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www.DigiTrainee.com Company Confidential
WCDMA Overview
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Development of Mobile communication
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3G Evolution
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3G Spectrum Allocation
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3G Application Services
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Multiple Access Technology
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Duplex Thechnology
Duplex Thecnology
- Frequency division duplex (FDD)
- Time Division Duplex (TDD)
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Duplex Technology
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Differences FDD & TDD
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WCDMA Network Architecture
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WCDMA Network Architecture
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WCDMA Network Evolution
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WCDMA Network Evolution
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Uu Interface Protocol Structure
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General Protocol
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UMTS Protocol Architecture: The Complete Picture (Packet Switched)
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UMTS Protocol Architecture: The Complete Picture (Circuit Switched)
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UMTS Protocol Architecture: Iub Interface Protocol
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Processing Procedure of WCDMA System
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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.
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Processing Procedure of WCDMA System
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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).
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Interleaving
Interleaving is used to damage symbol correlation and reduce the impact
caused by fast fading and interference of the channel.
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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) >
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Processing Procedure of WCDMA System
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Spreading Principle
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
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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.
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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
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Spectrum Analysis of Spreading & Dispreading in WCDMA-3G
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Spectrum Analysis of Spreading & Dispreading in WCDMA-3G
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Spreading and Scrambling
Symbols
OVSF code Scrambling
code
Chips after
spreading
and
scrambling 3.84M
3.84Mcps
3.84Mcps
xx sps
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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)
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WCDMA Channelization Code
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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.
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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.
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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.
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Primary Scrambling code
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Processing Procedure of WCDMA System
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Modulation Overview
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Modulation Overview
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Modulation Overview
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Demodulation
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WCDMA Modulation
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Processing Procedure of WCDMA System
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Propagation
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Fading
Fading
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Fading Categories
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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.
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Rake Receiver
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THANK’S