bin-mac: a hybrid mac for ultra-compact wireless sensor nodes

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]



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 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 Design

• Components:• Contention Resolution

• Binary Tree Collision Resolution

• Slot Consolidation

• Duty Cycle Adjustment



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



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



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



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



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



Implementation

• Embedded constraints

• No recursion

• No dynamic memory allocation

• Emulated a linked list of slots using an array



Flowchart for Base Station



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



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



Throughput



Latency



Success rate



Duty cycle



Energy efficiency



Throughput

Duty cycle

Scalability



• Event period is fixed at 48 ms

• Network size: from 10 to 150 nodes

Bin-MAC vs. RR



• 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





Thank You!

Questions?

[email protected]

bin-mac: a hybrid mac for ultra-compact wireless sensor nodes

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