Throughput Maximization for Multiuser MIMO Wireless Powered Communication Networks

We consider a harvest-then-transmit-based protocol in multi-user multiple-input-multiple-output wireless powered communication networks, where three separate optimization methods for energy beamforming, receive beamforming (RBF), and time-slot allocation are presented. From the three optimizations, we propose an optimal maximum throughput approach and a suboptimal zero-forcing (ZF)-RBF-based approach. The time slot is divided into two phases: The first phase is for energy transfer in downlink, and the second phase is for space-division multiple access in uplink. The optimal approach relies on iterations, whereas the ZF-RBF approach does not require any iterations for simple implementation. Simulation results show that the proposed schemes offer spatial multiplexing gain for a wide range of path-loss exponent and harvested energy level, with the ZF-RBF approach exhibiting a limitation when the harvested energy level is low.