Slotted Contention-Based Energy-Efﬁcient MAC Protocols in Delay-Sensitive
This paper considers slotted duty-cycled medium access control (MAC) protocols, where sensor nodes periodically and synchronously alternate their operations between active and sleep modes to save energy. In order to transmit data from one node to another, both nodes must be in active mode. The synchronous feature makes these protocols more appropriate for delay-sensitive applications compared to asynchronous protocols. With asynchronous protocols, additional delay is needed for the sender to meet the receiver's active period. This is eliminated with synchronous approaches where nodes sleep and wake up all together. Moreover, contention-based feature makes the protocols --considered in this paper-- conceptually distributed and more dynamic compared to TDMA-based protocols. Duty cycling allows obtaining significant energy saving vs. full duty cycle (sleepless) random access MAC protocols. However, it may result in significant latency. Forwarding a packet over multiple hops often requires multiple operational cycles (sleep latency), where nodes have to wait for the next cycle to forward data at each hop. Timeliness issues of slotted contention-based WSN MAC protocols is deal t with in this paper, where a comprehensive review and taxonomy of state-of-the-art synchronous MAC protocols is provided. The main contribution is to study and classify the protocols from the delay-efficiency perspective.
Wireless Sensor Networks, MAC Protocols, Synchronous Protocols, Delay, QoS
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