A Novel Rotated Constellation-Based LLR Detector for Flexible NOMA Based OFDM-IM Scheme

OFDM-IM NOMA is a newly created flexible scheme for future generation communication systems. For the downlink OFDM-IM NOMA system, a low-complexity “rotated constellation based log likelihood ratio (LLR) detector” has been proposed in this work. This detector is made by combining the Constellation rotation-based concept and the two-stage Log-Likelihood Ratio algorithm together. By using the rotated Constellation based concept, successive interference cancellation (SIC) process can be avoided, additionally the two-stage Log-Likelihood Ratio algorithm has a lesser complexity. As a result, the proposed detector is able to reduce the complexity significantly. Complexity analysis and simulation results show that the proposed detector achieves significantly lower computational complexity and much better error performance than the earlier introduced maximum likelihood (ML) based detector under different scenarios for the OFDM-IM NOMA scheme.