Low-Complexity Equalization and Detection for OTFS-NOMA

Orthogonal time frequency space (OTFS) modulation has recently emerged as a potential 6G candidate waveform which provides improved performance in high-mobility scenarios. In this paper we investigate the combination of OTFS with non-orthogonal multiple access (NOMA). Existing equalization and detection methods for OTFS-NOMA, such as minimum-mean-squared error with successive interference cancellation (MMSE-SIC), suffer from poor performance and high complexity. Motivated by this, in this paper we propose a low-complexity method for equalization and detection for OTFS-NOMA. The proposed method uses an equalizer based on the least-squares with QR factorization (LSQR) algorithm and a novel reliability zone (RZ) detection scheme which estimates the reliable symbols of the users and then uses interference cancellation to remove multi-user interference (MUI). We present numerical results which demonstrate the superiority of our proposed method, in terms of symbol error rate (SER), to the existing MMSE-SIC benchmark scheme. Additionally, we present results which illustrate that a judicious choice of RZ thresholds is important for optimizing the performance of the proposed algorithm.