Enhancing RF energy harvesting performance with cooperative beam selection for wireless sensors

RF energy harvesting is a promising potential solution to provide convenient and perpetual energy supplies to low-power wireless sensor networks. In this paper, we investigate the energy harvesting performance of a wireless sensor node powered by harvesting RF energy from an existing multiple-antenna transmitter. Specifically, we propose a random unitary beamforming (RUB) based cooperative beam selection scheme to enhance the energy harvesting performance at the sensor. Under a constant total transmission power constraint, the multiple-antenna transmitter selects the best active beams for data transmission, while satisfying the energy harvesting requirement at the sensor. We derive an exact closed-form expression for the distribution function of harvested energy in a coherence time at the sensor, as well as the throughput of the existing system over Rayleigh fading channels. We further investigate the performance tradeoff of the average harvested energy at the sensor versus the throughput of the existing system.