Cognitive Multiuser Energy Harvesting Decode-and-Forward Relaying System With Direct Links

In this paper, we study an underlay cognitive energy harvesting decode-and-forward (DF) relaying communications system with multiple secondary users (SUs) and a primary destination. By utilizing power splitting receiver, the relay is capable of harvesting radio frequency energy from SU and retransmitting data with harvested energy. Both direct and relaying links are taken into consideration in selecting the best SU, and furthermore exploited for data transmission by employing selection combining receiver at the secondary destination. To evaluate the system performance, analytical outage probabilities for both selection and fixed DF relaying protocols have been provided under Rayleigh fading channel. Moreover, we further derive their asymptotic expressions of outage probability. With the given asymptotic expressions, we confirm that the system diversity approaches to <inline-formula> <tex-math notation="LaTeX">$N+1$ </tex-math></inline-formula> for selection DF relaying and reaches <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> for fixed DF relaying. Numerical and simulation results are demonstrated to verify our proposed analysis.