Wireless-Powered Relays Assisted Batteryless IoT Networks Empowered by Energy Beamforming.

In this letter, we propose an energy beamforming empow-ered relaying scheme for a batteryless IoT network, where wireless-powered relays are deployed between the hybrid access point (HAP) and batteryless IoT devices to assist the uplink information transmission from the devices to the HAP. In particular, the HAP first exploits energy beamforming to effi-ciently transmit radio frequency (RF) signals to transfer energy to the relays and as the incident signals to enable the information backscattering of bat-teryless IoT devices. Then, each relay uses the harvested energy to forward the decoded signals from its corresponding batteryless IoT device to the HAP, where the maximum-ratio combing is used for further performance improvement. To maximize the network sum-rate, the joint optimization of energy beamforming vectors at the HAP, network time scheduling, power allocation at the relays, and relection coefficient at the users is investi-gated. As the formulated problem is non-convex, we propose an alternating optimization algorithm with the variable substitution and semi-definite re-laxation (SDR) techniques to solve it efficiently. Specifically, we prove that the obtained energy beamforming matrices are always rank-one. Numerical results show that compared to the benchmark schemes, the proposed scheme can achieve a significant sum-rate gain.