Distributed processing techniques for beamforming in wireless sensor networks

A main task in distributed beamforming (DBF) techniques for wireless sensor networks (WSNs) is to maximize the received signal power at the access point (AP) while inflicting small interfering effect on unintended receivers. When the DBF nodes are unaware of the directions of unintended receivers, interference at the latter receivers may be substantially reduced by forming a beampattern with a narrow mainlobe that is pointed towards the AP. However, such an approach requires the DBF nodes to be sporadically scattered over a large area and, hence, increases the probability of the loss of their inter-connection. Assuming that nodes are uniformly distributed in the network, we show how the DBF nodes can be intelligently selected to ameliorate the network disconnectivity problem. In turn, when the directions of unintended receivers are known, one may aim to apply the so-called null-steering beamforming approach to effectively nullify the received power at those directions. However, it can be shown that implementing a null-steering beamformer in WSNs requires each node to be aware of the locations of all other nodes in the network; a requirement that opposes the distributed nature of WSNs. For such a scenario, we approximate the null-steering beamformer with another beamformer that is amenable to a distributed implementation.