High-Dimensional Superposition NOMA and its User Pairing Strategy

A novel power-domain non-orthogonal multiple access (NOMA) scheme with high-dimensional modulation is proposed. Signals for two users, each of which selected from a high-dimensional modulation constellation matrix, are superimposed on the same time-frequency resource for transmissions. While inter-user interference is treated as noise at the receiver of the far user, successive interference cancellation is used at the receiver of the near user. By analyzing the upper bounds of the detection errors, the power allocation factor is derived, which depends only on the relative power gain of the two users, i.e., the ratio between the squared of the two channel gains, but not on the operating signal-to-noise ratio. This nice feature allows us to perform user pairing easily for a system with more than two users. The optimal user pairing strategy that minimizes the total power consumption is analytically derived. Simulation results show that our proposed design outperforms some benchmark scheme.