X-MAC A short preamble MAC protocol for duty-cycled ：X-MAC短前导MAC协议的义务循环.ppt

X-MAC:A short preamble MAC protocol for duty-cycled wireless sensor networks Michael Buettner,Gary V.Yee,Eric Anderson,Richard HanTelvis CalhounWireless Sensor Networks CSC8908-005Dr.Li09/17/2021OutlineoDuty Cycled MACsoCommon IssuesoDuty Cycled MAC protocolsoXMACoConclusionsDuty Cycled MACSoUse awake,sleep intervals to conserve energyoKey parameters nSleep timenWake timenEnergy consumed during the awake state and the sleep state.oThe period of a duty cycle is equivalent to its sleep time plus awake time.Idle Listening ProblemoIdle Listening consumes substantial energy oSynchronized protocols nNodes awake on a scheduleoAsynchronized protocol nUses low power listening oHybrids nCombine synchronized and asynchronized.Low Power ListeningoSender uses longer preamble to allow the receiver to awake periodically.Asynchronized Protocols oAdvantagesnUse extended preamblenSender and receiver can have decoupled duty cycles.nNo synchronization overhead.nAwake periods are much shorteroDisadvantagesnFrame exchange delay even if receiver awakes before preamble endsnOverhearing problem nPreamble latency is expensive for multihop routesSMACoSynchronizes sensor clustersoNodes periodically wake-up to receive synchronization info from its neighbors.nMitigates need for system wide synchronization.nNodes can belong to more that one virtual cluster.oCommunicate using RTS-CTSoCan use adaptive listeningnNeighbor briefly wakes up at the end of overheard RTS,CTSnReduces one-hop latencyT-MACoListen for a short time after awake period.oSleeps if IDLE.oImproves on S-MAC by shortening the awake period if IDLE.oFor variable payloads,T-MAC uses 20%of energy used in S-MAC.BMACoUses local schedulesoSend preamble that is slightly longer than the sleep period.oLong preamble assures that the neighbor will receive packet.oProvides API to adjust sleep period.oSuffers from overhearing problem.Other MethodsoWiseMACnReduces the extended preamble length and energynPut next awake time in ACKs.nTransmit to node only slightly before awake time specified in ACKoHardware-Only MechanismnLow power radio circuit that listens for the preamble.nWake-On-Radio periodically listens for preamble then wakes up main radio circuit.XMACoShort preamblenReduce latency and reduce energy consumptionoTarget in preamblenMinimize overhearing problem.oStrobed preamblenReduces latency for the case where destination is awake before preamble completes.oReduces per-hop latency and energyoDynamic duty-cycle algorithmAsynchronous Duty CyclingoOverhearing Energy loss is proportional to number of receivers in range.oShort preamble packets.oNon-receivers return to sleep more quickly.oBad in high density sensor networks.StrobingoReduce time and energy wasted sending preamble nWhen target wakes before the endnMany successive transmitters send full preamble to a single target a single target.oXMAC uses strobed preamble.nAddresses problem when target wakes before the end.nSend preamble packetnListen for early acknowledgement packetnPreamble period must be greater than sleep period.Distributed CoordinationoDistributed Coordination FeaturenSensor overhears strobed preamble to target.nExecute random backoff longer than preamble period+datanSend to target after backoff.nTarget remains awake after receiving another Packetizing Radio SupportoStreaming radios transmit the raw packet from MAC layer.oPacketizing radios add own preamble,header and CRC.oPacketizing radios do not support extended preambles.oXMACs strobed preamble packets work for packetizing radios.Energy ModelsEnergy to send a packetEnergy to receive a packetConclusionsoEvaluation shows savings over low power listening.oGains continue as network density increases.oUnable to schedule sufficiently small listening periods ReferencesoM.Buettner,G.V.Yee,E.Anderson,and R.Han,X-MAC:a short preamble MAC protocol for duty-cycled wireless sensor networks,in Proceedings of the 4th international conference on Embedded networked sensor systems Boulder,Colorado,USA:ACM,2006.oG.P.Halkes,T.v.Dam,and K.G.Langendoen,Comparing energy-saving MAC protocols for wireless sensor networks,Mob.Netw.Appl.,vol.10,pp.783-791,2005.