Performance analysis of nonorthogonal multiple access‐based underlay cognitive relay network

Summary This paper considers cooperative non‐orthogonal multiple access (NOMA) scheme in an underlay cognitive radio (CR) network. A single‐cell downlink cooperative NOMA system has been considered for the secondary network, consisting of a base station (BS) and two secondary users, ie, a far user and a near user. The BS employs NOMA signaling to send messages for the two secondary users where the near user is enabled to act as a half‐duplex decode‐and‐forward (DF) relay for the far user. We derive exact expressions for the outage probability experienced by both the users and the outage probability of the secondary system assuming the links to experience independent, nonidentically distributed Rayleigh fading. Further, we analyze the ergodic rates of both the users and the ergodic sum rate of the secondary network. The maximum transmit power constraint of the secondary nodes and the tolerable interference power constraint at the primary receiver are considered for the analysis. Further, the interference caused by the primary transmitter (PT) on the secondary network is also considered for the analysis. The performance of the proposed CR NOMA network has been observed to be significantly better than a CR network that uses conventional orthogonal multiple access (OMA) scheme. The analytical results are validated by extensive simulation studies. This paper proposes a cooperative nonorthogonal multiple access (NOMA) scheme in an underlay cognitive radio (CR) network. The outage probability and ergodic rates experienced by the users in the secondary network are derived. The interference caused by the primary transmitter (PT) on the secondary network is also considered for the analysis and results are compared with conventional orthogonal multiple access (OMA) scheme.