REVIEW 1 minor 62 references
On the Impossibility of Lossless Waveform Rank Reduction for Certain Redundant Arrays
T0 review · 0 major / 1 minor · reviewed 2026-05-24 · grok-4.3
Pith's one-line read Certain redundant arrays cannot achieve lossless waveform rank reduction due to their redundancy patterns.
desk verdict The paper shows that identical sum co-arrays do not guarantee the same identifiability at low waveform rank, because subspace properties of the redundancy pattern matter, and it gives a necessary condition based on that. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The subspace properties of the array redundancy pattern that control whether identifiability is preserved when waveform rank is reduced.
What would settle it
Finding that an array with an unfavorable redundancy pattern still achieves full parameter identifiability at reduced waveform rank would contradict the impossibility claim.
Extended reading notes
Core claim
Array geometries with identical sum co-arrays can exhibit markedly different identifiability properties at low waveform rank because parameter identifiability at reduced waveform rank depends on subspace properties of the array redundancy pattern; a novel necessary condition shows that the unfavorable redundancy patterns of certain redundant arrays fundamentally limit their performance.
Load-bearing premise
Parameter identifiability at reduced waveform rank is governed by the subspace properties of the array redundancy pattern.
Editorial extensions
If this is right
- Identifiability at reduced WR depends on redundancy pattern subspaces rather than only the sum co-array.
- Some arrays with identical sum co-arrays have different low-WR identifiability.
- Maximizing identifiability at reduced WR requires satisfying a new necessary condition on the redundancy pattern.
- The results motivate redundancy-aware design of arrays and waveforms for efficient sensing.
Reading between the lines
- Array design for MIMO systems may need to prioritize specific redundancy patterns to enable low-rank operation.
- Waveform design could potentially be adapted to mitigate unfavorable redundancy in existing arrays.
- Simulations comparing identifiability for arrays like nested arrays versus others at reduced WR could test the condition further.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper examines the effects of array redundancy and waveform rank (WR) on parameter identifiability in MIMO active sensing. It claims that identifiability at reduced WR depends critically on subspace properties of the array redundancy pattern rather than solely on the sum co-array. Geometries sharing identical sum co-arrays are shown to exhibit different identifiability at low WR. A novel necessary condition is derived for maximizing identifiability under WR reduction, indicating that unfavorable redundancy patterns in certain redundant arrays impose fundamental performance limits.
Significance. If the central claims hold, the work offers useful insights for resource-efficient MIMO sensing by demonstrating that redundancy patterns affect identifiability beyond standard co-array properties. The emphasis on subspace properties and the necessary condition could guide redundancy-aware array and waveform design. The observation that identical co-arrays yield differing performance is a potentially valuable distinction if supported by the derivations.
minor comments (1)
- The title emphasizes 'impossibility of lossless waveform rank reduction,' but the abstract uses the milder phrasing 'fundamentally limits their performance'; clarifying this distinction in the introduction would improve consistency.
Simulated Author's Rebuttal
We thank the referee for reviewing our manuscript and for their summary recognizing the potential insights into redundancy patterns and identifiability beyond standard co-array properties. No specific major comments were provided in the report.
Circularity Check
No significant circularity; derivation grounded in standard subspace analysis
full rationale
The paper's central claim derives a necessary condition for identifiability at reduced waveform rank from subspace properties of the array redundancy pattern, as stated in the abstract. This follows directly from linear-algebraic properties of sum co-arrays without reduction to fitted parameters, self-definitional loops, or load-bearing self-citations. Array geometries with identical co-arrays yielding different performance is presented as an observation from those properties, not a renaming or ansatz smuggled via prior work. No equations or steps in the provided text equate a prediction to its input by construction. The result is self-contained against external benchmarks of array signal processing.
Assumptions & free parameters
assumptions (1)
- domain assumption Parameter identifiability is determined by the dimension or rank of certain subspaces formed by the array manifold and waveform matrix.
Cite this review
Pith. "Pith review of On the Impossibility of Lossless Waveform Rank Reduction for Certain Redundant Arrays." pith.science (2026). https://pith.science/paper/SSDAX46C
@misc{pith2026230506478,
author = {Pith},
title = {Pith review of: On the Impossibility of Lossless Waveform Rank Reduction for Certain Redundant Arrays},
year = {2026},
howpublished = {\url{https://pith.science/paper/SSDAX46C}},
note = {Machine review of arXiv:2305.06478}
}
read the original abstract
Efficient use of spatio-temporal resources, including sensor arrays and transmit waveforms, is a key challenge in modern MIMO active sensing systems. This paper studies the impact of array redundancy and waveform rank (WR) on active sensing performance. Specifically, we show that parameter identifiability at reduced WR critically depends on subspace properties of the so-called array redundancy pattern. We show that array geometries with identical sum co-arrays can exhibit markedly different identifiability properties at low WR. We derive a novel necessary condition for maximizing identifiability at reduced WR, which reveals that the unfavorable redundancy patterns of certain redundant arrays fundamentally limits their performance. The results yield new insights into resource-efficient sensing systems, motivating redundancy-aware array and waveform design.
Figures
Reference graph
Works this paper leans on
-
[1]
Radar taking off: New capabilities for UA Vs,
P . H¨ ugler, F. Roos, M. Schartel, M. Geiger, and C. Waldsc hmidt, “Radar taking off: New capabilities for UA Vs,” IEEE Microwave Magazine , vol. 19, no. 7, pp. 43–53, 2018
work page 2018
-
[2]
D. Ma, N. Shlezinger, T. Huang, Y . Liu, and Y . C. Eldar, “Jo int radar- communication strategies for autonomous vehicles: Combin ing two key automotive technologies,” IEEE Signal Processing Magazine , vol. 37, no. 4, pp. 85–97, 2020
work page 2020
-
[3]
Automotive r adars: A review of signal processing techniques,
S. M. Patole, M. Torlak, D. Wang, and M. Ali, “Automotive r adars: A review of signal processing techniques,” IEEE Signal Processing Magazine, vol. 34, no. 2, pp. 22–35, 2017
work page 2017
-
[4]
I. Bilik, O. Longman, S. Villeval, and J. Tabrikian, “The rise of radar for autonomous vehicles: Signal processing solutions and futu re research directions,” IEEE Signal Processing Magazine , vol. 36, no. 5, pp. 20– 31, 2019
work page 2019
-
[5]
S. Sun, A. P . Petropulu, and H. V . Poor, “MIMO radar for adv anced driver-assistance systems and autonomous driving: Advant ages and challenges,” IEEE Signal Processing Magazine , vol. 37, no. 4, pp. 98– 117, 2020
work page 2020
-
[6]
Automotive radar signal processing: Researc h directions and practical challenges,
F. Engels, P . Heidenreich, M. Wintermantel, L. St¨ acker, M. Al Kadi, and A. M. Zoubir, “Automotive radar signal processing: Researc h directions and practical challenges,” IEEE Journal of Selected Topics in Signal Processing, vol. 15, no. 4, pp. 865–878, 2021
work page 2021
-
[7]
4D automotive radar sensing for au tonomous vehicles: A sparsity-oriented approach,
S. Sun and Y . D. Zhang, “4D automotive radar sensing for au tonomous vehicles: A sparsity-oriented approach,” IEEE Journal of Selected Topics in Signal Processing , vol. 15, no. 4, pp. 879–891, 2021
work page 2021
-
[8]
Survey of RF com muni- cations and sensing convergence research,
B. Paul, A. R. Chiriyath, and D. W. Bliss, “Survey of RF com muni- cations and sensing convergence research,” IEEE Access , vol. 5, pp. 252–270, 2017
work page 2017
Show all 62 references
-
[9]
Toward millimeter-wave joint radar commun ications: A signal processing perspective,
K. V . Mishra, M. Bhavani Shankar, V . Koivunen, B. Otterst en, and S. A. V orobyov, “Toward millimeter-wave joint radar commun ications: A signal processing perspective,” IEEE Signal Processing Magazine , vol. 36, no. 5, pp. 100–114, 2019
2019
-
[10]
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. Z heng, 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
2021
-
[11]
A n information-theoretic approach to joint sensing and commu nication,
M. Ahmadipour, M. Kobayashi, M. Wigger, and G. Caire, “A n information-theoretic approach to joint sensing and commu nication,” IEEE Transactions on Information Theory , pp. 1–1, 2022
2022
-
[12]
Levanon and E
N. Levanon and E. Mozeson, Radar Signals. John Wiley & Sons, 2004
2004
-
[13]
Pillai, K
U. Pillai, K. Y . Li, I. Selesnick, and B. Himed, W aveform Diversity: Theory & Applications . McGraw-Hill Professional, 2011
2011
-
[14]
F. Gini, A. D. Maio, and L. Patton, Eds., W aveform Design and Di- versity for Advanced Radar Systems , ser. Radar, Sonar and Navigation. Institution of Engineering and Technology, 2012
2012
-
[15]
H. He, J. Li, and P . Stoica, W aveform Design for Active Sensing Systems: A Computational Approach . Cambridge University Press, 2012
2012
-
[16]
Waveform div ersity in radar signal processing,
R. Calderbank, S. D. Howard, and B. Moran, “Waveform div ersity in radar signal processing,” IEEE Signal Processing Magazine , vol. 26, no. 1, pp. 32–41, 2009
2009
-
[17]
Overview of radar waveform diversity,
S. D. Blunt and E. L. Mokole, “Overview of radar waveform diversity,” IEEE Aerospace and Electronic Systems Magazine , vol. 31, no. 11, pp. 2–42, 2016
2016
-
[18]
Spatial diversity in radars—models and detection p erformance,
E. Fishler, A. Haimovich, R. Blum, L. Cimini, D. Chizhik , and R. V alen- zuela, “Spatial diversity in radars—models and detection p erformance,” IEEE Transactions on Signal Processing , vol. 54, no. 3, pp. 823–838, 2006
2006
-
[19]
Multiple-input multipl e-output (MIMO) radar and imaging: degrees of freedom and resolution ,
D. W. Bliss and K. W. Forsythe, “Multiple-input multipl e-output (MIMO) radar and imaging: degrees of freedom and resolution ,” in 37th Asilomar Conference on Signals, Systems and Computers , vol. 1, 2003, pp. 54–59 V ol.1
2003
-
[20]
MIMO radar with colocated antennas ,
J. Li and P . Stoica, “MIMO radar with colocated antennas ,” IEEE Signal Processing Magazine, vol. 24, no. 5, pp. 106–114, Sept 2007. 13
2007
-
[21]
The unifying role of the co array in aperture synthesis for coherent and incoherent imaging,
R. T. Hoctor and S. A. Kassam, “The unifying role of the co array in aperture synthesis for coherent and incoherent imaging,” Proceedings of the IEEE , vol. 78, no. 4, pp. 735–752, Apr 1990
1990
-
[22]
Linear imaging with senso r arrays on convex polygonal boundaries,
R. J. Kozick and S. A. Kassam, “Linear imaging with senso r arrays on convex polygonal boundaries,” IEEE Transactions on Systems, Man, and Cybernetics , vol. 21, no. 5, pp. 1155–1166, Sep 1991
1991
-
[23]
Hybrid be amforming for active sensing using sparse arrays,
R. Rajam¨ aki, S. P . Chepuri, and V . Koivunen, “Hybrid be amforming for active sensing using sparse arrays,” IEEE Transactions on Signal Processing, vol. 68, pp. 6402–6417, 2020
2020
-
[24]
Transmit beamformin g for MIMO radar systems using signal cross-correlation,
D. R. Fuhrmann and G. San Antonio, “Transmit beamformin g for MIMO radar systems using signal cross-correlation,” IEEE Transactions on Aerospace and Electronic Systems, vol. 44, no. 1, pp. 171–186, 2008
2008
-
[25]
Phased-MIMO radar: A t radeoff between phased-array and MIMO radars,
A. Hassanien and S. A. V orobyov, “Phased-MIMO radar: A t radeoff between phased-array and MIMO radars,” IEEE Transactions on Signal Processing, vol. 58, no. 6, pp. 3137–3151, 2010
2010
-
[26]
Time-divisi on beam- forming for MIMO radar waveform design,
A. J. Duly, D. J. Love, and J. V . Krogmeier, “Time-divisi on beam- forming for MIMO radar waveform design,” IEEE Transactions on Aerospace and Electronic Systems , vol. 49, no. 2, pp. 1210–1223, 2013
2013
-
[27]
To- ward dual-functional radar-communication systems: Optim al waveform design,
F. Liu, L. Zhou, C. Masouros, A. Li, W. Luo, and A. Petropu lu, “To- ward dual-functional radar-communication systems: Optim al waveform design,” IEEE Transactions on Signal Processing , vol. 66, no. 16, pp. 4264–4279, 2018
2018
-
[28]
Joint transmit beamforming for multiuser MIMO communicat ions and MIMO radar,
X. Liu, T. Huang, N. Shlezinger, Y . Liu, J. Zhou, and Y . C. Eldar, “Joint transmit beamforming for multiuser MIMO communicat ions and MIMO radar,” IEEE Transactions on Signal Processing , vol. 68, pp. 3929–3944, 2020
2020
-
[29]
Further results on th e Cram´ er–Rao bound for sparse linear arrays,
M. Wang, Z. Zhang, and A. Nehorai, “Further results on th e Cram´ er–Rao bound for sparse linear arrays,” IEEE Transactions on Signal Processing, vol. 67, no. 6, pp. 1493–1507, 2019
2019
-
[30]
Super-resolution with sparse arrays: A non-asymptotic an alysis of spatio-temporal trade-offs,
P . Sarangi, M. C. H¨ uc¨ umeno˘ glu, R. Rajam¨ aki, and P . P al, “Super-resolution with sparse arrays: A non-asymptotic an alysis of spatio-temporal trade-offs,” 2023. [Online]. Availabl e: https://arxiv.org/abs/2301.01734
2023
-
[31]
A bandwidth efficient dual-func tion radar communication system based on a MIMO radar using OFDM wave- forms,
Z. Xu and A. Petropulu, “A bandwidth efficient dual-func tion radar communication system based on a MIMO radar using OFDM wave- forms,” IEEE Transactions on Signal Processing , vol. 71, pp. 401–416, 2023
2023
-
[32]
On the number of signals res olvable by a uniform linear array,
Y . Bresler and A. Macovski, “On the number of signals res olvable by a uniform linear array,” IEEE Transactions on Acoustics, Speech, and Signal Processing, vol. 34, no. 6, pp. 1361–1375, 1986
1986
-
[33]
On unique localization of multip le sources by passive sensor arrays,
M. Wax and I. Ziskind, “On unique localization of multip le sources by passive sensor arrays,” IEEE Transactions on Acoustics, Speech, and Signal Processing, vol. 37, no. 7, pp. 996–1000, 1989
1989
-
[34]
Direction-of-ar rival estimation in applications with multipath and few snapshots,
A. Nehorai, D. Starer, and P . Stoica, “Direction-of-ar rival estimation in applications with multipath and few snapshots,” Circuits, Systems and Signal Processing, vol. 10, no. 3, pp. 327–342, 1991
1991
-
[35]
Resolving manifold ambiguities in direction-of-arrival estimation for nonun iform linear antenna arrays,
Y . Abramovich, N. Spencer, and A. Gorokhov, “Resolving manifold ambiguities in direction-of-arrival estimation for nonun iform linear antenna arrays,” IEEE Transactions on Signal Processing , vol. 47, no. 10, pp. 2629–2643, 1999
1999
-
[36]
On parameter ide ntifiability of MIMO radar,
J. Li, P . Stoica, L. Xu, and W. Roberts, “On parameter ide ntifiability of MIMO radar,” IEEE Signal Processing Letters , vol. 14, no. 12, pp. 968–971, 2007
2007
-
[37]
On parameter ident ifiability of MIMO radar with waveform diversity,
H. Wang, G. Liao, Y . Wang, and X. Liu, “On parameter ident ifiability of MIMO radar with waveform diversity,” Signal Processing , vol. 91, no. 8, pp. 2057–2063, 2011
-
[38]
Direction o f arrival estimation in MIMO radar systems with nonlinear reflectors,
G. Shulkind, G. W. Wornell, and Y . Kochman, “Direction o f arrival estimation in MIMO radar systems with nonlinear reflectors, ” in IEEE International Conference on Acoustics, Speech and Signal P rocessing (ICASSP), 2016, pp. 3016–3020
2016
-
[39]
Parameter identifia bility of space- time MIMO radar,
Z. Hu, J. Peng, K. Luo, and T. Jiang, “Parameter identifia bility of space- time MIMO radar,” Digital Signal Processing, vol. 90, pp. 10–17, 2019
2019
-
[40]
On parameter identifiabilit y of diversity- smoothing-based MIMO radar,
J. Shi, Z. Y ang, and Y . Liu, “On parameter identifiabilit y of diversity- smoothing-based MIMO radar,” IEEE Transactions on Aerospace and Electronic Systems, vol. 58, no. 3, pp. 1660–1675, 2022
2022
-
[41]
Three-way arrays: rank and uniqueness o f trilinear de- compositions, with application to arithmetic complexity a nd statistics,
J. B. Kruskal, “Three-way arrays: rank and uniqueness o f trilinear de- compositions, with application to arithmetic complexity a nd statistics,” Linear Algebra and its Applications , vol. 18, no. 2, pp. 95–138, 1977
1977
-
[42]
Optimally sparse representat ion in general (nonorthogonal) dictionaries via ℓ1 minimization,
D. L. Donoho and M. Elad, “Optimally sparse representat ion in general (nonorthogonal) dictionaries via ℓ1 minimization,” Proceedings of the National Academy of Sciences , vol. 100, no. 5, pp. 2197–2202, 2003
2003
-
[43]
Pushing the limits of spa rse support recovery using correlation information,
P . Pal and P . P . V aidyanathan, “Pushing the limits of spa rse support recovery using correlation information,” IEEE Transactions on Signal Processing, vol. 63, no. 3, pp. 711–726, Feb 2015
2015
-
[44]
Target detection and lo calization using MIMO radars and sonars,
I. Bekkerman and J. Tabrikian, “Target detection and lo calization using MIMO radars and sonars,” IEEE Transactions on Signal Processing , vol. 54, no. 10, pp. 3873–3883, 2006
2006
-
[45]
On signal models for MIMO radar,
B. Friedlander, “On signal models for MIMO radar,” IEEE Transactions on Aerospace and Electronic Systems , vol. 48, no. 4, pp. 3655–3660, 2012
2012
-
[46]
Hadamard, Khatri-Rao, Kroneck er and other matrix products,
S. Liu and G. Trenkler, “Hadamard, Khatri-Rao, Kroneck er and other matrix products,” International Journal of Information and Systems Sciences, vol. 4, no. 1, pp. 160–177, 2008
2008
-
[47]
On probing signal design fo r MIMO radar,
P . Stoica, J. Li, and Y . Xie, “On probing signal design fo r MIMO radar,” IEEE Transactions on Signal Processing , vol. 55, no. 8, pp. 4151–4161, 2007
2007
-
[48]
Skolnik, Introduction to radar systems , 2nd ed
M. Skolnik, Introduction to radar systems , 2nd ed. McGraw-Hill Book Company, 1981
1981
-
[49]
Signal covariance matr ix optimization for transmit beamforming in MIMO radars,
T. Aittom¨ aki and V . Koivunen, “Signal covariance matr ix optimization for transmit beamforming in MIMO radars,” in F orty-First Asilomar Conference on Signals, Systems and Computers , 2007, pp. 182–186
2007
-
[50]
Sign aling strategies for the hybrid MIMO phased-array radar,
D. R. Fuhrmann, J. P . Browning, and M. Rangaswamy, “Sign aling strategies for the hybrid MIMO phased-array radar,” IEEE Journal of Selected Topics in Signal Processing , vol. 4, no. 1, pp. 66–78, 2010
2010
-
[51]
Coarrays, MUSIC, and the Cram´ e r-Rao bound,
M. Wang and A. Nehorai, “Coarrays, MUSIC, and the Cram´ e r-Rao bound,” IEEE Transactions on Signal Processing , vol. 65, no. 4, pp. 933–946, Feb 2017
2017
-
[52]
Tao and V
T. Tao and V . H. Vu, Additive Combinatorics , ser. Cambridge Studies in Advanced Mathematics. Cambridge University Press, 2006
2006
-
[53]
MIMO radar space–ti me adaptive processing using prolate spheroidal wave functions,
C.-Y . Chen and P . P . V aidyanathan, “MIMO radar space–ti me adaptive processing using prolate spheroidal wave functions,” IEEE Transactions on Signal Processing , vol. 56, no. 2, pp. 623–635, 2008
2008
-
[54]
Towards a mathe matical theory of super-resolution,
E. J. Cand` es and C. Fernandez-Granda, “Towards a mathe matical theory of super-resolution,” Communications on Pure and Applied Mathematics, vol. 67, no. 6, pp. 906–956, 2014
2014
-
[55]
Superresolution via sparsity constrain ts,
D. L. Donoho, “Superresolution via sparsity constrain ts,” SIAM Journal on Mathematical Analysis , vol. 23, no. 5, pp. 1309–1331, 1992
1992
-
[56]
Tse and P
D. Tse and P . Viswanath, Fundamentals of Wireless Communication . Cambridge University Press, 2005
2005
-
[57]
Massive MIMO for next generation wireless systems,
E. G. Larsson, O. Edfors, F. Tufvesson, and T. L. Marzett a, “Massive MIMO for next generation wireless systems,” IEEE Communications Magazine, vol. 52, no. 2, pp. 186–195, 2014
2014
-
[58]
Robustness of differ ence coarrays of sparse arrays to sensor failures—Part I: A theory motivated by coarray MUSIC,
C.-L. Liu and P . P . V aidyanathan, “Robustness of differ ence coarrays of sparse arrays to sensor failures—Part I: A theory motivated by coarray MUSIC,” IEEE Transactions on Signal Processing , vol. 67, no. 12, pp. 3213–3226, 2019
2019
-
[59]
Dual-function MI MO radar communications system design via sparse array optimizatio n,
X. Wang, A. Hassanien, and M. G. Amin, “Dual-function MI MO radar communications system design via sparse array optimizatio n,” IEEE Transactions on Aerospace and Electronic Systems , vol. 55, no. 3, pp. 1213–1226, 2019
2019
-
[60]
Adaptive and fas t com- bined waveform-beamforming design for mmwave automotive j oint communication-radar,
P . Kumari, N. J. Myers, and R. W. Heath, “Adaptive and fas t com- bined waveform-beamforming design for mmwave automotive j oint communication-radar,” IEEE Journal of Selected Topics in Signal Pro- cessing, vol. 15, no. 4, pp. 996–1012, 2021
2021
-
[61]
Jafarkhani, Space-Time Coding: Theory and Practice
H. Jafarkhani, Space-Time Coding: Theory and Practice . Cambridge University Press, 2005
2005
-
[62]
Stoica and R
P . Stoica and R. L. Moses, Spectral analysis of signals . Pearson Prentice Hall Upper Saddle River, NJ, 2005
2005
Reviewed May 24, 2026 · model on record in the stance chip above.
Discussion (0). Sign in to comment.