Dual-mode index modulation based OFDM system over NOMA networks

Non-orthogonal multiple access (NOMA) scheme is strongly recommended due to its ability to serve multiple users sharing the same frequency and time resources for next-generation radio access networks. Index modulation (IM) over the orthogonal frequency division multiplexing (OFDM) system creates a new dimension for data transmission in terms of subcarrier indices selection bits to enhance the spectral efficiency (SE) through selection diversity gain. By combining IM and conventional OFDM with NOMA, multiple users reap the aforesaid benefits with the variation of power allocation factors and subcarrier indices pattern. Inspired by OFDM-IM NOMA, a dual-mode OFDM-IM technique with NOMA (DM-OFDM-IM NOMA) users is proposed in this paper. The proposed method increases the SE using indices selection bits and data transmission through all the OFDM subcarriers employing different constellation sets. The error performance of the proposed method is evaluated using the maximum-likelihood (ML) and log-likelihood ratio (LLR) detection techniques. The simulation results for the proposed method validates the improvement in SE compared to conventional method over different modulation order. Also, the computational complexity is presented for proposed and existing OFDM-IM NOMA technique using both ML and LLR detectors. (C) 2021 Elsevier B.V. All rights reserved.