Dual Index Modulation for Affine Frequency Division Multiplexing Communications

Affine frequency division multiplexing (AFDM) is an emerging multicarrier modulation technique that processes signals in the discrete affine Fourier domain, enabling reliability for high-mobility communications. In order to further improve spectral efficiency (SE), this paper proposes an AFDM scheme with dual index modulation (DIM), referred to as AFDM-DIM. Specifically, information bits are transmitted not only by the traditional symbol constellation, but also jointly through the active states of subcarriers and the corresponding pre-chirp parameter configurations, which can enhance SE and improve robustness against doubly selective fading channels. We also develop two detector algorithms, i.e., maximum likelihood (ML) and joint minimum mean square error–ML (MMSE–ML) for the proposed AFDM-DIM system. We further derive an upper bound on the average bit error rate via pairwise error probability analysis based on ML detection, and compare the SE between the proposed AFDM-DIM scheme with the existing AFDM-index modulation (IM) systems. Simulation results demonstrate that the proposed AFDM-DIM scheme achieves superior performance compared to other existing AFDM-IM schemes.