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

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

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

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

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

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

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

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

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

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

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

AEA (cont.) C B D tx A lost ASK Inconsistency problem

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

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

Experimental setup Simulation platform –Qualnet Physical layer model –TR 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

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

Simulation results (cont.)

Data gathering application

Simulation results (cont.)

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