Performance Analysis for NOMA with M-QAM Modulation

This paper investigates the performance of an uplink Non-orthogonal Multiple Access (NOMA) with discrete M-QAM modulation and fixed power coefficients. Specifically, an uplink NOMA with a base station and two users are considered and two different performance metrics, namely bit error rate and spectral efficiency, are investigated. We provide closed-form expressions for the average spectral efficiency of NOMA with M-QAM which shows that the performance of the weak user is limited to a certain value which depends on the power coefficients solely. Moreover, results of closed-form expressions and simulation are compared to verify the expressions and to analyze the performance of the proposed NOMA system. The simulation results show that increasing the power coefficient of weak user can improve the weak user's performance in high SNRs, but it does not work well in low SNRs.