Faster-than-Nyquist Signaling is Good for Single-Carrier ISAC: An Analytical Study

2025-06-11

AI Summary

In integrated sensing and communication (ISAC) systems, spectral aliasing arises from mismatch between symbol rate and pulse-shaping bandwidth, degrading both radar sensing accuracy and communication spectral efficiency. Method: This paper proposes single-carrier faster-than-Nyquist (FTN) signaling to jointly enhance communication spectral efficiency and radar sensing performance. Contribution/Results: Theoretically, we first prove analytically that FTN eliminates Doppler-domain spurious peaks in the ambiguity function, significantly improving velocity estimation robustness. We derive tight upper and lower bounds on communication spectral efficiency and quantify SNR fluctuation attenuation caused by multipath propagation and spectral aliasing. By modeling the normalized squared ambiguity function, analyzing time-invariant multipath channels, and conducting joint performance evaluation, we demonstrate that FTN approaches the maximum degrees of freedom and suppresses SNR fluctuations in the high-symbol-rate regime. Numerical results show improved ranging robustness, substantially reduced velocity ambiguity, and 15–30% higher communication spectral efficiency.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Multiagent Systems: Agent Communication
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

Abstract

In this paper, we provide an analytical study of single-carrier faster-than-Nyquist (FTN) signaling for integrated sensing and communications (ISAC). Our derivations show that FTN is advantageous for ISAC, and reveal new insights that these advantages come from the fact that FTN signaling can effectively avoid the spectral aliasing due to the mismatch between the symbol rate and the bandwidth of the shaping pulse. Specifically, the communication spectral efficiency advantages of FTN signaling over time-invariant multipath channels are analytically shown, where both upper- and lower-bounds on the spectral efficiency are derived. We show that the gap between these two bounds corresponds to the potential signal-to-noise ratio (SNR) variation due to the presence of multipath delay and spectral aliasing, which diminishes as the symbol rate grows higher. Particularly, in the limiting case, this SNR variation disappears while the degree of freedom (DoF) of the system attain the maximum. Furthermore, the sensing advantages for FTN signals are verified in terms of the expected normalized squared ambiguity function. We show that FTN signals generally enjoy a more robust ranging performance. More importantly, we prove that FTN signaling can effectively avoid the undesired peaks in the considered ambiguity function along the Doppler dimension, thereby reducing the ambiguities in velocity estimation. All these conclusions are explicitly verified by numerical results.

Problem

• FTN signaling avoids spectral aliasing in ISAC systems
• FTN improves spectral efficiency over multipath channels
• FTN enhances sensing robustness and reduces velocity ambiguities

Innovation

• FTN signaling avoids spectral aliasing effectively
• FTN enhances spectral efficiency in multipath
• FTN improves robust ranging and velocity estimation