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; they trade off spatial reuse and collision avoidance via a combination of omnidirectional and directional transmission modes. It is argued that the benefit of spatial reuse achieved by a MAC protocol that uses a 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. We present detailed simulation experiments of the popular IEEE 802.11 MAC protocol and its variants that make use of a directional transmission mode in sufficiently random networks. 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.