Generalized BER Performance Analysis for SIC-Based Uplink NOMA

Non-orthogonal multiple access (NOMA) is well known for enhancing the spectral and energy efficiency by allowing multiple users to share the network resources more effectively. While most existing studies focus on downlink NOMA, this paper shifts the focus to uplink NOMA, presenting novel generalized closed-form bit error rate (BER) performance analysis for imperfect successive interference cancellation (SIC) receivers under fading channels. To accommodate various scenarios, the derived expressions are generalized for any arbitrary rectangular/square M-ary quadrature amplitude modulation order, number of NOMA users, and number of base station antennas. It is shown that these expressions are essential for designing optimal uplink power allocation (PA) strategies and mitigating SIC error floors, as evidenced by the proposed PA algorithm which achieves significant performance gains. The results also show that the BER performance of uplink NOMA can surpass that of its orthogonal multiple access counterpart under certain operating conditions and equivalent transmission rates and powers.