A Distributed Directional-to-Directional MAC Protocol for Asynchronous Ad Hoc Networks

The use of directional antennae in ad hoc networks has received growing attention in recent years. However, most existing directional MAC protocols assume interchangeable directional and omnidirectional modes of operation. Such operation reduces the spatial gain and introduces the asymmetry-in-gain problem. In this paper, we propose a directional-to-directional (DtD) MAC protocol for ad-hoc networks that operates in the directional mode exclusively. The protocol is fully distributed, does not require any synchronization, eliminates the asymmetry-in-gain problem, and alleviates the deafness problem. To study the performance of the proposed DtD MAC, we develop an analytical model that estimates the saturation throughput as a function of the number of antenna sectors, packet size and number of contending nodes. The analytical results are validated by extensive simulations with the QualNet simulator. We show that the DtD MAC protocol is practical to take the advantage of directional antennae to improve network throughput and achieve better fairness in ad-hoc networks.