  Wireless RF power transmission promises battery-less, resilient, and
perpetual wireless sensor networks. Through the action of controllable Energy
Transmitters (ETs) that operate at-a-distance, the sensors can be re-charged by
harvesting the radiated RF energy. However, both the charging rate and
effective charging range of the ETs are limited, and thus multiple ETs are
required to cover large areas. While this action increases the amount of
wireless energy injected into the network, there are certain areas where the RF
energy combines destructively. To address this problem, we propose a
duty-cycled random-phase multiple access (DRAMA). Non-intuitively, our approach
relies on deliberately generating random interferences, both destructive and
constructive, at the destination nodes. We demonstrate that DRAMA optimizes the
power conversion efficiency, and the total amount of energy harvested. Through
real-testbed experiments, we prove that our proposed scheme provides
significant advantages over the current state of the art in our considered
scenario, as it requires up to 70\% less input RF power to recharge the energy
buffer of the sensor in the same time.
