An Energy-efficient MAC-Layer Retransmission Algorithm for Cluster-based Sensor Networks

In a typical sensor network application scenario, occurrence of an event triggers data collection. In such cases, a mobile sink node moves into the sensing area or a node is activated to serve as a cluster head and collect data from the sensor nodes deployed in the area. In such applications, only the number of nodes in the area is known which makes TDMA-type protocols infeasible. Different data collection algorithms have been proposed for such applications aiming at reducing energy usage, increasing throughput, or reducing delay. However, most of those solutions assume some form of contention-free MAC protocol, making them less practical. Recently proposed synchronized, shared contention window (SSCW) based 802.11 DCF protocol is a contention based solution and has demonstrated superior performance in terms of delay and throughput compared with the standard binary exponential backoff (BEB) based 802.11 DCF and 802.15.4 (ZigBee) protocols. We propose an energy-efficient algorithm based on the contention window concept. We study the energy cost and time delay of our method assuming different sizes of the contention window and determine the optimal value that minimizes the energy cost for a given number of nodes in the cluster. Compared with SSCW protocol, the proposed protocol improves energy efficiency by 36%-400% with throughput still within 82%-75% of SSCW.