Outage Analysis for Underlay Cognitive TWRN with Multi-Antenna Sources in Nakagami-M Fading

In this paper, we investigate the outage performance of a cooperative and cognitive radio system where two secondary users (SUs) communicate through a relay via the two-way relaying. The coexistence of SUs with the primary users (PUs) in the same spectrum is possible by using underlay protocol, where the interference at the PU receiver is under a predefined threshold. Focusing on the cooperation process among the SU nodes and making use of the underlay cognitive approach, we derive the exact user outage probability(OP) in closed-form. Furthermore, the tight closed-form expression for the end to end OP is also derived, which is declared when any of a SU is in the outage. Our analysis employs transmit/receive beamforming at the SU nodes and analog network coding at relay node where opportunistic selection algorithm is deployed for selecting best relay in underlay scenario. Furthermore, we have derived the asymptotic performance and thus focus on the performance gain achieved by multi-relay and multiantenna diversity under Nakagami-m fading. Besides, we also evaluate the optimized locations for the relay under practical scenarios to minimize the OP. Monte Carlo simulation results are presented to corroborate the proposed analysis.