Repeated Index Modulation-OFDM With Coordinate Interleaving: Performance Optimization and Low-Complexity Detectors

This article investigates performance of an advanced scheme of index modulation for orthogonal frequency division multiplexing (IM-OFDM), called the repeated index modulation-OFDM with coordinate interleaving (RIM-OFDM-CI), which achieves higher transmission reliability than the conventional IM-OFDM with coordinate interleaving (IM-OFDM-CI). We first derive the approximated expressions for the symbol error probability (SEP) of RIM-OFDM-CI. The obtained SEP provides an insight into the impact of system parameters on the error performance, which allows for selection of an optimum constellation rotation angle to minimize SEP. Two enhanced detectors, namely, the log likelihood ratio (LLR) and greedy detector for RIM-OFDM-CI are proposed. The proposed detectors not only achieve nearly same performance as the maximum likelihood detector but also significantly reduce detection complexity of the RIM-OFDM-CI system. Simulation results are reported to validate advantages of the proposed RIM-OFDM-CI and low-complexity detectors against benchmarks.