A Modified Power Saving Mode in IEEE 802.11 Distributed Coordinator Function Mr. Ye Minghua

1. A Modified Power Saving Mode in IEEE 802.11 Distributed Coordinator Function Mr. Ye Minghua Supervisor: Dr. Lau Chiew Tong CeMNET School of Computer Engineering

2. Outline • Vision and challenge • Background and Review of Power saving mode in IEEE 802.11 • Our proposed algorithm • Simulation result • Conclusion and future work

3. Vision “Computing and communication anytime, anywhere and to anybody else” • Challenge • Mobility and Flexibility • Standardized communication protocol (IEEE802.11, Blue Tooth, etc.) • Finite battery power of mobile device

5. Energy Consumption model • Active mode • Transmit state • Receiving state • Idle state • Power Saving mode

6. Power Saving Mechanism for IEEE 802.11 • Idle receiving state is dominating power waste; • The cost of power state transition. • 800 micro-second for a doze to awake transition; • During this transition, a node will consume twice the power than idle mode. Note: Conservative estimation, depend on hardware implementation.

7. Example of the operation

8. Our proposed algorithm • The time synchronization beacon is moved to the end of the ATIM window; • The beacon sender will operate in the promiscuously listening mode within the ATIM window; • Scheduling information will be computed and sent along with the beacon.

9. The Beacon transmission • In each of the ATIM window, the station that send the ATIM announcement first will send the timing beacon; • Parameter Beacon_tran_time • IF (clock mod aBeacon_interval == Beacon_tran_time) THEN { all STAs defer any of their ongoing transmission }; • Specific STA will transmit beacon at Beacon_tran_time + SIFS

10. Implementation details – inside ATIM window • each node will piggyback the number_of_pending_packets for current destination in each ATIM announcement packet transmitted; • Only one specific node have to operate in the promiscuously listening mode within the ATIM window; • Beacon is transmitted by this node along with the scheduling information which explicitly gives out the order of transmission.

11. Implementation details – outside ATIM window • All STAs transmit their announced data packets according to the scheduling; • STAs can switch to doze if the following criteria satisfied: • Finished sending the announced packets of its own; • No packets destined for it as stated in the schedule; • Remaining time of current beacon interval is larger than 1600 microseconds. (conservatively consider 800 microseconds for both state transitions)

12. Example of the operation Beacon Interval Beacon Interval Beacon ATIM Window ATIM Window Xmit ATIM Xmit Beacon Rcv Beacon Rcv ACK Station A RCV ATIM Rcv Beacon Xmit Beacon Send ACK Station B Rcv Beacon Rcv Beacon Station C Power-saving state

13. Simulation • we developed the simulation programs using C++; • The simulator closely follows the protocol details of Power Saving Mode in 802.11 (802.11PSM) and our proposed algorithm (S-PSM); • beacon generation, ATIM window, contention based DCF access procedure and 2Mbps physical layer.

14. Parameters used in Simulation

15. Simulation result

16. Conclusion • Up to 70% of the total energy saving; • Only a little bit longer delay than traditional IEEE802.11 PSM in some cases; • Probability of collision is greatly reduced by schedule which ensure the data transmission to be contention free; • Maintain the network performance comparing with PSM of 802.11, throughput, delivery ratio, average packet delay, etc.

17. Future work • Investigate the possibility of applying this mechanism to the multi-hop scenario; • Achieve more efficiency by dynamically adjusting the ATIM window size; • Research the integration and interaction of MAC layer protocol and the routing layer. • Investigate the time synchronization issue.

18. Thank you!