Backscatter-Aided Relay Communications in Wireless Powered Hybrid Radio Networks

In this paper, we exploit the radio diversity gain in a multi-user hybrid radio network wirelessly powered by a power beacon station (PBS). Each user has a dual-mode radio that can switch between the passive and active modes, according to the channel and energy conditions. This provides extra degree of freedom to improve the overall network performance. As such, we propose a throughput maximization problem by jointly optimizing the PBS' energy beamforming and the radios' transmission scheduling strategies in two modes. We show that the throughput maximization is easily tractable by solving a semi-definite program. However, it becomes non-convex and intractable when we allow radios' cooperation in data transmissions. To this end, we propose a set of heuristic algorithms with different complexities for cooperative relay transmissions, which are shown to significantly improve the sum throughput compared to the non-cooperative case. The simulation results show that a simple adaptive scheme can achieve the maximum throughput according to the PBS' power supply.