On the Effects of LOS Path and Opportunistic Scheduling in Energy Harvesting Relay Systems

In this paper, we investigate the effects of line-of-sight (LoS) path and opportunistic scheduling (OS) on dualhop energy harvesting (EH) relay systems, where the LoS path exists between source and EH relay. We first study a single-destination case and show that the system diversity order is one and the outage behavior decays as log(SNR)/SNR, with SNR denoting the transmit signal-to-noise ratio (SNR) at the source. In the presence of a strong LoS path, asymptotic results reveal that the easing-off factor log(SNR) can be eliminated and a faster decay rate, 1/SNR, is achieved. Afterward, the OS of the second hops (N destinations) is considered, and its separate as well as joint effects on the system outage behavior are examined. In addition, the choice of power-splitting factor is discussed and the impacts of EH constraint on the performance limit compared with conventional relay system are investigated, showing that under the same transmit-power consumption from the fixed energy supply, the EH relay system could achieve the same performance with that of conventional relay system if the wireless power transfer in the first hop is lossless and the energy conversion efficiency at EH relay tends to be unity.