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arxiv: 2511.17878 · v2 · submitted 2025-11-22 · 📡 eess.SP

OFDM-ISAC Beyond CP Limit: Performance Analysis and Mitigation Algorithms

Peishi Li , Ming Li , Rang Liu , Qian Liu , A. Lee Swindlehurst This is my paper

Pith reviewed 2026-05-17 07:06 UTC · model grok-4.3

classification 📡 eess.SP
keywords OFDMISACcyclic prefixinter-symbol interferenceinter-carrier interferencesuccessive interference cancellationSINRrange-Doppler map
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The pith

OFDM-ISAC can maintain high sensing performance beyond the cyclic prefix limit through a structured echo model and successive interference cancellation.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper develops a framework for OFDM-based integrated sensing and communications when target echoes have delays longer than the cyclic prefix used for communications. It introduces a general echo model that captures the coupling between inter-symbol and inter-carrier interference resulting from this insufficiency. From this model, closed-form expressions are derived for the signal-to-interference-plus-noise ratio and the second-order moments of the range-Doppler map, along with an approximation for the peak sidelobe level ratio, all showing linear deterioration with excess delay. Two mitigation algorithms are proposed: a low-complexity DFT-based successive interference cancellation method and a super-resolution ESPRIT-based one. Both methods are shown through analysis and simulation to improve performance significantly while remaining compatible with standard OFDM formats.

Core claim

A unified analytical and algorithmic framework is presented for OFDM-ISAC beyond the CP limit. A general echo model explicitly captures the structured coupling of ISI and ICI. Closed-form SINR and RDM second-order moment expressions are derived along with an approximate PSLR, all deteriorating approximately linearly with the normalized excess delay. Standard-compatible SIC-DFT and SIC-ESPRIT methods mitigate these effects, with simulations showing more than 4 dB SINR improvement and SIC-ESPRIT reducing range and velocity RMSE by about one order of magnitude, approaching the performance of a sufficiently long CP.

What carries the argument

general echo model capturing the structured coupling of ISI and ICI caused by CP insufficiency, which supports both performance analysis and the design of mitigation algorithms

If this is right

  • Signal quality metrics such as SINR degrade linearly with the amount by which echo delay exceeds the CP duration.
  • SIC-DFT provides a low-complexity way to cancel interference while staying compatible with existing OFDM standards.
  • SIC-ESPRIT achieves super-resolution estimation and reduces range and velocity errors by roughly ten times.
  • The proposed methods enable reliable sensing at longer ranges without requiring changes to the transmitted waveform or increased CP overhead.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The linear relationship between degradation and excess delay could guide the selection of CP lengths that optimize the trade-off between communication efficiency and sensing range.
  • These techniques might be combined with other ISAC enhancements such as waveform design or beamforming for further performance gains in practical deployments.
  • Validating the model against real-world channel measurements would help assess its applicability across different environments and hardware setups.

Load-bearing premise

The general echo model that explicitly captures the structured coupling of ISI and ICI caused by CP insufficiency accurately represents real propagation and hardware effects for the scenarios considered.

What would settle it

Comparing the analytically predicted SINR and range-Doppler map statistics against measurements from a real OFDM-ISAC system with controlled excess delays would test whether the linear degradation holds and whether the algorithms achieve the expected improvements.

Figures

Figures reproduced from arXiv: 2511.17878 by A. Lee Swindlehurst, Ming Li, Peishi Li, Qian Liu, Rang Liu.

Figure 1
Figure 1. Figure 1: Illustration of transmit and echo signals. ISI and IC [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Range profiles generated using the 2D-DFT sensing [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: SINR and PSLR versus CP length, where the target is [PITH_FULL_IMAGE:figures/full_fig_p007_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: SINR and PSLR versus number of iterations. [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: RDM comparisons. -40 -35 -30 -25 -20 -15 -10 SNR (dB) 10-1 100 101 102 103 Range RMSE (m) Standard-CP, SIC-DFT Standard-CP, SIC-ESPRIT Standard-CP, TDCC Standard-CP, FDCC Standard-CP, MTCC Standard-CP, DFT Standard-CP, ESPRIT Sufficient-CP, DFT Sufficient-CP, ESPRIT (a) Range estimation RMSE. -40 -35 -30 -25 -20 -15 -10 SNR (dB) 10-1 100 101 102 Velocity RMSE (m/s) Standard-CP, SIC-DFT Standard-CP, SIC-ESP… view at source ↗
Figure 7
Figure 7. Figure 7: RMSE for range and velocity estimation versus the [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
read the original 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 excess delay beyond the CP. To mitigate these effects, we propose two standard-compatible successive interference cancellation (SIC) methods: SIC-DFT, a low-complexity DFT-based scheme, and SIC-ESPRIT, a super-resolution subspace approach. Simulations corroborate the analysis and demonstrate consistent gains over representative benchmarks. Both algorithms provide more than $4$~dB SINR improvement under CP-insufficient conditions, while SIC-ESPRIT reduces range/velocity root-mean-square-errors (RMSE) by about one order of magnitude, approaching the performance achievable with a sufficiently long CP. These results offer both theoretical insight and practical solutions for reliable long-range OFDM-ISAC sensing beyond the CP limit.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 3 minor

Summary. The manuscript develops a general echo model for OFDM-ISAC systems when target echoes exceed the cyclic prefix duration, explicitly capturing the structured coupling between ISI and ICI. From this model the authors derive closed-form SINR expressions, range-Doppler map second-order moments, and an approximate PSLR, all shown to degrade approximately linearly with normalized excess delay. Two successive-interference-cancellation algorithms (SIC-DFT and SIC-ESPRIT) are then proposed; Monte-Carlo simulations are used to corroborate the analysis and to report >4 dB SINR gains together with roughly an order-of-magnitude reduction in range/velocity RMSE relative to representative benchmarks.

Significance. If the underlying echo model is representative, the work supplies both analytical insight into CP-limited OFDM sensing and two standard-compatible mitigation techniques that could meaningfully extend the usable sensing range of OFDM-ISAC systems. The provision of closed-form expressions and reproducible simulation results constitutes a concrete strength.

major comments (1)
  1. [Simulation Results] Simulation section: all numerical results (SINR gains, RMSE reductions, and PSLR values) are generated by feeding the identical analytical echo model into both the closed-form derivations and the Monte-Carlo trials. While this establishes internal consistency, the central claim that the algorithms “approach the performance achievable with a sufficiently long CP” under realistic conditions rests on an untested assumption that the structured ISI/ICI coupling accurately represents measured channels, phase noise, I/Q imbalance, and non-ideal clutter.
minor comments (3)
  1. [Section III] The transition from the general echo model to the closed-form SINR expression would benefit from an explicit statement of the statistical assumptions placed on the data symbols and noise.
  2. [Figures 4-7] Figure captions should indicate whether the plotted curves are exact closed-form results or Monte-Carlo averages, and whether error bars represent one or two standard deviations.
  3. [Section IV-C] The complexity analysis of SIC-ESPRIT should be compared quantitatively with the DFT-based method and with the benchmark algorithms already cited.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive assessment of the manuscript, the recognition of its significance, and the recommendation for minor revision. We address the major comment point by point below.

read point-by-point responses

  1. Referee: [Simulation Results] Simulation section: all numerical results (SINR gains, RMSE reductions, and PSLR values) are generated by feeding the identical analytical echo model into both the closed-form derivations and the Monte-Carlo trials. While this establishes internal consistency, the central claim that the algorithms “approach the performance achievable with a sufficiently long CP” under realistic conditions rests on an untested assumption that the structured ISI/ICI coupling accurately represents measured channels, phase noise, I/Q imbalance, and non-ideal clutter.

    Authors: We thank the referee for this observation. The Monte-Carlo trials are deliberately driven by the same analytical echo model used to derive the closed-form SINR, RDM second-order moments, and approximate PSLR. This is the standard and necessary approach to verify that the numerical results match the theoretical predictions under the exact conditions for which the expressions were obtained. The structured ISI/ICI coupling is not an arbitrary assumption but follows directly from the time-domain signal model when the echo delay exceeds the CP; the derivations and simulations therefore test the consequences of that coupling in a controlled and reproducible manner. We agree that the current results do not incorporate additional hardware impairments (phase noise, I/Q imbalance) or measured channel data. These effects are largely additive to the interference we analyze and can be superimposed on the model in future studies. To address the concern, we will add a concise paragraph in the simulation section that explicitly states the modeling assumptions, clarifies that the reported gains are with respect to the CP-induced interference, and identifies experimental validation with real-world impairments as an important direction for follow-on work. This addition will better frame the scope and applicability of the claims without altering the existing numerical results. revision: partial

Circularity Check

0 steps flagged

No significant circularity; derivations are self-contained from echo model

full rationale

The paper starts from a general echo model that explicitly structures ISI/ICI coupling for CP-insufficient delays, then derives closed-form SINR, RDM second-moment, and approximate PSLR expressions shown to degrade linearly with normalized excess delay. These steps constitute forward analytical derivation from stated model assumptions rather than any reduction to fitted inputs, self-definitions, or self-citation chains. The SIC-DFT and SIC-ESPRIT algorithms are introduced as mitigation methods and evaluated in simulations that apply the identical model; this is standard corroboration and does not render the analytical results circular by construction. No uniqueness theorems, ansatzes smuggled via citation, or renamings of known results are indicated as load-bearing in the abstract or description. The framework remains self-contained against its modeling premises.

Axiom & Free-Parameter Ledger

1 free parameters · 0 axioms · 0 invented entities

The central claims rest on an extended echo model for CP-insufficient cases and standard assumptions about additive noise and channel statistics; no new physical entities are introduced.

free parameters (1)
  • normalized excess delay
    Parameter that controls the linear deterioration of SINR and PSLR in the derived expressions.

pith-pipeline@v0.9.0 · 5585 in / 1359 out tokens · 99149 ms · 2026-05-17T07:06:55.908276+00:00 · methodology

discussion (0)

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