ISAC-Enabled OFDM Radar: ICI and Off-Grid Effect Suppression via Signal Reconstruction

Orthogonal frequency-division multiplexing (OFDM) has drawn a lot of attention in the study of integrated sensing and communications (ISAC). However, the fundamental drawback of Doppler intolerance limits its applicability in highly dynamic scenarios such as vehicular applications. In addition, the delay and Doppler shift that are non-integer times the resolution cause the off-grid effect, leading to scalloping loss and increasing the sidelobes. In this work, a super-resolution range-doppler map (RDM) modeling algorithm with low complexity is proposed to suppress these impacts. The proposed algorithm models the RDM contributed by the detected targets jointly via 2D surface fitting and then reconstructs and subtracts the corresponding signal components from the original received signal. Consequently, the weaker targets hiding under the inter-carrier interference (ICI) and off-grid effect become detectable. The communications capability is not impacted since the algorithm is only deployed at the radar receiver. In addition, two variants of the algorithm are illustrated, showing a trade-off between accuracy and complexity. Simulation results demonstrate that the proposed algorithms can effectively suppress ICI and mitigate off-grid effects, while simultaneously enhancing the accuracy of delay and Doppler estimation. It is indicated that the proposed algorithms can provide sufficient improvements in multi-target scenarios.