The deafness problems and solutions in wireless ad hoc networks using directional antennas

This paper addresses the issue of deafness in directional antennas for wireless ad hoc networks. Deafness is caused when a node X repeatedly attempts to communicate with node Y but is unsuccessful, because Y is presently tuned to some other antenna beam. In this paper, we first outline the different factors which contribute to such deafness in directional antennas and its significant impact on network performance. We then propose two schemes to overcome deafness scenarios which are transparent to the underlying directional MAC protocol in use. In addition, we also claim that IEEE 802.11 short retry limit (SRL) needs a special handling in directional environment because of the presence of deafness. We have done a detailed performance evaluation of our schemes with different directional MAC protocols running over switched beam antennas and the initial results are found to be very promising.