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 Architecture
WCDMA Network Evolution
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 termi nals. - 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.
Processing Procedure of WCDMA System
Channel Coding in WCDMA
Channel coding can enhance symbol correlation to recover signals in the case of interference. 123456
7
8 9 10 11 12 13 14
15
16 17 18 19 20 21 22
Code type -
Voice service: Convolutional code (1/2 and 1/3).
-
Data service: Turbo code (1/3).
23
24 25
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 x 1(t ) , x 2(t ) …. -
Self correlation determines multipath interference.
-
Mutual correlation determines multiple access interference.
Self-correlation function -
R (τ )
=< x 1(t )
x 1(t +τ )
，
>
Mutual-correlation function -
V (τ )
=< x 1(t )
x 2(t +τ )
，
>
Processing Procedure of WCDMA System
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
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
Integral: Decision: UE2 de-spreading with c2: De-spreading result: Integral: Decision :
+2 0 +4
-4
+4/4 = +1
-4/4 = -1
-2
+1 +1 +1 +1 +1 +1 +1 +1 0
-2
0
-2
0 +2
0 +2
-4
+4
-4/4 = -1
+4/4 = +1
Spectrum Analysis of Spreading & Dispreading in WCDMA-3G
Spectrum Analysis of Spreading & Dispreading in WCDMA-3G
Spreading and Scrambling
Symbols
xx sps
3.84Mcps
3.84M
OVSF code
Scrambling code 3.84Mcps
Chips after spreading and scrambling
WCDMA Channelization Code Cch,4,0 =(1,1,1,1)
Cch,2,0 = (1,1) Cch,4,1 = (1,1,-1,-1) Cch,1,0 = (1) Cch,4,2 = (1,-1,1,-1)
Cch,2,1 = (1,-1) Cch,4,3 = (1,-1,-1,1) SF = 1
SF = 2
SF = 4
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
Processing Procedure of WCDMA System
Modulation Overview
Modulation Overview
Modulation Overview
Demodulation
WCDMA Modulation
Processing Procedure of WCDMA System
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 frequencyselective 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.
Rake Receiver
