1、Efficient MAC Protocols for Wireless Sensor NetworksMahendra KumarProperties of a Well Defined MAC Protocol Energy EfficientScalabilityAdaptability to changes in network topologyLatency, throughput, bandwidthFairness not so importantReason of Energy WasteCollisionOverhearingControl Packet overheadId

2、le ListeningOverremittingExisting MAC ProtocolsSensor-MAC (S-MAC) : Listen-sleepTimeout-MAC (T-MAC) : Activation eventWiseMAC : Preamble SamplingS-MACMain goal reduce power consumptionThree major components:Periodic sleep-listenCollision and overhearing avoidanceMessage passingPeriodic Sleep-ListenE

3、ach node goes to sleep for some time,and then wakes up and listens to see if any other node wants to talk to it.During Sleep it turn off its radio.Collision and Overhearing AvoidanceInterfering nodes go to sleep after they hear an RTS or CTS packet.Duration field in each transmitted packet indicates

4、 how long the remaining transmission will be.S-MACMaintaining SynchronizationThe listen/sleep scheme requires synchronization among neighboring nodes.Updating schedules is accomplished by sending a SYNC packet.Advantages/DisadvantagesEnergy waste caused by idle listening is reduced by sleep schedule

5、s.Sleep and listen periods are predefined and constant which decreases the efficiency of the algorithm under variable traffic load.Timeout-MAC (T-MAC)Proposed to enhance the poor results of S-MAC protocol under variable traffic load.Listen period ends when no activation event has occurred for a time

6、 threshold TA.Reduce idle listening by transmitting all messages in bursts of variable length, and sleeping between bursts.times out on hearing nothing.S-MAC Vs T-MACAdvantages/DisadvantagesGives better result under variable load.Suffers from early sleeping problem node goes to sleep when a neighbor

7、 still has messages for it. WiseMACAll nodes defined to have two communication channels.Data channel uses TDMAControl channel uses CSMAPreamble sampling used to decrease idle listening time.Nodes sample the medium periodically to see if any data is going to arrive.WiseMACAdvantages/DisadvantagesDyna

8、mic preamble length adjustment results in better performance.Conflict when one node starts to send the preamble to a node that is already receiving another nodes transmission where the preamble sender is not within range. Hidden terminal problemOther MAC ProtocolsSIFT :Event DrivenTRAMA : Traffic Ad

9、aptive MAC, TDMA Based MAC ProtocolTime SyncNeededTypeAdaptivity toChangesAdvantagesDisadvantagesS-MACNoCSMA, Contention-basedGoodEnergy waste caused by idle listening is reduced bysleep schedules.Simplicity.Sleep and listen periods are predefined and constant, whichdecreases the efficiency of theal

10、gorithm under variable trafficload.T-MACNoCSMA,ContentionbasedGoodGives better results undervariable loadsEarly sleeping problem.WiseMACNoCSMA,Preamble basedGoodDynamic preamble length adjustment results in betterperformance undervariable traffic conditions.Decentralized sleep-listen scheduling resu

11、lts in differentsleep and wake-up times foreach neighbor of a node. Hiddenterminal problemTRAMAYesTDMA/CSMAGoodHigher percentage of sleeptime and less collisionprobability is achievedcompared to CSMA basedprotocols.Without considering the transmissions and receptions, theduty cycle is at least 12.5 %,which is a considerably highvalue.SIFTNoCSMA/CA, ContentionWindow-basedGoodVery low latency is achi