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”