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arxiv: 2605.23564 · v2 · pith:F7UF5L6Inew · submitted 2026-05-22 · 📡 eess.SP

FMCW-Based Integrated Sensing and Communication System: Design, Implementation, and Experimental Measurements

Murat Temiz , Colin Horne , Matthew A. Ritchie , Christos Masouros This is my paper

Pith reviewed 2026-05-25 03:15 UTC · model grok-4.3

classification 📡 eess.SP
keywords integrated sensing and communicationFMCW radarphase modulationindex modulationvehicular networksradar signal processingDoppler effectswaveform design
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The pith

FMCW chirps jointly modulated by phase and index modulation transmit data while keeping radar sensing as the primary function in vehicular networks.

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

The paper proposes a radar-centric ISAC system that applies a two-layer modulation scheme to FMCW chirps. Phase modulation and index modulation are added to the chirps to carry communication data. A new radar signal processing method is introduced to limit the degradation this causes to sensing performance. The system is tested in simulation at 2.4 GHz and 24 GHz under Doppler conditions and verified with a hardware loopback experiment. The work shows how waveform parameters can be tuned to balance communication throughput against sensing accuracy and out-of-band emissions.

Core claim

FMCW chirps can be jointly modulated via phase modulation and index modulation to embed data while a dedicated radar signal processing technique restores sensing accuracy, enabling a radar-centric ISAC waveform that achieves measured throughputs of 25 Mbps at 2.4 GHz and 50 Mbps at 24 GHz under Doppler effects.

What carries the argument

Two-layer modulation scheme (phase modulation combined with index modulation on FMCW chirps) plus a novel radar signal processing technique that compensates for the modulation effects on range-Doppler maps.

If this is right

  • Communication throughput can be increased to 50 Mbps at 24 GHz while sensing remains the dominant function.
  • Waveform parameters can be adjusted on the fly to trade communication rate for lower out-of-band emissions or higher sensing precision.
  • The same hardware can support both sensing and data exchange in vehicular networks without separate communication radios.
  • Proof-of-concept hardware with loopback measurements confirms that the modulation and demodulation chain works in practice.

Where Pith is reading between the lines

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

  • The approach may extend to other frequency bands if the compensation technique scales with wavelength and bandwidth.
  • Dynamic parameter adjustment could allow the system to respond to changing traffic density or regulatory emission limits without redesign.
  • If the compensation holds in real multipath environments, the architecture could reduce the need for dedicated spectrum allocation for vehicular radar and V2X links.

Load-bearing premise

The new radar signal processing technique fully compensates for the sensing degradation caused by index and phase modulation even when Doppler shifts from moving vehicles are present.

What would settle it

A field test in which the range-Doppler estimation error after the proposed processing exceeds the error obtained from unmodified FMCW chirps under the same vehicular Doppler conditions.

Figures

Figures reproduced from arXiv: 2605.23564 by Christos Masouros, Colin Horne, Matthew A. Ritchie, Murat Temiz.

Figure 1
Figure 1. Figure 1: Radar-centric ISAC example: FMCW radar sig [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: IM-PM-FMCW ISAC frame structure. The communication receiver can efficiently demodu￾late the IM and PM data, while the proposed radar receiver utilizes a novel correction method to mitigate the range and velocity artifacts caused by IM and PM within FMCW chirps. These architectures are fully compatible with current RF and digital front-ends. • It also extensively evaluates sensing performance, out￾of-band e… view at source ↗
Figure 3
Figure 3. Figure 3: Joint ISAC transmitter and radar receiver architecture for IM-PM-FMCW waveform. [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: The proposed dual-polarized communication receiver architecture to receive and demodulate the signals [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Signal processing for the demodulation of IM. [PITH_FULL_IMAGE:figures/full_fig_p007_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Experimental measurements and real-time signal processing, where UCL’s ARESTOR is used as ISAC [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: Communication signal processing and demodulation for each polarization in the receiver. [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
Figure 10
Figure 10. Figure 10: Throughput achieved via IM and PM using B1 = {40, 55} MHz at Fc = 2.4 GHz and B2 = {150, 250} MHz at Fc = 24 GHz bands, Tc = 10µs, M = 4. SNR [dB] 0 10 20 30 40 Throughput [Mbits/s] 0 10 20 30 40 50 60 B1 T c =5µs L=10 B1 T c =10µs L=20 B1 T c =20µs L=40 B1 T c =50µs L=100 B2 T c =5µs L=20 B2 T c =10µs L=40 B2 T c =20µs L=80 B2 T c =50µs L=200 [PITH_FULL_IMAGE:figures/full_fig_p011_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: Throughput achieved using B1 = {40, 55} MHz at Fc = 2.4 GHz and B2 = {150, 250} MHz at Fc = 24 GHz bands, M = 64. hardware implementation is conducted exclusively in the 2.4 GHz band due to ARESTOR limitations and in accor￾dance with UK ISM regulations [43]. Furthermore, I = 50 FMCW chirps are transmitted in each communication frame. Note that the proposed method does not vary the carrier frequency; inste… view at source ↗
Figure 12
Figure 12. Figure 12: Normalized power spectrum density of IM-PM [PITH_FULL_IMAGE:figures/full_fig_p012_12.png] view at source ↗
Figure 15
Figure 15. Figure 15: The trade-off between the ISL and data rate in [PITH_FULL_IMAGE:figures/full_fig_p012_15.png] view at source ↗
Figure 16
Figure 16. Figure 16: Range-velocity images of targets obtained using [PITH_FULL_IMAGE:figures/full_fig_p013_16.png] view at source ↗
Figure 18
Figure 18. Figure 18: depicts the throughput of the IM-PM-FMCW ISAC with [Tc = 10µs and L = 10] and [Tc = 100µs and L = 100], obtained from measurements. The highest throughput is achieved when Tc = 10µs, where the IM can also significantly contribute to the final throughput since the chirp duration is short, resulting in a higher chirp repetition frequency. The throughput achieved only with PM is the same in all of these case… view at source ↗
Figure 19
Figure 19. Figure 19: Range profile of a single target with IM-PM [PITH_FULL_IMAGE:figures/full_fig_p014_19.png] view at source ↗
Figure 20
Figure 20. Figure 20: Range profile of a single target with IM-PM [PITH_FULL_IMAGE:figures/full_fig_p015_20.png] view at source ↗
read the original abstract

This study proposes a radar-centric integrated sensing and communication (ISAC) system utilizing a two-layer modulation scheme for vehicular networks. Frequency-modulated continuous wave (FMCW) chirps are jointly modulated via phase modulation (PM) and index modulation (IM) to transmit data while maintaining sensing as the primary function. To support this, a novel radar signal processing technique is developed to mitigate the impacts of IM and PM on sensing accuracy, alongside a communication receiver architecture designed to successfully demodulate IM and PM data within FMCW chirps. System performance is evaluated through simulations in the 2.4 GHz and 24 GHz bands under Doppler effects, achieving communication throughputs of 25 Mbps and 50 Mbps, respectively. Furthermore, a proof-of-concept hardware implementation is realized, and experimental measurements via a loopback cable are performed to verify the feasibility of the architecture. Finally, it evaluates the fundamental trade-off between communication throughput, sensing accuracy, and out-of-band emission, demonstrating the system's flexibility to dynamically adjust waveform parameters to meet varying operational requirements.

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 / 2 minor

Summary. The manuscript proposes a radar-centric ISAC system for vehicular networks in which FMCW chirps are jointly modulated by phase modulation (PM) and index modulation (IM) to carry communication data while treating sensing as the primary function. A novel radar signal processing technique is introduced to mitigate the effects of PM and IM on range/Doppler estimation accuracy. System performance is evaluated via simulations at 2.4 GHz and 24 GHz under Doppler, reporting throughputs of 25 Mbps and 50 Mbps respectively, together with a proof-of-concept hardware implementation using loopback-cable measurements and an analysis of the throughput-sensing-OBE trade-off.

Significance. If the mitigation technique proves robust, the design offers a practical route to radar-centric ISAC waveforms that can dynamically trade communication rate against sensing fidelity. The simulations under Doppler and the explicit parameter-adjustment mechanism constitute concrete, falsifiable contributions; the loopback hardware results confirm basic waveform generation and demodulation feasibility.

major comments (1)
  1. [Experimental Measurements / Abstract] Abstract and Experimental Measurements section: the hardware validation consists solely of a static loopback-cable setup with no relative motion. Consequently the reported measurements exercise only the communication demodulator and waveform generation; they provide no empirical test of the novel radar processing block under Doppler, which is the load-bearing claim for restoring sensing accuracy in the vehicular regime asserted in the abstract and simulations.
minor comments (2)
  1. The description of the radar processing algorithm would benefit from an explicit block diagram or pseudocode showing how the IM/PM compensation is inserted into the standard FMCW range-Doppler pipeline.
  2. Clarify whether the reported throughputs assume perfect synchronization or include the overhead of the proposed demodulator.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive feedback. We address the major comment below and will revise the manuscript accordingly to ensure the claims accurately reflect the presented results.

read point-by-point responses

  1. Referee: Abstract and Experimental Measurements section: the hardware validation consists solely of a static loopback-cable setup with no relative motion. Consequently the reported measurements exercise only the communication demodulator and waveform generation; they provide no empirical test of the novel radar processing block under Doppler, which is the load-bearing claim for restoring sensing accuracy in the vehicular regime asserted in the abstract and simulations.

    Authors: We agree that the hardware implementation is a static loopback-cable setup without relative motion and therefore validates only the waveform generation and communication demodulation aspects. The novel radar signal processing for mitigating PM/IM effects under Doppler, along with the associated sensing accuracy results, is evaluated exclusively through simulations at 2.4 GHz and 24 GHz. The abstract and Experimental Measurements section describe the hardware as a proof-of-concept to verify architecture feasibility, without claiming empirical Doppler testing. To prevent any potential overstatement, we will revise the abstract and the relevant section to explicitly clarify the scope of the hardware measurements versus the simulation-based evaluation of the mitigation technique under Doppler. revision: yes

Circularity Check

0 steps flagged

No circularity; results from direct simulation and measurement

full rationale

The paper proposes a two-layer modulation on FMCW chirps plus a novel radar processing block, then reports throughput and accuracy numbers obtained from explicit simulations (2.4/24 GHz, Doppler) and loopback-cable hardware tests. No equations are shown that define a quantity in terms of itself, no fitted parameters are relabeled as predictions, and no load-bearing premise rests on a self-citation chain. The central claims therefore remain independent of the reported outputs and do not reduce to their inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review; no explicit free parameters, axioms, or invented entities are identifiable beyond standard assumptions in ISAC waveform design.

pith-pipeline@v0.9.0 · 5722 in / 1058 out tokens · 45176 ms · 2026-05-25T03:15:19.653676+00:00 · methodology

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