  Wireless energy transfer (WET) is emerging as an enabling green technology
for Internet of Things (IoT) networks. WET allows the IoT devices to wirelessly
recharge their batteries with energy from external sources such as dedicated
radio frequency transmitters called power beacons (PBs). In this paper, we
investigate the optimal deployment of PBs that guarantees a network-wide energy
outage constraint. Optimal positions for the PBs are determined by maximizing
the average incident power for the worst location in the service area since no
information about the sensor deployment is provided. Such network planning
guarantees the fairest harvesting performance for all the IoT devices.
Numerical simulations evidence that our proposed optimization framework
improves the energy supply reliability compared to benchmark schemes.
Additionally, we show that although both, the number of deployed PBs and the
number of antennas per PB, introduce performance improvements, the former has a
dominant role. Finally, our proposal allows to extend the coverage area while
keeping the total power budget fixed, which additionally reduces the level of
electromagnetic radiation in the vicinity of PBs.
