Experimental demonstration of nullforming from a fully wireless distributed array

Abstract

We consider distributed nullforming using an array of wireless transmitters that coordinate their transmissions to achieve destructive interference at a designated receiver. We describe the first experimental demonstration of distributed nullforming to a target receiver from an array of three distributed transmitters using (mostly) off-the-shelf hardware and simple and standard signal processing techniques. We are motivated by the goal of using distributed arrays to achieve increased spectrum reuse through interference cancellation. Our results show interference suppression in excess of 25dB over uncoordinated transmission. We build on our recent experimental demonstration of beamforming from a distributed antenna array after estimating and compensate for the combined effects of unknown propagation channels, hardware mismatches and clock drifts between the array nodes. The transmitters do not share clocks or have any wired back channels. They coordinate achieve nullforming entirely using in-band wireless message exchanges. Thus these methods can be implemented on portable mobile devices rather than being limited to Base Stations.