A Novel Opportunistic Buffer-Aided Relaying Scheme for Mitigating the Challenges of Single-Relay Energy Harvesting Systems

In this paper, a three-node cooperative network with an energy harvesting (EH) decode-and-forward (DF) buffer-aided (BA) relay is considered. The relay relies solely on the energy harvested from the radio frequency (RF) signal transmitted by the source. This energy is accumulated in an energy buffer to be subsequently used for data transmission based on the harvest-store-use (HSU) architecture. A novel relaying scheme, referred as energy-harvesting-first (EHF), is proposed. This scheme prioritizes energy harvesting (EH) when the content of the energy buffer falls below a predefined threshold. Moreover, opportunistic EH is triggered when significant energy levels fall on the relay and this energy can be completely stored in the finite-size energy buffer. An additional threshold level on the data buffer content further controls the switching between the transmission and reception modes. A Markov chain analysis is performed, where the state transition probabilities are calculated and used to determine the analytical expressions of the outage probability (OP) and average packet delay (APD). An elaborate analysis is also presented highlighting the impact of the parameters of the relaying scheme on the system performance.