Chirp-Permuted AFDM: A Versatile Waveform Design for ISAC in 6G

TL;DR

This paper introduces CP-AFDM, a new waveform for 6G that enhances AFDM's properties for reliable sensing and communication, while enabling spectral efficiency and security through chirp-permutation domain techniques.

Contribution

The paper proposes CP-AFDM, a novel waveform that improves AFDM's performance and introduces multifunctional applications like index modulation and physical-layer security.

Findings

Enhanced ambiguity function resolution and PSLR in Doppler domain.

Maintains core AFDM characteristics like robustness to doubly-dispersive channels.

Enables spectral efficiency and security improvements through permutation domain techniques.

Abstract

We present a novel multicarrier waveform, termed chirp-permuted affine frequency division multiplexing (CP-AFDM), which introduces a unique chirp-permutation domain on top of the chirp subcarriers of the conventional AFDM. Rigorous analysis of the signal model and waveform properties, supported by numerical simulations, demonstrates that the proposed CP-AFDM preserves all core characteristics of affine frequency division multiplexing (AFDM) - including robustness to doubly-dispersive channels, peak-to-average power ratio (PAPR), and full delay-Doppler representation - while further enhancing ambiguity function resolution and peak-to-sidelobe ratio (PSLR) in the Doppler domain. These improvements establish CP-AFDM as a highly attractive candidate for emerging sixth generation (6G) use cases demanding both reliability and sensing-awareness. Moreover, by exploiting the vast degree of freedom in the chirp-permutation domain, two exemplary multifunctional applications are introduced: an index modulation (IM) technique over the permutation domain which achieves significant spectral efficiency gains, and a physical-layer security scheme that ensures practically perfect security through permutation-based keying, without requiring additional transmit energy or signaling overhead.