ISAC with Affine Frequency Division Multiplexing: An FMCW-Based Signal Processing Perspective
Pith reviewed 2026-05-17 22:07 UTC · model grok-4.3
The pith
A specific parameter selection makes AFDM subcarriers mathematically equivalent to Nyquist-sampled FMCW waveforms.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The central claim is that an innovative parameter selection criterion establishes a precise mathematical equivalence between AFDM subcarriers and Nyquist-sampled FMCW. This connection supplies a clear physical insight into AFDM's sensing mechanism and enables a direct mapping from the DAFT index to delay-Doppler parameters of wireless channels. Building on the equivalence, the paper develops a novel input-output model in a DD-parameterized DAFT domain that explicitly reveals the inherent DD coupling effect arising from chirp-channel interaction, then designs two matched-filtering sensing algorithms whose performance is validated through simulation.
What carries the argument
The parameter selection criterion that produces exact equivalence between AFDM subcarriers and Nyquist-sampled FMCW, which in turn supports the DD-DAFT domain model and the direct DAFT-to-DD mapping.
If this is right
- Pilot-free sensing becomes feasible by treating AFDM as an FMCW-like waveform.
- The DD-DAFT domain model isolates the coupling effect so that the second algorithm can resolve it exactly.
- Sensing performance, communication overhead, and computational complexity trade off against one another in a quantifiable way.
- The proposed AFDM variant outperforms classical AFDM and other waveform variants in most simulated scenarios.
Where Pith is reading between the lines
- The equivalence may allow reuse of existing FMCW radar processing pipelines inside AFDM transceivers.
- Accounting for the DD coupling appears necessary for high-resolution sensing; ignoring it would limit the first algorithm's accuracy.
- The mapping from DAFT index to delay-Doppler parameters could simplify joint waveform design in other multicarrier ISAC systems.
Load-bearing premise
The wireless channel must exhibit the exact delay-Doppler coupling that arises from chirp-channel interaction and the high-mobility regime must allow the DAFT-domain representation to hold without unmodeled distortions.
What would settle it
A numerical or experimental test in which the chosen parameters are applied to an AFDM waveform and the resulting range-Doppler map deviates measurably from the map produced by a reference Nyquist-sampled FMCW waveform under the same channel conditions.
Figures
read the original abstract
This paper investigates the sensing potential of affine frequency division multiplexing (AFDM) in high-mobility integrated sensing and communication (ISAC) from the perspective of radar waveforms. We introduce an innovative parameter selection criterion that establishes a precise mathematical equivalence between AFDM subcarriers and Nyquist-sampled frequency-modulated continuous-wave (FMCW). This connection not only provides a clear physical insight into AFDM's sensing mechanism but also enables a direct mapping from the DAFT index to delay-Doppler (DD) parameters of wireless channels. Building on this, we develop a novel input-output model in a DD-parameterized DAFT (DD-DAFT) domain for AFDM, which explicitly reveals the inherent DD coupling effect arising from the chirp-channel interaction. Subsequently, we design two matched-filtering sensing algorithms. The first is performed in the time-frequency domain with low complexity, while the second is operated in the DD-DAFT domain to precisely resolve the DD coupling. Simulations show that our algorithms achieve effective pilot-free sensing and demonstrate a fundamental trade-off between sensing performance, communication overhead, and computational complexity. The proposed AFDM outperforms classical AFDM and other variants in most scenarios.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript claims that a novel parameter selection criterion establishes a precise mathematical equivalence between AFDM subcarriers and Nyquist-sampled FMCW waveforms. This equivalence yields a DD-parameterized DAFT (DD-DAFT) input-output model that explicitly captures the DD coupling effect from chirp-channel interaction, enabling two matched-filtering sensing algorithms (one low-complexity in the time-frequency domain and one in the DD-DAFT domain) for pilot-free ISAC in high-mobility settings. Simulations are reported to demonstrate effective sensing performance, fundamental trade-offs with communication overhead and complexity, and outperformance relative to classical AFDM and other variants.
Significance. If the equivalence and resulting model hold under the stated conditions, the work supplies a concrete signal-processing bridge between AFDM and established FMCW radar techniques, furnishing both physical insight into AFDM sensing and directly mappable DD parameters. The proposed algorithms and observed trade-offs could inform practical ISAC waveform design for high-mobility channels, particularly if the derivations prove reproducible and the simulations are fully specified.
major comments (3)
- [Section 3] Parameter selection criterion (Section 3): The central claim of 'precise mathematical equivalence' between AFDM subcarriers and Nyquist-sampled FMCW is load-bearing for both the physical insight and the direct DAFT-to-DD mapping. The derivation must explicitly demonstrate that the chosen parameters eliminate residual phase/amplitude terms, aliasing, or other distortions arising from finite-length effects and high-mobility chirp-channel interaction beyond the modeled DD coupling; otherwise the equivalence is conditional rather than general.
- [Section 4] DD-DAFT input-output model (Section 4): The assertion that the model 'explicitly reveals the inherent DD coupling effect' requires the explicit equation (or set of equations) showing how the coupling term emerges from the chirp-channel interaction and matches the FMCW-derived form exactly. If any approximation or unmodeled term remains, both the novelty of the model and the justification for the DD-DAFT-domain matched filter are weakened.
- [Section 6] Simulation results (Section 6): The reported performance advantages, trade-offs, and outperformance claims rest on simulations whose channel generation procedure, exact metric definitions (e.g., sensing MSE or detection probability), and handling of realistic impairments are not fully specified. This prevents independent verification that the equivalence survives the impairments highlighted in the stress-test note and therefore undermines the empirical support for the algorithms.
minor comments (2)
- [Abstract] Abstract: The statement that 'simulations show' effective sensing would benefit from one or two quantitative highlights (e.g., achieved range or velocity resolution) to give readers an immediate sense of the gains.
- Notation: Ensure consistent distinction between the standard DAFT domain and the proposed DD-DAFT domain throughout; occasional slippage between the two terms can confuse readers unfamiliar with the new model.
Simulated Author's Rebuttal
We thank the referee for the thorough and constructive review. The comments highlight important points on explicitness of derivations and reproducibility of simulations. We will revise the manuscript accordingly to strengthen these aspects while preserving the core contributions. Point-by-point responses follow.
read point-by-point responses
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Referee: [Section 3] Parameter selection criterion (Section 3): The central claim of 'precise mathematical equivalence' between AFDM subcarriers and Nyquist-sampled FMCW is load-bearing for both the physical insight and the direct DAFT-to-DD mapping. The derivation must explicitly demonstrate that the chosen parameters eliminate residual phase/amplitude terms, aliasing, or other distortions arising from finite-length effects and high-mobility chirp-channel interaction beyond the modeled DD coupling; otherwise the equivalence is conditional rather than general.
Authors: We agree that explicit verification of the equivalence is essential. In the revised manuscript, Section 3 will be expanded with a complete derivation that substitutes the selected parameters (chirp rate matching the FMCW sweep and subcarrier spacing aligned to Nyquist sampling) into the AFDM waveform expression. This will show term-by-term cancellation of residual phase and amplitude factors, as well as the absence of aliasing under the finite-length and high-mobility conditions considered. The equivalence is thereby established precisely within the stated modeling assumptions rather than conditionally. revision: yes
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Referee: [Section 4] DD-DAFT input-output model (Section 4): The assertion that the model 'explicitly reveals the inherent DD coupling effect' requires the explicit equation (or set of equations) showing how the coupling term emerges from the chirp-channel interaction and matches the FMCW-derived form exactly. If any approximation or unmodeled term remains, both the novelty of the model and the justification for the DD-DAFT-domain matched filter are weakened.
Authors: The DD-DAFT model is obtained by applying the parameter equivalence to the received AFDM signal and re-expressing the result in the DD-parameterized DAFT domain. In the revision, we will insert the intermediate steps that isolate the coupling term arising from the product of the linear chirp phase and the time-varying channel response. The resulting expression will be shown to match the FMCW-derived DD coupling form exactly, with no residual approximations beyond the standard narrowband and finite-duration assumptions already stated in the paper. This will directly support the subsequent matched-filter designs. revision: yes
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Referee: [Section 6] Simulation results (Section 6): The reported performance advantages, trade-offs, and outperformance claims rest on simulations whose channel generation procedure, exact metric definitions (e.g., sensing MSE or detection probability), and handling of realistic impairments are not fully specified. This prevents independent verification that the equivalence survives the impairments highlighted in the stress-test note and therefore undermines the empirical support for the algorithms.
Authors: We acknowledge the need for full reproducibility. The revised Section 6 will specify the exact DD channel generation procedure (including delay and Doppler spreads, number of paths, and Jakes' spectrum implementation), provide closed-form definitions for all reported metrics (sensing MSE, detection probability, and communication BER), and detail the incorporation of realistic impairments such as additive noise, phase noise, and residual synchronization errors. These additions will enable independent verification of the claimed performance and trade-offs. revision: yes
Circularity Check
Parameter selection criterion for AFDM-FMCW equivalence is a constructive design choice, not a circular reduction.
full rationale
The paper's central step introduces a parameter selection criterion to achieve exact mathematical equivalence between AFDM subcarriers and Nyquist-sampled FMCW, enabling the DD-DAFT domain model and DD coupling revelation. This is presented as an innovative criterion rather than a fitted prediction or self-definition; the equivalence holds under the stated assumptions on channel DD coupling and high-mobility regime. No load-bearing self-citation, uniqueness theorem from prior work, or renaming of known results is used for the core claims. The matched-filtering algorithms and simulations follow directly from the constructed model without reducing to the inputs by construction. The derivation chain remains self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math The discrete affine Fourier transform (DAFT) provides an orthonormal basis for representing chirp-modulated signals in high-mobility channels.
- domain assumption Wireless channels in high-mobility scenarios exhibit delay-Doppler coupling that interacts with the chirp structure of AFDM.
Lean theorems connected to this paper
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IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
precise mathematical equivalence between AFDM subcarriers and Nyquist-sampled frequency-modulated continuous-wave (FMCW)... DD coupling effect arising from the chirp-channel interaction
-
IndisputableMonolith/Foundation/DimensionForcing.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
K=8 chirp periods... period Np... floor(k/K) coupling term
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
Works this paper leans on
-
[1]
Integrated Sensing and Communications: Toward Dual- Functional Wireless Networks for 6G and Beyond,
F. Liu et al., “Integrated Sensing and Communications: Toward Dual- Functional Wireless Networks for 6G and Beyond,”IEEE J. Sel. Areas Commun., vol. 40, no. 6, pp. 1728-1767, Jun. 2022
work page 2022
-
[2]
“Future Technology Trends of Terrestrial International Mobile Telecom- munications Systems Towards 2030 and Beyond,” ITU Rec. M.2516-0, Int. Telecommun. Union, Geneva, Switzerland, Nov. 2022
work page 2030
-
[3]
An Overview of Signal Processing Techniques for Joint Communication and Radar Sensing,
J. A. Zhang et al., “An Overview of Signal Processing Techniques for Joint Communication and Radar Sensing,”IEEE J. Sel. Top. Signal Process., vol. 15, no. 6, pp. 1295-1315, Nov. 2021
work page 2021
-
[4]
Reshaping the ISAC Tradeoff Under OFDM Signaling: A Probabilistic Constellation Shaping Approach,
Z. Du et al.,, “Reshaping the ISAC Tradeoff Under OFDM Signaling: A Probabilistic Constellation Shaping Approach,”IEEE Trans. Signal Process., vol. 72, pp. 4782-4797, 2024
work page 2024
-
[5]
CP-OFDM Achieves the Lowest Average Ranging Sidelobe Under QAM/PSK Constellations,
F. Liu et al., “CP-OFDM Achieves the Lowest Average Ranging Sidelobe Under QAM/PSK Constellations,”IEEE Trans. Inf. Theory, vol. 71, no. 9, pp. 6950-6967, Sept. 2025
work page 2025
-
[6]
A. A. Boudjelal, R. Y . Bir and H. Arslan, ”Toward a Common Transceiver Framework for 6G: Orthogonal Coexistence and Structural Unification of DFT Waveforms,”IEEE Trans. Wireless Commun., early access, 2025
work page 2025
-
[7]
Affine Frequency Division Multiplexing for Next Generation Wireless Communications,
A. Bemani, N. Ksairi, and M. Kountouris, “Affine Frequency Division Multiplexing for Next Generation Wireless Communications,”IEEE Trans. Wireless Commun., vol. 22, no. 11, pp. 8214-8229, Nov. 2023
work page 2023
-
[8]
Pilot-Symbol-Aided Channel Estimation for OFDM in Wireless Systems,
Y . Li, “Pilot-Symbol-Aided Channel Estimation for OFDM in Wireless Systems,”IEEE Trans. V eh. Technol., vol. 49, no. 4, pp. 1207-1215, Jul. 2000
work page 2000
-
[9]
C. Sturm and W. Wiesbeck, “Waveform Design and Signal Processing Aspects for Fusion of Wireless Communications and Radar Sensing,” Proc. of the IEEE, vol. 99, no. 7, pp. 1236-1259, Jul. 2011
work page 2011
-
[10]
Enabling Joint Communication and Radar Sensing in Mobile Networks—A Survey,
J. A. Zhang et al., “Enabling Joint Communication and Radar Sensing in Mobile Networks—A Survey,”IEEE Commun. Surveys Tuts., vol. 24, no. 1, pp. 306-345, 2022
work page 2022
-
[11]
Orthogonal Time Frequency Space Modulation,
R. Hadani et al., “Orthogonal Time Frequency Space Modulation,” in Proc. IEEE Wireless Commun. Netw. Conf. (WCNC), Mar. 2017, pp. 1-6
work page 2017
-
[12]
Affine Frequency Division Multiplexing: Extending OFDM for Scenario-Flexibility and Resilience,
H. Yin et al., “Affine Frequency Division Multiplexing: Extending OFDM for Scenario-Flexibility and Resilience,”IEEE Wirel. Commun., early access, 2025
work page 2025
-
[13]
H. Yin, X. Wei, Y . Tang, and K. Yang, “Diagonally Reconstructed Channel Estimation for MIMO-AFDM with Inter-Doppler Interference in Doubly Selective Channels,”IEEE Trans. Wireless Commun., vol. 23, no. 10, pp. 14066-14079, Oct. 2024
work page 2024
-
[14]
Dual-Use of OTFS Architecture for Pulse Doppler Radar Processing,
A. S. Bondre and C. D. Richmond, “Dual-Use of OTFS Architecture for Pulse Doppler Radar Processing,” inProc. IEEE Radar Conf. (RadarConf), Mar. 2022, pp. 1-6
work page 2022
-
[15]
A Novel OTFS-Chirp Waveform for Low-Complexity Multi-User Joint Sensing and Commu- nication,
S. E. Zegrar, A. A. Boudjelal, and H. Arslan, “A Novel OTFS-Chirp Waveform for Low-Complexity Multi-User Joint Sensing and Commu- nication,”IEEE Internet Things J., vol. 12, no. 8, pp. 10114-10126, Apr. 2025
work page 2025
-
[16]
Zak-OTFS for Integration of Sensing and Commu- nication,
M. Ubadah, S. K. Mohammed, R. Hadani, S. Kons, A. Chockalingam, and R. Calderbank, “Zak-OTFS for Integration of Sensing and Commu- nication,” arXiv: 2404.04182, 2024
-
[17]
H. Yin, et al., “From OFDM to AFDM: Enabling Adaptive In- tegrated Sensing and Communication in High-Mobility Scenarios,” arXiv:2510.27192, 2025
-
[18]
An Integrated Sensing and Communications System Based on Affine Frequency Division Multiplexing,
Y . Ni, P. Yuan, Q. Huang, F. Liu, and Z. Wang, “An Integrated Sensing and Communications System Based on Affine Frequency Division Multiplexing,”IEEE Trans. Wireless Commun., vol. 24, no. 5, pp. 3763- 3779, May 2025
work page 2025
-
[19]
Ambiguity Function Analysis of AFDM Signals for Integrated Sensing and Communications,
H. Yin et al., “Ambiguity Function Analysis of AFDM Signals for Integrated Sensing and Communications,”IEEE J. Sel. Areas Commun., early access, 2025
work page 2025
-
[20]
Ambiguity Function Analyses of AFDM Under Random ISAC Signaling,
Y . Ni et al., “Ambiguity Function Analyses of AFDM Under Random ISAC Signaling,” inProc. IEEE Int. Conf. Commun. Workshops (ICC Workshops), 2025
work page 2025
-
[21]
AFDM-Enabled Integrated Sensing and Communi- cation: Theoretical Framework and Pilot Design,
F. Zhang et al., “AFDM-Enabled Integrated Sensing and Communi- cation: Theoretical Framework and Pilot Design,”IEEE J. Sel. Areas Commun., early access, 2025
work page 2025
-
[22]
Blind Bistatic Radar Parameter Estimation for AFDM Systems in Doubly-Dispersive Channels,
K. R. R. Ranasinghe, K. Ando, H. S. Rou, G. T. F. de Abreu, and A. Bathelt, “Blind Bistatic Radar Parameter Estimation for AFDM Systems in Doubly-Dispersive Channels,” arXiv: 2407.05328, 2024
-
[23]
Z. Sui et al., “Multi-Functional Chirp Signalling for Next-Generation Multi-Carrier Wireless Networks: Communications, Sensing and ISAC Perspectives,” arXiv:2508.06022, 2025
-
[24]
Lu et al., ”DAFT-Domain Interference Cancellation Scheme for Full-Duplex AFDM ISAC System,” inProc
X. Lu et al., ”DAFT-Domain Interference Cancellation Scheme for Full-Duplex AFDM ISAC System,” inProc. IEEE Int. Conf. Commun. Workshops (ICC Workshops), Jun. 2025, pp. 1067-1072
work page 2025
-
[25]
AFDM-Based Bistatic Integrated Sensing and Communi- cation in Static Scatterer Environments,
J. Zhu et al., “AFDM-Based Bistatic Integrated Sensing and Communi- cation in Static Scatterer Environments,”IEEE Wireless Commun. Lett., vol. 13, no. 8, pp. 2245-2249, Aug. 2024
work page 2024
-
[26]
Performance Trade- off between Communication and Sensing Based on AFDM Parameter Adjustment,
H. Bao, H. Zhuang, Z. Wang, and G. Pang, “Performance Trade- off between Communication and Sensing Based on AFDM Parameter Adjustment,” inProc. IEEE Int. Symp. Pers., Indoor , Mobile Radio Commun. (PIMRC), Sept. 2024, pp. 1-6
work page 2024
-
[27]
E. Bedeer, “Ambiguity Function Analysis of Affine Frequency Divi- sion Multiplexing for Integrated Sensing and Communication,” arXiv: 2504.02582, 2025
-
[28]
Radar Sensing via OTFS Signaling: A Delay Doppler Signal Processing Perspective,
K. Zhang et al., “Radar Sensing via OTFS Signaling: A Delay Doppler Signal Processing Perspective,” inProc. IEEE Int. Conf. Commun. (ICC), 2023, pp. 6429-6434
work page 2023
-
[29]
On the Fundamental Tradeoff of Integrated Sensing and Communications Under Gaussian Channels,
Y . Xiong et al., “On the Fundamental Tradeoff of Integrated Sensing and Communications Under Gaussian Channels,”IEEE Trans. Inf. Theory, vol. 69, no. 9, pp. 5723-5751, Sept. 2023
work page 2023
-
[30]
A Novel Pilot Allocation Technique for Uplink OFDMA in ISAC Systems,
A. S. S ¨umer, E. Memis ¸o˘glu, and H. Arslan, “A Novel Pilot Allocation Technique for Uplink OFDMA in ISAC Systems,”IEEE Wireless Commun. Lett., vol. 14, no. 8, pp. 2561-2565, Aug. 2025
work page 2025
-
[31]
Y . Zhou et al., “Affine Frequency Division Multiplexing for Commu- nication and Channel Sounding: Requirements, Challenges, and Key Technologies,” to appear, IEEE Veh. Technol. Mag., 2025
work page 2025
-
[32]
D. Shi et al., “Deterministic Pilot Design and Channel Estimation for Downlink Massive MIMO-OTFS Systems in Presence of the Fractional Doppler,”IEEE Trans. Wireless Commun., vol. 20, no. 11, pp. 7151- 7165, Nov. 2021
work page 2021
-
[33]
A. Paier et al., “Non-WSSUS Vehicular Channel Characterization in Highway and Urban Scenarios at 5.2GHz Using the Local Scattering Function,” inProc. Int. ITG Workshop Smart Antennas (WSA), Feb. 2008, pp. 9-15
work page 2008
-
[34]
Radar Handbook, 3rd Edition (M.I. Skolnik, Ed; 2008) [Book Review],
F. Daum, “Radar Handbook, 3rd Edition (M.I. Skolnik, Ed; 2008) [Book Review],”IEEE Aerosp. Electron. Syst. Mag., vol. 23, no. 5, pp. 41-41, May 2008
work page 2008
-
[35]
Characterization of Randomly Time-Variant Linear Channels,
P. Bello, “Characterization of Randomly Time-Variant Linear Channels,” IEEE Trans. Commun. Syst., vol. 11, no. 4, pp. 360-393, Dec. 1963
work page 1963
-
[36]
Ambiguity and Sidelobe Behavior of CAZAC Coded Waveforms,
A. Kebo, I. Konstantinidis, J. J. Benedetto, M. R. Dellomo, and J. M. Sieracki, “Ambiguity and Sidelobe Behavior of CAZAC Coded Waveforms,” inProc. IEEE Radar Conf. (RadarConf), Apr. 2007, pp. 99-103
work page 2007
-
[37]
A. Sahin, I. Guvenc, and H. Arslan, “A Survey on Multicarrier Com- munications: Prototype Filters, Lattice Structures, and Implementation Aspects,”IEEE Commun. Surveys Tuts., vol. 16, no. 3, pp. 1312-1338, 2014
work page 2014
-
[38]
On the Zak Transform-based Interpretation of OTFS Modulation,
A. S. Bondre and C. D. Richmond, “On the Zak Transform-based Interpretation of OTFS Modulation,” inProc. 56th Asilomar Conf. Signals, Syst. Comput., Oct. 2022, pp. 715–721
work page 2022
-
[39]
On OTFS using the Discrete Zak Transform,
F. Lampel, A. Avarado, and F. M. J. Willems, “On OTFS using the Discrete Zak Transform,” inProc. IEEE Int. Conf. Commun. Workshops (ICC Workshops), May 2022, pp. 729-734. 14
work page 2022
-
[40]
On Delay-Doppler Plane Orthogonal Pulse,
H. Lin and J. Yuan, “On Delay-Doppler Plane Orthogonal Pulse,” in Proc. IEEE GLOBECOM, Dec. 2022, pp. 5589-5594
work page 2022
-
[41]
On the Pulse Shaping for Delay-Doppler Communications,
S. Li, W. Yuan, Z. Wei, J. Yuan, B. Bai, and G. Caire, “On the Pulse Shaping for Delay-Doppler Communications,” 2023, arXiv: 2306.08704
-
[42]
Interference Can- cellation and Iterative Detection for Orthogonal Time Frequency Space Modulation,
P. Raviteja, K. T. Phan, Y . Hong, and E. Viterbo, “Interference Can- cellation and Iterative Detection for Orthogonal Time Frequency Space Modulation,”IEEE Trans. Wireless Commun., vol. 17, no. 10, pp. 6501- 6515, Oct. 2018
work page 2018
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