Energy efficient communications in ad hoc networks using directional antennas

Directional antennas can be useful in significantly increasing node and network lifetime in wireless ad hoc networks. In order to utilize directional antennas, an algorithm is needed that will enable nodes to point their antennas to the right place at the right time. In this paper we present an energy-efficient routing and scheduling algorithm that coordinates transmissions in ad hoc networks where each node has a single directional antenna. Using the topology consisting of all the possible links in the network, we first find shortest cost paths to be energy efficient. Then, we calculate the amount of traffic that has to go over each link and find the maximum amount of time each link can be up, using end-to-end traffic information to achieve that routing. Finally, we schedule nodes´ transmissions, trying to minimize the total time it takes for all possible transmitter-receiver pairs to communicate with each other. We formulate this link problem as solving a series of maximal-weight matching in a graph. Furthermore, we propose a method that can enable our scheduling algorithm to work in a distributed and adaptive fashion. We demonstrate that our algorithm achieves all the possible transmitter/receiver gains possible from using directional antennas. In addition, we illustrate through simulation that our routing scheme achieves up to another 45% improvement in energy cost for routing.