1. Energy-efficient Sleep-mode Operations for Broadband Wireless Access Systems You-Lin Chen and Shiao-Li Tsao Department of Computer Science, National Chiao Tung University, Hsinchu, Taiwan, R.O.C {youlin, sltsao}@cs.nctu.edu.tw

2. Outline Introduction 802.16e sleep mode operations Energy-efficient schedulers for sleep mode operations ◦ Periodic on-off scheme (PS) ◦ Aperiodic on-off scheme (AS) Simulation results Conclusions

3. Introduction Broadband wireless access systems usually provide sleep-mode operations for mobile stations to conserve energy during idle modes The wireless mobile devices are normally battery-operated ◦ the energy-efficiency is an important issue

4. Introduction The IEEE 802.16e offers several sleep-mode classes that can be applied to mobile subscriber stations to reduce their power consumptions for different applications An IEEE 802.16e MS can switch to sleep mode to save power ◦ sleep period : BS buffer incoming packets ◦ listen period : BS send queued packet to MS

5. Introduction An MS should try to stay in sleep periods as much as possible to conserve its energy In this study, two scheduling schemes for sleep- mode operations are presented to maximize sleep periods of an MS while the QoSs of connections on the MS can be also guaranteed

6. 802.16e sleep mode operations Parameters are negotiated by an MS and a BS ◦ The time to sleep / listen ◦ The length of each period MS try to stay in sleep period as much as possible

7. 802.16e sleep mode operations The first class ◦ It is recommended for BE or NRT-VR service

8. 802.16e sleep mode operations The second class ◦ It is recommended for UGS or RT-VR service

9. 802.16e sleep mode operations The third class ◦ It is recommended for multicast connections or management operations

10. 802.16e sleep mode operations If an MS establishes multiple connections, the actual sleep periods are determined by the sleep- mode operations associated with all connections

11. Energy-efficient schedulers for sleep mode operations The sleep and listen periods must be in unit of an OFDM frame If the resources are available, the BS can group the data that should be delivered in a number of OFDM frames and schedule them into a single frame to an MS

12. Energy-efficient schedulers for sleep mode operations In this work, only sleep-mode scheduling schemes for an MS with multiple real-time connections are considered

13. Periodic On-Off Scheme (PS) Let an MS sleep for a fixed period and then listen for a fixed period in a round-robin basis The PS groups the packets and schedules them in the less number of OFDM frames The PS also achieves the QoS of all connections

14. Periodic On-Off Scheme N S : the number of OFDM frames in a sleep period N A : the number of OFDM frames in a listen period T frame : the length of an OFDM frame B frame : BS can supply the max resources in an OFDM frame D i : delay constraint PS i : average packet size for connection i TI i : average inter packet arrive time for connection i

15. Periodic On-Off Scheme P avg : average power consumption P S : power consumption during sleep mode P A : power consumption during listen mode

16. Aperiodic On-Off Scheme (AS) The AS schedules resource to an MS and make the OFDM frame be fully used Step 1. sort all connections on an MS based on their delay constraint Step 2. assign priority to connections Step 3. schedule all connections

17. Aperiodic On-Off Scheme

18. Simulation results Simulations are conducted to evaluate the power consumption of an MS in terms of the number of listen and sleep frames

19. Simulation results Loose / tight delay constraint Length of OFDM frame is 5 ms Maximal data rate the BS provided is 1600 kbps

20. Simulation results Percentage of sleep periods of an MS

21. Simulation results Average packet delays

22. Simulation results Percentage of sleep periods of an MS under the tight delay constraint

23. Conclusions Two scheduling schemes for sleep-mode operations were proposed They minimize the power consumption of an MS while the QoSs of connections on the MS are also guaranteed