Non-Contiguous Wi-Fi Spectrum for ISAC: Impact on Multipath Delay Estimation

2026-02-20

AI Summary

This study addresses the degradation of delay estimation in integrated sensing and communication (ISAC) systems operating over discontinuous Wi-Fi bands, where spectral gaps induce sidelobes and spurious peaks in the delay response, severely compromising dense multipath resolution. By modeling channel state information, the work analyzes how non-contiguous spectra affect delay resolution and conducts a systematic evaluation integrating Cramér–Rao lower bound (CRLB) analysis with delay response characteristics. It reveals, for the first time, a coupling-induced oscillatory effect between the geometric structure of band gaps and time-delay separability, and proposes a normalized leakage metric to predict regions where delay estimation fails—thereby overcoming limitations of conventional local CRLB assessments. Results demonstrate that while enlarging the frequency aperture sharpens the mainlobe, it concurrently exacerbates spectral leakage and sidelobe interference; the proposed metric effectively identifies practically unresolvable delay intervals.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Intelligent Robots: State Estimation

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Responsible Web: Measurement, analysis, and circumvention of Web censorship
• Security and Privacy: Large-scale security measurements

Abstract

Leveraging channel state information from multiple Wi-Fi bands can improve delay resolution for ranging and sensing when a wide contiguous spectrum is unavailable. However, frequency gaps shape the delay response, introducing sidelobes and secondary peaks that can obscure closely spaced multipath components. This paper examines multipath delay estimation for Wi-Fi-compliant multiband configurations using channel state information (CSI). For a two-path model with unknown complex gains and delays, the Cram\'er-Rao lower bound (CRLB) for delay separation is derived and analyzed, confirming the benefit of larger frequency aperture, while revealing pronounced, separation-dependent oscillations driven by gap geometry and inter-path coupling. Given the local nature of Cram\'er-Rao lower bound, the delay response is analyzed next. In the single-path case, the combined subband responses determine how delay-domain sidelobe levels are distributed. The dominant peak spacing is set primarily by the separation between subband center frequencies. In the two-path case, increased aperture sharpens the mainlobe but also intensifies sidelobes and leakage, yielding competing peaks and, in some regimes, a dominant peak shifted from the true delay. Finally, a normalized leakage metric is introduced to predict problematic separations and to identify regimes where local Cram\'er-Rao lower bound analysis does not capture practical peak-leakage behavior in delay estimation.

Problem

• Non-Contiguous Spectrum
• Multipath Delay Estimation
• Wi-Fi ISAC
• Frequency Gaps
• Channel State Information

Innovation

• Non-contiguous spectrum
• Multipath delay estimation
• Cramér-Rao lower bound
• Channel state information
• Sidelobe leakage