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The TDMA-based MAC Protocols for WSNs ----- EMACs and LMAC

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  1. The TDMA-based MAC Protocols for WSNs----- EMACs and LMAC EMACs: IEEE VTC 2004-Spring LMAC: INSS 2004 Wang, Sheng-Shih Feb. 21, 2005

  2. Advantage of a TDMA based, energy-efficient, self-organizing MAC protocol for WSNs L. F. W. van Hoesel†, T. Nieberg†, H. J. Kip††, and P. J. M. Havinga† † Department of Electrical Engineering, Mathematics and Computer Science University of Twente, The Netherlands †† Nedap N. V., Groenlo, The Netherlands IEEE Vehicular Technology Conference(VTC2004-Spring)

  3. European Research Project EYES • Website: http://eyes.eu.org Applications Data Splitting Connected active set formation (Multipath) Routing Clustering EMACs TDMA-based Dynamic Topology

  4. Overview --- EMACs … frame frame frame frame frame time … timeslot TC DATA CR • CR: Communication Request Section • TC: Traffic Control Section • DATA: Data Section

  5. Overview --- Clustering

  6. Overview --- Clustering (cont’d) anchor bridge nonmember • Both the anchor and bridge nodes are regarded as the active nodes • All active nodes comprise the connected dominating subset

  7. EMACs • Main goal • Minimize energy consumption • Operation modes • Active • Forward messages to a destination • Accept data from passive nodes • Passive • Keep track of the active node • Dormant • Enter low power states

  8. EMACs --- Frame Structure … frame frame frame frame frame … time slot An active node autonomously picks its own time slot CR TC DATA • CR: Communication Request Section • TC: Traffic Control Section • DATA: Data Section

  9. EMACs --- Frame Structure (cont’d) • Communication Request Section • An active node listens for incomingrequests from passive nodes • The passive node sends the request if any data • Traffic Control Section • An active node transmits a shortcontrolmessage • The possible acknowledgement to the request • Control and synchronization messages (e.g., slot schedule table) • The passive node listens the message from its active node • Data Section • Used for the actual transfer of data

  10. EMACs --- Operation • Node A is an active node, while nodes B, C, and D are all passive nodes • Nodes B, C, and D are node A’s neighbors • Nodes B, C, and D intend to send packets to node A … A C … B … D …

  11. EMACs --- Operation (cont’d) • In CR section, nodes B, C, and D send their own requests to node A (via random backoff mechanism) … A C … B … D …

  12. EMACs --- Operation (cont’d) • Suppose the transmission of node C is allowed • In TC section, node A broadcasts a control message (w/ ack. of the request, slot schedule table, etc) … A C … B … D …

  13. EMACs --- Operation (cont’d) • In DATA section, node C transmits the data to node A (w/o any collision) … A C … B … D …

  14. EMACs --- Operation (cont’d) • In CR section, nodes B and D send their own requests to node A (via random backoff mechanism) … A C … B … D …

  15. EMACs --- Operation (cont’d) • Suppose the transmission of node B is allowed • In TC section, node A broadcasts a control message (w/ ack. of the request, slot schedule table, etc) … A C … B … D …

  16. EMACs --- Operation (cont’d) • In DATA section, node B transmits the data to node A (w/o any collision) … A C … B … D …

  17. EMACs --- Operation (cont’d) • In CR section, node D sends its own request to node A (via random backoff mechanism) … A C … B … D …

  18. EMACs --- Operation (cont’d) • Suppose the transmission of node D is allowed • In TC section, node A broadcasts a control message (w/ ack. of the request, slot schedule table, etc) … A C … B … D …

  19. EMACs --- Operation (cont’d) • In DATA section, node D transmits the data to node A (w/o any collision) … A C … B … D …

  20. Schedule Challenges Request collision Time slot selection Node role determination EMACs --- Operation (cont’d) A … B … C … D … transmitting/receiving state power-saving state

  21. Request Collision • The node will not receive any acknowledgement from the active node • The node sends the request in the next active node’s time slot

  22. Time Slot Selection • The active node sends the time schedule table in the TC • The table contains the assignment of time slots occupied by the active node and its one-hop neighbors • The information is encoded by a number of bits • A node can pick an unused time slot for itself

  23. Time Slot Selection (cont’d) The occupied time slots for 0010110… ? (OR bit sets) 6 0110110… 1111110… 3 1001110… 5 0111100… ? 5 free time slot 4 2 1 1001100… 4 ? 7 1101100… 1110100… 0101100…

  24. Node Role Determination • Based on passive clustering • The anchor (cluster head) and bridge (gateway node) are regarded as the activenodes • The nonmember (ordinary node) is regarded as the passivenode

  25. Simulation • Simulator: OMNet++ • Routing protocol: DSR • Network environment • Number of nodes: 46 • Number of data sources: 5 (5-byte length data) • Number of the sink: 1 • Size: 5 by 5 times the transmission range of a node • Network types • Static • Dynamic • Random waypoint model

  26. Simulation --- Static Network EMACs is able to prolong the lifetime with 30% to 55% compared to SMAC

  27. Simulation --- Dynamic Network EMACs is able to extend the lifetime with a factor of 2.2 to 2.7 compared to SMAC

  28. Question • Source • Frequent transceiver state switch • Results • Increase energy consumption • Increase latency • Solution • LMAC

  29. A Lightweight Medium Access Protocol (LMAC) for Wireless Sensor Networks L. F. W. van Hoesel and P. J. M. Havinga † Department of Electrical Engineering, Mathematics and Computer Science University of Twente, The Netherlands International Workshop on Networked Sensing Systems (INSS 2004)

  30. Frame Structure … frame frame frame frame frame … timeslot TC DATA • TC: Traffic Control Section • DATA: Data Section

  31. Operation • All nodes should be awake in all TCs • A node always transmits a control message in its own TC, all neighbors should receive the control message • A node is addressed: listen to the data section • A node is not addressed: switch off transceiver, and wake up at the next time slot • Control message: 12 bytes

  32. Simulation --- Static Network LMAC reduces preamble transmissions and transceiver state switches

  33. Summary • EMACs vs. LMAC • Active vs. passive • Advantages of EMACs/LAMC (compared to SMAC) • Energy conservation (mainly about idlelistening) • Delivery ratio • Drawbacks of EMACs/LMAC (compared to SMAC) • High latency

  34. Energy-Efficient Medium Access Control Koen Langendoen and Gertjan Halkes Delft University of Technology Book Chapter in the Embedded Systems Handbook R. Zurawski (editor), CRC press, to appear in Aug. 2005

  35. Simulation Parameters

  36. Simulation Result --- Latency Average delay for one hop transmission is half the length of a frame Adaptive listening mechanism (messages can travel about 2 hops during one active period)

  37. Conclusion • EMACs and LMAC are robust in the dynamic network • TDMA-based protocol • Less energy consumption due to free of idle listening • Incur high latency • Overhead of schedule computing and distribution through the network limit the applications