Two-Layer Coding with Flexible Layer-Partitioning for Dual-Mode OFDM-IM

Dual mode orthogonal frequency division multiplexing with index modulation (DM-OFDM-IM) employs two distinguishable constellations across all subcarriers to address the low spectral efficiency of OFDM-IM. Recent studies on OFDM-IM-based systems have focused on constellation design, index pattern selection, and channel coding. A two-layer coding (TLC) scheme with successive cancellation decoding (SCD) has been proposed to improve the bit error rate (BER) of conventional OFDM-IM. However, it has not been applied to DM-OFDM-IM, and its frame error rate (FER) performance has not yet been evaluated. In this paper, we propose a method that applies TLC combined with SCD to DM-OFDM-IM. This approach addresses the challenge of DM-OFDM-IM, which faces greater difficulty in distinguishing index patterns compared to conventional OFDM-IM. We analyze the capacity of DM-OFDM-IM with TLC and demonstrate its advantage over conventional DM-OFDM-IM in terms of achievable rate. Furthermore, we propose a flexible layer-partitioning (FLP) scheme between two codewords, enabling a more flexible range of code rate variations. In addition, when decoding the second layer with SCD, only the estimated index pattern needs to be considered instead of all possible index patterns. It is shown via simulations that the proposed DM-OFDM-IM achieves a lower FER than conventional DM-OFDM-IM under various modulation parameters.