Energy Efficiency of Wireless Information and Power Transfer with Massive MIMO

Massive MIMO, a building block of future SG systems, is attractive for wireless information and energy transfer. This is largely due to its ability to focus energy towards desired spatial locations. In this paper, the overall energy efficiency of a wirelessly powered massive MIMO system is investigated where a multi-antenna base-station uses wireless energy transfer to charge single-antenna energy harvesting users on the downlink The users exploit the harvested energy to transmit information to the base-station on the uplink Using a scalable model for the circuit power consumption at the base-station, the energy efficiency performance (measured in bits/joule) of the overall system is characterized. A closed-form expression is derived for the energy efficiency-optimal downlink transmit power in terms of the key system parameters such as the number of base-station antennas and the number of users. Simulation results suggest that it is energy efficient to operate the system in the massive MIMO regime. As the number of antennas becomes large, increasing the transmit power as well as serving more users help improve the energy efficiency for moderate to large number of antennas.