Sidelobe Reduction and Capacity Improvement of Open-Loop Collaborative Beamforming in Wireless Sensor Networks

<pre>Collaborative beamforming (CBF) with a finite number of collaborating nodes (CNs) produces sidelobes that are highly dependent on the collaborating nodes' locations.</pre><pre>The sidelobes cause interference and affect the communication rate of unintended receivers located within the transmission range.</pre><pre>Nulling is not possible in an open-loop CBF since the collaborating nodes are unable to receive feedback from the receivers.</pre><pre>Hence, the overall sidelobe reduction is required to avoid interference in the directions of the unintended receivers.</pre><pre>However, the impact of sidelobe reduction on the capacity improvement at the unintended receiver has never been reported in previous works.</pre><pre>In this paper, the effect of peak sidelobe (PSL) reduction in CBF on the capacity of an unintended receiver is analyzed.</pre><pre>Three meta-heuristic optimization methods are applied to perform PSL minimization, namely genetic algorithm (GA), particle swarm algorithm (PSO) and a simplified version of the PSO called the weightless swarm algorithm (WSA).</pre><pre>An average reduction of $20 \: \text{dB}$ in PSL alongside $162\%$ capacity improvement is achieved in the worst case scenario with the WSA optimization.</pre><pre>It is discovered that the PSL minimization in the CBF provides capacity improvement at an unintended receiver only if the CBF cluster is small and dense.</pre>