1. Adaptive Waiting Time Threshold Estimation Algorithm for Power Saving in Sleep Mode of IEEE 802.16e Khyati Sanghvi, Piyush Kumar Jain, Debabrata Das International Institute of Information Technology, India Abhijit Lele Motorola India Research Labs, Bangalore, India IEEE International Conference on Communication System Software and Middleware (COMSWA 2008)

2. Outline Introduction Proposed Algorithm Example Analytical Model Simulation Conclusion

3. Introduction Portable mobile devices are characterized by limited compute capacity and energy availability. Sleep mode is a key feature introduced in IEEE 802.16e standard, which ensures power-efficient operation of battery operated mobile devices.

4. Introduction – 802.16e sleep mode operations Power Saving Class of Type I Power Saving Class of Type II Power Saving Class of Type III … T S_init (Initial sleep window) 2 x T S_init TLTL 4 x T S_init T S_max Incoming packet TLTL TSTS Incoming packets … TSTS normal operation sleep windows listening windows MOB_TRF-IND

5. Motivation TRF-IND(-)TRF-IND(+) Wake mode Frame no. 2141 Listening window In PSC of type I, The 802.16e standard does not define when to take decision to trigger sleep mode. Packet arrival times in non real time traffic are unpredictable. 4 DL Data arrival DL Sleeping Period Active Period REQREP MS BS Waiting time threshold? REQREP …

6. Motivation Waiting time threshold – MSS wait for longer duration before switching to sleep mode at low traffic, leading to less sleep duration. – MSS wait for lower duration before switching to sleep mode at high traffic, leading to frequent sleep–active transitions.

7. Motivation Waiting time threshold – MSS wait for longer duration before switching to sleep mode at low traffic, leading to less sleep duration. – MSS wait for lower duration before switching to sleep mode at high traffic, leading to frequent sleep–active transitions. Frame no. 4 MS longer Waiting time threshold longer TRF-IND(+) DL Frame no. 4 MS Waiting time threshold longer TRF-IND(+) DL Sleeping Period

8. Motivation Waiting time threshold – MSS wait for longer duration before switching to sleep mode at low traffic, leading to less sleep duration. – MSS wait for lower duration before switching to sleep mode at high traffic, leading to frequent sleep–active transitions. Frame no. 4 MS W TRF-IND(+) DL Frame no. 4 MS Waiting time threshold longer TRF-IND(+) DL TRF-IND(+) W DL Active Period

9. Goal This paper proposes a novel algorithm for estimating optimum waiting time threshold to reduce the energy consumption.

10. Definitions Sleeping Period Active Period Sleeping Period MS SLSLAWAWREQSLSL … S: Sleep Window L: listening window A: Packets serving W: Waiting time duration T th : Waiting time threshold REQ : REQ/RSP message change T th REQ

11. Example Sleeping PeriodActive Period MS SLSLAW TRF-IND(+) DL UL T th T th_min is minimum limit of waiting time threshold. REQ

12. Example Active Period SLSLAW TRF-IND(+) DL A UL MS REQ Sleeping Period The MS will enter packet serving duration immediately

13. Example Active Period SLSLAW TRF-IND(+) DL A UL W T th MS REQ Sleeping Period When packet serving time is over, the Ms will estimate waiting time duration

14. Example A W β is a constant with unit sec -1. λ new is new arrival rate, λ n is weighted arrival rate after n th packet arrival, λ n-1 is weighted arrival rate after (n-1) th packet arrival AW DL UL REQSLSL T th

15. Example Active Period SLSLAW TRF-IND(+) DL A UL W Sleeping Period REQSLS T th MS REQ Sleeping Period The MS will wait the estimated waiting time duration

16. Valid Example A UL WREQSLSL T th TRF-IND(+) AW DL β = 4.865 α = 0.01 1/100 1/1000 0.00101 20ms 19.9567015 ms REQSL A …

17. Valid Example A W T th W AW DL UL A 1/100 1/10 0.991 β = 4.865 α = 0.01 20.4334715 ms 20 ms

18. Analytical Model Case 1: When UL or DL MAP arrives at MSS during waiting time threshold duration Case 2: When UL MAP is present at MSS for transmission during n th sleep interval while there is no DL frame arrival at BS for MSS Case 3: When DL MAP arrives at BS for MSS during n th sleep interval while there is no UL frame present at MSS Case 4 When UL frame is present at MSS for transmission with at least one DL frame arrival at BS for the MSS in the nth sleep interval Active Period Sleeping Period LAWAWREQSLSL … CASE 1CASE 2CASE 3CASE 4

19. Definitions AWAWREQS1LS2L … λ = mean arrival rate λd = mean downlink arrival rate λu = mean uplink arrival rate t t = arrival time of UL or DL frame t n = sleep interval during n-th sleep cycle S i = total sleep and listening interval till the i-th sleep cycle Tth_mean = mean waiting time threshold Ei = energy consumption for case i where i= {1, 2, 3, 4} Di = average delay in transmission of DL frame at BS for MSS due to MSS being in sleep mode for case i where i={1, 2, 3, 4} E th = energy consumption at MSS during waiting time threshold E s = energy consumption at MSS during sleep mode E = total energy consumption at MSS D = total average delay at MSS Tint_mean = mean inter arrival time DL/UL MAP

20. Case 1: When UL or DL MAP arrives at MSS during waiting time threshold duration Sleeping Period AWREQS1LS2L … DL / UL MAP t Tth_mean t n = 0

21. Case 1: When UL or DL MAP arrives at MSS during waiting time threshold duration Sleeping Period REQS1LS2L … AW Tth_mean DL / UL MAP t t n = 0

22. Case 2: When UL MAP is present at MSS for transmission during n th sleep interval while there is no DL frame arrival at BS for MSS Sn AWREQS1LS2 … UL MAP t Sn-1 tntn L

23. Sn AWREQS1LS2 … UL MAP t Sn-1 tntn L

24. Case 3: When DL MAP arrives at BS for MSS during n th sleep interval while there is no UL frame present at MSS Sleeping Period AWREQS1LS2L … DL MAP

25. Case 3: When DL MAP arrives at BS for MSS during n th sleep interval while there is no UL frame present at MSS Sleeping Period AWREQS1LS2L … DL MAP

26. Case 4 When UL frame is present at MSS for transmission with at least one DL frame arrival at BS for the MSS in the n th sleep interval Sleeping Period AWREQS1LS2L … UL MAPDL MAP

27. Case 4 When UL frame is present at MSS for transmission with at least one DL frame arrival at BS for the MSS in the n th sleep interval Sleeping Period AWREQS1LS2L … UL MAPDL MAP

28. Analytical Model Active Period Sleeping Period AWREQS1LS2L … CASE 1CASE 2CASE 3CASE 4

29. Simulation We have validated our simulation model with published simulation results performed on NS2 platform. The total simulation time is 400 sec and results are obtained by taking average value of 100 samples of traffic sequence for each arrival rate λ. Mean arrival rate λ varies from 0.05 to 1.0. One frame duration= 5ms α = 0.01, β = 4.865, listening duration L = 5ms, initial sleep duration tmin = 10ms and maximum sleep duration tmax = 160ms

30. Simulation Energy consumption values for waiting time threshold duration and sleep duration is taken as Eth = 280mw and Es= 10mw, respectively Furthermore, fixed waiting time threshold for existing algorithm is taken as Tth = 25ms and proposed algorithm uses minimum waiting time threshold Tth_min = 5ms and maximum waiting time threshold Tth_max = 50ms. In case- I the ratio of DL versus UL traffic is taken as R = 4 where R = λd / λu In case- II the ratio of DL versus UL traffic is taken as R = 1/4 where R = λ d / λu.

31. Simulation

36. Conclusion This paper attempts to modify the existing constant waiting time threshold scheme by making it adaptive to the varying downlink and uplink traffic pattern. We observe that traffic arrival pattern is an important factor for the waiting time threshold control.