OFDM-ISAC Beyond CP Limit: Performance Analysis and Mitigation Algorithms
Peishi Li, Ming Li, Rang Liu, Qian Liu, and A. Lee Swindlehurst

TL;DR
This paper analyzes the limitations of OFDM-ISAC beyond the cyclic prefix (CP) limit, providing a unified model, performance metrics, and proposing interference cancellation algorithms that significantly improve sensing accuracy.
Contribution
It introduces a comprehensive echo model for OFDM-ISAC beyond the CP limit, derives key performance metrics, and proposes two effective interference mitigation algorithms.
Findings
SINR and RDM metrics deteriorate linearly with excess delay beyond CP
Proposed SIC-DFT and SIC-ESPRIT algorithms improve SINR by over 4 dB
SIC-ESPRIT reduces range/velocity RMSE by about an order of magnitude.
Abstract
Orthogonal frequency division multiplexing (OFDM) is well-suited for integrated sensing and communications (ISAC), yet its cyclic prefix (CP) is dimensioned for communications-grade multipath and is generally insufficient for sensing. When echoes exceed the CP duration, inter-symbol and inter-carrier interference (ISI/ICI) break subcarrier orthogonality and degrade sensing. This paper presents a unified analytical and algorithmic framework for OFDM-ISAC beyond the CP limit. We first develop a general echo model that explicitly captures the structured coupling of ISI and ICI caused by CP insufficiency. Building on this model, we derive closed-form signal-to-interference-plus-noise ratio (SINR) and range-Doppler Map (RDM) second-order moment, together with an approximate peak sidelobe level ratio (PSLR), both of which are shown to deteriorate approximately linearly with the normalized…
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