Nonlinear energy harvesting based cognitive relaying with best relay selection

This paper proposes a cognitive relaying scheme based on nonlinear energy harvesting, in which the licensed spectrum of the primary system is shared with the secondary system. The primary system comprises of an access point (AP) and multiple primary users (PUs). An energy-constrained secondary transmitter (ST), multiple secondary relays (SRs) and a secondary destination (SD) constitute the secondary system. ST uses the interference signal from AP to harvest energy. The transmit power of ST and relays should be strictly controlled to not exceed the interference constraint of all the PUs. The relay that has correctly decoded the ST's data in the first-hop and brings the strongest signal power to the SD in the second-hop is selected to help ST transmit data to SD. Over the statistical properties of Rayleigh fading channels, we analyze the outage probability and throughput of the secondary system. We also present several benchmark systems for the performance comparison. Numerical results show that the protocol greatly improves spectrum efficiency and communication performance, and we emphasize the influence of various parameters on system performance.