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arxiv: 2605.23429 · v3 · pith:4AF57HZ3new · submitted 2026-05-22 · 📡 eess.SP · cs.CR

Communication Security and Sensing Privacy in FMCW-Based ISAC Through Signal Modulation

Murat Temiz , Christos Masouros This is my paper

Pith reviewed 2026-05-25 03:55 UTC · model grok-4.3

classification 📡 eess.SP cs.CR
keywords ISACphysical layer securitysensing privacyindex modulationphase codingFMCWambiguity functionradar-centric signaling
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The pith

Index modulation and phase coding over FMCW chirps secure data transmission while making velocity estimation infeasible for passive sensing eavesdroppers.

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

The paper establishes a radar-centric signaling approach for integrated sensing and communication that layers index modulation for data security and phase coding to protect sensing information. The design perturbs the ambiguity function of the chirps so that an unauthorized passive receiver cannot reliably determine target velocity and suffers impaired range estimation. Legitimate users retain full sensing and communication capability through dedicated transmitter and receiver architectures. Simulations indicate that the scheme supports high data throughput under these security constraints.

Core claim

The proposed framework employs index modulation and phase coding over FMCW chirps to provide robust physical layer security for data transmission while simultaneously enhancing sensing privacy by rendering target velocity estimation practically infeasible for unauthorized passive sensing hardware and significantly impairing its range estimation capabilities.

What carries the argument

Index modulation combined with explicitly designed phase coding applied to FMCW chirps, which perturbs the resulting ambiguity function.

If this is right

  • High data throughput remains achievable alongside the added security layers.
  • Legitimate receiver architectures support both communication demodulation and sensing operations without degradation.
  • Unauthorized passive hardware cannot perform reliable velocity estimation.
  • Range estimation accuracy at the eavesdropper is substantially reduced.
  • The transmitter architecture enables the combined index modulation and phase coding on each chirp.

Where Pith is reading between the lines

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

  • The same waveform perturbation principle could be tested on other continuous-wave radar waveforms beyond FMCW.
  • Systems deploying this design may need new regulatory guidelines for spectrum sharing that account for built-in sensing privacy.
  • Combining the physical-layer approach with conventional encryption could create layered security without additional spectrum overhead.
  • Hardware implementations would need to verify that the phase coding does not introduce unexpected peak-to-average power ratio increases.

Load-bearing premise

The phase coding can be designed to perturb the ambiguity function enough to impair an eavesdropper's velocity and range estimation while leaving the legitimate receiver's sensing and communication performance intact, assuming the eavesdropper is restricted to passive sensing hardware.

What would settle it

An experiment in which a passive sensing eavesdropper accurately recovers target velocity from the modulated FMCW signal despite the phase coding would falsify the central claim.

Figures

Figures reproduced from arXiv: 2605.23429 by Christos Masouros, Murat Temiz.

Figure 1
Figure 1. Figure 1: A typical ISAC scenario, where the ISAC transceiver transmits ISAC signals to communicate with the CU and perform sensing using the same signals. Meanwhile, the S-Eve aims to exploit the ISAC signals for unauthorized sensing, and the C-Eve attempts to eavesdrop on the communication. obtained through passive sensing, which may include target classification and recognition [18]. Various methods have been rec… view at source ↗
Figure 2
Figure 2. Figure 2: The proposed ISAC transceiver that transmits ISAC signals for communications and sensing, and receives and [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Transmission of Sec-FMCW signaling, including pilot chirps for channel estimation (CE). [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Illustration of IM-PC-FMCW chirps in the fre [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: depicts the AFs of the optimized Sec-FMCW signal for sensing privacy in comparison with the FMCW and IM-PC-FMCW signals. As seen in this figure, the Sec￾FMCW has sidelobes in the desired locations of the AF, which are much higher than the sidelobes of the random phase-coded IM-PC-FMCW chirp. In addition to the data transmitted via phase codes, the proposed Sec-FMCW signaling utilizes index modulation, whic… view at source ↗
Figure 6
Figure 6. Figure 6: The proposed communication receiver architecture to receive the communication data. [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Maximum throughput that can be achieved by CU [PITH_FULL_IMAGE:figures/full_fig_p011_7.png] view at source ↗
Figure 10
Figure 10. Figure 10: Uncompensated matched-filter range profiles ob [PITH_FULL_IMAGE:figures/full_fig_p011_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: The PSL and ISL versus throughput in relation [PITH_FULL_IMAGE:figures/full_fig_p012_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: Range-velocity maps obtained by ISAC sensing receiver and S-Eve, SNR = 20 dB. [PITH_FULL_IMAGE:figures/full_fig_p013_12.png] view at source ↗
Figure 13
Figure 13. Figure 13: Mean range and velocity errors of the target [PITH_FULL_IMAGE:figures/full_fig_p014_13.png] view at source ↗
read the original abstract

This study proposes a novel radar-centric signaling design and architecture for secure integrated sensing and communication (ISAC) systems. The proposed framework is designed to provide robust physical layer security for data transmission while simultaneously enhancing sensing privacy. It employs index modulation and phase coding over frequency-modulated continuous-wave radar (FMCW) chirps, where index modulation (IM) provides an outer layer of data security, and we explicitly design the phase coding (PC) to perturb the resulting signal's ambiguity function (AF) to enhance sensing privacy. This design reduces the risk of unauthorized surveillance by rendering target velocity estimation practically infeasible for unauthorized passive sensing hardware (i.e., a sensing eavesdropper, S-Eve) and significantly impairing its range estimation capabilities. Furthermore, this study also presents the transmitter and receiver architectures required for effective modulation and demodulation of the proposed ISAC signaling and for performing sensing at the legitimate sensing hardware. Simulation results show that the proposed approach achieves high data throughput while enhancing communication security and sensing privacy.

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

2 major / 2 minor

Summary. The paper proposes a radar-centric ISAC signaling scheme that combines index modulation (IM) with explicitly designed phase coding (PC) applied to FMCW chirps. IM is intended to add an outer layer of communication security, while PC is designed to perturb the transmitted waveform's ambiguity function (AF) so that a passive sensing eavesdropper (S-Eve) cannot reliably estimate target velocity and suffers degraded range estimation. The manuscript presents transmitter and receiver architectures for modulation/demodulation and legitimate sensing, and reports simulation results indicating high data throughput together with the claimed security and privacy gains.

Significance. If the selective-impairment claim can be rigorously established, the work would offer a concrete waveform-level mechanism for simultaneously protecting communication confidentiality and sensing privacy in FMCW-based ISAC, an area of growing practical interest. The explicit presentation of end-to-end transmitter/receiver architectures and the use of standard FMCW waveforms are positive features that could facilitate reproducibility and extension.

major comments (2)
  1. [Abstract / receiver architectures] Abstract and receiver-architecture section: the AF is a property of the transmitted waveform alone. The manuscript must therefore demonstrate, with explicit matched-filter or correlator derivations and quantitative AF plots or metrics, that the legitimate receiver (using knowledge of the PC) fully restores a clean AF while an S-Eve without that knowledge cannot. No such compensation analysis or residual-degradation bounds appear to be provided; without them the selective-privacy claim rests on an unverified assumption.
  2. [Simulation results] Simulation-results section: performance claims for both communication security and sensing privacy are reported, yet the text supplies neither the exact simulation parameters (chirp bandwidth, duration, SNR ranges, number of Monte-Carlo trials) nor error bars or statistical significance tests. This prevents independent verification of the reported throughput and privacy gains.
minor comments (2)
  1. [Transmitter architecture] Notation for the phase code and index-modulation mapping should be introduced with a single consistent table or equation block rather than scattered across the architecture diagrams.
  2. [Abstract] The abstract states that velocity estimation is rendered 'practically infeasible'; the manuscript should replace this qualitative statement with a concrete metric (e.g., CRLB degradation factor or probability of correct velocity estimate) in the privacy-analysis subsection.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments, which help clarify the presentation of our results. We address each major comment below.

read point-by-point responses

  1. Referee: [Abstract / receiver architectures] Abstract and receiver-architecture section: the AF is a property of the transmitted waveform alone. The manuscript must therefore demonstrate, with explicit matched-filter or correlator derivations and quantitative AF plots or metrics, that the legitimate receiver (using knowledge of the PC) fully restores a clean AF while an S-Eve without that knowledge cannot. No such compensation analysis or residual-degradation bounds appear to be provided; without them the selective-privacy claim rests on an unverified assumption.

    Authors: We agree that the ambiguity function is determined by the transmitted waveform. The legitimate receiver applies a compensation step using its knowledge of the phase coding within the matched-filter/correlator processing. In the revised manuscript we will add the explicit matched-filter derivations for both the compensated (legitimate) and uncompensated (S-Eve) cases, together with quantitative AF plots and residual-degradation metrics that demonstrate restoration of the clean AF at the legitimate receiver. revision: yes

  2. Referee: [Simulation results] Simulation-results section: performance claims for both communication security and sensing privacy are reported, yet the text supplies neither the exact simulation parameters (chirp bandwidth, duration, SNR ranges, number of Monte-Carlo trials) nor error bars or statistical significance tests. This prevents independent verification of the reported throughput and privacy gains.

    Authors: We acknowledge the omission. The revised manuscript will list all exact simulation parameters (chirp bandwidth, duration, SNR ranges, number of Monte-Carlo trials) and will include error bars on all performance curves together with any applicable statistical significance information. revision: yes

Circularity Check

0 steps flagged

No circularity; design proposal with no self-referential reductions

full rationale

The provided abstract and description outline a proposed ISAC signaling architecture using index modulation and explicitly designed phase coding on FMCW chirps to achieve security and privacy goals. No equations, fitted parameters, or derivations are shown that reduce by construction to the inputs (e.g., no self-definitional AF perturbation that is both the input and the claimed output, no fitted quantities renamed as predictions). No self-citations are invoked as load-bearing for uniqueness theorems or ansatzes. The central content is a design proposal plus simulation results, which remain independent of the enumerated circular patterns and do not require the result to be presupposed in the inputs.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract only; no free parameters, axioms, or invented entities are specified in the available text.

pith-pipeline@v0.9.0 · 5705 in / 1099 out tokens · 18428 ms · 2026-05-25T03:55:35.410045+00:00 · methodology

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