Beamformer design and utility optimization for hybrid information and energy transfer with massive MIMO

Consider a massive multiple-input multiple-output (MIMO) system, where the base station employing space-division multiple access simultaneously transmits information and energy to the information and energy users, respectively. The objective is to maximize the energy harvesting utility of the energy users, while guaranteeing the outage probability requirements of the information users. Since conventional beamformers, such as the maximum ratio transmission (MRT) and zero-forcing (ZF) beamformers, are designed for information transmission, a hybrid beamformer is first proposed to improve both the spectral efficiency (SE) of the information users and the harvested power (HP) of the energy users. Then, based on the analysis of SE and HP, the utility maximization problem is formulated and solved, followed by the proposal of a power allocation scheme for the hybrid information and energy transfer system. Theoretical and simulated results are presented to show that the hybrid beamformer is able to improve the SE-HP trade-off in comparison to the MRT and ZF beamformers, and gives the best energy harvesting utility at the expense of moderate complexity