High Utilization Resource Allocation and Performance Evaluation for GPRS Networks

1. 無線分封數據服務網路之高使用率資源分配策略與效能評估無線分封數據服務網路之高使用率資源分配策略與效能評估 High Utilization Resource Allocation and Performance Evaluation for GPRS Networks 研 究 生：蔡鎮年 指導教授：柯開維 博士

2. Outline • Introduction • Background • Resource Allocation Strategy for GPRS • Analytical Model • Numerical Result • Conclusion

3. Introduction (1/2) • Radio resource allocation for GPRS • Single rate vs. multirate • Time slots vs. radio blocks • Different strategies to partition the available cell capacity • Complete Sharing (CS) • Complete Partitioning (CP) • Partial Sharing (PS)

4. Introduction (2/2) • This thesis • Focuses on CP and PS strategy. • Allocates downlink radio resource by radio blocks. • Two types (rates) of GPRS user. • Analyzes and evaluates performance for different strategy.

5. Background • GPRS network architecture • GPRS air interface • TBF and TFI

6. GPRS Network Architecture (1/2) • It fits in with the existing GSM PLMN • Two new network elements • Serving GPRS Support Node (SGSN) • Gateway GPRS Support Node (GGSN) • Many new interfaces • Gb, Gi, Gn, etc.

7. GPRS Network Architecture (2/2)

8. GPRS Air Interface • Frequency-Division Duplex, FDD • Combination of Frequency and Time division multiple access, FDMA/TDMA • 52-multiframe • Physical channels and logical channels

9. GPRS Air Interface52-multiframe

10. GPRS Air InterfacePhysical Channels • Eight physical channels (TS0 to TS7) per carrier. • The physical channel that is used for packet logical channels is called a packet data channel (PDCH).

11. TBF and TFI (1/3) • A temporary block flow (TBF) is a physical connection between the MS and the network side to support data transfer. • Once the data transfer is finished, the TBF is released.

12. TBF and TFI (2/3) • Each TBF is identified by a temporary flow identity (TFI) assigned by the network. • PDCH multiplexing • TBFs which belonging to different MS can share the same PDCH.

13. TBF and TFI (3/3)

14. Resource Allocation Strategy for GPRS • Radio resource partition strategies • Complete Partitioning (CP) • Partial Sharing (PS)

15. Resource Allocation Strategy Complete Partitioning • TS0 to TS4 are GSM user only, and TS5 to TS7 are GPRS user only • This two partitions are independent

16. Resource Allocation StrategyPartial Sharing • A shared time slot • This two partitions are dependent

17. Analytical Model for CP • In CP case, GSM and GPRS partitions are independent, so we can analyze this two partitions separately. • System description • State definition • State transition diagrams • Balance equations • Performance metrics

18. Analytical Model for CPSystem Description • Two types of user • Class 1 (1+1) and class 2 (2+1) • The request is Poisson. • Arrival rate are λ1 and λ2, respective. • The service time of each request is exponential distribution • Mean service time are 1/μ1 and 1/μ2, respective.

19. Analytical Model for CPState Definition • State x=(i, j, k) • i = the number of PDCH is used • j = the number of class 1 user • k = the number of class 2 user • An example

20. Analytical Model for CPState Transition Diagrams • Define R = j + 2k, and MAX_PDCH is the maximum number of GPRS time slot that can be used. • Four cases

21. Analytical Model for CPState Transition Diagrams • The most straightforward • No need to consider i An example MAX_PDCH = 3

22. Analytical Model for CPState Transition Diagrams Generalized state transition diagram for case 1

23. Analytical Model for CPBalance Equations

24. Analytical Model for CPPerformance Metrics • According steady-state probabilities, we can fine the class 1 and class 2 blocking probability (Pb1 and Pb2), and radio resource utilization U.

25. Analytical Model for PS (1/2) • PS case is more complex than CP case. • In addition to GPRS user, there is GSM user in the system as well. • GSM user • New call and handover call are Poisson • Arrival rate • Service time is exponential distribution • Mean service time

26. Analytical Model for PS (2/2) • State x=(i, j, k, l, m) • i = the number of PDCH being used • j = the number of GPRS class 1 user • k = the number of GPRS class 2 user • l = the number of GSM user • m = indicate who is using shared TS • 12 different cases, 12 different balance equations.

27. Analytical Model for PSPerformance Metrics (1/2) • According to these balance equations, we can calculate steady-state probabilities, and compute performance metrics as well. • GPRS class 1 blocking probability • GPRS class 2 blocking probability

28. Analytical Model for PSPerformance Metrics (2/2) • GSM new call blocking probability • GSM handover call blocking probability • Radio resource utilization

29. Numerical Result • Comparison between analytic and simulated result. • Comparison between CP and PS for GPRS traffic. • Utilization vs. load • Define • GPRS load • GSM load

30. Comparison between analytic and simulated result (1/2) • CP case

31. Comparison between analytic and simulated result (2/2) • PS case

32. Comparison between CP and PS for GPRS request

33. Utilization vs. offered load (1/2) • CP case

34. Utilization vs. offered load (2/2) • PS case

35. Conclusion • Radio block based CP and PS strategies was proposed. • Built analytic model for both strategies. • Verified analytic model by simulation. • Showed that PS case scheme performed better than CP one. • GPRS radio resource can be fully utilized easily.

36. Future work • Impact of cell-reselection. • Priority for GSM handover call. • Preemptive mechanism. • Adaptive resource allocation.

37. The End