O. E. Falowo and H. A. Chan

1. Optimal RAT Selection Policy to Minimize Call Blocking Probability in Next Generation Wireless Networks O. E. Falowo and H. A. Chan Department of Electrical Engineering University of Cape Town 21st August, 2008

2. PresentationOverview • Introduction • Need for Joint Call Admission Control • Existing RAT Selection Approaches • Optimal RAT Selection JCAC Scheme • System Model • Performance Evaluation

3. Service/ Application Layer Control Layer Transport Layer Access Layer Introduction Next Generation Networks

4. Access Network Wireless Wireline Next Generation Network Service/ Application Layer Control Layer Transport Layer Access Layer

5. Satellite coverage WiMAX coverage 3G coverage WLAN coverage Next Generation Wireless Network Heterogeneous Architecture Satellite IP Gateway WLAN Gateway GGSN Connectivity Service Network Node SGSN Access Service Network Node WiMAX Base Station Access Router Node B Fixed Earth Station MT-2 RNC AP MT-1 AP AP Node B • Different RATs coexist • Subscribers can seamlessly roam across different RATs

6. RAT 2 RAT J RAT 1 Need for JCAC Algorithm • In next generation wireless network, there is need to make joint call admission decisions Can the arriving call be admitted or not? Call admission decision JCAC Into which RAT should the call be admitted? RAT selection decision

7.  Network load Network resources > Network load Network resources < Network load Network resources Need for JCAC Algorithm • Efficient Radio Resource Utilization Desirable condition Poor QoS Poor resource utilization • Service Continuity- Users’ Mobility B RAT-2 A RAT-1 C

8. Call Admission Control • Service-Class Differentiation- Prioritization • Voice • Video • Data

9. RAT 2 RAT J RAT 1 Need for JCAC JCAC in heterogeneous wireless network is necessary for the following reasons: • Efficient radio resource utilization - Increased revenue • Enhanced QoS provisioning – Improvedusers’ satisfaction • Overall service cost reduction • Overall network stability

10. PresentationOverview • Introduction • Need for Joint Call Admission Control • Existing RAT Selection Approaches • Optimal RAT Selection JCAC Scheme • System Model • Performance Evaluation

11. Existing RAT Selection Approaches • Random-Selection Based • Load-Based • Service-Class Based • Service-Cost Based • Layer-Based • Path-Loss Based • Computational Intelligence Based RAT 2 RAT J RAT 1 Which Network?

12. RAT 1 RAT 2 RAT 3 Limitation of Existing Schemes JRRM Class-1 calls Class-2 calls Class-1 calls • In a non-uniform service heterogeneous wireless networks, existing RAT-selection schemes do no guarantee minimum call blocking probability

13. PresentationOverview • Introduction • Need for Joint Call Admission Control • Existing RAT Selection Approaches • Optimal RAT Selection JCAC Scheme • System Model • Performance Evaluation

14. Objectives of the OJCAC Scheme • Minimize call blocking probability • Guarantee the QoS requirements of all accepted calls • Prioritize handoff calls over new calls

15. Components of the Proposed Scheme • Joint Call Admission Controller • Arrival Rate measurement Unit • Optimal Policy Determination Unit • Bandwidth Reservation Unit

16. Bandwidth Reservation Unit Fixed or dynamic thresholds Availablebandwidth C2 C1 CJ t2 t1 tj RAT-J Access networks RAT-1 RAT-2

17. RAT-1 RAT-J Class-1 calls Class-K calls System Model • The heterogeneous network comprises J number of RATs • Supports K classes of calls JRRM Heterogeneous Network

18. RAT 1 RAT 2 RAT 3 System Model JRRM Class-1 calls Class-2 calls Class-1 calls A Two-Class Three-RAT Heterogeneous Wireless Networks

19. where Markov Chain Model State space of the System • mi,j denotes number of new class-i calls in RAT j • ni,j denotes number of handoff class-i calls in RAT j • di,j denotes the set of indices of all class-i calls that can be supported by RAT-j • An admissible state, denoted by s, is the number of users in each class that can be simultaneously supported in the system

20. Action Space • Set of all possible actions • State dependent aindenotes the action taken on arrival of a new class-i call aihdenotes the action taken on arrival of a handoff class-i call hi denotes the set of indices of all RAT-j that support class-i calls

21. Linear Programming Optimization Given any values of threshold Toj for rejecting new calls in RAT-j (j=1,…,J) in a heterogeneous wireless network, there exist optimal values of ij and ij (j=1,…,J, i dj) that minimize the overall blocking probability in the heterogeneous wireless network

22. Performance Evaluation • New call blocking probability • Handoff call dropping probability

23. Effect of varying the call arrival rate on new call blocking probability

24. Effect of varying the call arrival rate on overall new call blocking probability for OJCAC and EJCAC schemes

25. Effect of varying the call arrival rate on handoff call dropping probability

26. Effect of varying call arrival rate on overall handoff call dropping probability for OJCAC and EJCAC schemes

27. Effect of varying the call arrival rate on the call blocking/ dropping probability of class-1 calls

28. Effect of varying the call arrival rate on the call blocking/ dropping probability of class-2 calls

29. Effect of varying the new call rejection threshold, T0 on the call blocking / dropping probability

30. Conclusion • An optimal RAT selection policy has been proposed to minimize call blocking probability in heterogeneous wireless networks • Using Markov decision process and linear programming technique, an analytical model has been developed to evaluate the performance of the proposed OJCAC Scheme • Results show that the proposed OJCACscheme reduces call blocking probability in the heterogeneous wireless networks

31. THANK YOU