A Low Complexity Two-Stage LLR Detector for Downlink OFDM-IM NOMA

OFDM-IM based Non-Orthogonal Multiple Access is a recently developed scheme, where flexibility is provided by both NOMA and OFDM-IM with an adjustable power allocation coefficient and an adjustable subcarrier activation ratio, respectively. However, the computational complexity of the Maximum Likelihood (ML) detector, used in the OFDM-IM NOMA scheme is very high. In this letter, a low complexity “two-stage Log-Likelihood Ratio (LLR)” detector is proposed for the OFDM-IM NOMA scheme. Computer simulation results and complexity analysis verify that the proposed detector performs almost the same as the ML-based detector in all the various conditions, with much reduced computational complexity.