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 e 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 e 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

e 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 e 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 T frame : length of an OFDM frame B frame : BS can supply the maximal resources in an OFDM frame N S : number of OFDM frame in a sleep period N A : 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 P S : power consumption of a MSS in sleep mode P A : power consumption of a MSS in listen mode Maximize here to reduce average power consumption P A > P S

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 B j,i : amount of data required by connection i in the j th OFDM frame B k : amount of data for other connections of the MSS has been scheduled in k th OFDM frame (k >= j) ; (0 <= B k <= B frame ) j k

13 Bandwidth and delay constrains of AS j k 2 5 If B frame = 10 k j = 2 k = 4 (4-2+1) x 10 <= 35 If T frame = 10 k D i = 35

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 e 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