Evaluating Energy Efficiency in Two-Way MIMO CRNs: A Joint Approach to Relay Selection and Precoder Design

This paper explores the energy-efficiency (EE) performance of a multiple-input multiple-output (MIMO) equipped cognitive radio network, where multiple two-way (TW) half-duplex (HD) relays facilitate communication between two secondary transceivers (STs). To achieve full diversity with reduced complexity, we employ relay selection through three distinct schemes. We further optimize the precoders at both transceivers and selected relay node to maximize the EE of the secondary system (SS), while taking into account quality-of-service (QoS), transmit power, and interference constraints. The resulting non-convex optimization problem is addressed using a combination of singular value decomposition (SVD), fractional programming theory, and an alternating optimization algorithm. Numerical results demonstrate the efficacy of our proposed solution in enhancing the EE and the probability of feasibility (PoF) of the SS.