Joint User and Relay Selection based Cooperative NOMA with Imperfect CSI

In this paper we consider the deployment of mobile relay nodes in a Cooperative Non Orthogonal Multiple Access (CNOMA) system with variable gain Amplify and Forward relaying. In a multiuser downlink scenario, two users are chosen as the NOMA destination pairs based on the channel quality and another suitable user is chosen to act as the relay node. Two standard relay selection protocols are examined here viz. the partial relay selection (PRS) and optimal relay selection (ORS). An outdated channel condition induced by the user mobility condition is considered in this paper and the impact of channel correlation on the system performance is analyzed. The outage performance and ergodic sum rate capacity of the users is observed under the two relay selection schemes. Further, the impact of user node velocity on the relay selection and outage performance have been reported. It is observed that the optimal relay selection has an overall better performance compared to partial relay selection. However, the impact of user velocity and time delay is lesser in case of partial relay selection. Hence, partial relay selection method has a more stable performance in case of imperfect CSI compared to optimal relay selection.