Solving the hidden and exposed terminal problems using directional-antenna based MAC protocol for wireless sensor networks

A critical design issue for wireless sensor networks (WSNs) is the development of medium access control (MAC) protocols that efficiently reduce power consumption. WSNs sensor nodes are generally powered by batteries which provide a limited amount of energy, and it is often difficult to recharge or replace batteries. Therefore power aware and energy efficient MAC protocols at each layer of the communications are very essential for wireless sensor networks. Fairness to both the usage of a channel and messages may also be traded as for improved power consumptions. In case of classical antennas, unfair channel allocation and wastage of channels between each node can be happened, which is directly affects throughput performance. On the other hand these can bring a problem such as MAC-deadlock, hidden and exposed terminal problem. To overcome these problems a directional antennas have been extensively used in designing MAC protocols for wireless sensor networks. Directional antennas provide many advantages over the classical antennas. These advantages include spatial reuse channel and increases in coverage range distance. One of the main considerations in designing MAC protocols for static wireless sensor networks is to reduce power consumption at the sensor nodes. This is usually done by imposing transmission and receiving schedules on the sensor nodes from only one side at same time. Since it is desirable for a sensor network to be self managed, these schedules need to be worked out by individual nodes in a distributed fashion. In this paper, we show that directional antennas can be used effectively to solve a common hidden and exposed terminal problem by using an energy efficient MAC protocol for wireless sensor networks. This directional Antenna could be rotated in case of base station node to avoid directional hidden terminal problem. Our MAC protocol conserves energy at the nodes by calculating a scheduling strategy at individual nodes and by avoiding packet collisions almost completely.