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Scheduling Beacon Transmission to Improve Delay for Receiver-initiated-MAC Based Wireless Sensor Networks

Many low-energy MAC and routing protocols have been proposed for Wireless Sensor Networks (WSNs) since reducing energy consumption is a primary concern to meet the requirements of practical applications. Reducing delivery delay is, indeed, another promising requirement in WSNs because a large part of applications of WSNs intends to watch the sensed objects in real time although the amount of allowable delay differs according to cases. In this paper, we deal with a class of receiver-initiated MAC protocols, which is a promising energy-efficient MAC mechanism, and propose to schedule beacon timings so as to reduce the delivery delay of data packets. The key idea is to schedule beacon timings in the sequence of distance from leaf node to the sink node and reduce the time of packets staying at each node. Specifically, each sensor node selects a time slot to send beacon in a distributed manner based on their distances (i.e., hop counts) from the sink node, and autonomously adjusts its beacon timing to avoid frame collisions. Computer simulations show that the proposed protocol can collect data in a shorter time with less energy consumption than the conventional receiver-initiated MAC protocols.