Performance Analysis of Relay Assisted Cooperative Non-Orthogonal Multiple Access Systems

Non-orthogonal multiple access (NOMA) is a promising multiple access technique for the fifth generation (5G) wireless communications. In order to enhance the performance gains of NOMA systems, a relay assisted cooperative NOMA scheme is designed in this paper. In the proposed scheme, the concept of NOMA is exploited to realize the transmission of the source information in the second time slot. The destination can only receives a single data symbol in conventional cooperative systems, while the destination can reliably acquire two data symbols in two time slots. Therefore, the proposed scheme can achieve higher achievable rate performance than existing schemes. Moreover, the complex power allocation algorithm can be avoided to alleviate the complexity of cooperative NOMA systems. For Rayleigh fading channels, we derive exact expressions for two important performance metrics of the proposed scheme, i.e., the outage probability and the achievable rate. In addition, asymptotic results are presented in terms of simple elementary functions to provide useful insights to guide the practical implementation. Monte-Carlo simulations are provided to demonstrate the performance of the proposed scheme and the accuracy of the derived analytical results.