Throughput analysis of wireless-powered communications with energy beamforming and adaptive time switching

This paper studies a wireless-powered communication network consisting of a hybrid access-point (AP) equipped with multiple antennas and a single-antenna user. The user is assumed to have no embedded power supply. Thus, it needs to first harvest energy from RF signals sent by the AP in the downlink (DL) before transmitting its information to the AP in the uplink (UL). We consider the scenario that the user transmits with fixed rate and the full channel state information is available at the AP side. This enables the AP to adaptively adjust the time duration of DL energy transfer to maximize the system throughput. We then characterize the average throughput of the considered network by deriving a closed-form expression for the probability density function of the adaptive DL energy transfer time. The asymptotic analysis of the system throughput is also performed to gain more insights. Numerical results are finally provided to verify the theoretical analysis, which show that the proposed adaptive time switching scheme always outperforms its fixed time switching counterpart.