  Wireless Energy Transfer (WET) is emerging as a potential solution for
powering small energy-efficient devices. We propose strategies that use
multiple antennas at a power station, which wirelessly charges a large set of
single-antenna devices. Proposed strategies operate without Channel State
Information (CSI) and we attain the distribution and main statistics of the
harvested energy under Rician fading channels with sensitivity and saturation
energy harvesting (EH) impairments. A switching antenna strategy, where a
single antenna with full power transmits at a time, provides the most
predictable energy source, and it is particularly suitable for powering sensor
nodes with highly sensitive EH hardware operating under non-LOS (NLOS)
conditions; while other WET schemes perform alike or better in terms of the
average harvested energy. Under NLOS switching antennas is the best, while when
LOS increases transmitting simultaneously with equal power in all antennas is
the most beneficial. Moreover, spatial correlation is not beneficial unless the
power station transmits simultaneously through all antennas, raising a
trade-off between average and variance of the harvested energy since both
metrics increase with the spatial correlation. Moreover, the performance gap
between CSI-free and CSI-based strategies decreases quickly as the number of
devices increases.
