A Throughput-Efficient On-Demand Synchronous X-MAC Protocol for Wireless Sensor Networks

Abstract

This paper proposes a hybrid duty-cycle Medium Access Control (MAC) protocol named as On-demand Synchronous X-MAC (OSX-MAC) to improve the performance of the X-MAC protocol. X-MAC, one of typical asynchronous duty-cycle MAC protocols, was designed to save energy in Wireless Sensor Networks (WSNs) by allowing active receivers to immediately respond in the middle of the short preamble transmission. X-MAC, however, still inefficiently wastes a lot of time before delivering data frames due to two drawbacks; the unavailability of the receiver's exact wakeup time and the lack of a mechanism to deal with collision frequented in congested WSNs. To solve these two problems, OSX-MAC is equipped with two techniques, an On-demand Schedule Exchange (OSE) scheme and an Adaptive Backward Binary Exponential Backoff (AB-BEB) algorithm. Without periodic schedule exchanges, OSE enables receivers to explicitly provide their wakeup time whenever they acknowledges their sender. After that, the sender transmits its short preambles near the informed wakeup time of its receiver. To reduce the degree of collisions, AB-BEB determines the waiting time backwardly from the wakeup time of the receiver, not the waiting time forwardly from the current time like the legacy BEB. It also pessimistically adjusts the contention window (CW). Namely it does not reset the CW to the predetermined initial size but gradually decreases the CW size for new transmissions. Simulation experiments confirmed that OSX-MAC outperformed both S-MAC and X-MAC in terms of throughput and energy usage in WSNs.