Performance analysis of opportunistic NOMA strategy in uplink coordinated multi-points systems

Non-orthogonal multiple access (NOMA) has attracted a great deal of interest due to its potential contribution to the 5th generation (5G) mobile networks. In conventional power-domain NOMA, one of the disadvantages is that the edge-users which are far from the receivers may suffer edge-interference issue, and they may not be served if the propagation channels are extremely poor. In this study, an amplify-and-forward (AF) user-relay based opportunistic NOMA (UR-ONOMA) strategy, which aims to adaptively improve the coverage of high-quality service to the far-end edge users with weak channel scenarios, is designed for the uplink cooperative networks. The transmission data rates of a two-layer UR-ONOMA strategy are theoretically analyzed, and the closed-form expressions of outage probability are derived and evaluated. The numerical results show that the proposed cooperative UR-ONOMA has superior performance in terms of outage probability and throughput than the NOMA without the aid of user-relays when the far-end users are with weak channels.