  In this paper, we investigate a multi-node multi-antenna wireless-powered
sensor networks (WPSN) comprised of one power beacon and multiple sensor nodes.
We have implemented a real-life multi-node multi-antenna WPSN testbed that
operates in real time. We propose a beam-splitting beamforming technique that
enables a power beacon to split microwave energy beams towards multiple nodes
for simultaneous charging. We experimentally demonstrate that the
beam-splitting beamforming technique achieves the Pareto optimality. For a
perpetual operation of the sensor nodes, we adopt an energy neutral control
algorithm that keeps a sensor node alive by balancing the harvested and the
consumed power. The joint beam-splitting and energy neutral control algorithm
is designed by means of the Lyapunov optimization technique. By experiments, we
have shown that the proposed algorithm can successfully keep all sensor nodes
alive by optimally splitting energy beams towards multiple sensor nodes.
