MAC Protocols for Sensor Networks

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The characteristics of sensor networks

Tight constraints
Computation power
Storage
Primary functions
Sample the environment for sensory information
Propagate data back to the infrastructure
Traffic pattern
Little activity in lengthy period
Intensive traffic in short time
Highly correlated traffic
End to end flows are required to be fair

An adaptive rate control scheme

The metrics for evaluation of a sensor network MAC protocol
Fair bandwidth allocation from each node to the base station over multihops is desired.
Energy efficiency is desired, including energy spent in listening for the channel and all packets transmissions and forwarding.

An adaptive rate control scheme

Simulation settings
Various CSMA schemes with different settings on: random delay, listening time, backoff scheme
Single cell topology
Small data packets 30 bytes
CSMA versus IEEE 802.11
Results on throughput
Randomness improves the throughput performance

S-MAC (Sensor-Networks)

Energy consumption in the intermediate nodes
When the traffic is light, S-MAC still outperforms 802.11 MAC
Reason1:S-MAC has synchronization overhead of sending and receiving SYNC packets
Reason2:S-MAC introduces more latency and actually uses more time to transmit the same amount of data