Subspace-Based Super-Resolution Sensing for Bi-Static ISAC with Clock Asynchronism

TL;DR

This paper presents a novel subspace-based framework for bi-static ISAC sensing that effectively estimates target parameters despite clock asynchronism, achieving super-resolution in delay estimation and outperforming existing methods.

Contribution

It introduces a new TO alignment algorithm and joint angle-delay estimation method that handle clock asynchronism, enabling super-resolution sensing in practical Wi-Fi systems.

Findings

Significantly improves parameter estimation accuracy.

Achieves super-resolution in delay domain comparable to synchronized systems.

Demonstrates effectiveness through extensive simulations and real experiments.

Abstract

Bi-static sensing is an attractive configuration for integrated sensing and communications (ISAC) systems; however, clock asynchronism between widely separated transmitters and receivers introduces time-varying time offsets (TO) and phase offsets (PO), posing significant challenges. This paper introduces a signal-subspace-based framework that estimates decoupled angles, delays, and complex gain sequences (CGS)-- the target-reflected signals -- for multiple dynamic target paths. The proposed framework begins with a novel TO alignment algorithm, leveraging signal subspace or covariance, to mitigate TO variations across temporal snapshots, enabling coherent delay-domain analysis. Subsequently, subspace-based methods are developed to compensate for TO residuals and to perform joint angle-delay estimation. Finally, leveraging the high resolution in the joint angle-delay domain, the framework compensates for the PO and estimates the CGS for each target. The framework can be applied to both single-antenna and multi-antenna systems. Extensive simulations and experiments using commercial Wi-Fi devices demonstrate that the proposed framework significantly surpasses existing solutions in parameter estimation accuracy and delay resolution. Notably, it uniquely achieves a super-resolution in the delay domain, with a probability-of-resolution curve tightly approaching that in synchronized systems.