Synchronous Contention-Based MAC Protocols for Delay-Sensitive Wireless Sensor Networks: A Review and Taxonomy
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Date
2013-04-06
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Abstract
Duty cycling allows obtaining significant energy saving compared
to full duty cycle (sleepless) random access MAC protocols.
However, it may result in significant latency. In slotted
duty-cycled medium access control (MAC) protocols, sensor nodes
periodically and synchronously alternate their operations between
active and sleep modes. The sleep mode allows a sensor node to
completely turn off its radio and save energy. In order to
transmit data from one node to another, both nodes must be in
active mode. The synchronous feature makes the protocols more
appropriate for delay-sensitive applications compared to
asynchronous protocols. The latter involve additional delay for
the sender to meet the receiver's active period, which is
eliminated with synchronous approach where nodes sleep and wake up
all together. Despite the possible increase of contention by
grouping active periods, the delay due to packets retransmissions
after collisions is less significant compared to the waiting time
of asynchronous protocols. Furthermore, contention-based feature
makes the protocol conceptually distributed and more dynamic
compared to TDMA-based. This manuscript deals with timeliness
issues of slotted contention-based WSN MAC protocols. It provides
a comprehensive review and taxonomy of state-of-the-art
synchronous MAC protocols. The performance objective considered in
the proposed taxonomy is the latency, in the context of
energy-limited WSN, where energy is considered as a constraint for
the MAC protocol that yields the need of duty-cycling the radio.
The main contribution is to study and classify these protocols
from the delay efficiency perspective. The protocols are divided
into two main categories: static schedule and adaptive schedule.
Adaptive schedule are split up into four subclasses: adaptive
grouped schedule, adaptive repeated schedule, staggered schedule,
and reservation schedule. Several state-of-the-art protocols are
described following the proposed classification, with
comprehensive discussions and comparisons with respect to their
latency.
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Keywords
Wireless Sensor Networks, MAC protocols,, Synchronous Protocols, Delay, QoS