Cooperative Dual-Mode OFDM Index Modulation Based Downlink Multi-User NOMA System

To fulfil the demand for high energy and spectral efficiency (SE) while serving multiple users concurrently for next-generation 6G systems, both non-orthogonal multiple access (NOMA) and orthogonal frequency division multiplexing (OFDM) aided index modulation (IM) endorse the requirements. NOMA serves several users concurrently while sharing the frequency and time resources. In addition, the single-mode OFDM-IM system improves the SE by broadcasting the additional bits of active subcarrier selection. Meanwhile, dual-mode OFDM-IM relatively enhances the SE via transmitting different constellation sets over a subblock OFDM vector. Furthermore, broadcasting the baseband NOMA symbols over a dual-mode OFDM-IM scheme improves the SE compared to the conventional IM schemes. This paper describes a dual-mode aided cooperative relaying OFDM-IM-based downlink hybrid NOMA system serving multiple users simultaneously. The Monte Carlo simulation results demonstrate that the bit error rate (BER) performance of the proposed system accessed using the maximum likelihood (ML) detector for different modulation schemes is significantly better as compared to the existing cooperative relaying OFDM-IM-aided NOMA systems, including single-mode and hybrid systems.