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Wireless Sensor Networks COE 499 Medium Access Control

Wireless Sensor Networks COE 499 Medium Access Control. Tarek Sheltami KFUPM CCSE COE www.ccse.kfupm.edu.sa/~tarek. Outline. Traditional MAC protocols Asynchronous sleep techniques Sleep-scheduled techniques Contention free protocols. Traditional MAC protocols. ALOHA protocol CSMA

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Wireless Sensor Networks COE 499 Medium Access Control

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  1. Wireless Sensor Networks COE 499Medium Access Control Tarek Sheltami KFUPM CCSE COE www.ccse.kfupm.edu.sa/~tarek

  2. Outline • Traditional MAC protocols • Asynchronous sleep techniques • Sleep-scheduled techniques • Contention free protocols

  3. Traditional MAC protocols • ALOHA protocol • CSMA • Hidden terminal problem • Exposed terminal problem (a) hidden node (b) exposed node

  4. Traditional MAC protocols • ALOHA protocol • CSMA • Hidden terminal problem • Exposed terminal problem (a) hidden node (b) exposed node

  5. Traditional MAC protocols.. • MACA • RTS • CTS • IEEE 802.11 (CSMA/CA) • IEEE 802.15.4 MAC (LR-WPAN)

  6. Energy efficiency in MAC protocols • Power management in IEEE 802.11RTS • Power aware medium-access with signalling (PAMAS)

  7. Asynchronous sleep techniques • Secondary wake-up radio • One low power Tx/Rx always on and main Tx/Rx always off • Low power listening/preamble sampling

  8. Asynchronous sleep techniques.. Transmitter/receiver-initiated cycle receptions (TICER/RICER)

  9. Asynchronous sleep techniques.. Reconfigurable MAC protocol (B-MAC)

  10. Sleep-scheduled techniques • Sensor MAC (S-MAC) • All node wake up and go to sleep simultaneously

  11. Sleep-scheduled techniques.. • Timeout MAC (T-MAC) • Very similar to S-MAC, however, The length of each cycle is kept constant, but the end of the active period is determined dynamically by the use of a timeout mechanism • Data-gathering MAC (D-MAC)

  12. Sleep-scheduled techniques.. • Delay-efficient sleep scheduling (DESS) • each node picks a unique slot out of k slots to use as a reception slot and publishes this to its neighbors • Asynchronous sleep schedules A (7,3,1) design for slotted asynchronous wake-up (P2+P+1, P+1, 1)

  13. Contention-free protocols • Stationary MAC and Startup (SMACS) • Each node need only maintain local synchronization • During the starting phase, each node decides on a common communication slot with a neighboring node through handshaking on a common control channel • Each link also utilizes a unique randomly chosen frequency or CDMA frequency hopping code • It is assumed that there are sufficiently many frequencies/codes (no contention) • The slot is then used periodically, once each cycle, for communication between the two nodes.

  14. Contention-free protocols • BFS/DFS-based scheduling • BFS, each node gets contiguous time slots • DFS, each node does not have contiguous slots, but the slots from each sensor source to the sink are contiguous, ensuring that intermediate node buffers are not filled up during data-gathering.

  15. Contention-free protocols.. • Reservation-based synchronized MAC (ReSync) • Each node choose a unique time slot of k and publishes this to its neighbors • Traffic-adaptive medium access (TRAMA) • A distributed TDMA technique that allows for flexible and dynamic scheduling of time slots • Time epochs are divided into a set of short signaling slots, followed by a set of longer transmission slots • Neighbor protocol (NP) • Schedule exchange protocol (SEP) • Adaptive election algorithm (AEA)

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