Directional antenna with busy tone for capacity boosting and energy savings in wireless ad-hoc networks

Directional antennas are well known for being capable of performance improvement in wireless ad-hoc networks. In the IEEE 802.11 MAC protocol when two nodes are communicating with each other, all other nodes in the transmission zone are required to remain idle. With the use of directional antennas, it is possible to have two pairs of nodes located in each other´s transmission range to communicate simultaneously; this increases the spatial reuse of the wireless channel. However, directional antennas suffer from deafness and hidden terminal problems and therefore new mechanisms are required for exploitation of the directional antennas in an intelligent manner. In this paper we present a scheme based on switched beam directional antenna with busy tone for controlling the directional antenna beams for maximum spatial reuse and saving in energy consumption. The purpose of the busy tone signal is to inform nodes in the transmission zone about the current transmission which helps solving hidden terminal and deafness problems. We present performance evaluation results which confirm the significant improvement in both throughput and energy consumption. We also study the effect of the number of beams on the throughput and energy consumption.