THE EFFECT OF DIRECTIONAL ANTENNAS ON SLOTTED CSMA AD HOC NETWORKS

The performance of wireless ad hoc network are mostly limited by the self interference caused by the network members. Smart antennas and carrier sensing multiple access (CSMA) have been considered separately as efficient methods for self-interference reduction. In this paper we analyze the effect of directional antennas on the transmission capacity of slotted CSMA networks. The analysis is based on a Poisson point process shot noise model for the aggregate interference. The effect of directional antennas is shown to be equivalent to network density scaling. This scaling is expressed through a single parameter, which depends only on the antenna and the channel exponential decay factor. The paper also presents a useful bound on rate ratio of a pair of slotted CSMA networks. This bound is used to demonstrate the transmission capacity gain of slotted CSMA over slotted ALOHA networks. In particular it is shown that if the antennas have very narrow beams then the advantage of CSMA over ALOHA is negligible.