A cross layer scheme for adaptive antenna array based wireless ad hoc networks in multipath environments

A medium access control (MAC) protocol (NULLHOC) for ad hoc networks of nodes with antenna arrays is presented. The antenna array is used for transmit and receive beamforming with the purpose of increasing spatial reuse by directing nulls at active transmitters and receivers in the neighborhood. In contrast to previous work with directional antennas, our approach is applicable to multipath channels, such as occur indoors or in other rich scattering environments. The MAC protocol is designed to support the control information exchange needed to direct nulls toward other users involved in existing communication sessions. Knowledge of the channel coefficients between a transmitter or receiver and its neighbors is used to design transmit or receive beamformer weights that implement the requisite nulling. Simulations are used to demonstrate the improvements in throughput and transmit powers that are obtained in this approach relative to the IEEE 802.11 MAC protocol. We also analyze the effects of channel estimation errors on our protocol and propose a simple modification of the basic (NULLHOC) protocol to minimize their impact.