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Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes

Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes. Vahid Salmani and Pai H. Chou Center for Embedded Computer Systems Department of Electrical Engineering and Computer Science University of California, Irvine May 17, 2012. Outline. Problem Statement Bin-MAC Design

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Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes

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  1. Bin-MAC: A Hybrid MACfor Ultra-Compact Wireless Sensor Nodes • Vahid Salmani and Pai H. Chou • Center for Embedded Computer Systems • Department of Electrical Engineering and Computer Science • University of California, Irvine • May 17, 2012

  2. Outline • Problem Statement • Bin-MAC Design • Contention Resolution • Binary Tree Collision Resolution • Slot Consolidation • Duty Cycle Adjustment • Performance • Conclusions Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  3. Problem Definition • Ultra-compact wireless nodes • Infant Monitoring • Predicting cerebral palsy in pre-term infants • Small Memory (4KB) • No complex protocol • Limited data buffer • Bounded transmission delay, or collected samples will be lost • Clock drift • Hard or impossible to achieve precise time synchronization • Limited battery • No carrier sensing hardware on sensors • Single-hop, star topology • most of the real-world deployments have been single-hop [1] Eco node Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  4. Problem Definition • Need a “simple” hybrid MAC • Minimal overhead • Majority of existing MACs are not applicable: • Tight clock synchronization • Too complex (large footprint) • B-MAC, X-MAC, or SCP: at least 18 KB [5] • Z-MAC: even more complex [6] • Light-weight Protocols • CSMA/CA • Carrier Sensing • Round Robin Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  5. Bin-MAC Design • Binary Medium Access Control • Receiver initiated • Base station (BS) broadcasts query messages • Nodes reply to them • Most of the burden is placed on the BS • To keep the nodes as simple as possible • Reservation-based • Round-robin style • No scheduling phase • Analogous to the scheduled contention scheme • query messages contains a range of node IDs instead of a single node ID Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  6. Bin-MAC Design • Components: • Contention Resolution • Binary Tree Collision Resolution • Slot Consolidation • Duty Cycle Adjustment Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  7. Contention Resolution • Nodes do not perform carrier-sensing • Scheduled contention • Each time slot is assigned to a range of nodes e.g. [0 : 10] • A rang has one active transmitter • Inactive nodes in the range are allowed to transmit in the slot • If more than one node transmit in the slot • A collision occurs which needs to be resolved • All colliding nodes will acquire their own time slot Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  8. Possible Cases for a Time Slot • Three cases may happen in response to the BS’s query: • Reception: a data message is successfully received • Idle: there is no response, so the slot is unused • Collision: detected at the BS using an RCD technique Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  9. Binary Tree Collision Resolution • Performed when the BS detects a collision to assign new time slots • Two or more nodes in the range have transmitted simultaneously • The range is split in half and a new query is issued for each half • This will continue until the collision is resolved • We keep track of the new slots as contention is resolved Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  10. Slot Consolidation • Idle slots are removed to save bandwidth • The range of idle slots is merged the adjacent non-idle slots • BS can keep an idle counter for slots to remove those that are idle for a number of consecutive rounds Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  11. Duty Cycle Adjustment • Conserving energy by keeping the nodes in sleep mode until they are really being pulled • Nodes need to know the number of slots in the round • Query messages contain the current number of slots Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  12. Implementation • Embedded constraints • No recursion • No dynamic memory allocation • Emulated a linked list of slots using an array Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  13. Flowchart for Base Station Performed in each time slot after transmitting the query Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  14. Bin-MAC Features • One of the most light-weight hybrid protocols ever designed • Deterministic contention resolution enables bounded latency on data transmissions • Worst case: O(lgn) • Can be applied to delay-sensitive applications with real-time constraints Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  15. Performance • Simulated the Telos platform (CC2420) with auto-acknowledgement • Compare Bin-MAC with: • CSMA/CA (best performance under low contention) • Round Robin (best performance under high contention) • Z-MAC* (simplified version of Z-MAC for star topology) • Network: Star topology, 20 sensor nodes and a base station • Event period: from 112 ms to 16 ms • Event size: 1100 bytes i.e.10 successful transmissions Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  16. Throughput Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  17. Latency Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  18. Success rate Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  19. Duty cycle Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  20. Energy efficiency Throughput Duty cycle Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  21. Scalability • Event period is fixed at 48 ms • Network size: from 10 to 150 nodes Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  22. Bin-MAC vs. RR • Event period is fixed at 48 ms • Network size: from 10 to 150 nodes Round Robin Bin-MAC Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  23. Conclusions • Bin-MAC • very light-weight hybrid MAC protocol • designed for ultra-compact wireless sensor nodes • adaptive to the contention level • able to handle larger scales • Deterministic, binary tree-like contention resolution • Suited for applications with real-time constraints • No clock synchronization is required • No carrier sensing hardware on sensor nodes Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

  24. Thank You! Questions? vsalmani@uci.edu Bin-MAC: A Hybrid MAC forUltra-Compact Wireless Sensor Nodes Vahid Salmani and Pai H. Chou,University of California, Irvine

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