Supplementary Index Bit Aided Transmit Diversity Scheme for Enhanced DCT-OFDM With Index Modulation

In this letter, a novel supplementary index bit aided transmit diversity (SIB-TD) approach is proposed for an enhanced discrete cosine transform based orthogonal frequency division multiplexing with index modulation (EDCT-OFDM-IM) system. Specifically, conventional index modulation (IM) is employed for the first antenna, i.e., the main branch, and the non-activated subcarriers' indices in one index modulation group are utilized for the IM mapping on the same index modulation group for the second antenna, i.e., the diversity branch. Hence, each subcarrier can not be synchronously activated on the two antennas. Finally, the non-activated subcarriers of one antenna will transmit the same modulated symbols of the other antenna to exploit the diversity gain. At the receiver, a maximum likelihood group-wise receiver is also developed by detecting the main and diversity branches jointly. Simulation results demonstrate the superiority of the proposed scheme over both the conventional EDCT-OFDM-IM and the DFT-OFDM with Alamouti code either with or without IM respectively, even under the imperfect channel estimation.