Directional medium access control for ad hoc networks

Using directional antennas in ad hoc networks may introduce the well-known deafness problem, exacerbate the hidden terminal problem and the exposed terminal problem, add difficulty on mobile communication, and distort the operation of existing routing and TCP protocols. Although a lot of studies have been undertaken on the directional MAC protocols, most of them focus only on one or several aspects in their design and performance evaluations, and a comprehensive comparative study is missing. In this paper, we first explore the design space of directional MAC and present a taxonomy of existing schemes. Then, we discuss the major problems in using directional antennas under different category of MAC schemes. After that, we propose coordinated directional medium access control (CDMAC), a novel directional MAC protocol to improve throughput via facilitating the simultaneous contention-free communications for multiple local node-pairs. We evaluate our CDMAC, one representative existing scheme and IEEE 802.11 via extensive ns2 simulations. Our results show CDMAC provides a satisfactory solution to all the major problems and significantly improves the throughput performance.