Joint Phase Noise and Off-Grid Channel Estimation for AFDM Systems via Sparse Bayesian Learning
Pith reviewed 2026-05-10 04:32 UTC · model grok-4.3
The pith
A sparse Bayesian learning method jointly estimates phase noise and off-grid effects in AFDM to approach perfect channel state information.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The paper establishes that by projecting the phase noise onto a reduced-rank subspace and evolving the grid dynamically to remove off-grid mismatches, all within a sparse Bayesian learning EM loop that jointly refines the channel and noise estimates, the estimation error floor is lifted and performance approaches that of perfect channel state information.
What carries the argument
JPNCE-SBL, an algorithm that integrates reduced-rank subspace projection for Wiener phase noise and iterative dynamic grid evolution for fractional shifts inside an EM-based sparse Bayesian learning procedure for joint estimation.
If this is right
- The joint updates prevent error propagation between phase noise and channel estimates.
- Dynamic grid evolution avoids the need for dense global grids, reducing computation.
- Performance in normalized mean square error and bit error rate significantly exceeds that of existing methods.
- Under practical phase noise, results nearly match the perfect channel state information benchmark.
Where Pith is reading between the lines
- The technique may extend to other OFDM variants or systems with similar phase noise impairments.
- Real-world deployment could benefit from reduced pilot overhead due to better estimation accuracy.
- Further analysis might explore the method's robustness when the Wiener process assumption is violated.
Load-bearing premise
The reduced-rank subspace projection captures enough of the phase noise energy and the dynamic grid updates remove off-grid errors without creating new inaccuracies or requiring full densification.
What would settle it
Experimental results where JPNCE-SBL shows no improvement in NMSE or BER over benchmarks, or fails to approach perfect CSI performance in the presence of practical phase noise, would disprove the effectiveness of the approach.
Figures
read the original abstract
In practical affine frequency division multiplexing (AFDM) systems, the intricate coupling of oscillator phase noise (PN) and off-grid fractional shifts traps conventional estimators in a severe high-SNR error floor. To address these challenges, we propose a joint PN and channel estimation method based on sparse Bayesian learning (JPNCE-SBL). Specifically, a reduced-rank subspace projection is first introduced to capture the dominant eigen-energy of the Wiener PN process. Concurrently, a dynamic grid evolution strategy is designed to iteratively eliminate off-grid errors without requiring computationally prohibitive global grid densification. Both components are integrated into a unified Expectation-Maximization (EM) framework, where the channel and PN estimates are jointly updated at each iteration to prevent error propagation. Simulation results demonstrate that JPNCE-SBL significantly outperforms existing benchmarks in both NMSE and BER, closely approaching the perfect channel state information case under practical PN conditions.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes JPNCE-SBL, a joint phase noise (PN) and off-grid channel estimation algorithm for affine frequency division multiplexing (AFDM) systems. It combines sparse Bayesian learning with a reduced-rank subspace projection to capture dominant eigen-energy of the Wiener PN process, a dynamic grid evolution strategy to mitigate off-grid errors without global densification, and an EM framework for iterative joint updates of channel and PN estimates. Simulations are reported to show substantial gains in NMSE and BER over benchmarks, approaching perfect-CSI performance under practical PN conditions.
Significance. If the central claims hold after verification, the work addresses a practically relevant coupling of impairments in AFDM that limits high-SNR performance in high-mobility or mmWave scenarios. The combination of reduced-rank PN modeling with adaptive SBL grid refinement offers a structured way to avoid both error floors and excessive complexity, which could inform estimator design in related multicarrier and OTFS-like systems.
major comments (2)
- [Abstract and §3 (method description)] The performance claim that the method eliminates the high-SNR error floor rests on the reduced-rank subspace projection capturing 'dominant eigen-energy' of the Wiener PN process (Abstract). For a Wiener phase-noise covariance (Toeplitz with linearly growing diagonals), eigenvalue decay is slow; a fixed low-rank truncation therefore leaves a residual variance that grows with SNR. The manuscript reports neither the captured-energy fraction nor the truncation-error norm at the operating SNRs used in the simulations, so it is impossible to confirm that the approximation remains harmless precisely where the error floor would otherwise appear.
- [Abstract and simulation results section] The abstract asserts that JPNCE-SBL 'significantly outperforms existing benchmarks in both NMSE and BER' and 'closely approaches the perfect channel state information case,' yet supplies no details on channel models, PN variance parameters, grid sizes, number of Monte Carlo runs, or statistical significance. Without these, the empirical support for the central claim cannot be verified or reproduced.
minor comments (2)
- [§3] Clarify the exact rank selection criterion for the subspace projection and whether it is fixed or SNR-dependent.
- [§4] Add a brief complexity analysis (flops per iteration) to quantify the benefit of avoiding global grid densification.
Simulated Author's Rebuttal
We thank the referee for the detailed and constructive comments. We address each major comment below and outline the revisions we will make to strengthen the manuscript.
read point-by-point responses
-
Referee: [Abstract and §3 (method description)] The performance claim that the method eliminates the high-SNR error floor rests on the reduced-rank subspace projection capturing 'dominant eigen-energy' of the Wiener PN process (Abstract). For a Wiener phase-noise covariance (Toeplitz with linearly growing diagonals), eigenvalue decay is slow; a fixed low-rank truncation therefore leaves a residual variance that grows with SNR. The manuscript reports neither the captured-energy fraction nor the truncation-error norm at the operating SNRs used in the simulations, so it is impossible to confirm that the approximation remains harmless precisely where the error floor would otherwise appear.
Authors: We acknowledge that explicitly reporting the captured eigen-energy fraction and the norm of the truncation error at the simulated SNRs would provide stronger justification for the reduced-rank approximation, particularly given the known slow decay of eigenvalues in the Wiener process covariance. Although our numerical results demonstrate that JPNCE-SBL eliminates the high-SNR error floor and approaches perfect-CSI performance, we will add these quantitative metrics (e.g., percentage of captured energy and residual norm) for the relevant SNR range in the revised Section III and/or simulation results to allow direct verification of the approximation quality. revision: yes
-
Referee: [Abstract and simulation results section] The abstract asserts that JPNCE-SBL 'significantly outperforms existing benchmarks in both NMSE and BER' and 'closely approaches the perfect channel state information case,' yet supplies no details on channel models, PN variance parameters, grid sizes, number of Monte Carlo runs, or statistical significance. Without these, the empirical support for the central claim cannot be verified or reproduced.
Authors: The simulation parameters—including the specific channel model (e.g., number of paths and delay-Doppler spreads for AFDM), PN variance values, dynamic grid sizes, number of Monte Carlo realizations, and other settings—are fully specified in the Simulation Results section of the manuscript. To address the concern about verifiability, we will revise the abstract to include a concise summary of the key parameters (PN variance range, Monte Carlo count, and grid evolution details) while respecting length limits. If statistical significance measures (e.g., error bars) are not already shown, we will add them to the revised figures. revision: partial
Circularity Check
No significant circularity detected
full rationale
The manuscript proposes JPNCE-SBL by introducing a reduced-rank subspace projection to capture dominant Wiener PN eigen-energy and a dynamic grid evolution within an EM framework for joint estimation. No equations, derivations, or self-citations are exhibited in the provided text that reduce any claimed prediction or result to its own inputs by construction. The central claims rest on the proposed algorithmic integration and simulation validation against benchmarks, which remain independent of tautological redefinitions or fitted-input renamings. This is the normal case of a method paper whose performance claims are externally falsifiable via the reported NMSE/BER curves.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Phase noise follows a Wiener process whose energy is concentrated in a low-dimensional subspace
- domain assumption Channel and PN effects admit sparse representations amenable to SBL
Reference graph
Works this paper leans on
-
[1]
A vision of 6G wireless sy stems: Applications, trends, technologies, and open research pro blems,
W. Saad, M. Bennis, and M. Chen, “A vision of 6G wireless sy stems: Applications, trends, technologies, and open research pro blems,” IEEE Network, vol. 34, no. 3, pp. 134–142, 2020
2020
-
[2]
Non-ortho gonal AFDM: A promising spectrum-efficient waveform for 6G high-m obility communications,
Y . Zhang, Q. Yi, L. Musavian, T. Xu, and Z. Liu, “Non-ortho gonal AFDM: A promising spectrum-efficient waveform for 6G high-m obility communications,” in Proc. IEEE 36th Int. Symp. Pers., Indoor Mobile Radio Commun. (PIMRC) , Istanbul, Turkiye, 2025, pp. 1–6
2025
-
[3]
Gen - eralized spatial modulation aided affine frequency divisio n multi- plexing,
Z. Sui, Z. Liu, L. Musavian, L.-L. Y ang, and L. Hanzo, “Gen - eralized spatial modulation aided affine frequency divisio n multi- plexing,” IEEE Trans. Wireless Commun. , early access, 2025, doi: 10.1109/TWC.2025.3613062
-
[4]
X. Zhang, H. Yin, Y . Tang, Y . Ge, Y . Zeng, M. Wen, Z. Liu, et al. , “A unified multicarrier waveform framework for next-generati on wireless networks: Principles, performance, and challenges,” IEEE Commun. Surveys Tuts., early access, 2026, doi: 10.1109/COMST.2026.3672602
-
[5]
H. S. Rou et al. , “From orthogonal time-frequency space to affine frequency-division multiplexing: A comparative study of n ext-generation waveforms for integrated sensing and communications in dou bly disper- sive channels,” IEEE Signal Process. Mag. , vol. 41, no. 5, pp. 71–86, Sep. 2024
2024
-
[6]
Affine frequency division multiplexing with index modulation: Full diversity condition, performance analys is, and low- complexity detection,
Y . Tao et al. , “Affine frequency division multiplexing with index modulation: Full diversity condition, performance analys is, and low- complexity detection,” IEEE J. Sel. Areas Commun. , vol. 43, no. 4, pp. 1041–1055, Apr. 2025
2025
-
[7]
MIMO-AFDM outperforms MIMO-OFDM in the face of hardware impairments,
Z. Sui et al., “MIMO-AFDM outperforms MIMO-OFDM in the face of hardware impairments,” arXiv preprint arXiv:2601.00502 , 2026
-
[8]
OFDM systems in the presence of pha se noise: Consequences and solutions,
S. Wu and Y . Bar-Ness, “OFDM systems in the presence of pha se noise: Consequences and solutions,” IEEE Trans. Commun. , vol. 52, no. 11, pp. 1988–1996, Nov. 2004
1988
-
[9]
Channel estim ation and carrier recovery in the presence of phase noise in OFDM relay systems,
R. Wang, H. Mehrpouyan, M. Tao, and Y . Hua, “Channel estim ation and carrier recovery in the presence of phase noise in OFDM relay systems,” in Proc. IEEE Global Commun. Conf. (GLOBECOM) , Austin, TX, USA, Dec. 2015, pp. 1–6
2015
-
[10]
Matched filtering-bas ed channel estimation for AFDM systems in doubly selective cha n- nels,
X. Li, Z. Liu, Z. Zhou, and P . Fan, “Matched filtering-bas ed channel estimation for AFDM systems in doubly selective cha n- nels,” IEEE Trans. Wireless Commun. , 2026. [Online]. Available: https://arxiv.org/abs/2507.0926
-
[11]
Channel es timation for AFDM with superimposed pilots,
K. Zheng, M. Wen, T. Mao, L. Xiao, and Z. Wang, “Channel es timation for AFDM with superimposed pilots,” IEEE Trans. V eh. Technol., vol. 74, no. 2, pp. 3389–3394, Feb. 2025
2025
-
[12]
Off-grid channel estimation with sparse Bayesian learni ng for OTFS systems,
Z. Wei et al., “Off-grid channel estimation with sparse Bayesian learni ng for OTFS systems,” IEEE Trans. Wireless Commun. , vol. 21, no. 9, pp. 7407–7426, Sep. 2022
2022
-
[13]
Joint sparse graph for enhanced MIMO-AFDM receiver design,
Q. Luo, J. Zhu, Z. Liu, Y . Tang, P . Xiao, G. Chen, and J. Shi , “Joint sparse graph for enhanced MIMO-AFDM receiver design,” IEEE Trans. Wireless Commun., vol. 25, pp. 3272–3286, 2026
2026
-
[14]
Grid evolution for dou bly fractional channel estimation in OTFS systems,
X. Li, P . Fan, Q. Wang, and Z. Liu, “Grid evolution for dou bly fractional channel estimation in OTFS systems,” IEEE Trans. V eh. Technol., vol. 74, no. 2, pp. 3486–3490, Feb. 2025
2025
-
[15]
The variational inference appro ach to joint data detection and phase noise estimation in OFDM,
D. D. Lin and T. J. Lim, “The variational inference appro ach to joint data detection and phase noise estimation in OFDM,” IEEE Trans. Signal Process., vol. 55, no. 5, pp. 1862–1874, May 2007
2007
-
[16]
Joint estimation of channel and oscillator phase noise in MIMO systems,
H. Mehrpouyan et al. , “Joint estimation of channel and oscillator phase noise in MIMO systems,” IEEE Trans. Signal Process. , vol. 60, no. 9, pp. 4790–4807, Sep. 2012
2012
-
[17]
S ubspace- based phase noise estimation in OFDM receivers,
P . Mathecken, S. Werner, T. Riihonen, and R. Wichman, “S ubspace- based phase noise estimation in OFDM receivers,” in Proc. IEEE Int. Conf. Acoust., Speech Signal Process. (ICASSP) , Apr. 2015, pp. 3227– 3231
2015
-
[18]
Sparse Bayesian learnin g of delay- Doppler channel for OTFS system,
L. Zhao, W.-J. Gao, and W. Guo, “Sparse Bayesian learnin g of delay- Doppler channel for OTFS system,” IEEE Commun. Lett. , vol. 24, no. 12, pp. 2766–2769, Dec. 2020
2020
-
[19]
Bayesian compressive sensing for NLOS mmWave imaging under imprecisely multiangle surfaces,
Y . Xu et al. , “Bayesian compressive sensing for NLOS mmWave imaging under imprecisely multiangle surfaces,” IEEE Signal Process. Lett., vol. 32, pp. 2075–2079, 2025
2075
-
[20]
Maximum likelihood-based grid less DoA estimation using structured covariance matrix recovery an d SBL with grid refinement,
R. R. Pote and B. D. Rao, “Maximum likelihood-based grid less DoA estimation using structured covariance matrix recovery an d SBL with grid refinement,” IEEE Trans. Signal Process. , vol. 71, pp. 802–815, Mar. 2023
2023
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.