an efficient mac protocol for wireless sensor networks：一种有效的无线传感器网络mac协议

Efficient MAC Protocols for Wireless Sensor Networks,Mahendra Kumar,Properties of a Well Defined MAC Protocol,Energy EfficientScalabilityAdaptability to changes in network topologyLatency, throughput, bandwidthFairness not so important,Reason of Energy Waste,CollisionOverhearingControl Packet overheadIdle ListeningOverremitting,Existing MAC Protocols,Sensor-MAC (S-MAC) : Listen-sleepTimeout-MAC (T-MAC) : Activation eventWiseMAC : Preamble Sampling,S-MAC,Main goal reduce power consumptionThree major components:Periodic sleep-listenCollision and overhearing avoidanceMessage passing,Periodic Sleep-Listen,Each 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 Avoidance,Interfering nodes go to sleep after they hear an RTS or CTS packet.Duration field in each transmitted packet indicates how long the remaining transmission will be.,S-MAC,Maintaining Synchronization,The listen/sleep scheme requires synchronization among neighboring nodes.Updating schedules is accomplished by sending a SYNC packet.,Advantages/Disadvantages,Energy waste caused by idle listening is reduced by sleep schedules.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 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-MAC,Advantages/Disadvantages,Gives better result under variable load.Suffers from early sleeping problem node goes to sleep when a neighbor still has messages for it.,WiseMAC,All 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.,WiseMAC,Advantages/Disadvantages,Dynamic 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