SEP of Cooperative NOMA with Selection Combining

Mobile gadgets and wireless technology have had a tremendous impact on people's lives during the last few decades. Non-Orthogonal Multiple Access (NOMA) have become a key principle in the development of Fifth-Generation (5G) wireless network radio access methods. Most recently, significant growth has been seen in cooperative NOMA methods to improve spectral efficiency and broadcast range. In this paper, we have analyzed the performance of a two-user power domain downlink NOMA system. In this system to achieve diversity, Selection Combining (SC) is employed at the far user to combine the signal from the base station and the signal retransmitted from the near user. We derive Symbol Error Probability (SEP) of the proposed system in the presence of a Rayleigh fading channel. Further, we also find the optimum power allocation coefficients to obtain minimum SEP. The numerical results reveal that the proposed Full Channel State Information (CSI) SC cooperative NOMA performs better than the traditional NOMA systems. Further, it is observed that when the number of near user increases, the SEP of the system decreases because of the additional diversity paths.