Radar-Centric AFDM Waveform With Chirp-Domain Index Modulation for ISAC

This paper presents a radar-centric framework for integrated sensing and communication (ISAC) that utilizes affine frequency-division multiplexing (AFDM). We propose chirp-domain index modulation (CDIM) as a method to embed data without compromising radar performance. In this method, each AFDM block is assembled using a pair of predetermined chirp coefficients chosen from a radar-compliant lookup table. These chirp pairs are equivalent in terms of ambiguity, meaning that the embedded communication symbols preserve the radar’s correlation properties and compactness of ambiguity. The suggested AFDM-IM waveform maintains a constant signal envelope and performs matched filtering for high-resolution range-Doppler estimation. Chirp selection embeds communication data structurally, rather than using traditional amplitude or phase modulation. This enables the receiver to detect the index with low complexity. Simulation results demonstrate that AFDM-IM can estimate radar signals even when transmitted over doubly dispersive channels and can also efficiently send modest amounts of data. The proposed framework strikes a good balance between sensing fidelity and communication throughput, making it a viable choice for next-generation ISAC systems.