Effects of directional antennas on 802.11e

Nodes, using CSMA/CA type medium access control (MAC) protocols (e.g. IEEE 802.11e) and omnidirectional antennas, in an ad-hoc network may not be able to transmit packets to each other concurrently due to spatial contention for the shared wireless medium. The maximum network performance depends on the maximum number of possible concurrent transmissions. This can be maximized in a multi-hop ad-hoc network using directional antennas. Neighboring nodes falling outside the transmission region are less vulnerable to co-channel interference. Directional antennas allow increased transmission range by reducing noise, interference and multi-path fading. We emphasize the interference reduction capability of directional antennas in the context of suburban ad-hoc networks (SAHN). We build an analytical model, based on the basic channel access mechanism of IEEE 802.11, to show the effect of interference on network performance along multiple hops using three antenna schemes; multiple fixed directional antennas, omnidirectional antennas with multiple frequency channels and omnidirectional antennas with single frequency channel. We extend our analyses for IEEE 802.11e to accommodate different traffic classes. We also verify our analyses with extensive simulations.