WSNs are constrained on power, processing, storage and size that make
them more di?±cult than traditional wireless networks to design and build
practical applications.
Di?®erent MAC layer protocols are proposed for WSNs. TDMA-based protocols
provide excellent energy savings, but are not scalable and are not adaptive
to the dynamic changes of the number of nodes in the network. TDMA
protocols also require strict synchronization among nodes in the network.
CSMA-based protocols are adaptive to the changes in the network dynamics
and can accommodate a large number of nodes in the network without
requiring strict node synchronization, but still su?®er from idle listening and
collision problems.
The IEEE 802.11 DCF protocol is not suitable for use in WSNs since it
is not originally designed for multi-hop networks and su?®ers from the idle
listening problem which is a major source of energy waste.
SMAC exploits the IEEE 802.11 DCF power save mode and tries to adapt
it to the unique characteristic of a WSN. SMAC introduces a periodic listen/
sleep cycle to reduce energy waste in idle listening. On the other hand,
periodic listen/sleep cycles cause a latency problem. SMAC with adaptive listening,
TMAC, and DMAC try to solve the latency problem in SMAC while
keeping the energy consumption at low level. WiseMAC achieves more energy
savings over SMAC by exploiting the preamble sampling technique, but
does not provide better latency results than SMAC.
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