Spread Spectrum OFDM-IM with Efficient Precoded Matrix and Low Complexity Detector

This paper introduces a novel scheme that employs efficient precoded matrices for index modulation orthogonal frequency division multiplexing namely (EP-OFDM-IM). This technique implements Discrete Fourier Transform (DFT) and Fast Walsh Hadamard Transform (FWHT) precoded matrices for spreading the subset of active M-ary data symbols and their indices to transmit additional information. This aims to enhance the system's transmit diversity (TD) by exploiting multipath and index diversities. Moreover, a low complex minimum means square error greedy detector (MMSE-GD) is proposed that can achieve optimal performance for perfect channel state information (CSI) and superior performance compared to maximum likelihood (ML) under imperfect CSI. The theoretical analysis based on pair-wise error probability is derived to estimate the bit error probability (BEP) of the proposed scheme for the performance analysis. Simulation results demonstrate that our proposed scheme EP-OFDM-IM significantly outperforms various existing competitive benchmark IM schemes. Specifically, at a spectral efficiency (SE) of 1.5 bps/Hz, and BEP of 10-3, our proposed scheme achieves addition of 15dB gain.