1. Hao Chen, Guoliang Yao, Hao Liu National ASIC System Engineering Research Center Southeast University WICOM 2008

2. Outline  Introduction  TA-MAC Design  Simulation Result  Conclusion

3. Introduction  In wireless sensor networks, the crucial challenge is energy conservation since nodes are usually powered by batteries whose available energy are limited, and expected to be worked in a remote and inhospitable environment without attendance during their lifetime.

4. Introduction  Some problems in S-MAC Fixed active period ○ latency per hops equals to at least one sleep period which is even longer when selecting low duty cycle Synchronization for all nodes ○ Prone to form multi-schedules which lead to More idle listening and overhearing No communication ○ Nodes will switch to sleep state after active phase Keep in idle state till the end of this cycle

5. TA-MAC Design  Synchronization  Sleeping Policy  Extra Transferring Cycle (ETC)

6. TA-MAC Design  Synchronization S-MAC ○ Active sleep/ Passive sleep ○ May exist border nodes which have to perform two or more schedules TA-MAC ○ At first, a sink broadcasts the SYNC packet. ○ Neighboring nodes keeps awake until get the SYNC packet.

7. TA-MAC Design  Sleeping Policy S-MAC ○ Still exits energy waste if a node ends its data transmission right in the sleep phase ○ Receipt RTS or CTS packet TA-MAC ○ Give another method

8. TA-MAC Design  Extra Transferring Cycle (ETC) S-MAC ○ Fixed duty cycle (for one packet) ○ Traffic load become high Packets stored in queue may overflow The packets should stay more time in network TA-MAC ○ Extra transferring cycle Increase the chances of transmission in one frame (DATA / ACK)

9. TA-MAC Design  Extra Transferring Cycle (ETC) Sign bit Cleared sign bit

10. Simulation Result

11.  latency over nine-hop network

12. Simulation Result  delivery over nine-hop network

13. Simulation Result  average energy consumption per node over nine-hop network

14. Conclusion  TA-MAC reduces end-to-end latency via offering extra chances of data transmission.  Simulation results show that our scheme presents both lower end-to-end latency and higher energy efficiency than S- MAC.