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Single OVSF code assignment in W-CDMA
彭瑱瑞
Outline
Introduction Code Assignment Strategy Conclusion My proposal and project Reference
Introduction
Voice Terminal (VT)
Video Terminal (VDT)
Data Terminal (DT)
Base Station
Dedicated Channel
Dedicated Channel
Dedicated Channel
Code = Resource
Code 1
Code 2
Code 3
e.g. One base station can support only 512x256=131072 codes on Downlink channel
Revolution
2G 3G
Voice Short messag
e
Voice Short messag
e
Video Internet
Low bit rate
High bit rate
Large file
OCSF-CDMA
MC-CDMAOVSF-CDMA
Why use OVSF?
MC-CDMA requires multiple transceiver units to support higher date rates, thus increased hardware complexity
OVSF-CDMA has several constraints such as code blocking, coarsely quantized data rates and a limitation on the maximum data rate
Basic knowledge
SF
chiprateR
Chip rate= chips / s
SF= chips / bit
Maximum chip rate= 3.84M chips/s
Maximum SF= 256 chips/bit
skbitsM
R /15256
84.3
chip
bit
OVSF code architecture
Code blocking definition
We define OVSF code blocking as the condition that a new call cannot be supported although the system has excess capacity to support the rate requirement of the call
If system have no enough capacity, we call that call blocking
Code blocking example
R
2R
4R
8R
16R
32R
1 65432 13121110987 20191817161514 262524232221 323130292827
1 2 3 4 5 6 7 169 10 11 12 13 14 158
1 2 3 4 5 6 7 8
1 2 3 4
1 2
1C6,1
C5,1 C5,2
C4,1 C4,2 C4,3 C4,4
1
2
3
4
5
6
=blocking
=assigned
=freeTotal capacity=32 Free capacity=10 Request rate=8
Code assignment strategy
1. Random
2. Leftmost
3. Nonrearrangeable compact assignment
4. Crowded first
5. Weight crowded first
Random
R
2R
4R
8R
16R
32R
1 65432 13121110987 20191817161514 262524232221 323130292827
1 2 3 4 5 6 7 169 10 11 12 13 14 158
1 2 3 4 5 6 7 8
1 2 3 4
1 2
1C6,1
C5,1 C5,2
C4,1 C4,2 C4,3 C4,4
1
2
3
4
5
6
=blocking
=assigned
=freeRequest 1= 2R Request 2= R Request3 = 2R
Leftmost
R
2R
4R
8R
16R
32R
1 65432 13121110987 20191817161514 262524232221 323130292827
1 2 3 4 5 6 7 169 10 11 12 13 14 158
1 2 3 4 5 6 7 8
1 2 3 4
1 2
1C6,1
C5,1 C5,2
C4,1 C4,2 C4,3 C4,4
1
2
3
4
5
6
=blocking
=assigned
=freeRequest 1= 2R Request 2= R Request 3= 2R
Leftmost
Advantage Vacant the right-hand tree for high rate service Make left-hand tree more compact
Disadvantage Too much proactive reassignment
NCA
Choose the most crowded tree to assign code is better
Compact index The total number of assignable codes in its different
neighborhood
Compact index
R
2R
4R
8R
16R
32R
1 65432 13121110987 20191817161514 262524232221 323130292827
1 2 3 4 5 6 7 169 10 11 12 13 14 158
1 2 3 4 5 6 7 8
1 2 3 4
1 2
1C6,1
C5,1 C5,2
C4,1 C4,2 C4,3 C4,4
1
2
3
4
5
6
=blocking
=assigned
=free
C1,1= 1+2+4+8+9 =24 C1,9= 2+4+4+8+9 =27 C1,25= 1+1+1+1+9 =13
24 27 27 27 27252524 13
8 1010
3
NCA
Advantage Make the code tree more compact without proactive
reassignment
Disadvantage All compact indices need to be recalculated before
each code assignment, and it is time consuming
Crowded-first
R
2R
4R
8R
16R
32R
1 65432 13121110987 20191817161514 262524232221 323130292827
1 2 3 4 5 6 7 169 10 11 12 13 14 158
1 2 3 4 5 6 7 8
1 2 3 4
1 2
1
=blocking
=assigned
=candidateRequest 2R
2 0 0 26 66 14
1
2
3
4
5
6
Crowded-first
Advantage Make the code tree more compact without proactive
reassignment and less computation complexity than NCA
Disadvantage Need to calculate recursively
Weighted crowded-first
1 65432 13121110987 20191817161514 262524232221 323130292827
1 2 3 4 5 6 7 169 10 11 12 13 14 158
1 2 3 4 5 6 7 8
1 2 3 4
1 2
1
1
2
3
4
5
6
=blocking
=assigned
=free
R
2R
4R
8R
16R
32RC6,1
C5,1 C5,2
C4,1C4,2 C4,3 C4,4
1 1 3 3 3 3 3 3 3 3 1 1
0 02 2 2 2
1 1
0
Weighted crowded-first
Advantage Faster decision than crowded-first
Disadvantage Little higher code blocking probability than crowded-fir
st
Other
Novel code assignment Region division code assignment Dynamic code assignment
Conclusion
Wireless bandwidth is a precious resource ,thus its resource management is important
The main idea is to keep the code tree less fragmented so as to accept more calls
Different Scope
1 65432 13121110987 20191817161514 262524232221 323130292827
1 2 3 4 5 6 7 169 10 11 12 13 14 158
1 2 3 4 5 6 7 8
1 2 3 4
1 2
1
1
2
3
4
5
6
=blocking
=assigned
=free
R
2R
4R
8R
16R
32RC6,1
C5,1 C5,2
C4,1C4,2 C4,3 C4,4
20 24 24 24 24 18 19 19
Compact indexCrowded first
Code blocking ?(R,2R,4R,8R)=(40,10,10,40)
Call blocking
My project
Simulation ProgramSimulate system environment Implement all code assignment algorithmsComputation code blocking probability
New performance metric
Plot the simulation result
Reference
Leftmost: R. Fantacci and S. Nannicini, “Multiple Access Protocol for Integration of Variable Bit Rate Multimedia Traffic in UMTS/IMT-2000 Based on Wideband CDMA,” IEEE J. Selected Areas in Comm.,vol. 18, no. 8, pp. 1441-1454, Aug. 2000.
Dynamic code assignment: T. Minn and K.-Y. Siu, “Dynamic Assignment of Orthogonal Variable-Spreading-Factor Codes in W-CDMA,” IEEE J. Selected Areas in Comm., vol. 18, no. 8, pp. 1429-1440, Aug. 2000.
NCA: Y. Yang and T.-S.P. Yum, “Nonrearrangeable Compact Assignment of Orthogonal Variable-Spreading-Factor Codes for Multi-Rate Traffic,” Proc. IEEE Vehicular Technology Conf. 2001 Fall,pp. 938-942, 2001.
Crowded-first: Y.-C. Tseng, C.-M. Chao, and S.-L. Wu, “Code placement and replacement strategies for wideband CDMA OVSF code tree management,” in Proc. of IEEE GLOBECOM, vol. 1, pp. 562–566, 2001.
Weighted crowded-first: Angelos N. Rouskas and Dimitrios N. Skoutas, “OVSF Codes Assignment and Reassignment at The Forward Link of W-CDMA 3G System”