Associate Prof. Yuh-Shyan Chen Dept. of Computer Science and Information Engineering

1. Chapter 11Code Placement and Replacement Strategiesfor Wideband CDMA OVSF/ROVSF Code Tree Management Associate Prof. Yuh-Shyan Chen Dept. of Computer Science and Information Engineering National Chung-Cheng University

2. 1. Introduction

3. 1. Introduction

4. 2G GSM 2.5G GPRS 3G UMTS 1. Introduction

5. 1. Introduction Iu Uu BS MSC/ VLR GMSC RNC UE BS Iur-CS USIM Iub Iur HLR Cu ME BS Iur-PS RNC SGSN GGSN BS UE UTRAN CN Structural network architecture 3G UMTS system architecture

6. 1. Introduction OVSF code tree

7. 1. Introduction

8. 2. Problem statement • Code placement problem • Code blocking probability • Internal fragmentation • Code replacement problem • Code reassignment cost

9. :4R : new request : used code Example of OVSF Code Tree Code blocking

10. :2R : new request : used code Example of OVSF Code Tree Code blocking

11. : 3R : new request : used code Example of OVSF Code Tree Internal fragmentation

12. : 3R : new request : used code Example of OVSF Code Tree Internal fragmentation

13. 3. Code placement and replacement strategies • Y.-C. Tseng and C.-M. Chao, "Code Placement and Replacement Strategies for Wideband CDMA OVSF Code Tree Management", IEEE Trans. on Mobile Computing, Vol. 1, No. 4, Oct.-Dec. 2002, pp. 293-302. • Tseng’s Code placement schemes • Random placement scheme • Leftmost placement scheme • Crowded-first placement scheme

14. A new call of rate 2R

15. 3. Code replacement strategy • Tseng’s Code replacement schemes • Find the minimum-cost branch • Based on DCA • Relocate until done • Based on code placement schemes

16. A Code Replacement Example A new call of rate 8R

17. Multi-Code Approach • C.-M. Chao, Y.-C. Tseng, and L.-C. Wang, "Reducing Internal and External Fragmentations of OVSF Codes in WCDMA Systems with Multiple Codes", IEEE Wireless Communications and Networking Conf. (WCNC), 2003.

18. Tseng’s multi-code assignment • Order of Assignment: • increasing • decreasing • Co-location of Codes: • united strategy • separated strategy • Assignment of Individual Codes: • Random • Leftmost • Crowded-first-space • Crowded-first-code

19. 3. Code Placement and Replacement Strategies • Tseng’s internal fragmentation solution n: number of multicode N(i): ideal (optimal) n n n n single code … multi-code Number of code 1 2 3 4 … N(i)=Number of 1s in (i)2 For any given i, we can find a N(i) N(i)

20. 3. Code Placement and Replacement Strategies Internal Fragmentations

21. Tseng’s multi-code assignment Possible candidates for 6R (n=2: 4R+2R) (decreasing): Leftmost: {C8,1 , C16,3} Crowded-first-space: {C8,8 , C16,14} Crowded-first-code: {C8,3 , C16,7}

22. Tseng’s multi-code re-assignment • Dynamic code assignment (DCA) scheme was proposed to solve the single-code reassignment problem • Authors utilize the DCA scheme as a basic construction block. When moving codes around. Authors also consider where to place those codes that are migrated so as to reduce the potential future reassignment cost (this issue is ignored in DCA).

23. Tseng’s multi-code re-assignment New requested call: 6R (n=2: 4R+2R) (decreasing): Free capacity: 9R Leftmost

24. Our Single-Code Placement and Replacement Strategies • Yuh-Shyan Chen and Ting-Lung Lin, "Code Placement and Replacement Schemes for W-CDMA Rotated-OVSF Code Tree Management," is submitted to The International Conference on Information Networking, ICOIN 2004, Feb. 18 - Feb. 20, 2004, Korea.

25. Outline • Introduction • Background Knowledge • Code Placement and Replacement Strategies • Performance Analysis • Simulation Results • Conclusion

26. I. Introduction • This paper proposes a code replacement scheme based on ROVSF code tree • This scheme aims to develop • Code placement strategy • Reduce blocking probability • Code replacement strategy • Reduce reassignment cost

27. Motivation • Existing OVSF-based scheme has a lower spectral efficiency and a higher system overhead • This study aims to develop a more efficient channelization code scheme

28. Contributions • An alternative solution for code placement and replacement schemes is proposed • Advantage of the ROVSF-based scheme • Lower blocking probability • Better spectral efficiency • Lower reassignment cost • Keep the system overhead low

29. II. Background Knowledge • Related Works • OVSF Code Tree • Rotated-OVSF Code Tree • Linear-Code Chain

30. Related Works • OVSF-based Scheme • Dynamic Code Assignment • IEEE Journal on Selected Areas in Comm., Aug. 2000 • Single-code Placement & Replacement • Proc. of IEEE Trans. on Mobile Computing, 2002. (Y.C. Tseng) • Multi-code Assignment • IEEE Wireless Comm. and Networking Conf., 2003. (Y.C. Tseng) • OVSF-like Scheme • FOSSIL • Proc. of IEEE ICC, 2001.

31. Review of OVSF Property

32. Our of ROVSF Property

33. : used code : orthogonal codes Important Properties of ROVSF Code Tree • A ROVSF code is cyclic orthogonal to its two children codes

34. : used code : orthogonal codes Important Properties of ROVSF Code Tree (cont.) • A ROVSF code is cyclic orthogonal to any descendent codes

35. : used code Important Properties of ROVSF Code Tree (cont.) • A ROVSF code is not cyclic orthogonal to any descendent of its brother code X X X X

36. Linear-Code Chain • A collection of mutually orthogonal codes • Every node of a OVSF code tree is mapping to the corresponding node of a ROVSF code tree to form the linear-code chain • Prior to designate where to allocate each supported request • Rate restriction of transmission requests • Reduce blocking of high-rate request

37. : used code Code Placement in OVSF Code Tree

38. : used code Example of Linear-Code Chain

39. Two Types of Linear-Code Chain

40. III. Code Placement and Replacement Strategies • Placement Scheme • Linear-Code Chain (LCC) Placement Phase • Non-linear-Code Chain (NCC) Placement Phase • Replacement Scheme • Dynamic Adjustment Operation of Linear-Code Chain

41. : used code : new request LCC Placement Phase • If exists (bk, bk-1, bk-2, 0,…, 0) and β< j,then the assignment is failed even if bβ= 0 1R (1, (1, 1), 0) (1, 0, 0) (1, 0, 1) X X X X

42. : used code : new request Example of LCC Placement Phase • If bβ= 1 and there is bγ= 1 and γ<β, then the assignment is failed 2R (1, 1, 1) (1, 0, 1) (1, 1, 1) X

43. NCC Placement Phase • If YR is failed in LCC placement phase, then enters NCC placement phase • If there exists linear-code chain (bk=1, 0,…,0), where γ =log2Y and γ= k, we may assign YR to neighboring node of node N of linear-code chain on the same level of ROVSF code tree, where transmission rate of node N is 2k

44. Example of NCC Placement Phase 2R (1, 1, 1) (0, (1, 1), 0) X X X X X X X

45. Summary of Code Placement • More codes are assigned in linear-code chain will result in a lower blocking probability • Dynamic adjustment operation of linear-code chain is introduced in code replacement scheme

46. Replacement Scheme • The purpose of this procedure • Force the code blocking probability to zero • We adopt the same concept of DCA algorithm • ROVSF-version DCA algorithm • Our proposed placement strategy is adopted while relocating each code

47. : used code : minimum-cost branch : occupied code Example of Replacement Scheme 4R cost = 1 cost = 2 cost = 4 cost = 3

48. Dynamic Adjustment Operation • Aims to overcome drawbacks of fixed length of LCC • Maximum transmission rate is limited • Not applicable to variable traffic patterns • If exists BW=(bk, bk-1, bk-2,…, b1, b0), where bi = 0 • If an incoming transmission rate is 2k+t, where 1 ≤t≤n-k, we can adjust the length of linear-code chain to be k+t+1

49. : used code : minimum-cost branch : occupied code Example of Dynamic Adjustment Operation 4R 1R 2R cost = 1 cost = 2

50. IV. Performance Analysis • We define the set of allowable states to be • The steady-state probability πv can be determined using the following equation: where π0 is the steady-state probability being in state 0: