Distributed Slot Scheduling Algorithm for Hybrid CSMA/TDMA MAC in Wireless Sensor Networks

Wireless Sensor Networks(WSNs) consist of many self organized sensor nodes to monitor various activities like temperature, pressure, health condition, intrusion detection, etc. These sensor nodes mostly sense the events happening around them, process the sensed data, and send it to the base station using multiple hops. The base station is connected to the outside world who wants to access these sensed and processed data. In WSN, one of the most important challenge is to handle the collision during data transmission by multiple sensor nodes at the same point of time. The collision during data transmission is handled by proper MAC protocol. The MAC protocols for WSN are broadly categorized into 3 types, i.e. schedule, random, and hybrid. Among these 3 types of MAC protocols, the hybrid MAC protocols try to combine the advantage of both schedule and random based MAC protocols. In this paper, we proposed a distributed slot scheduling algorithm for hybrid MAC algorithm. This algorithm mainly focuses on preparing a schedule which bridges the gap between a feasible and an optimal schedule to handle the collision during the data transmission. In our proposed approach, first we find out two-hop neighbors of each node, then a particular slot is allotted to each node in order to prepare a feasible schedule using the RD-TDMA algorithm. Finally, the feasible schedule is fine tuned in a novel way to improve the efficiency in handling the collision by reducing the number of allotted slots. The proposed algorithm out performs the existing RD-TDMA algorithm in terms of number of slots required to handle the collision. The performance of the proposed protocol is carried out using Castalia simulator.