Energy-efficient Sleep-mode Operations for Broadband Wireless Access Systems

1. Energy-efficient Sleep-mode Operations for Broadband Wireless Access Systems You-Lin Chen and Shiao-Li Tsao IEEE 64th Vehicular Technology Conference, Sep. 2006

2. Outline • Introduction • 802.16e sleep mode operations and power consumption issues • Energy-efficient scheduler for sleep-mode operations • Simulation results • Conclusions and future work

3. Introduction • Mobile devises are normally battery-operated • IEEE 802.16e specifies three power-saving class for different applications • MSS should stay in sleep periods as much as possible but not to violate the QoS requirements

4. 802.16e sleep mode operations and power consumption issues

5. Actual sleep periods

6. Example of two scheduling schemes

7. Periodic on-off scheme (PS) • Sleep and listen for a fixed period in a round-robin basis • Based on IEEE 802.16e power-saving class of type-2 • Schedule the packets in fewer OFDM frames without violating the QoS

8. Example of periodic on-off scheme (PS)

9. Maximal data transmit and receive in a listen period • Tframe: length of an OFDM frame • Bframe: BS can supply the maximal resources in an OFDM frame • NS: number of OFDM frame in a sleep period • NA: number of OFDM frame in a listen period • Qi {PSi , TIi, Di}: QoS parameters of connection i • PSi: average packet size for connection i • TIi: average inter-packet arrive time for connection i • Di: delay constraint of any two consecutive packets for connection i

10. PS scheduling area under constraint

11. Average power consumption PA > PS PS: power consumption of a MSS in sleep mode PA: power consumption of a MSS in listen mode Maximize here to reduce average power consumption

12. Aperiodic on-off scheme (AC) • Using the type-3 power-saving class • First sorts all connections • Tight delay constraint packet has higher priority • Connection i: The first priority connection • Bj,i: amount of data required by connection i in the jth OFDM frame • Bk: amount of data for other connections of the MSS has been scheduled in kth OFDM frame (k >= j) ; (0 <= Bk <= Bframe) j k

13. Bandwidth and delay constrains of AS If Bframe= 10 k j 2 k 5 If Tframe= 10 k Di = 35 j = 2 (4-2+1)x10 <= 35 k = 4

14. Example of Aperiodic on-off scheme

15. Simulation results • The length of an OFDM frame is 5 ms • The maximal data rate from BS to a MS is 1600 kbps • Traditional scheme • Assign OFDM frames to a MSS whenever the MSS needs to send or to receive packets

16. QoS parameters of four different real-time connections

17. Percentage of sleep periods of a MSS by different scheduling schemes

18. Average packet delays for different scheduling schemes

19. Percentage under the tight delay constraints

20. Conclusion and future work • Two scheduling schemes for sleep-mode in IEEE 802.16e • These schemes minimize the power consumption of a MSS under QoS • Increase 15% to 50% more sleep time than traditional approach • Applying to multiple-MSS and global optimization for a BS’s point of view

21. Thank you