Channel Allocation for the GPRS Design and Performance Study

1. Channel Allocation for the GPRS Design and Performance Study Huei-Wen Ferng, Ph.D. Assistant Professor Department of Computer Science and Information Engineering (CSIE) Nation Taiwan University of Science and Technology (NTUST) Wireless Communications and Networking Engineering (WCANE) Lab URL: mail.ntust.edu.tw/~hwferng E-mail: hwferng@mail.ntust.edu.tw

2. Introduction Channel allocation schemes System model and assumptions Performance study and numerical examples Conclusions Outline

3. GPRS Architecture

4. Service Requirements • Blocking vs. forced termination • From the viewpoint of users, one may feel more uncomfortable when an on-going call is abruptly terminated than directly getting blocked before his service. • Generally speaking, less forced termination than blocking. • Delay-sensitive vs. non-delay-sensitive • Voice is more sensitive than data.

5. Design Principles • Channel reservation • It privileges handoff calls. • Priority • Priority among buffers • Differentiation between voice and data requests • Service priority between new voice calls and handoff voice calls • Differentiation between new calls and handoff calls • Buffering strategy • Allows more net input rates • Threshold control • Throttles different rates of new calls and handoff calls

6. Channel Allocation Schemes An example of dynamic allocation of the uplink data transfer

7. : no priority for voice and data buffers, no threshold control. • : higher priority for voice buffer, no threshold control. • : higher priority for voice buffer with threshold control. • : similar to the 2nd scheme with handoff the highest pri. • : similar to the 2nd scheme with channel reservation. Channel Allocation Schemes • Basic Dynamic Channel Allocation (DCA): • For a data request, DCA allocates at most n channels to the request. • For a voice call,only onechannel is allocated. • Five DCAs are proposed based on service priority, threshold control, channel reservation, and buffering strategies.

8. Voice buffer Data buffer CAS1 Scheme New voice (handoff) calls FIFO New data packets This scheme is proposed for reference.

9. CAS2 Scheme When buffer is empty. High priority New voice (handoff) calls Voice buffer Low priority New data packets Data buffer

10. Voice buffer High priority Data buffer Low priority CAS3 Scheme When buffer is empty Handoff call first. Then, new voice call. New voice (handoff) calls New data packets

11. New voice (handoff) calls Handoff voice calls New voice calls Voice buffer High priority Blockedwhen exceeding the threshold Data buffer Low priority CAS4 Scheme When buffer is empty New data packets

12. Voice buffer High priority Data buffer Low priority CAS5Scheme When buffer is empty. New voice (handoff) calls New call and handoff call Handoff call New data packets

13. System Model and Assumptions • GSM (new) voice call and GPRS (new) data packet arrive according to Poisson processes with ratesλv and λd, respectively. • GSM (new and handoff) voice call holding time, GPRS packet • transmission time, and GSM user dwelling time followexponential • distributionswith mean 1/μv, 1/μdand 1/η, respectively.. • Static data users are assumed for simplicity. • Each GSM user moves to any adjacent cell in a uniform manner; same traffic load as well as same number of channels are assumed to any cell. (resulting in homogenous cells).

14. Simulation Environment • Square cell structure • 6x6 wrapped mesh cells • Homogeneous cells

15. Analysis of Channel Allocation Scheme • Define state space • Write balance equations based on the state transition diagram • Use the recursive approach to obtain results

16. Define state space

17. State transition diagram For convenience, let us define two sets of indicator functions

18. State transition diagram

19. State transition diagram

20. Blocking probabilities

21. Delay times Using Little’s formula:

22. Parameters Setting

23. Performance Measures • Blocking probability for a new voice call • Forced termination probability for a handoff voice call • Data packet dropping probability • Delays • Cost comparisons among different schemes

24. The Effect of Data Buffering (on new voice blocking probability)

25. The Effect of Data Buffering (on forced termination probability)

26. The Effect of Data Buffering (on data dropping probability)

27. The Effect of Data Buffering (on delays of data packet) Delays of new voice calls and handoff voice calls are similar to probabilities.

28. The Effect of Data Buffering • Data buffer size affects little to new call blocking probability and • handoff call forced termination probability, except CAS1. • Increasing data buffer size greatly improves data dropping probability. • The effects on delays of new voice calls and handoff calls are similar to blocking probability and forced termination probability, respectively. • Increasing data buffer size raises data packet delay time.

29. The Effect of Threshold Control(on blocking/termination probability) Decreasing Tv makes new voice call blocking increase and improves forced termination probability.

30. The Effect of Threshold Control(on data dropping probability) Because lower value of Tv permits fewer queued new voice calls in the system; therefore, data packets have a better chance to be served, thus data dropping probability decreases.

31. The Effect of Threshold Control(on delays of new voice calls and handoff voice calls)

32. The Effect of Threshold Control(on delays of data packets)

33. Schemes Comparison (new voice blocking probability for various traffic load) The best to worst schemes areCAS2, CAS3, CAS4,andCAS5.

34. Schemes Comparison (forced termination probability for various traffic load) The best to worst schemes areCAS5, CAS4,CAS3and,CAS2.

35. Schemes Comparison (data dropping probability for various traffic load) CAS4performs best in terms of data dropping probability.

36. Schemes Comparison (delays of new voice calls for various traffic load)

37. Schemes Comparison (delays of handoff voice calls for various traffic load)

38. Schemes Comparison (delays of data packets for various traffic load)

39. Effect of data user mobility and computation illustration on channel reservation The performance of voice calls is not sensitive to variation of ηd because voice calls have higher precedence over data packets. When CG increases, performance of new voice calls and data packets becomes poor.

40. Effect of different data traffic models • The exponential distribution may not be appropriate in modeling data traffic. • Instead, the Pareto distribution can be used to capture the nature of data traffic.

41. Cost function: Cost comparisons (fixedτ3)

42. Cost comparisons(fixedτ2)

43. Cost comparisons (fixedτ1)

44. Conclusions We have examined and compared the improvement of channel allocation schemes using four techniques. • We conclude: • Buffering for both voice calls and data packets reduces blocking probability, forced termination probability, and data dropping probability but it increases delay times. • The threshold control is an effective approach to reduce • forced termination and data dropping probabilities. But it • enlarges new voice call blocking probability.

45. Conclusions • Although reservation greatly improves forced termination • probability and delay time for handoff voice call, it causes • the performance of new voice call and data service poor. • Finally, we suggest scheme CAS3andCAS4 to be used in the GPRS system.

46. The End Thank You!