Sidelobe Control in Collaborative Beamforming via Node Selection

Collaborative beamforming (CB) is a power efficient method for data communications in wireless sensor networks (WSNs) which aims at increasing the transmission range in the network by radiating the power from a cluster of sensor nodes in the directions of the intended base stations or access points (BSs/APs). The CB average beampattern shows a deterministic behavior and the mainlobe of the CB sample beampattern is independent of the particular node locations. However, the CB for a cluster of a finite number of collaborative nodes results in a sample beampattern with sidelobes that severely depend on the particular node locations. High level sidelobes can cause unacceptable interference when they occur at directions of unintended BSs/APs. Therefore, sidelobe control in CB has a potential to decrease the interference at unintended BSs/APs and increase the network transmission rate by enabling simultaneous multilink CB. Traditional sidelobe control techniques are proposed for centralized antenna arrays and are not suitable for WSNs. In this paper, we show that scalable and low-complexity sidelobe control techniques suitable for CB in WSNs can be developed based on a node selection technique which makes use of the randomness of the node locations. A node selection algorithm with low-rate feedback is developed to search over different node combinations. The performance of the proposed algorithm is analyzed in terms of the average number of search trials required for selecting the collaborative nodes, the resulting interference, and the corresponding transmission rate improvements. Our simulation results show that the interference can be significantly reduced and the transmission rate can be significantly increased when node selection is implemented with CB. The simulation results also show close agreement with our theoretical results.