Dual-Mode Index Modulation Aided AFDM for Future High Mobility Communications

In this paper, a novel dual-mode affine frequency division multiplexing (AFDM-DM) scheme is proposed for high-mobility communications to improve both bit error rate (BER) performance and spectral efficiency (SE). Specifically, chirps of AFDM in each subblock are partitioned into two carefully designed groups, and information is conveyed jointly through index bits that determine two distinct constellation modes, as well as the constellation bits modulated by the corresponding modes. Furthermore, the minimum Euclidean distance (MED) is derived to demonstrate the BER advantage over conventional index modulation aided AFDM (AFDM-IM), and the theoretical BER is obtained via pairwise error probability (PEP) analysis. Simulation results demonstrate that the proposed enhanced-throughput scheme achieves superior BER performance compared to AFDM-IM and traditional orthogonal frequency division multiplexing (OFDM) variants under linear time-varying (LTV) channels.