14_23_41_1. WCDMA RAN Principle .pdf

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WCDMA Overview


Development of Mobile communication


3G Evolution


3G Spectrum Allocation


3G Application Services


Multiple Access Technology


Duplex Thechnology

Duplex Thecnology

- Frequency division duplex (FDD)

- Time Division Duplex (TDD)


Duplex Technology


Differences FDD & TDD


WCDMA Network Architecture


WCDMA Network Evolution


Uu Interface Protocol Structure


General Protocol


UMTS Protocol Architecture: The Complete Picture (Packet Switched)


UMTS Protocol Architecture: The Complete Picture (Circuit Switched)


UMTS Protocol Architecture: Iub Interface Protocol


Processing Procedure of WCDMA System


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.


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).


Interleaving

Interleaving is used to damage symbol correlation and reduce the impact

caused by fast fading and interference of the channel.


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) >


Spreading Principle

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


De-spreading Principle

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×c1＋ UE2×c2： 0 -2 0 -2 0 +2 0 +2

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


Spectrum Analysis of Spreading & Dispreading in WCDMA-3G


Spreading and Scrambling

Symbols

OVSF code Scrambling

code

Chips after

spreading

and

scrambling 3.84M

3.84Mcps

3.84Mcps

xx sps


WCDMA Channelization Code

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)


WCDMA Channelization Code


Purpose of WCDMA Channelization Code

Channelization code is used to distinguish different physical channels of

one transmitter

For downlink, channelization code ( OVSF code ) is used to separate

different physical channels of one cell

For uplink, channelization code ( OVSF code ) is used to separate

different physical channels of one UE

For voice service (AMR), downlink SF is 128, it means there are 128

voice services maximum can be supported in one WCDMA carrier;

For Video Phone (64k packet data) service, WCDMA downlink SF is 32,

it means there are 32 voice services maximum can be supported in one

WCDMA carrier.


Purpose of WCDMA Scrambling Code

Scrambling code is used to distinguish different transmitters

For WCDMA downlink, scrambling code is used to separate different

cells in one carrier

For WCDMA uplink, scrambling code is used to separate different UEs in

one carrier

In addition to spreading, part of the process in the transmitter is the

scrambling operation. This is needed to separate terminals or base

stations from each other.


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.


Primary Scrambling code


Modulation Overview


Demodulation


WCDMA Modulation


Propagation


Fading

Fading


Fading Categories


Diversity Technique

Method for improving the reliability of a message signal by using two or

more communication channels with different characteristics.

The following classes of diversity schemes can be identified:

- Time diversity: Multiple versions of the same signal are transmitted at different

time instants

- Frequency diversity: The signal is transmitted using several frequency

channels or spread over a wide spectrum that is affected by frequency-

selective fading

- Space diversity: The signal is transmitted over several different propagation

paths. In the case of wired transmission, this can be achieved by transmitting

via multiple wires

- Polarization diversity: Multiple versions of a signal are transmitted and

received via antennas with different polarization.

- Multiuser diversity: Multiuser diversity is obtained by opportunistic user

scheduling at either the transmitter or the receiver.

- Cooperative diversity: Achieves antenna diversity gain by using the

cooperation of distributed antennas belonging to each node.

https://en.wikipedia.org/wiki/Channel_(communications)

https://en.wikipedia.org/wiki/Time_diversity

https://en.wikipedia.org/w/index.php?title=Frequency_diversity&action=edit&redlink=1

https://en.wikipedia.org/wiki/Fading

https://en.wikipedia.org/wiki/Space_diversity

https://en.wikipedia.org/wiki/Polarization_(waves)

https://en.wikipedia.org/w/index.php?title=Multiuser_diversity&action=edit&redlink=1

https://en.wikipedia.org/wiki/Cooperative_diversity


Rake Receiver


THANK’S

14_23_41_1. WCDMA RAN Principle .pdf

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