Performance Modeling of Level Switching in Multitier Mobile Communication Systems

1. Performance Modeling of Level Switching in Multitier Mobile Communication Systems By C.K. Ng and H.W. Chan Natasha Moodliar Suvelee Sarpotdar

2. AGENDA • Introduction • Performance Model • Level Switching Schemes • Performance Analysis • Enhancement of the Model • Conclusions • Future Work

3. Introduction • MCS - Mobile Communication Systems - Cordless, Cellular, Mobile Satellite • MCS have specific characteristics • MCS have benefits and deficiencies

4. Introduction • Mobile Users (MU) have to subscribe to multiple MCS. • MU’s may need different mobile terminals (MT). • For single MT, need to manually switch

5. Introduction • One Solution: - replace all MCS’s with a new MCS - ineffective, costly, time-consuming • Faster and Easier Solution: - integrate existing MCS to form a multitier environment. - e.g.: roaming facility

6. Multitier Environment of mobile communication systems. • Integration of different MCS • Provides MU to communicate with anyone, anywhere, anytime. • Reduces Location Management (LM) cost. • Reduces Conversation cost (CV)

7. Multitier System • Issues with feasibility - interoperability, QoS, security etc. • Researchers concentrate on specific problems. • Key Success Factor of multitier systems not addressed.

8. Key Success Factor of multitier systems. • effective and efficient scheme • dynamically select most appropriate tier • optimize signaling traffic and performance.

9. Multitier System • Performance Model • Evaluation Mechanism • Performance Analysis: Stochastic model

10. Introduction • Model to represents multitier environment as a single system. • Continuous-time stochastic model. - State-transition rates - Costs (LS, calls rejected & dropped)

11. Motivation • Several LS schemes for optimizing total system cost based on triggering events. • Performance in terms of total system cost is analyzed and compared. • Find optimal LS scheme.

12. Performance Model • Structure • Stochastic Model • Cost Model

13. Structure • Mobile Terminal • Level • Service Area • Cell

14. Cell • Own radio equipment • Cell size is determined by the dimensions of the geographical area served by of the base station. • Designed to handle expected no. of MUs • Assigned a no. of frequency bands i.e. channels for communication.

16. Mobile-Terminal-Centric Approach 2 types of MT activities: • Calling related: -call arrival -call completion -call arrival rate and call completion rate used to model the calling pattern of an MT.

17. Mobile-Terminal-Centric Approach • Movement Related Activities: - parameterized by the cell-boundary crossing rate. - level dependent - 2 statuses: under coverage not under coverage

18. State transition diagram for a single level system

19. Performance Model Structure

20. Stochastic Model • 3 events in the proposed model: a) Call Arrival b) Call Completion c) Cell-Boundary Crossing • Poisson processes with independent negative exponential distributions. • Modeled by a continuous-time, discrete state stochastic process.

21. Stochastic Model • Sxyz1z2z3…zi…zL

22. Stochastic Model • Model representation:

23. Stochastic Model • n = no. of states in the system • rjk= rate of transition from state j to k

24. Transition rate diagram for single-level system

25. State transition diagram for a single level system

26. Steady State Probability • Πj (j=1….n)

27. Cost Model • Performance evaluation of the system is based on total communication cost (COMM cost) in terms of cost units per unit time.

31. Cost Model • Transition Cost & Activity Cost

32. Level Switching Schemes • No Level Switching (NLS) • Aggressive Level Switching (ALS) • Reactive Level Switching (RLS) • Selective Level Switching (SLS)

33. No Level Switching (NLS)

34. Aggressive Level Switching (ALS)

35. Reactive Level Switching (RLS)

36. Selective Level Switching (SLS)

37. Agenda • Performance Analysis • Experimental Setup • Results • Enhanced Model • Future Work/Critique • Conclusion

38. Performance Analysis • Total COMM cost calculated in steady state • Steps for analyzing • Different parameters such as L, δ, τ, σi, βi and unit costs (defined in cost model) are defined for the model • Compute total no. of states using

39. Performance Analysis (Cont’d…) • Steps continued… • Compute transition rates • Solve linear equations to compute steady state probabilities for each state for each scheme • Compute total cost using transition rates, steady state probabilities and unit costs

40. Stochastic Model • n = no. of states in the system • rjk= rate of transition from state j to k

41. Performance Analysis (Cont’d…) • Steps continued… • Compute transition rates • Solve linear equations to compute steady state probabilities for each state for each scheme • Compute total cost using transition rates, steady state probabilities and unit costs

42. Experimental Setup • Each LS scheme is analyzed for individual cost groups and total cost CT • Cost groups – penalty cost CP, conversation cost CC, location management cost CL, switching costs CS • System is analyzed for • Considering each level as an independent system and no switching between the levels • Switching between levels is considered

43. Experimental Setup (Cont’d…)

44. Basic Parameter Values • βi – are between 0 and 1 with 1 indicating global coverage • Unit call rejection penalty cost cτ and unit call dropout penalty cost cd – high values to indicate importance of being able to continue or receive calls • Absolute values of time and cost variables is not so important in analysis

45. Experimental Setup (Cont’d…)

46. Results

47. Summary of results

48. Total Cost of Level Switching vs Penalty Cost

49. Total Cost of Level Switching vs unit conversation cost

50. Total Cost of Level Switching vs location management cost