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X-MAC: A short preamble MAC protocol for duty-cycled wireless sensor networks

X-MAC: A short preamble MAC protocol for duty-cycled wireless sensor networks . Michael Buettner, Gary V. Yee, Eric Anderson, Richard Han. Telvis Calhoun Wireless Sensor Networks CSC8908-005 Dr. Li 09/17/2008. Outline. Duty Cycled MACs Common Issues Duty Cycled MAC protocols XMAC

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X-MAC: A short preamble MAC protocol for duty-cycled wireless sensor networks

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  1. X-MAC: A short preamble MAC protocol for duty-cycled wireless sensor networks Michael Buettner, Gary V. Yee, Eric Anderson, Richard Han Telvis Calhoun Wireless Sensor Networks CSC8908-005 Dr. Li 09/17/2008

  2. Outline • Duty Cycled MACs • Common Issues • Duty Cycled MAC protocols • XMAC • Conclusions

  3. Duty Cycled MACS • Use awake, sleep intervals to conserve energy • Key parameters • Sleep time • Wake time • Energy consumed during the awake state and the sleep state. • The period of a duty cycle is equivalent to its sleep time plus awake time.

  4. Idle Listening Problem • Idle Listeningconsumes substantial energy • Synchronized protocols • Nodes awake on a schedule • Asynchronized protocol • Uses low power listening • Hybrids • Combine synchronized and asynchronized.

  5. Low Power Listening • Sender uses longer preamble to allow the receiver to awake periodically.

  6. Asynchronized Protocols • Advantages • Use extended preamble • Sender and receiver can have decoupled duty cycles. • No synchronization overhead. • Awake periods are much shorter • Disadvantages • Frame exchange delay even if receiver awakes before preamble ends • Overhearing problem • Preamble latency is expensive for multihop routes

  7. SMAC • Synchronizes sensor clusters • Nodes periodically wake-up to receive synchronization info from its neighbors. • Mitigates need for system wide synchronization. • Nodes can belong to more that one virtual cluster. • Communicate using RTS-CTS • Can use adaptive listening • Neighbor briefly wakes up at the end of overheard RTS, CTS • Reduces one-hop latency

  8. T-MAC • Listen for a short time after awake period. • Sleeps if IDLE. • Improves on S-MAC by shortening the awake period if IDLE. • For variable payloads, T-MAC uses 20% of energy used in S-MAC.

  9. BMAC • Uses local schedules • Send preamble that is slightly longer than the sleep period. • Long preamble assures that the neighbor will receive packet. • Provides API to adjust sleep period. • Suffers from overhearing problem.

  10. Other Methods • WiseMAC • Reduces the extended preamble length and energy • Put next awake time in ACKs. • Transmit to node only slightly before awake time specified in ACK • Hardware-Only Mechanism • Low power radio circuit that listens for the preamble. • Wake-On-Radio periodically listens for preamble then wakes up main radio circuit.

  11. XMAC • Short preamble • Reduce latency and reduce energy consumption • Target in preamble • Minimize overhearing problem. • Strobed preamble • Reduces latency for the case where destination is awake before preamble completes. • Reduces per-hop latency and energy • Dynamic duty-cycle algorithm

  12. Asynchronous Duty Cycling • Overhearing Energy loss is proportional to number of receivers in range. • Short preamble packets. • Non-receivers return to sleep more quickly. • Bad in high density sensor networks.

  13. Strobing • Reduce time and energy wasted sending preamble • When target wakes before the end • Many successive transmitters send full preamble to a single target a single target. • XMAC uses strobed preamble. • Addresses problem when target wakes before the end. • Send preamble packet • Listen for early acknowledgement packet • Preamble period must be greater than sleep period.

  14. Distributed Coordination • Distributed Coordination Feature • Sensor overhears strobed preamble to target. • Execute random backoff longer than preamble period + data • Send to target after backoff. • Target remains awake after receiving another

  15. Packetizing Radio Support • Streaming radios transmit the raw packet from MAC layer. • Packetizing radios add own preamble, header and CRC. • Packetizing radios do not support extended preambles. • XMAC’s strobed preamble packets work for packetizing radios.

  16. Energy Models Energy to receive a packet Energy to send a packet

  17. Conclusions • Evaluation shows savings over low power listening. • Gains continue as network density increases. • Unable to schedule sufficiently small listening periods

  18. References • M. Buettner, G. V. Yee, E. Anderson, and R. Han, "X-MAC: a short preamble MAC protocol for duty-cycled wireless sensor networks," in Proceedings of the 4th international conference on Embedded networked sensor systems Boulder, Colorado, USA: ACM, 2006. • G. P. Halkes, T. v. Dam, and K. G. Langendoen, "Comparing energy-saving MAC protocols for wireless sensor networks," Mob. Netw. Appl., vol. 10, pp. 783-791, 2005.

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