New Insights into Channel vs Subspace Codes for Large-Scale Beamspace MIMO Channel Sensing
Pith reviewed 2026-05-10 01:20 UTC · model grok-4.3
The pith
The sensing performance of the maximum likelihood angle estimator in nonadaptive single-RF beamspace MIMO is governed by the minimum subspace distance and beam gain of the beamformers.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The sensing performance of the ML angle estimator in nonadaptive channel sensing with a single RF chain is governed by the minimum subspace distance and beam gain of the used beamformers. An exact expression for the subspace distance of binary linear channel codes mapped to BPSK is derived, which illuminates the relationship between subspace and Hamming distance. This result reveals why good Hamming distance alone is insufficient for sensing and shows that well-known families of channel codes such as Reed-Muller codes yield zero subspace distance and thereby poor sensing performance when used naively. Beamspace subspace codes based on sparse antenna selection patterns from Golomb rulers are近
What carries the argument
The minimum subspace distance of the beamformer codebook, which together with beam gain determines distinguishability of angle hypotheses under the noncoherent ML estimator.
If this is right
- Reed-Muller codes yield zero subspace distance and thereby poor sensing performance when used naively without proper codebook pruning.
- Good Hamming distance alone is insufficient for sensing performance.
- Beamspace subspace codes based on sparse antenna selection patterns (Golomb rulers) provide near-optimal subspace distance.
- These codes can be leveraged with convolutional beamspaces to enable hardware- and sample-efficient channel sensing with theoretical guarantees in large-scale multiantenna communications.
Where Pith is reading between the lines
- The subspace distance metric may be used to design optimal beamformer codebooks for arbitrary large array sizes.
- Results from noncoherent coding theory could be applied to further optimize the sensing scheme.
- Tradeoffs between subspace distance and beam gain can be explored for different SNR regimes in practical systems.
Load-bearing premise
The nonadaptive channel sensing problem with a single RF chain naturally maps to a noncoherent decoding problem without additional unstated conditions on noise or channel statistics.
What would settle it
Numerical evaluation of the ML angle estimator error probability for beamformer sets with different minimum subspace distances and beam gains that either matches or deviates from the dependence predicted by the exact expression.
Figures
read the original abstract
This paper provides novel insights into channel and subspace codes in nonadaptive channel sensing with a single RF chain. Observing that this problem naturally maps to a noncoherent decoding problem, we show that the sensing performance of the maximum likelihood (ML) angle estimator, which does not require knowledge of the typically unknown channel coefficient, is governed by two key terms: the minimum subspace distance and beam gain of the used beamformers. We derive an exact expression for the subspace distance of binary linear channel codes mapped to BPSK, which illuminates the relationship between subspace and Hamming distance, used to design subspace and channel codes, respectively. Our result also reveals why good Hamming distance alone is insufficient for sensing, and shows that well-known families of channel codes such as Reed-Muller codes, yield zero subspace distance and thereby poor sensing performance when used naively without proper codebook pruning. Finally, we introduce so-called beamspace subspace codes based on sparse antenna selection patterns (Golomb rulers), which we show provide near-optimal subspace distance. We demonstrate that this property of judiciously designed sparse arrays can be leveraged together with beamforming gain via convolutional beamspaces, enabling hardware- and sample-efficient channel sensing with theoretical guarantees in large-scale multiantenna communications.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper claims that the nonadaptive single-RF beamspace MIMO channel sensing problem naturally maps to noncoherent decoding, such that the performance of the maximum-likelihood angle estimator (which does not require knowledge of the unknown channel coefficient) is governed by the minimum subspace distance and the beam gain of the beamformers. It derives an exact closed-form expression for the subspace distance of BPSK-mapped binary linear codes and its relation to Hamming distance, shows that families such as Reed-Muller codes yield zero subspace distance without pruning, and constructs beamspace subspace codes based on Golomb-ruler sparse arrays that achieve near-optimal subspace distance while permitting convolutional beamspace gain for hardware- and sample-efficient sensing with theoretical guarantees.
Significance. If the algebraic derivations and explicit constructions hold, the work supplies useful design insights for channel sensing in large-scale MIMO systems by identifying subspace distance (rather than Hamming distance alone) as the governing metric and by providing concrete, implementable code families. The mapping to noncoherent detection, the closed-form distance relation, and the Golomb-ruler constructions with convolutional gain are concrete strengths that could inform practical single-RF sensing architectures.
major comments (2)
- [System model and mapping to noncoherent decoding] The central mapping of nonadaptive sensing to noncoherent decoding (stated in the abstract and introduction) rests on the assumption of a constant unknown complex gain over the sensing interval together with standard complex AWGN; the system-model section should explicitly confirm that no further restrictions on noise variance, angle discretization, or channel sparsity are required for the stated performance relationships to hold, as this assumption is load-bearing for the ML estimator claim.
- [Subspace distance derivation] The exact closed-form subspace distance for BPSK-mapped binary linear codes (derived in the section on subspace distance) is used to prove zero distance for Reed-Muller codes and near-optimality for Golomb-ruler patterns; the derivation should include a brief verification that the expression reduces correctly to the Hamming-distance relation in the BPSK case and does not introduce hidden parameter dependence.
minor comments (2)
- [Abstract] The abstract states that the constructions 'enable hardware- and sample-efficient channel sensing with theoretical guarantees' but does not list the specific performance metrics or simulation parameters used in the demonstrations; adding a short quantitative summary would improve clarity.
- [Notation and preliminaries] Notation for subspace distance, beam gain, and convolutional beamspace should be introduced once and used consistently; a short notation table or reminder in the first section would aid readability.
Simulated Author's Rebuttal
We thank the referee for the careful reading, positive assessment, and recommendation for minor revision. We address each major comment below and will incorporate the requested clarifications into the revised manuscript.
read point-by-point responses
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Referee: [System model and mapping to noncoherent decoding] The central mapping of nonadaptive sensing to noncoherent decoding (stated in the abstract and introduction) rests on the assumption of a constant unknown complex gain over the sensing interval together with standard complex AWGN; the system-model section should explicitly confirm that no further restrictions on noise variance, angle discretization, or channel sparsity are required for the stated performance relationships to hold, as this assumption is load-bearing for the ML estimator claim.
Authors: We agree that the system-model section should make these assumptions explicit. In the revised manuscript we will add a clarifying paragraph in the system model section stating that the mapping to noncoherent decoding and the ML angle estimator performance relations hold under the standard complex AWGN model with constant unknown complex gain over the sensing interval, without requiring any further restrictions on noise variance, angle discretization, or channel sparsity. revision: yes
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Referee: [Subspace distance derivation] The exact closed-form subspace distance for BPSK-mapped binary linear codes (derived in the section on subspace distance) is used to prove zero distance for Reed-Muller codes and near-optimality for Golomb-ruler patterns; the derivation should include a brief verification that the expression reduces correctly to the Hamming-distance relation in the BPSK case and does not introduce hidden parameter dependence.
Authors: We thank the referee for this suggestion. We will add a short verification remark (or short paragraph) in the subspace distance section that explicitly shows the closed-form expression reduces to the known Hamming-distance relation under BPSK mapping and confirms the absence of hidden parameter dependence. This addition will support the subsequent claims about Reed-Muller codes and Golomb-ruler constructions. revision: yes
Circularity Check
No significant circularity; derivations are algebraic and self-contained
full rationale
The paper maps nonadaptive single-RF beamspace sensing to noncoherent decoding under standard complex AWGN and constant unknown gain assumptions, then algebraically derives an exact closed-form subspace distance for BPSK-mapped binary linear codes (relating it to Hamming distance), proves zero distance for unpruned Reed-Muller codes, and explicitly constructs Golomb-ruler sparse arrays achieving near-optimal distance while enabling convolutional beamspace gain. These steps use direct definitions and standard code properties without parameter fitting, self-citation load-bearing premises, or renaming of known results as new derivations. The claim that ML angle estimation performance is governed by minimum subspace distance and beam gain follows directly from the mapping and distance expressions, remaining independent of the target performance claims.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Nonadaptive single-RF-chain channel sensing maps naturally to a noncoherent decoding problem
invented entities (1)
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beamspace subspace codes based on Golomb rulers
no independent evidence
Reference graph
Works this paper leans on
-
[1]
An overview of signal processing techniques for joint communication and radar sensing,
J. A. Zhang, F. Liu, C. Masouros, R. W. Heath, Z. Feng, L. Zheng, and A. Petropulu, “An overview of signal processing techniques for joint communication and radar sensing,”IEEE Journal of Selected Topics in Signal Processing, vol. 15, no. 6, pp. 1295–1315, 2021
work page 2021
-
[2]
The integrated sensing and communication revolution for 6G: Vision, techniques, and applications,
N. Gonz ´alez-Prelcic, M. Furkan Keskin, O. Kaltiokallio, M. Valkama, D. Dardari, X. Shen, Y . Shen, M. Bayraktar, and H. Wymeersch, “The integrated sensing and communication revolution for 6G: Vision, techniques, and applications,”Proceedings of the IEEE, vol. 112, no. 7, pp. 676–723, 2024
work page 2024
-
[3]
Integrated sensing and communications: Toward dual-functional wire- less networks for 6G and beyond,
F. Liu, Y . Cui, C. Masouros, J. Xu, T. X. Han, Y . C. Eldar, and S. Buzzi, “Integrated sensing and communications: Toward dual-functional wire- less networks for 6G and beyond,”IEEE Journal on Selected Areas in Communications, vol. 40, no. 6, pp. 1728–1767, 2022
work page 2022
-
[4]
Cellular wireless networks in the upper mid-band,
S. Kang, M. Mezzavilla, S. Rangan, A. Madanayake, S. B. Venkatakrish- nan, G. Hellbourg, M. Ghosh, H. Rahmani, and A. Dhananjay, “Cellular wireless networks in the upper mid-band,”IEEE Open Journal of the Communications Society, vol. 5, pp. 2058–2075, 2024
work page 2058
-
[5]
T. S. Rappaport, R. W. Heath Jr, R. C. Daniels, and J. N. Murdock, Millimeter Wave Wireless Communications. Prentice Hall, Pearson Education, 2015
work page 2015
-
[6]
E. Bj ¨ornson, C.-B. Chae, R. W. Heath Jr, T. L. Marzetta, A. Mezghani, L. Sanguinetti, F. Rusek, M. R. Castellanos, D. Jun, and ¨O. T. Demir, “Towards 6G MIMO: Massive spatial multiplexing, dense arrays, and interplay between electromagnetics and processing,”arXiv preprint arXiv:2401.02844, 2024
-
[7]
J. G. Andrews, T. E. Humphreys, and T. Ji, “6G takes shape,”IEEE BITS the Information Theory Magazine, vol. 4, no. 1, pp. 2–24, 2024
work page 2024
-
[8]
6G wireless systems: Vision, requirements, challenges, insights, and opportunities,
H. Tataria, M. Shafi, A. F. Molisch, M. Dohler, H. Sj ¨oland, and F. Tufvesson, “6G wireless systems: Vision, requirements, challenges, insights, and opportunities,”Proceedings of the IEEE, vol. 109, no. 7, pp. 1166–1199, 2021
work page 2021
-
[9]
Channel estimation and hybrid precoding for millimeter wave cellular systems,
A. Alkhateeb, O. E. Ayach, G. Leus, and R. W. Heath, “Channel estimation and hybrid precoding for millimeter wave cellular systems,” IEEE Journal of Selected Topics in Signal Processing, vol. 8, pp. 831– 846, 10 2014
work page 2014
-
[10]
Efficient beam align- ment for millimeter wave single-carrier systems with hybrid MIMO transceivers,
X. Song, S. Haghighatshoar, and G. Caire, “Efficient beam align- ment for millimeter wave single-carrier systems with hybrid MIMO transceivers,”IEEE Transactions on Wireless Communications, vol. 18, no. 3, pp. 1518–1533, 2019
work page 2019
-
[11]
Fast millimeter wave beam alignment,
S. Gorinsky, J. Tapolcai, H. Hassanieh, O. Abari, M. Rodriguez, M. Abdelghany, D. Katabi, and P. Indyk, “Fast millimeter wave beam alignment,”Proceedings of the 2018 Conference of the ACM Special Interest Group on Data Communication, pp. 432–445, 2018
work page 2018
-
[12]
Millimeter wave communications,
O. Abari, H. Hassanieh, M. Rodriguez, and D. Katabi, “Millimeter wave communications,”Proceedings of the 15th ACM Workshop on Hot Topics in Networks, pp. 169–175, 2016
work page 2016
-
[13]
Falp: Fast beam alignment in mmwave systems with low-resolution phase shifters,
N. J. Myers, A. Mezghani, and R. W. Heath, “Falp: Fast beam alignment in mmwave systems with low-resolution phase shifters,”IEEE Transac- tions on Communications, vol. 67, no. 12, pp. 8739–8753, 2019
work page 2019
-
[14]
F. Dong, W. Wang, Z. Huang, and P. Huang, “High-resolution angle- of-arrival and channel estimation for mmwave massive mimo systems with lens antenna array,”IEEE Transactions on Vehicular Technology, vol. 69, no. 11, pp. 12963–12973, 2020
work page 2020
-
[15]
Dual-function MIMO radar communications system design via sparse array optimization,
X. Wang, A. Hassanien, and M. G. Amin, “Dual-function MIMO radar communications system design via sparse array optimization,”IEEE Transactions on Aerospace and Electronic Systems, vol. 55, no. 3, pp. 1213–1226, 2019
work page 2019
-
[16]
Sparse array sensor selection in ISAC with identifiability guarantees,
R. Rajam ¨aki and P. Pal, “Sparse array sensor selection in ISAC with identifiability guarantees,” in58th Asilomar Conference on Signals, Systems, and Computers, pp. 90–94, 2024
work page 2024
-
[17]
Coarrays, MUSIC, and the Cram ´er-Rao bound,
M. Wang and A. Nehorai, “Coarrays, MUSIC, and the Cram ´er-Rao bound,”IEEE Transactions on Signal Processing, vol. 65, pp. 933–946, Feb 2017
work page 2017
-
[18]
Super- resolution with sparse arrays: A non-asymptotic analysis of spatio- temporal trade-offs,
P. Sarangi, M. C. H ¨uc¨umeno˘glu, R. Rajam ¨aki, and P. Pal, “Super- resolution with sparse arrays: A non-asymptotic analysis of spatio- temporal trade-offs,”IEEE Transactions on Signal Processing, pp. 1–14, 2023
work page 2023
-
[19]
M. G. Amin, ed.,Sparse Arrays for Radar, Sonar, and Communications. Wiley-IEEE, 2024
work page 2024
-
[20]
Active learning and CSI acquisition for mmWave initial alignment,
S.-E. Chiu, N. Ronquillo, and T. Javidi, “Active learning and CSI acquisition for mmWave initial alignment,”IEEE Journal on Selected Areas in Communications, vol. 37, no. 11, pp. 2474–2489, 2019
work page 2019
-
[21]
Deep learning for channel sensing and hybrid precoding in tdd massive mimo ofdm systems,
K. M. Attiah, F. Sohrabi, and W. Yu, “Deep learning for channel sensing and hybrid precoding in tdd massive mimo ofdm systems,”IEEE Transactions on Wireless Communications, vol. 21, no. 12, pp. 10839– 10853, 2022
work page 2022
-
[22]
On single-user interactive beam alignment in next generation systems: A deep learning viewpoint,
A. Khalili, S. Rangan, and E. Erkip, “On single-user interactive beam alignment in next generation systems: A deep learning viewpoint,”2021 IEEE International Conference on Communications Workshops (ICC Workshops), vol. 00, pp. 1–6, 2021
work page 2021
-
[23]
High dimensional channel estimation using deep generative networks,
E. Balevi, A. Doshi, A. Jalal, A. Dimakis, and J. G. Andrews, “High dimensional channel estimation using deep generative networks,”IEEE Journal on Selected Areas in Communications, vol. 39, no. 1, pp. 18–30, 2021
work page 2021
-
[24]
Learning site-specific probing beams for fast mmWave beam alignment,
Y . Heng, J. Mo, and J. G. Andrews, “Learning site-specific probing beams for fast mmWave beam alignment,”IEEE Transactions on Wire- less Communications, vol. 21, no. 8, pp. 5785–5800, 2022
work page 2022
-
[25]
Active sensing for communica- tions by learning,
F. Sohrabi, T. Jiang, W. Cui, and W. Yu, “Active sensing for communica- tions by learning,”IEEE Journal on Selected Areas in Communications, vol. 40, no. 6, pp. 1780–1794, 2022
work page 2022
-
[26]
Model-based online millimeter- wave channel sensing with learned empirical priors,
P. Khirwadkar, B. D. Rao, and P. Pal, “Model-based online millimeter- wave channel sensing with learned empirical priors,” inICASSP 2025- 2025 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), pp. 1–5, IEEE, 2025
work page 2025
-
[27]
Linear block coding for efficient beam discovery in millimeter wave communication networks,
Y . Shabara, C. E. Koksal, and E. Ekici, “Linear block coding for efficient beam discovery in millimeter wave communication networks,”IEEE INFOCOM 2018 - IEEE Conference on Computer Communications, vol. 00, pp. 2285–2293, 2018
work page 2018
-
[28]
Single-bit millimeter wave beam alignment using error control sounding strategies,
V . Suresh and D. J. Love, “Single-bit millimeter wave beam alignment using error control sounding strategies,”IEEE Journal of Selected Topics in Signal Processing, vol. 13, no. 5, pp. 1032–1045, 2019
work page 2019
-
[29]
T. Zheng, J. Zhu, Q. Yu, Y . Yan, and L. Dai, “Coded beam training,” IEEE Journal on Selected Areas in Communications, vol. 43, no. 3, pp. 928–943, 2025
work page 2025
-
[30]
On-grid angle-of-arrival estimation in large-scale MIMO systems using channel codes,
N. Ghaddar, L. Wang, and W. Yu, “On-grid angle-of-arrival estimation in large-scale MIMO systems using channel codes,”2025 IEEE Inter- national Symposium on Information Theory, 2025
work page 2025
-
[31]
Convolutional beamspace for linear arrays,
P.-C. Chen and P. P. Vaidyanathan, “Convolutional beamspace for linear arrays,”IEEE Transactions on Signal Processing, vol. 68, pp. 5395– 5410, 2020. JOURNAL OF LATEX CLASS FILES, VOL. 13, NO. 9, SEPTEMBER 2025 13
work page 2020
-
[32]
Channel estimation for mmWave using the convolutional beamspace approach,
P.-C. Chen and P. P. Vaidyanathan, “Channel estimation for mmWave using the convolutional beamspace approach,”IEEE Transactions on Signal Processing, vol. 72, pp. 2921–2938, 2024
work page 2024
-
[33]
In-sector compressive beam acquisition for mmWave and THz radios,
H. Masoumi, M. Verhaegen, and N. J. Myers, “In-sector compressive beam acquisition for mmWave and THz radios,”IEEE Transactions on Communications, vol. 73, no. 4, pp. 2752–2768, 2025
work page 2025
-
[34]
Structured sensing matrix design for in-sector compressed mmWave channel estimation,
H. Masoumi, N. J. Myers, G. Leus, S. Wahls, and M. Verhaegen, “Structured sensing matrix design for in-sector compressed mmWave channel estimation,”2022 IEEE 23rd International Workshop on Signal Processing Advances in Wireless Communication (SPAWC), vol. 00, pp. 1–5, 2022
work page 2022
-
[35]
Robust gridless estimation of angles and delays for full-dimensional wideband mmWave channels,
T.-M. Yang and Y .-P. Lin, “Robust gridless estimation of angles and delays for full-dimensional wideband mmWave channels,”IEEE Open Journal of Signal Processing, vol. 4, pp. 31–43, 2023
work page 2023
-
[36]
C. Feng, H. Wang, and Y . Zeng, “Convolutional beamspace beamform- ing for low-complexity far-field and near-field MU-MIMO communica- tions,”arXiv, 2024
work page 2024
-
[37]
Subspace coding for spatial sensing,
H. Mahdavifar, R. Rajam ¨aki, and P. Pal, “Subspace coding for spatial sensing,”2024 IEEE International Symposium on Information Theory (ISIT), vol. 00, pp. 2394–2399, 2024
work page 2024
-
[38]
Analog subspace coding: A new approach to coding for non-coherent wireless networks,
M. Soleymani and H. Mahdavifar, “Analog subspace coding: A new approach to coding for non-coherent wireless networks,”IEEE Trans- actions on Information Theory, vol. 68, no. 4, pp. 2349–2364, 2022
work page 2022
-
[39]
An overview of signal processing techniques for millimeter wave MIMO systems,
R. W. Heath, N. Gonzlez-Prelcic, S. Rangan, W. Roh, and A. M. Sayeed, “An overview of signal processing techniques for millimeter wave MIMO systems,”IEEE Journal of Selected Topics in Signal Processing, vol. 10, no. 3, pp. 436–453, 2016
work page 2016
-
[40]
Application of boolean algebra to switching circuit design and to error detection,
D. E. Muller, “Application of boolean algebra to switching circuit design and to error detection,”Transactions of the IRE professional group on electronic computers, no. 3, pp. 6–12, 1954
work page 1954
-
[41]
A class of multiple-error-correcting codes and the decoding scheme,
I. S. Reed, “A class of multiple-error-correcting codes and the decoding scheme,” tech. rep., 1953
work page 1953
-
[42]
Reed–muller codes: Theory and algorithms,
E. Abbe, A. Shpilka, and M. Ye, “Reed–muller codes: Theory and algorithms,”IEEE Transactions on Information Theory, vol. 67, no. 6, pp. 3251–3277, 2021
work page 2021
-
[43]
Reed-muller codes achieve capacity on erasure channels,
S. Kudekar, S. Kumar, M. Mondelli, H. D. Pfister, E. S ¸as ¸o ˘glu, and R. Urbanke, “Reed-muller codes achieve capacity on erasure channels,” inProceedings of the Forty-Eighth Annual ACM Symposium on Theory of Computing, STOC ’16, (New York, NY , USA), p. 658–669, Associ- ation for Computing Machinery, 2016
work page 2016
-
[44]
A proof that reed-muller codes achieve shannon capacity on symmetric channels,
E. Abbe and C. Sandon, “A proof that reed-muller codes achieve shannon capacity on symmetric channels,” in2023 IEEE 64th Annual Symposium on Foundations of Computer Science (FOCS), pp. 177–193, 2023
work page 2023
-
[45]
G. Reeves and H. D. Pfister, “Reed–muller codes on bms channels achieve vanishing bit-error probability for all rates below capacity,”IEEE Transactions on Information Theory, vol. 70, no. 2, pp. 920–949, 2024
work page 2024
-
[46]
Lower bounds on the maximum cross correlation of signals (corresp.),
L. Welch, “Lower bounds on the maximum cross correlation of signals (corresp.),”IEEE Transactions on Information Theory, vol. 20, no. 3, pp. 397–399, 1974
work page 1974
-
[47]
Theorems in the additive theory of numbers,
R. Bose and S. Chowla, “Theorems in the additive theory of numbers,” Commentarii Mathematici Helvetici, vol. 37, no. 1, pp. 141–147, 1962
work page 1962
-
[48]
Convolutional beamspace for linear arrays,
P.-C. Chen and P. P. Vaidyanathan, “Convolutional beamspace for linear arrays,”IEEE Transactions on Signal Processing, vol. 68, pp. 5395– 5410, 2020
work page 2020
-
[49]
Novel sensing methodology for initial align- ment using mmwave phased arrays,
R. R. Pote and B. D. Rao, “Novel sensing methodology for initial align- ment using mmwave phased arrays,” in2023 57th Asilomar Conference on Signals, Systems, and Computers, pp. 475–479, 2023. JOURNAL OF LATEX CLASS FILES, VOL. 13, NO. 9, SEPTEMBER 2025 14 APPENDIX PROOF OFTHEOREM1 The ML decoder succeeds if| bbH l y|<| bbH k y|∀l= 1, . . . , Ng, l̸=k. Th...
work page 2023
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