  Massive MIMO is attractive for wireless information and energy transfer due
to its ability to focus energy towards desired spatial locations. In this
paper, the overall power transfer efficiency (PTE) and the energy efficiency
(EE) of a wireless-powered massive MIMO system is investigated where a
multi-antenna base-station (BS) uses wireless energy transfer to charge
single-antenna energy harvesting users on the downlink. The users may exploit
the harvested energy to transmit information to the BS on the uplink. The
overall system performance is analyzed while accounting for the nonlinear
nature of practical energy harvesters. First, for wireless energy transfer, the
PTE is characterized using a scalable model for the BS circuit power
consumption. The PTE-optimal number of BS antennas and users are derived. Then,
for wireless energy and information transfer, the EE performance is
characterized. The EE-optimal BS transmit power is derived in terms of the key
system parameters such as the number of BS antennas and the number of users. As
the number of antennas becomes large, increasing the transmit power improves
the energy efficiency for moderate to large number of antennas. Simulation
results suggest that it is energy efficient to operate the system in the
massive antenna regime.
