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Dual-mode index modulation aided orthogonal frequency division multiplexing (DM-OFDM) is recently proposed, where subcarriers are partitioned into OFDM subblocks, divided into two groups within each subblock, and modulated by two differentiable constellation alphabets. In DM-OFDM, additional bits can be transmitted through indices of subcarriers modulated by the same constellation alphabet. In this letter, generalized DM-OFDM (GDM-OFDM) is proposed, where the number of subcarriers modulated by the same constellation mode in each subblock is alterable. By applying such enhancements, the spectral efficiency can be improved at the cost of marginal performance loss. Moreover, since the bit error rate performance of GDM-OFDM degrades at low signal-to-noise ratios, an interleaving technique is employed to address this issue. At the receiver, a maximum-likelihood detector and a reduced-complexity log-likelihood ratio detector are employed for demodulation. Simulation results demonstrate that the proposed GDM-OFDM is capable of enhancing the spectral efficiency compared with DM-OFDM at the cost of negligible performance loss, and the interleaved GDM-OFDM can harvest on performance gain over GDM-OFDM.
Mao et al. (Mon,) studied this question.