Energy-efficient Hybrid Precoding for Beamspace MIMO Systems with Lens Array

The beamspace MIMO can significantly reduce the number of power radio frequency (RF) chains in millimetre-wave (mmWave) communications by utilizing lens antenna array. However, most existing studies consider the phase shifters (PSs) as the main components of the analog beamformer, which result in a significant loss of energy efficiency. In the paper, we propose a switch selection network to solve this problem, where the analog component of beamspace MIMO systems is realized by a sub-connected switch network rather than the PS. Based on the proposed architecture, an optimal hybrid cross-entropy (HCE) based hybrid precoding scheme is designed to maximize the achieveable sum-rate, where the probability distribution of the hybrid precoder is updated by minimizing CE with unadjusted probabilities and smoothing constant. Simulation results show that the proposed HCE-based hybrid precoding can not only effectively achieve the satisfied sum-rate performance, but also outperform the PSs schemes with regard to energy efficiency.