Cooperative NOMA in cognitive radio networks: A study on imperfect CSI, SIC and hardware impairments over Nakagami-m fading channel

This paper proposes a cooperative uplink-downlink non orthogonal multiple access (NOMA) in an overlay cognitive radio network (CR). We examine the impact of imperfect channel state information (impCSI), imperfect successive interference cancellation (impSIC) and residual hardware impairments (RHI) on the cooperative cognitive radio network over Nakagami-m fading channels. We derive the exact outage probabilities of primary user (PU) and multicast secondary users (SUs) under perfect/imperfect conditions for fixed and adaptive power allocations. We show that the use of multiple relays enhances the diversity order, but with fixed power allocation in perfect/imperfect case and adaptive power allocation in imperfect case both suffer from an error floor, which reduces the diversity order to zero. On the other hand, the adaptive power allocation for the perfect case achieves full diversity gain. We validate the analytical results with Monte Carlo simulations and demonstrate the diversity gains of the considered schemes.