ISAC with Affine Frequency Division Multiplexing: An FMCW-Based Signal Processing Perspective

TL;DR

This paper explores AFDM's potential for high-mobility sensing in ISAC, establishing a mathematical link to FMCW and developing efficient DD-aware sensing algorithms.

Contribution

It introduces a novel parameter selection criterion, a DD-DAFT domain model, and two matched-filtering algorithms for AFDM-based sensing.

Findings

AFDM can be effectively used for pilot-free sensing in high-mobility scenarios.

The proposed algorithms outperform classical AFDM in various scenarios.

A fundamental trade-off exists between sensing performance, overhead, and complexity.

Abstract

This paper investigates the sensing potential of affine frequency division multiplexing (AFDM) in high-mobility integrated sensing and communication (ISAC) from the perspective of radar waveforms. We introduce an innovative parameter selection criterion that establishes a precise mathematical equivalence between AFDM subcarriers and Nyquist-sampled frequency-modulated continuous-wave (FMCW). This connection not only provides a clear physical insight into AFDM's sensing mechanism but also enables a direct mapping from the DAFT index to delay-Doppler (DD) parameters of wireless channels. Building on this, we develop a novel input-output model in a DD-parameterized DAFT (DD-DAFT) domain for AFDM, which explicitly reveals the inherent DD coupling effect arising from the chirp-channel interaction. Subsequently, we design two matched-filtering sensing algorithms. The first is performed in the time-frequency domain with low complexity, while the second is operated in the DD-DAFT domain to precisely resolve the DD coupling. Simulations show that our algorithms achieve effective pilot-free sensing and demonstrate a fundamental trade-off between sensing performance, communication overhead, and computational complexity. The proposed AFDM outperforms classical AFDM and other variants in most scenarios.