Cooperative NOMA System With Virtual Full Duplex User Relaying

Cooperative non-orthogonal multiple access (NOMA) system employs user relaying to enhance performance. Although full-duplex (FD) user relaying scheme does not incur additional bandwidth for relaying, the imperfect self-interference cancellation degrades the performance significantly. Alternatively, a virtual full-duplex (VI-D) user relaying scheme can be used. In this paper, we study a cooperative NOMA system in cognitive radio scenario using VI-D relaying scheme, where two half-duplex (HD) secondary users take turn to relay message of a primary user with decode-and-forward (DF) strategy. First, we derive the closed-form and asymptotic expressions of the outage probability and ergodic rate of the users. Then, we demonstrate the outage probability, ergodic rate, and ergodic sum rate performance of the proposed scheme using Monte Carlo simulations. We also provide a comprehensive comparison between the proposed VI-D user relaying and existing FD and HD user relaying in orthogonal multiple access and NOMA systems. The simulation results verify the analytical results and demonstrate the advantages of the proposed VI-D user relaying over existing schemes.