A Power Efficient MAC Protocol for Wireless Ad hoc Networks that uses Directional Antennas

In this paper we address the issue of designing an adaptive power aware MAC layer protocol for multi hop ad-hoc networks which comprises of wireless nodes that are equipped with directional antennas instead of the traditional omni-directional ones. The fact that nodes have the ability to transmit directionally facilitates spatial reuse and optimises the use of transmission power. Our MAC layer protocol focuses primarily on power optimization in such multihop ad hoc networks. It does this in two different ways-(a) by adaptively optimizing the transmission power of a node such that unnecessary interference between parallel transmissions are eradicated yet network connectivity is maintained. We achieve the above task by implementing a local algorithm for constructing a one-parameter family of theta graphs, where each node increases its power until it has a neighbour in every theta sector around it. We show that it is possible to use such local geometric theta -constraint to ensure full network connectivity, (b) by putting a node to "sleep" when it is not transmitting, receiving or routing data. This local decision again yields a connected, capacity-preserving, global topology. We evaluate the performance of our protocol with that of the classical versions of 802.11 on the network simulator called NS-2. Our protocol shows significant improvements in throughput, power conservation and network life time when compared to standard 802.11.