Repeated Index Modulation with Coordinate Interleaved OFDM

In this work, a novel index modulation scheme for orthogonal frequency division multiplexing (IM-OFDM), referred to as repeated index modulation with coordinate interleaved OFDM (RIM-CI-OFDM), is proposed to improve the error performance of the conventional IM-OFDM with coordinated interleaving (IM-OFDM-CI) system. Unlike the conventional scheme, RIM-CI-OFDM allows two distinguishable clusters of sub-carriers to employ the same indices of active sub-carriers, while the CI principle is jointly applied to the M-ary data symbols from both of these clusters. As a result, the proposed scheme not only outperforms IM-OFDM-CI in terms of index and M-ary symbol error performances but also provides a better tradeoff between the reliability and the spectral efficiency (SE). In addition, our scheme allows the number of active sub-carriers to be any positive integer while it is fixed to an even number in the conventional IM-OFDM-CI. A low complexity maximum likelihood (lowML) detector, which enjoys the optimal error performance as the ML detector at much lower complexity, is also proposed. Finally, simulation results are presented to validate the better performance of the proposed RIM-CI-OFDM and lowML detector in comparison with benchmark schemes.