniversityTD&W&PCS BSS Course Team

1G(Analog)

NMT

AMPS

TACS

3G(Wideband)

IMT-2000

2G(Digital)

GSM900/1800/1900

CDMA IS-95

TDMA IS-136

PDC

Evolution of Mobile Communications

Birth of IMT2000

1985, FPLMTS being put forward FPLMTS: Future Public Land Mobile Telecommunication System

1996, renamed by IMT-2000 IMT2000: International Mobile Telecommunication 2000

Meaning of ‘2000’ frequency spectrum around 2000MHz

putting into business about 2002

data rate up to 2000kbps

Frequency Range 1992

1885-2025MHz(uplink),2110-2200MHz(downlink)

Mainly: 1920~1980 2110~2170

May,2000, spread frequency range 806-960MHz,1710-1885MHz & 2500-2690MHz

The Goal of 3G

Higher transmit rate

Rich and colorful service

Good voice quality

Larger capacity

Lower cost

Good secret performance

High frequency efficiency

Max rate up to 2Mb/s

Easy to transition from 2G

Duplex Mode

Downlink

Uplink

5 MHz channelFDD mode

Fq. 1

Fq. 2

Uplink and Downlink

5 MHz channel

. .. . ..TDD mode

Multiplexing （ Multiplex Access Technology ）： Transmit two or more voice signals through one pair of cables without mutual interference at the same time.

• Each carrier frequency equals one traffic channel• Voice is transmitted continuously in time domain

USER

1 USER

2 USER

3

Time

FrequencyFDMA

FDMA

• Increase frequency spectrum efficiency• Voice is transmitted uncontinuously in time domain• System synchronous is very import

USER1

USER2

USER3

Frequency

Time

TDMA

• Large capacity• High voice quality• Soft hand-over• Low sensitive to radio fading

USER2

USER3

USER1

CDMA Frequency

TimeCode

CDMA

UE Data Encoding & Interleaving

Spreading

RF Transmission

RF ReceivingDemodulationDespreading

Decoding & Deinteleaving

UE Data

Data transmission Procedure

ModulationBaseband modulation

Baseband

demodulation

Channel encoding

Purpose:

Inserting redundant information into data stream to make

the detect and correction of transmission error possible.

UnusableNon-coding ： BER<10-1 ~ 10-2

Convolutional coding ： BER<10-3Voice

services

Turbo coding ： BER<10-6Data

services

Principle of channel encoding

Inserting redundant information into original data to make

correction.

Convolutional encoding and Turbo encoding(1/2,1/3).

Increase noneffective load and transmission time.

Correct incontinuous error.

W C D M AT U R B OS P E A K

W W C C D D M M A AT T U U R R B B O OS S P P E E A A K K

W ？ C C D D M M A A

T T U ？ R R B B O O

S S P P E E A ？ K K

Interleaving

Purpose:

Break original data alignment and realign according to new

rule to decrease influence of short term fading.

May transform continuous error into random error.

Disadvantage:

Bring additional transmission time.

x1 x6 x11 x16 x21

x2 x7 … x22

x3 x8 … x23

x4 x9 … x24

x5 x10 … x25

Input Data A = (x1 x2 x3 x4 x5 … x25)

Output data A’= (x1 x6 x11 x16… x25)

e.g ：

Encoding and Interleaving

W C D M AT U R B OS P E A K

W W C C D D M M A AT T U U R R B B O OS S P P E E A A K K

W T S W T SC U P C U PD R E D R EM B A M B AA O K A O K

W ? ? C D D M M A AT ? ? U R R B B O O

S ? ? P E E A A K K

Encoding Interleaving

W T S ? ? ?? ? ? C U PD R E D R EM B A M B AA O K A O K

DeinterleavingDecoding

UE Data Encoding & Interleaving Spreading Modulation

RF Transmission

RF ReceivingDemodulationDespreading

Decoding & Deinteleaving

UE Data

Data transmission Procedure

SHANON Formula

C = Blog2(1+S/N)

Where, C is capacity of channel, b/s B is signal bandwidth, Hz S is average power for signal, W N is average power for noise, W

It is the basic principle and theory for spread spectrum communications.

Spread Spectrum Principles

radio channel

ReceiverTransmitter

spread De-spread

Noise

Extend wideband

User information bits are spread over a wide bandwidth by

multiplying high speed spread code(chip)

Spreading signal bandwidth wider than original signal

bandwidth W=3.84Mchip/s 、 Rvoice=12.2kbit/s

Channelization Code

Adopt OVSF code

Definition: C ch,SF,k, describe channelization code, SF:spread ， k:code number, 0 < k<SF-1

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)

Concept of orthogonal code

Orthogonal—

the result of multiplying and sum is 0

Code1 +1-1+1+1-1+1-1-1

Code2 -1+1+1-1-1+1+1-1

Mul -1-1+1-1+1+1-1+1

Sum 0

OrthogonalCode1 +1-1+1-1-1+1-1-1

Code2 +1+1-1+1-1-1+1-1

Mul +1-1-1-1+1-1-1+1

Sum -2

Non-orthogonal

Symbol

Spreading

Despreading

1-1

1-1

1

-1

1-1

1-1

Data = 010010

Spreading code

Spread signal= Data × code

Spreading code =1 -1 -1 1 -1 1 1 -1 ( SF = 8 )

Data = Spread signal × Spread code

Chip

Spreading and Despreading

S1xC1

S2XC2

W

S1

S2

spread

De-spread(S1xC1)+(S2xC2)

Air-IF air interface

[S1xC1+S2xC2]xC1=S1

[S1xC1+S2xC2]xC2

=S2

N

S

C1xC2=0,C1,C2,orthogonal

Direct spread technique

EXAMPLE

-1 1 -11-1 -11 1 -1 -1 11-1 1-1 1Dispread-1 1 -11-1 -11 1

1 -1 1 -1

-4 40 0

Judge -1 1

1 -1 1 -1

-1 1 Spread

Integral

1 1 1 1-1 -1 -1 -1

1 1 1 1 -11-11

Spread Spectrum Flow

f

S （ f ）

f0Signal spectrum before spreading

Signal

S （ f ）

ff0Signal spectrum after spreading

Signal

S （ f ）

ff0Signal spectrum after dispreading

SignalNoise

f

S （ f ）

f0Signal spectrum before dispreading

SignalNoise

Signal Pulse noise noise

Spread Spectrum Principles

Many code channels are individually“spread” and then added together tocreate a “composite signal”

Spread Spectrum Principles

UNWANTED POWERFROM OTHER SOURCES

Using the “right” mathematicalsequences any Code Channelcan be extracted from the receivedcomposite signal

Eb/No

PG

PG = 25dBPG = 25dB

Voice 12.2 kbpsVoice 12.2 kbps Data 64 kbpsData 64 kbps Data 384 kbpsData 384 kbpsNodeBNodeB

PG = 18dBPG = 18dB

PG = 10dBPG = 10dB

Processing Gain

Processing gain

Processing gain = Chip rate/Bit rate (PG = W/R)

Different services have dissimilar processing gains. As a

result, their service coverage radiuses are different.

WCDMA Coverage Estimation

Eb/No

• Eb/No Power spectrumPower spectrum

Eb/No Eb/No requiredrequired

Subscriber 1Subscriber 1NoiseNoise Subscriber 2Subscriber 2Subscriber 3Subscriber 3

Eb/No = = S R X W

N SN

X W R

= SN

X PG

Eb indicates the signal energy per bit, that is, Eb = S/R where S indicates signal

energy and R indicates service bit rate.

No indicates the noise power spectrum density, that is No = N/W where W

indicates bandwidth (3.84 M) and N indicates noise (total receiving power except

the signal itself).

WCDMA Coverage Estimation

Eb/No

Channel

Rate

(kbit/s)

Required

Error Block

Rate

Recommended

Value by 3GPP

12.2 <10-1 n.a

<10-2 5.1 dB

64 <10-1 1.5 dB

<10-2 1.7 dB

144 <10-1 0.8 dB

<10-2 0.9 dB

384 <10-1 0.9 dB

<10-2 1.0 dB

Static propagation condition Multi-path channel 1 Multi-path channel 2

Channel Rate

(kbit/s)

Required

Error Block

Rate

Recommended

Value by 3GPP

12.2 <10-1 n.a

<10-2 11.9 dB

64 <10-1 6.2 dB

<10-2 9.2 dB

144 <10-1 5.4 dB

<10-2 8.4 dB

384 <10-1 5.8 dB

<10-2 8.8 dB

Channel Rate

(kbit/s)

Required

Error Block

Rate

Recommended

Value by 3GPP

12.2 <10-1 n.a

<10-2 9.0 dB

64 <10-1 4.3 dB

<10-2 6.4 dB

144 <10-1 3.7 dB

<10-2 5.6 dB

384 <10-1 4.1 dB

<10-2 6.1 dB

Eb/No Values Under Different Channel Environments in 3GPP

Eb/No is related to the service type, moving speed, coding/decoding algorithm,

antenna diversify, power control, and multi-path environment

WCDMA Coverage Estimation

DATA

Orthogonal Variable Spreading Factor (OVSF)---Channelization code Scrambling code

Symbol rate Chip rate3.84Mcps

Chip rate3.84Mcps

Spreading process of WCDMA

Symbol rate × SF = 3.84Mcps Uplink SF range ： 4~256 Downlink SF range ： 4~512

Code Resource Allocation

Channelization code:

Channelization codes are based on the orthogonal variable

spreading factor (OVSF) technology. Transmission from a

single source are separated by channelization codes.

Scrambling code:

Scrambling codes are used after spreading, which will not

change the signal bandwidth. They are only used to

differentiate different UEs or Node Bs.

In WCDMA, code resources are mainly divided into channelization codes and scrambling codes.

Channelization code Resource

SF=8

SF=32

SF=16

Characteristic of channelization code

Premise of code allocation: ensure not occupied for the code in the root direction and

downwards subtree

Result of code allocation: block all low rate SC in subtree and high rate in upwards

root direction

Example

SF=64

SF=32

SF=16

SF= 8

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

` 0 1

0

SF=64

SF=32

SF=16

SF= 8

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

` 0 1

0

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

` 0 1

0

0 1 2 3 4 5 6 7` ` ` `

` `0 1 2 3

` 0 1

0

(a) (b)

(c) (d)

`

Idle

Allocated

Blocked

Scrambling code reuse

114

13

121

8

7

6 3

9

10

5 2114

13

121

8

7

6 3

9

10

5 2

114

13

121

8

7

6 3

9

10

5 2

114

13

121

8

7

6 3

9

10

5 2

114

13

121

8

7

6 3

9

10

5 2114

13

121

8

7

6 3

9

10

5 2

114

13

121

8

7

6 3

9

10

5 2

UE Data Encoding & Interleaving Spreading Modulation

RF Transmission

RF ReceivingDemodulationDespreading

Decoding & Deinteleaving

UE Data

Data transmission Procedure

WCDMA Modulation

Principles of WCDMA

Principle of WCDMA All users are simultaneously transmitting in the same frequency

bands

Each user interferes with each other

Adjacent cells use the same frequencies

Cell, users (terminals), and physical channels are separated by

code

Codes Channelization codes for separation of physical channels in the

uplink and separation of users in the downlink

Scrambling codes for separation of users/terminals in the uplink

and cells/sectors in the downlink.