On the Impact of Channel Aging and Doppler-Affected Clutter on OFDM ISAC Systems

TL;DR

This paper investigates how channel aging and Doppler-affected clutter impact OFDM-based ISAC systems, proposing models and methods for improved channel estimation and clutter suppression to enhance sensing and communication performance.

Contribution

It introduces an aging-aware channel estimator and a low-complexity clutter suppression pipeline tailored for OFDM ISAC systems affected by mobility and clutter.

Findings

Significant performance gains over block fading in low-to-moderate mobility.

Effective clutter suppression achievable with the proposed methods.

Communication beams alone are insufficient for high-resolution sensing.

Abstract

The temporal evolution of the propagation environment plays a central role in integrated sensing and communication (ISAC) systems. A slow-time evolution manifests as channel aging in communication links, while a fast-time one is associated with structured clutter with non-zero Doppler. Nevertheless, the joint impact of these two phenomena on ISAC performance has been largely overlooked. This addresses this research gap in a network utilizing orthogonal frequency division multiplexing waveforms. Here, a base station simultaneously serves multiple user equipment (UE) devices and performs monostatic sensing. Channel aging is captured through an autoregressive model with exponential correlation decay. In contrast, clutter is modeled as a collection of uncorrelated, coherent patches with non-zero Doppler, resulting in a Kronecker-separable covariance structure. We propose an aging-aware channel estimator that uses prior pilot observations to estimate the time-varying UE channels, characterized by a non-isotropic multipath fading structure. The clutter's structure enables a novel low-complexity sensing pipeline: clutter statistics are estimated from raw data and subsequently used to suppress the clutter's action, after which target parameters are extracted through range-angle and range-velocity maps. We evaluate the influence of frame length and pilot history on channel estimation accuracy and demonstrate substantial performance gains over block fading in low-to-moderate mobility regimes. The sensing pipeline is implemented in a clutter-dominated environment, demonstrating that effective clutter suppression can be achieved under practical configurations. Furthermore, our results show that dedicated sensing streams are required, as communication beams provide insufficient range resolution.