an adaptive energy-efficient mac protocol for wireless ：无线自适应能量有效的mac协议

An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Avanthi KoneruCSCE 5933October 24, 2005,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Agenda,IntroductionRelated WorkT-MAC Protocol DesignExperimentsReal Implementation,Introduction,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Sensor Network Stack,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Data Link Layer,Multiplexing of data streamsData frame detectionError ControlMedium Access control,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,The need,Traditional MAC protocols maximize packet throughput, minimize latency, provide fairness.Sensor networks minimize energy consumption,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Communication patterns,Local uni - / broadcastNodes to sink reporting,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,MSP430F149 processor with 2KB RAM and 60KB Flask memory115 kbps RFM TR1001 radioSimilar to Berkeley nodes,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Some Terminology,Idle listening problem: Most energy in traditional MAC protocols is wasted by idle listening.Duty Cycle: The fraction of time a system is actually employed in performing its function. The percent of time that the system is active as opposed to the time the system is inactive.,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Energy waste due to idle listening: Existing Solutions,TDMAMaintaining a TDMA schedule increases complexity.Keeping a list of neighbors schedules takes up valuable memory.Allocation of time slots needs coordination.Time synchronization is quintessential.Extra wake-up radioOperates on different frequency than communicationRequires additional components.,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Energy waste due to idle listening: Existing Solutions (.contd)S-MAC:,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Energy waste due to idle listening: Existing Solutions (.contd),S-MACFixed duty cycle :active state, sleep stateThroughput is reduced because only active part is used for communication.Latency increases because a message-generating event may occur during sleep time.,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Other forms of energy waste,CollisionsProtocol OverheadOverhearing,T-MAC Design Details,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,T-MAC Evolution,CSMA/CD,CSMA/CA,SMAC,TMAC,IEEE 802.11,IEEE 802.3,Carrier Sense Multiple Access with Collision Avoidance,Fixed duty cycle,Adaptive duty cycle,ARC,Adaptive Rate Control,DMAC/MMAC,Directional Antennas,Carrier Sense Multiple Access with Collision Detection,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,T(Timeout)-MAC Protocol Design,Every node periodically wakes up to communicate with its neighbors and then goes to sleep again until the next frame. The active time ends by time out when nothing is heard on the medium.Reduce idle listening by transmitting all messages in bursts of variable length and sleeping between bursts.,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Activation event,An active period ends when no activation event occurs for a time TA.Activation Events:The firing of a periodic frame timer;The reception of any data on the radio;The sensing of communication on the radio, e.g. during a collision;The end-of-transmission of a nodes own data packet or acknowledgement;The knowledge, through overhearing prior RTS and CTS packets, that a data exchange of a neighbor has ended.,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Clustering and Synchronization,Nodes exchange their schedule by periodically broadcasting SYNC packetNodes take following 2 steps to choose their scheduleListen for SYNC packets for a fixed amount of timeCase 1: No SYNC packets are receivedCase 2: SYNC packet is received.Case 3: Multiple SYNC packets are received.,Broadcast the chosen schedule by sending out SYNC packet.,Border nodes with 2 schedules broadcast twice,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Collision Avoidance,Nodes communicate with each other using a Request-To-Send (RTS), Clear-To-Send (CTS), Data, Acknowledgement (ACK) scheme which provides both collision avoidance and reliable transmission.,RTS,CTS,data,ACK,Sender,Receiver,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,RTS Operation,Fixed Contention IntervalContention for the medium is very high when every node starts transmitting their messages in a burst at the start of a frame.RTS transmission in T-MAC starts by waiting and listening for a random time within a fixed contention interval. This interval is tuned for maximum load.,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,RTS Retries,When a node sends an RTS, but does not receive a CTS back, one of following three things has happened:the receiving node has not heard the RTS due to collision; the receiving node is prohibited from replying due to an overheard RTS or CTS; the receiving node is asleep.In cases 1 & 2, it would be wrong if the nsending node goes to sleep.A node should retry by re-sending the RTS if it receives no answer. If there is still no reply after two retries,it should give up and go to sleep.,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Choosing TA,TA C + R + T C - length of the contention interval R - length of an RTS packet T - turn-around time (the short time between the end of the RTS packet & the beginning of the CTS packet).,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Overhearing Avoidance,In S-MAC, a node sleeps after overhearing an RTS or CTS destined for another node. Since a node is prohibited from sending during that time, it can not take part in any communication and may as well turn its radio off to save energy. This decreases the throughput by as much as 25%.But, a node may miss other RTS and CTS packets while sleeping and disturb some communication when it wakes up. Overhearing avoidance must not be used when maximum throughput is required.,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Asymmetric Communication,Early sleeping problem: a node goes to sleep when a neighbor still has messages. Nodes-to-sink communication pattern,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Proposed Solutions for early sleeping,Future request-to-send (FRTS)Taking priority on full buffers,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Future-Request-To-Send (FRTS),The idea is to let other node know that we still have a message for it, but are ourselves prohibited from using the medium.The FRTS packet contains the length of time for which communication is blocked.The node that receives the FRTS packet knows that it will be the future target of an RTS packet and must be awake by that time.,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Taking priority on full buffers,When nodes transmit/routing buffer are almost full, it may prefer sending to receiving.Advantages:Probability of early sleeping problem is reduced.The scheme introduces limited flow control in the network.T-MAC uses a threshold: a node may only use this scheme when it has lost contention at least twice.,Simulation Experiments,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Simulation setup and parameters,The simulation was created using OMNeT+ discrete event simulation package.The model was based on the real amount of energy consumed by the EYES nodes.20 A - sleeping4 mA - receiving 10 mA - transmitting A network of 100 nodes in a 10 by 10 grid, with a radio range of 8 neighbors for non-edge nodes.,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Protocols evaluated,CSMA never sleepsS-MAC protocol with a frame length of one second, and with several lengths of the active time, varying from 75 ms to 915 ms.T-MAC protocol with a frame length of 610 ms (20000 ticks of a quartz crystal) and an interval TA with a length of 15 ms.,Results,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Homogeneous local unicast with small messages (msglength = 20),An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Homogeneous local unicast with large messages (msglength = 100),An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Nodes to sink communication for small messages,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Nodes to sink communication for large messages,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Early sleeping problem,An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks,Event-based local unicast,An Adaptive Energy-Efficient MAC