A Novel Multiple-Input Multiple-Output OCDM Transmission System Based on Index Modulation

Orthogonal chirp division multiplexing (OCDM) offers significant advancements in resilience for the next-generation communication networks. Compared to OFDM, it demonstrates superior performance in multipath channel scenarios, especially with multiple input multiple output (MIMO) diversity. Motivated by the potential spectral efficiency of multi-domain index modulation (IM) technology, we introduce the IM architecture on the basis of MIMO-OCDM, named MIMO-OCDM-IM. In this scheme, particular subcarrier indices are designed to implicitly convey information bits by silencing unindexed subcarriers, and an $M$-QAM signal constellation is adopted to modulate information bits in active OCDM subcarriers ordinarily. Sequentially, two frequency domain equalizers are presented to compensate for the channel response, and a subsequent maximum likelihood (ML) detector is utilized to demodulate symbols. To address the computational burden caused by ML detection, a reduced complexity log-likelihood ratio (RC-LLR) detector is further proposed. Numerical simulation results demonstrate the enhanced performance of the proposed scheme in high-mobility scenarios and highlight the bit error rate (BER) and peak-to-average power ratio (PAPR) performance compared to the traditional OCDM-based and OFDM-based schemes.