Bin-MAC: A Hybrid MACfor Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou
Center for Embedded Computer SystemsDepartment of Electrical Engineering and Computer
ScienceUniversity of California, Irvine
May 17, 2012
Outline
• Problem Statement• Bin-MAC Design
• Contention Resolution
• Binary Tree Collision Resolution
• Slot Consolidation
• Duty Cycle Adjustment
• Performance• Conclusions
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
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]
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Eco node
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 for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
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 for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Bin-MAC Design
• Components:• Contention Resolution
• Binary Tree Collision Resolution
• Slot Consolidation
• Duty Cycle Adjustment
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
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 for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
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 for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
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 for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
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 for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
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 for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Implementation
• Embedded constraints
• No recursion
• No dynamic memory allocation
• Emulated a linked list of slots using an array
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Flowchart for Base Station
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Performed in each time slot after transmitting the
query
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 for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
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 for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Throughput
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Latency
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Success rate
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Duty cycle
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Energy efficiency
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Throughput
Duty cycle
Scalability
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
• Event period is fixed at 48 ms
• Network size: from 10 to 150 nodes
Bin-MAC vs. RR
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
• Event period is fixed at 48 ms
• Network size: from 10 to 150 nodes
Round Robin Bin-MAC
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 for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Bin-MAC: A Hybrid MAC for Ultra-Compact Wireless Sensor Nodes
Vahid Salmani and Pai H. Chou, University of California, Irvine
Thank You!
Questions?