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RT-Link: A Time-Synchronized Link Protocol for Energy-Constrained Multi-hop Wireless Networks

RT-Link: A Time-Synchronized Link Protocol for Energy-Constrained Multi-hop Wireless Networks. Anthony Rowe, Rahul Mangharam and Raj Rajkumar CMU SECON 2006. Outline. Introduction and Related works Protocol Overview Protocol Enhancements Implementation Evaluation Conclusion.

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RT-Link: A Time-Synchronized Link Protocol for Energy-Constrained Multi-hop Wireless Networks

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  1. RT-Link: A Time-Synchronized Link Protocol for Energy-ConstrainedMulti-hop Wireless Networks Anthony Rowe, Rahul Mangharam and Raj Rajkumar CMU SECON2006

  2. Outline • IntroductionandRelatedworks • ProtocolOverview • ProtocolEnhancements • Implementation • Evaluation • Conclusion

  3. Introduction • AMACprotocolforsensornetwork • TDMA-based • Hardware-basedtimesynchronization • Predictablelifetime(>2years) • boundedend-to-enddelay

  4. KeysforSensorNetMAC • Lifetime • Lowdutycycles • minimizetheradiousage • Delay • Eitherkeepsending • Orco-operateverywell(TDMA-based) Timesynchronizationisgood Buthowtoachievewithreasonablecost??

  5. SomeMACsforSensorNet • AsynchronousMAC–B-MAC • BerkeleyMAC • Carriersensemultipleaccess(CSMA)withlowpowerlistening(LPL) • LPL • OptionalRTS-CTS

  6. SomeMACsforSensorNet(Cont.) • LooselySynchronous • S-MAC • localsleep-wakeschedules • exchangesynchronizingpacketswithneighbors • FullySynchronized • TRAMA–scheduledslot • Assumetimesynchronizationisanorthogonalproblem • Time-syncprotocolsforSensorNet • Basicidea–timepacketexchange • Sufferforlinkerrorrate(upto50%)

  7. Outline • IntroductionandRelatedworks • ProtocolOverview • ProtocolEnhancements • Implementation • Evaluation • Conclusion

  8. ProtocolOverview Communicationcycle • Eachcycle • 32frames • Eachframe • startbysyncpulse • 325msslots • ScheduledSlots(SS)–formembernodes • ContentionSlots(CS)–forguestnodes • whenanodeisintransmissionslot,itsneighborsmustlistentothechannel • EverymembernodesmustlistentoallCS • So,theyneedcentralcontrol(Gateway)

  9. NewNode ProtocolOperations SendHellotoGWinCS Softwaretime-sync

  10. HowtoEnhance • Basicideaofscheduling • k-hopcoloring • TopologyControl • Degreehigh=>energyconsumptionhigh • Gatheringtopologyandprunenodes

  11. Interference-freeScheduling StableReceptiondistance(SRD) • Observations • Jammer-RXdistanceiscritical • Conclusion • Jammerhasnoeffectbeyond2*(SRD) • Concurrenttransmittermaybeplaced3*(SRD)

  12. ColoringandOrdering • Maxconcurrencyvsdelaysensitive • Getminimumdelay–NP-complete

  13. Heuristic • Dijkstra’sshortestpathspanningtree • BFSfromG,assignsmallestcolorthatsatisfy2-hopconstraint • Replacetheleaveswithlargervalue • Invertsthenumbers

  14. Outline • IntroductionandRelatedworks • ProtocolOverview • ProtocolEnhancements • Implementation • Evaluation • Conclusion

  15. HardwarePlatform • CMUFireFly–8-bitMicron+IEEE802.15.4

  16. TimeSynchronization–outdoor • WWVBatomicbroadcast(Wiki) • WWVB is a special NISTtime signal radio station near Fort Collins, Colorado • WWVB is the station that radio-controlled clocks throughout North America use to synchronize themselves. • The signal transmitted from WWVB is a continuous 60 kHz carrier wave, derived from a set of atomic clocks located at the transmitter site • Off-the-shelfWWVBreceiver

  17. Picture

  18. TimeSynchronization–Indoor • Carrier-currentAMbroadcast • LowpowerAMbroadcastingforcampus • NotlicensedinUS • Usebuildingpowerlinesasantenna

  19. TimeSynchronization–Indoor • AmodifiedFireFlyreceiveoutdooratomicclock • TransmittoAMstation • A(commercialAMreceiver)+(custominterfaceboard)receiveAMbroadcastandsynctheFireFly

  20. Performance • 5nodes • Separateseveralhundredfeet • Hardwired

  21. TDMASlotMechanics

  22. Outline • IntroductionandRelatedworks • ProtocolOverview • ProtocolEnhancements • Implementation • Evaluation • Conclusion

  23. EnergyModel–overaframe

  24. EnergyModel–overaframe • Tframe=Tactive+Tidle Activetimeoveraframe Minimumenergyconsumption Maximumenergyconsumption Lifetime

  25. LifetimeComparisons • SampleInterval • Eventgenerationrate • CheckInterval • TimebetweentwoconsecutiveLPL

  26. LifetimeComparisons

  27. LifetimeComparisons • Forhighsamplerate,hardwaresyncdoesn’thelp

  28. Delay • Simulationsetup • Topology • Onlyleafnodegeneratetraffic • Totaltrafficfixedto10001-bytepacket • Packetaggregationupto100bytes

  29. Delay--Result

  30. RealDeployment

  31. Conclusion • Hardwaretimesync,niceidea • Notsodifficulttoimplement • Highdatarate: • maybesoftwaretimesyncisenough • Lowdatarate • couldsoftwaretimesyncachievesimilarperformancewithhardwareone?FireFly??

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