AFDM-ISAC Design Amalgamating FMCW Radar and Carrier Aggregation

Carrier-aggregation (CA)-assisted affine frequency division multiplexing (AFDM) is conceived for integrated sensing and communication (ISAC) systems. A frequency-modulated continuous-wave (FMCW)-inspired dechirping receiver is developed to exploit the inherent pulse-compression property of AFDM chirp subcarriers for accurate delay-Doppler estimation. To further enhance sensing performance, a pair of CA schemes is proposed. The Type-I CA scheme improves sensing accuracy by aggregating echo signals across multiple CA bands prior to radar processing, thereby reducing estimation error with low hardware overhead. The Type-II CA scheme enhances range resolution by effectively enlarging the sensing bandwidth, where chirps from different CA bands are designed to form a continuous set of chirp signals. Based on this principle, variable subcarrier sensing and asynchronous sensing schemes are developed. For the communication receiver, the generalized input-output relationship of AFDM is derived under both fractional delay and fractional Doppler (FDFD) channels. To address the challenge of FDFD estimation, a cross-domain sensing-assisted channel estimation (CDS-CE) scheme is proposed to facilitate time-domain delay-Doppler parameter estimation and affine-domain channel coefficient recovery. Simulation results demonstrate that the proposed framework achieves significant improvements in sensing accuracy and resolution, as well as in channel estimation performance compared with state-of-the-art methods.