1. 1 A Throughput Enhancement Handover Algorithm for WiMAX Network Architecture Hao-Ming Chang and Gwo-Jong Yu Graduate School of Mathematical Sciences, Aletheia University

2. 2 Outline Introduction Network Architecture Handover Algorithm in Details Simulation Conclusion

3. 3 Outline Introduction Network Architecture Handover Algorithm in Details Simulation Conclusion

4. 4 Introduction While the technology of wireless network and the development of mobile station (MS) advance significantly User requirements for transmission quality is difficult to satisfy. IEEE 802.11 is the most common wireless connection Restrictions of transmission ranges and low mobility.

5. 5 Introduction -Cont. To support the mobile application of MS, IEEE 802.16e provides a handover process to satisfy the needs of users. BS still faces problems such as the restrictions on the range of MS and transmission quality variations. Due to signal strength variations when MS is moving. A more reliable handover process is required. Maintaining the transmission quality. Avoiding disconnection. Maximize the total throughput.

6. 6 Motivation Most handover algorithms consider signal strength, handover process, or handover delay, and improve efficiency of handover processes to some degree. Little works take all signal strength, handover delay, and base station load balance into consideration. Suggest a handover algorithm Consider all factors in an overall uniform view to choose the best target station. Signal strength Handover time costs Workload of base station

7. 7 Outline Introduction Network Architecture Handover Algorithm in Details Simulation Conclusion

8. 8 ASN-GW1 Internet ASN-GW3 CSN1 CSN2 CSN3 BS2 BS1 BS3 BS4 BS7 BS8 BS9 ASN-GW2 BS5 BS6

9. 9 Outline Introduction Network Architecture Handover Algorithm in Details Simulation Conclusion

10. 10 Handover Algorithm in Details Utilizes the signal strength measured by MS, moving speed of MS and the environment of BS to calculate the remaining service time. Take into account the workload of BS to balance the load in each BS. Signal Strength Compute the remaining service time Handover decision Handover Time Cost In same ASN-GW In different ASN-GW In different CSN The workload of each base station Concluding handover algorithm and process

11. 11 Signal Strength Affecting the Throughput Depending on the signal strength, the handover processes are discussed as follows. To decide the necessity of handover processes The amount of accumulated throughput and the remaining service time. The triggering time Depends on the signal strength received by the MS and the velocity of the MS.

12. 12 Calculation Distance between MS and BS The signal strength P r received by MS can be calculated through Pr and Pt: receiver and transmission power Gt and Gr: antenna gain of the base station and the mobile station D(MS, BS): the Distances between the mobile station and the base station PL(D(MS,BS)): path-loss in D(MS, BS) L: system loss

13. 13 Calculation Distance between MS and BS -Cont. The path-loss model PL(D(MS,BS)) can be calculated as d 0 : the environment variables γ: the path-loss exponent, which varies with the environment around base stations. X σ denotes shadowing effect and Gaussian distribution variable. X f is frequency correction variable, and f is frequency. X H is the mobile equipment’s antenna height.

14. 14 Calculation Distance between MS and BS -Cont. From Eq. (1) and (2), if a MS measure the signal strength from BS, the distance between the MS and BS can be calculated in

15. 15 The remaining service time can be computed by T move : the remaining service time. V: the maximum moving speed. The Remaining Service Time D(MS, BS) Case 1: Case 2:

16. 16 Handover Time Cost Affecting the Throughput In the neighboring BS, the remaining service time should take out the time cost of handover process. Introduce the time cost between MAC layers Different ASN-GWs Different CSNs

17. 17 MAC Layer Handover Time Cost Tcont: the time required for contention based ranging process of the MS. Trng: the average time required for the ranging of the MS. Tsync: the average time required for downlink synchronization of the MS. Tauth and Treg: the average time needed for the re-authorization and re-registration for the MS. T(SBS, MS): the time needed to transmit message between SBS and MS. T(SBS, nBS): the time to transmit message between SBS and nBS. Trendezvous: the time needed for the mobile equipment to wait for the noncompetitive frame time that the neighboring stations distribute specifically for the serving BS.

18. 18 ASN-GWs Handover Time Cost T(BS, ASN-GW): the time required to transmit message between BS and ASN-GW. T(AnchorASN, TargetASN): the time required to transmit message between two ASN-GW.

19. 19 CSNs Handover Time Cost Case 1: If time cost of binding update, is larger, the time cost of handover process will be TBU Case 2: If time cost of binding update, is smaller, the time cost of handover processes will be T pre +T L2 +T FNA TL2 : the time needed for the handover process in MAC layers when executing handover processes. TBU : the time needed for the PAR and home agent/ corresponding node to perform binding update. TFNA : the time needed to execute fast neighbor advertisement. Tpre : the time for mobile equipment to disconnect from the PAR when the mobile equipment is not receiving data transmissions.

20. 20 Workload of BS Affecting Throughput For each BS, the required resources and resources distribution will affect the system throughput. The required information need to calculate is the workload of the base station after handover processes of MS to TBSs. To calculate this information, the allocated symbol and subcarriers within one second can be used as an workload indicator.

21. 21 Usable Symbols of BS The total symbols that can be used for the base stations within one second can be calculate as C : the amount of subcarriers. C H : the amount used by the pilot and guard subcarriers. S : the amount of symbol within one frame. k : the number of symbols in each slot. Every frame has a length of T.

22. 22 Increased Workload When considering how much workload the mobile equipment is providing to the base stations The signal strength and the amount of data transmission is considered. The increased workload which produce on MS to TBSs can be calculate as D : the amount of throughput of the mobile equipment. b : the amount of data transmitted for each symbol.

23. 23 Concluding Handover Algorithm and Process The three factors discussed above are combined to a integrated handover algorithm. The equation used for choosing the TBS will be The handover algorithm will choose the maximize value to be TBS.

24. 24 T rate Calculation T rate is the transmission rate calculated after sensing the signal strength between MS and BS. The transmission rate of MS, which is variation due to the distance between BS and MS, and then find the corresponding value in table.

25. 25 T time Calculation T time is the time which is calculated based on the difference between remaining service time and handover time cost, which can be T hocost : he time cost of handover process.

26. 26 BS expectedvalue Calculation BS expectedvalue is the expected value for handover process on the station. It can be calculated by BS expectdvalue : the is the expected value for handover process on the station. BS workload : the workload of the base station after handover processes with mobile equipment,

27. 27 Outline Introduction Network Architecture Handover Algorithm in Details Simulation Conclusion

28. 28 Simulation Environment

29. 29 Time Parameter

30. 30 Compare with Handover Probability (S) (%) 1

31. 31 Total throughput Increase Rate (S)

32. 32 Outline Introduction Network Architecture Handover Algorithm in Details Simulation Conclusion

33. 33 Conclusion Proposed a higher throughput handover algorithm Considers signal strength, handover time costs, and workload of base station. Experimental results reveal that the proposed handover algorithm is more efficient. When MS is moving into a new network range. The times of handover process and total throughput are both improved, too.

34. 34 Any Question? Thank You.