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Performance Improvement for RF Energy-Harvesting Relays via Relay Selection

Energy harvesting (EH) is a promising technique to reduce energy consumption for information relaying. With EH capability, an intermediate node, acting as the relay, can replenish energy inherent in the radio-frequency (RF) signal from a source node and use the harvested energy to forward the received signal to the destination. To efficiently utilize the harvested energy, it is important to select proper relays to receive and forward the source signal. In this paper, we investigate the relay selection problem in the context of EH relays. Based on the celebrated time-switching relaying (TSR) protocol, we propose a new relay selection scheme that mitigates the risk of ill relay selection due to the mismatch between the source–relay and relay–destination channel conditions. In addition to the time-division (TD) block structure considered in TSR, we propose a full-duplex (FDX) block structure that improves the effective transmission time of EH relays. The performance of the proposed relay selection scheme in terms of the outage probability and the throughput using both TD and FDX block structures is analyzed. We also provide closed-form expressions of the outage probability under the high signal-to-noise ratio (SNR) assumption. Numerical results are presented to demonstrate the superiority of the proposed relay selection scheme compared with the existing ones.