Average Symbol Error Rate Analysis for Non-Orthogonal Multiple Access With M -Ary QAM Signals in Rayleigh Fading Channels

This letter investigates a symbol error rate (SER) performance of the downlink non-orthogonal multiple access (NOMA) scheme with symbol-level successive interference cancellation (SIC). Exact and closed-form expressions for average SERs of individual users are derived under Rayleigh fading channels considering imperfect SIC when the square quadrature amplitude modulation (QAM) symbols of two users are superposed and transmitted using NOMA. In addition, a power allocation criterion of NOMA is provided for the design of feasible QAM constellations when the modulation orders of two users are given.