Spatial reuse and collision avoidance in ad hoc networks with directional antennas

The quest for efficient medium access control (MAC) protocols for multi-hop ad hoc networks has aroused great interest in using directional antennas. Some MAC protocols using directional antennas have been proposed in the past, which trade off spatial reuse and collision avoidance via a combination of omnidirectional and directional transmission modes. In this paper, it is argued that the benefit of spatial reuse achieved by a MAC protocol that uses directional mode in all transmissions can outweigh the benefit of a conservative collision avoidance MAC protocol that sends some omni-directional control packets to silence potential interfering nodes. Detailed simulation experiments of the popular IEEE 802.11 MAC protocol and its variants that make use of directional transmission mode in sufficiently random networks are presented. It is concluded that, in contention-based MAC protocols for multi-hop networks infested with hidden terminals, the aggressive channel access scheme featured by all-directional transmissions indeed outperforms other conservative schemes in terms of enhanced throughput and reduced delay.