Performance Evaluation and Optimization of Cooperative NOMA over Rayleigh Fading Channels

In this paper we apply multi-carrier non-orthogonal multiple access to the relay network and evaluate the performance of the cooperative non-orthogonal multiple access (Co-NOMA) over Rayleigh fading channels. The messages from IoT devices at the source node are mapped on multiple resource elements in a non-orthogonal manner and broadcasted to the relay node and the base station. Then, the relay node decodes the received symbols, re-encodes it, and forwards it to the base station non-orthogonally. Different from the selection combining utilized in the literature, we employ maximum ratio combining in the joint detection. The analytical expressions of the outage probability and the sum data rate for the Co-NOMA system are derived. Based on the analysis, we optimize the superposition matrices which map the user messages onto the resource elements through the genetic algorithm. Numerical results are provided, which illustrate the superiority of both the maximum ratio combining in the detection and the superposition matrices from the optimization.