Reflections on Smart Antennas for MAC Protocols in Multihop Ad Hoc Networks

Smart and directional antennas can be used to improve the throughput performance of wireless communications in ad hoc networks. This improvement consists basically of minimizing collision and increasing simultaneous communications. Directional antennas reduce potential collision zone since data packets are directionally transmitted. Smart antennas are more intelligent than directional antennas since they can dynamically point pattern nulls in the direction of interfering stations. In this paper, we consider the link capacity achieved by a set of portable stations sharing the same medium and equipped with smart antennas. We present an overview of related work based on directional and smart antenna use to improve signal reception. We introduce and discuss the problem concerned with smart antenna use for transmission based on CSMA MAC protocols. This problem consists principally of beam selection and handoff. A CSMA MAC protocol within a station equipped with a smart antenna, has to interact with the physical layer to manage beam use. Our discussion, taking into account hidden node and exposed node problems, is motivated by underlying overhead, symmetry assumption and beacon use.