arXiv subjects

Vincent Savaux

Publications and source records attributed to Vincent Savaux.

6 recordsLinked to original sources

arXiv2026

Joint PAPR and OOBE Reduction for AFDM via Chirp Parameter Tuning

This paper addresses the joint reduction of the peak-to-average power ratio (PAPR) and out-of-band emissions (OOBE) in affine frequency division multiplexing (AFDM) systems by selecting the pre-chirp parameter c2. While existing approaches typically optimize either PAPR or OOBE independently, the proposed method jointly considers both metrics. To this end, a weighted cost function combining PAPR and OOBE is introduced to evaluate the trade-off between the two objectives. A pre-chirp selection scheme, inspired by the selected mapping (SLM) technique, is then employed to identify the optimal c2 value from a finite set of candidates, yielding a Pareto-optimal operating point within a discrete set. Simulation results demonstrate that the proposed approach simultaneously reduces both PAPR and OOBE compared with conventional AFDM. Moreover, its performance remains close to that of methods specifically optimized for a single objective, with only about a 1 dB degradation in PAPR reduction and a 2-3 dB degradation in OOBE suppression.

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arXiv2026

Making AFDM Secure Against Eavesdroppers: A Phase Function Design Approach

Affine frequency division multiplexing (AFDM) has recently emerged as a promising waveform for high-mobility communications due to its resilience to Doppler effects and its advantages for integrated sensing and communication (ISAC). AFDM modulates transmit data symbols using chirp subcarriers with two adjustable parameters. One is used for dealing with the Doppler effect and the second parameter can be used for physical layer security (PLS). In this paper, we focus on designing the second chirp parameter in the form of a generic phase function to enhance the robustness of the waveform against brute-force demodulation by the eavesdropper. In particular, we first derive a design criterion that reveals the brute-force demodulation complexity depends on the first derivative of the phase function. Then, we introduce a family of phase functions that can increase the brute-force demodulation complexity in an unbounded and controllable manner, while preserving chirp structure of AFDM. Our simulation results demonstrate that the proposed phase function design enhances the PLS performance of AFDM by several orders of magnitude compared with the conventional AFDM in terms of brute-force demodulation complexity.

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arXiv2026

AFDM: Evolving OFDM Towards 6G+

As sixth generation (6G) standardization accelerates, there is growing consensus in favor of evolutionary waveforms that add new capabilities while preserving compatibility with the orthogonal frequency division multiplexing (OFDM) core of 4G and 5G. This article positions affine frequency division multiplexing (AFDM) as such a candidate, providing structural robustness for high-mobility communications and integrated sensing and communication (ISAC) over doubly dispersive channels while remaining backward-compatible with the legacy OFDM air interface. We first develop a generalized fractional-delay-fractional-Doppler (FDFD) channel model that accounts for practical pulse-shaping filters and the resulting inter-sample coupling. Building on this model, we show that the AFDM transceiver reuses nearly the entire OFDM chain, adding only lightweight digital pre- and post-processing. We then analyze the impact of hardware impairments such as phase noise and carrier frequency offset, and examine the advanced functionalities enabled by the chirp-parameter domain, including index modulation and physical-layer security. Assessing reusability across the radio-frequency, physical, and higher layers, we conclude that AFDM offers an efficient path toward high-fidelity later versions of 6G and beyond (6G+) communications.

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arXiv2025

On the Robustness of AFDM and OTFS Against Passive Eavesdroppers

We investigate the robustness of affine frequency division multiplexing (AFDM) and orthogonal time frequency space (OTFS) waveforms against passive eavesdroppers performing brute-force demodulation to intercepted signals, under the assumption that eavesdroppers have no knowledge of chirp parameters (in AFDM) or the delay-Doppler grid configuration (in OTFS), such that they must search exhaustively over possible demodulation matrices. Analytical results show that the brute-force complexity scales as $\mathcal{O}(\sqrt{N})$ for OTFS and $\mathcal{O}(N^2)$ for AFDM, where $N$ is the number of subcarriers, indicating that AFDM has superior resilience over OTFS. Bit error rate (BER) simulations confirm the analysis by showing that, with AFDM, the signal remains nearly undecodable at the eavesdropper, while OTFS allows partial signal recovery under equivalent conditions.

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arXiv2025

On the Noise Robustness of Affine Frequency Division Multiplexing: Analysis and Applications

This paper investigates the robustness of affine frequency division multiplexing (AFDM) and orthogonal time frequency space (OTFS) modulation schemes against non-white Gaussian noise, which can model various sources of additive disturbances to the received signal. The proposed approach demonstrates that the performance of these waveforms depends on the ability of the demodulation matrix to whiten the noise-a property that is, in turn, related to the sparsity of the matrix. AFDM is shown to outperform OTFS and orthogonal frequency division multiplexing (OFDM), as its demodulation matrix is generally less sparse than those of the other waveforms. Based on this analysis, several application examples and use cases are presented, such as the use of AFDM and OTFS in narrowband signals or in coexistence with OFDM signals. Finally, simulation results confirm that AFDM achieves better performance than OTFS and OFDM in the presence of non-white noise, with gains exceeding 1 dB in most application scenarios.

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arXiv2025

Affine Frequency Division Multiplexing (AFDM) for 6G: Properties, Features, and Challenges

Affine frequency division multiplexing (AFDM) is an emerging waveform candidate for future sixth generation (6G) systems offering a range of promising features, such as enhanced robustness in heterogeneous and high-mobility environments, as well as inherent suitability for integrated sensing and communications (ISAC) applications. In addition, unlike other candidates such as orthogonal time-frequency space (OTFS) modulation, AFDM provides several unique advantages that strengthen its relevance to practical deployment and standardization in 6G. Notably, as a natural generalization of orthogonal frequency division multiplexing (OFDM), strong backward compatibility with existing conventional systems is guaranteed, while also offering novel possibilities in waveform design, for example to enable physical-layer security through its inherent chirp parametrization. In all, this article provides an overview of AFDM, emphasizing its suitability as a candidate waveform for 6G standardization. First, we provide a concise introduction to the fundamental properties and unique characteristics of AFDM, followed by highlights of its advantageous features, and finally a discussion of its potential and challenges in 6G standardization efforts and representative requirements.

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