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MMSN: Multi-Frequency Media Access Control for Wireless Sensor Networks

MMSN: Multi-Frequency Media Access Control for Wireless Sensor Networks. Cheoleun Moon Computer Science Div. at KAIST. Contents. Motivation Overhead Analysis New Protocol Framework Frequency Assignment Media Access Design Performance Evaluation Conclusions. Self-organize.

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MMSN: Multi-Frequency Media Access Control for Wireless Sensor Networks

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  1. MMSN:Multi-Frequency Media Access Control for Wireless Sensor Networks Cheoleun Moon Computer Science Div. at KAIST

  2. Contents • Motivation • Overhead Analysis • New Protocol Framework • Frequency Assignment • Media Access Design • Performance Evaluation • Conclusions

  3. Self-organize Ad-hoc Wireless Sensor Networks • Sensors & Actuators • Limited CPU and memorys • Limited radio bandwidth

  4. Multi-channel design needed Hardware appearing Software still lags behind • Multi-channel support in MICAz/Telos • More frequencies available in the future • Collision-based: B-MAC • Scheduling-based: TRAMA • Hybrid: Z-MAC Motivation • Limited single-channel bandwidth in WSN • 19.2kbps in MICA2, 250kbps in MICAz/Telos • The bandwidth requirement is increasing • Support audio/video streams (assisted living, …)

  5. Multi-Channel MAC in MANET • Require more powerful hardware/multiple transceivers • Listen to multiple channels simultaneously • Frequent Use of RTS/CTS Controls • For frequency negotiation • Due to using 802.11

  6. Basic Problems for WSN • Don’t use multiple transceivers • Energy • Cost • Packet Size • 30 bytes versus 512 bytes in MANET • RTS/CTS • Costly overhead

  7. RTS/CTS Overhead Analysis • RTS/CTS are too heavyweight for WSN: • Mainly due to small packet size: 30~50 bytes in WSN vs. 512+ bytes in MANET • From 802.11: RTS-CTS-DATA-ACK • From frequency negotiation: case study with MMAC • MMAC • RTS/CTS frequency negotiation • 802.11 for data communication

  8. Contributions • First multi-frequency MAC, specially designed for WSN • Developed four frequency assignment schemes • Supports various tradeoffs • New toggle transmission and toggle snooping for media access control

  9. F8 F7 F6 F5 F1 F4 F2 F3 Frequency Assignment Complications - Not enough frequencies - Broadcast Reception Frequency

  10. Frequency Assignment Schemes

  11. … ... T T T T c b tran b c tran Media Access Design (1/4) • Different frequencies for unicast reception • The same frequency for broadcast reception • Time is divided into slots, each of which consists of a broadcast contention period and a transmission period

  12. Media Access Design (2/4) • Case 1 • When a node has no packet to transmit

  13. Media Access Design (3/4) • Case 2 • When a node has a broadcast packet to transmit

  14. Media Access Design (4/4) • Case 3 • When a node has a unicast packet to transmit

  15. Toggle Snooping • During “back off (fself, fdest)”, toggle snooping is used

  16. Toggle Transmission • When a node has unicast packet to send transmits a preamble • fself so that no node sends to me • fdestso that no node sends to destination

  17. Simulation Configuration

  18. Performance Metrics • Aggregate MAC throughput • Total amount of data successfully delivered in MAC per unit time • Packet delivery ratio • (Total # of data packets delivered by MAC layer) (Total # of data packet the network layer requests MAC) • Channel access delay • Delay data packet from the network layer waits for the channel • Energy consumption

  19. Performance with Different #Physical Frequencies – With Light Load • Performance when delivery ratio > 93% • Scalable performance improvement • Overhead observed when #frequency is small • More scalable performance with Gossip than many-to-many traffic

  20. Performance with Different # Physical Frequencies – With Higher Load • When load is heavy, CSMA has 77% delivery ratio, while MMSN performs much better • MMSN needs less channels to beat CSMA, when the load is heavier

  21. Performance with Different System Load Observation: CSMA has a sharp decrease of packet delivery ratio, while MMSN does not. Reason: The non-uniform backoff in time-slotted MMSN is tolerant to system load variation, while the uniform backoff in CSMA is not.

  22. Conclusions • First multi-frequency MAC, specially designed for WSN, where single-transceiver devices are used • Explore tradeoffs in frequency assignment • Design toggle transmission and toggle snooping • MMSN demonstrated scalable performance in simulation

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