Energy-efficient collision-free medium access control for wireless sensor networks

1. Energy-efficient collision-free medium access control for wireless sensor networks Venkatesh Rajendran Katia Obraczka Garcia-Luna-Aceves Department of Computer Engineering University of California, Santa Cruz ACM SenSys’03 Speaker: Yung-Lin Yu

2. Outline • Introduction • TRAMA • NP(Neighbor Protocol) • SEP(Schedule Exchange Protocol) • AEA(Adaptive Election Algorithm) • Experimental setup • Simulation results • Conclusion

3. Introduction • The deployment of sensor network usually done in ad-hoc manner • Self-organize into a multi-hop wireless network • Nodes may be difficult to recharge • Nodes recharging may not be cost effective • Major challenge • Self adaptive to changes in traffic • Prolongs the battery life

4. TRAMA • Overview • TRAMA consists of three components • NP (Neighbor Protocol) • SEP (Schedule Exchange Protocol) • AEA (Adaptive Election Algorithm)

5. NP • Nodes can only join during random access periods • Main function of random access periods is node additions and deletions • All nodes must be transmit or receive state • The most energy consumption

6. NP (cont.) • Using signaling packets to gather neighborhood information • During the random access period • Updates about its one-hop neighborhood • Added or deleted • Keep-alive • Time out a neighbor

7. SEP • SEP establishes and maintains schedule information • The information is periodically broadcast • Each node has a SCHEDULE_INTERVAL • Winning slots • Node computes in the interval [t,t+ SCHEDULE_INTERVAL] • Last winning slot reserved for broadcasting the node’s schedule for the next interval

8. SEP (cont.) • Schedule packets • Nodes announce their schedule via Schedule packets • Using bitmap to transmit schedule packets • The length of bitmap is the number of one-hop neighbors • Eg. • A node has 4 one-hop neighbors with identities 14,7,5,4 • If broadcast , bitmap : 1111 • If multicast to 14 and 5, bitmap: 1010

9. SEP (cont.) • ChangeOver slot • The slot after which all the winning slots go unused • The maximum sleep periods • ChangeOver slot to last winning slot

10. SEP (cont.) • A summary of a node’s schedule • Sent with every data packet • Summary help minimize the effects of packet loss • In order not to excessive overhead, the schedule summary is 6 bytes

11. AEA • Purpose • To Decide node’s state (TX, RX, SL) • Re-use slots

12. C AEA (cont.) tx A D lost B 100 200 ASK 95 79 Inconsistency problem

13. AEA (cont.) • Node u is tx(u) • u wants to transmit • Let u.state = TX • Let u.receiver = u.reported.rxId • u gave up transmit • Call HandleNeedTransmissions • tx(u)belongs to N1(u) • tx(u).announcedReceiver = u • Let u.state = RX • Else u.state = SL

14. AEA (cont.) • atx(u) hidden from tx(u) • atx(u).announcedReceiver = u • Let u.state = RX • Else u.state = SL • HandleNeedTransmissions • ntx(u) = u • Let u.state = TX • Let u.receiver = u.reported.rxId • atx(u).announcedReceiver = u • Let u.state = RX • Else u.state = SL

15. Experimental setup • Simulation platform • Qualnet • Physical layer model • TR1000 • 50 nodes are uniformly distributed over a 500m x 500m area • 6 one-hop neighbors on average • 17 two-hop neighbors on average • 2 different types of traffic load • Synthetic data generation • Data gathering application

16. Simulation results • Synthetic traffic Average packet delivery ratio for synthetic traffic Average queuing delay for synthetic traffic

17. Simulation results (cont.)

18. Simulation results (cont.) • Data gathering application

19. Simulation results (cont.)

20. Simulation results (cont.)

21. Conclusion • TRAMA achieves • Energy-savings comparable to S-MAC • Delivery guarantees comparable to NAME • TRAMA has higher delay • It Suited for • Not delay sensitive • High delivery guarantees • Energy efficiency