REVIEW 2 major objections 4 minor 32 references
In multi-cell OFDM-ISAC, closed-form delay–Doppler SINR expressions turn constellation selection and per-subcarrier power allocation into tractable design.
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · deepseek-v4-flash
2026-08-01 07:28 UTC pith:S4OW3KYB
load-bearing objection Solid closed-form multi-cell ISAC SINR framework with a real caveat: the MF SINR is an offset-averaged quantity, not a true per-bin worst-case, so the derived power allocations optimize an average. the 2 major comments →
Constellation Selection and Power Allocation for Multi-Cell OFDM-ISAC: Managing Inter-Cell Interference and Sensing Sidelobes
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The central discovery: the delay–Doppler sensing SINR in multi-cell OFDM-ISAC has closed forms. Matched filtering (Eq. 22) is set by fourth-order constellation moments, inter-cell power-overlap terms, and noise; reciprocal filtering (Eq. 25) by inverse-symbol-power moments and interfering-to-sensing power ratios. Maximizing them gives opposite power laws — avoid interfered tones under MF, reinforce them under RF — and joint constellation/power selection becomes mixed-integer convex. A two-cell benchmark shows MF's sharing-versus-orthogonalization threshold; masked RF always prefers minimal overlap. Beyond-CP interference conserves energy, redistributing it via a Dirichlet-squared leakage ker
What carries the argument
The load-bearing object is the per-DD-bin SINR identity. It is built from the DD-domain cross-ambiguity kernel χ(ℓ,0)[k,p], evaluated with receive weight V_m[n] equal to the conjugate data symbol (matched filtering) or its reciprocal (reciprocal filtering). Constellation geometry enters only through two moments, µ4 = E|s|^4 and µ−2 = E|s|^−2. The derivation uses Parseval's theorem plus a maximum-entropy uniform-offset approximation that replaces the per-bin sidelobe level by an average over all non-peak bins, yielding Eq. (22) and Eq. (25); the beyond-CP extension is carried by the effective interference spectrum P_eff[n].
Load-bearing premise
The load-bearing premise is the maximum-entropy uniform-offset approximation of Appendix A (after Eq. 53): undesired monostatic target and clutter offsets are treated as equally likely, so one averaged sidelobe power represents the MF interference floor; the on-grid integer-delay model and the masked-RF footnote (which sets aside active-tone-pattern sidelobes) are related idealizations — if clutter concentrates at particular offset bins, the closed-form SINR and allocations a
What would settle it
Run the MF receiver of Section II in a scenario with exactly one strong stationary clutter point (zero Doppler, fixed delay) and one weak target at a different DD bin; compare the measured SINR at the weak-target bin to Eq. (22) using the true path powers. If the discrepancy grows as the clutter's offset distance varies while the averaged sidelobe power stays constant, the uniform-offset assumption is falsified. An even more direct check is to compute the per-bin sidelobe power E|χ_MF[k,p]|^2 from Eq. (49) and compare its peak over all non-peak bins to the average ρ̄_MF used in Eq. (22).
If this is right
- A base station can jointly pick, per subcarrier, a standard constellation and a power level to lower the DD-domain interference floor; simulations show weak-target peaks become visible under both filters.
- MF and RF need opposite power strategies: MF should reduce power on heavily interfered tones, RF should increase power there; both laws are closed-form and require only one-dimensional bisection or a square-root normalisation.
- The threshold in the two-cell benchmark tells cells when full spectral overlap is better than orthogonalization for MF; masked RF, by contrast, always reduces overlap when inter-cell coupling exists.
- Beyond-CP propagation delays do not create new interference energy; they redistribute it, so the derived MF/RF allocation laws survive by replacing the nominal inter-cell spectrum with the delay-distorted effective spectrum.
- Communication rate and reliability constraints can be traded against sensing SINR in a computable way, giving an explicit sensing–communication tradeoff curve.
Where Pith is reading between the lines
- The paper leaves implicit that, because the SINRs depend only on two constellation moments, other signal formats with known moments could plug into the same allocation framework without re-derivation.
- The uniform-offset approximation makes Eq. (22) an average-SINR statement; a natural extension is to re-derive or numerically check the per-bin SINR under concentrated clutter, where the power allocations could differ.
- The beyond-CP leakage kernel suggests a coordination idea the paper does not pursue: deliberately place interferer subcarriers so that leaked Dirichlet-squared sidelobes fall on sensing tones where the victim's weight is small.
- Since MF and RF prefer opposite spectrum-sharing structures, a mixed-filter network might split shared and orthogonalized tones between RF and MF cells rather than applying one policy globally.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper develops a modulation- and receive-filter-aware framework for multi-cell OFDM-ISAC. It derives closed-form DD-domain sensing SINR expressions for matched filtering (MF) and reciprocal filtering (RF), showing that MF depends on fourth-order constellation moments and power-overlap inter-cell terms while RF depends on inverse-symbol-power moments and ratio-type interference. Based on these expressions, it proposes MF and RF power-allocation laws (ramped water-filling and square-root), formulates joint constellation-selection and power-allocation problems as mixed-integer convex programs, analyzes spectrum-overlap coordination in a symmetric two-BS benchmark, and extends the interference model to beyond-CP delays with an effective spectrum characterization. The analytical formulas are validated by Monte Carlo simulations in Fig. 3, and the optimized profiles are shown to lower the DD-interference floor and improve weak-target visibility.
Significance. If the results are accepted, the paper provides a useful analytical bridge between finite-alphabet modulation, receive filtering, and multi-cell interference management in OFDM-ISAC. The closed-form SINR expressions (22) and (25) are credible and supported by the appendices and simulation; the identification of opposing MF/RF power-allocation behaviors (interference avoidance vs. compensation) is a valuable design insight. The mixed-integer convex reformulations are a practical step toward standards-compliant constellation selection and per-subcarrier power control. The beyond-CP leakage analysis, including the delay-distorted effective spectrum and the conservation of total interference energy, is a useful extension. The paper is generally self-contained and transparent about its approximations, though the per-bin interpretation of the MF SINR and one spectrum-coordination result need qualification.
major comments (2)
- [Section III-A / Appendix A, Eqs. (22), (53)-(55)] Equation (22) is presented as the 'per-bin' MF SINR, but the proof in Appendix A replaces every undesired monostatic path's DD offset by the offset-averaged sidelobe power rho_bar_MF. After Eq. (53), the relative DD offsets are modeled as i.i.d. uniform over G\{(0,0)}, so Eq. (22) is the SINR averaged over the offset distribution, not the SINR of a specified DD bin. This is a modeling choice, but the abstract's 'each range-Doppler bin' and Prop. 1's 'per-bin SINR' overstate what is proven. In a scene with strong stationary clutter near zero Doppler, or clutter sharing the target's bin, the true per-bin interference floor can be far above rho_bar_MF, and the MF power allocations (Prop. 3, Problem (33)) derived from this average are not necessarily optimal for that bin. Please rephrase Eq. (22) as an average SINR under the uniform-offset model and add a per-bin worst-case caveat.
- [Section III-E2 / Appendix D, Prop. 6 and Remark 3] The minimum-overlap conclusion for masked RF is derived from a surrogate that includes the mainlobe gain and the denominator terms in (37), but it omits active-tone-pattern-induced sidelobes and ambiguity peaks, as the footnote in Section III-E2 acknowledges. Since masked RF zeroes out subcarriers, the comb pattern inevitably creates additional DD responses that can dominate the overlap-versus-noise tradeoff. As stated, Remark 3 ('masked RF favours the minimum feasible overlap whenever inter-cell coupling is present') is stronger than the analysis supports. Please qualify Prop. 6 and Remark 3 to the considered mainlobe/denominator surrogate and discuss how tone-pattern sidelobes could affect the overlap choice.
minor comments (4)
- [Contributions bullet 2 / Prop. 3] The contributions list says 'closed-form optimal power allocation laws,' but Prop. 3 is explicitly a denominator-minimization surrogate with the numerator's profile-dependent term treated as negligible. The proposition itself is correctly labeled, but the contributions and conclusions should consistently use 'surrogate-optimal' to avoid overstatement.
- [Section II / Notational clarity] The symbol EISL is used in Section IV and in the introduction but is formally defined only in Appendix A (Eq. (52)). Consider defining it in the main text when it first appears.
- [Appendix B, Eq. (57)] The derivation of E[|χ^{(ℓ,0)}_{RF}[k,p]|^2] is only stated; a one-line expansion showing how the reciprocal filter 1/X leads to μ_{-2,n}/P_n would improve readability.
- [General / Typos] There are minor typographical issues, e.g., in Eq. (22) the large parentheses in the sidelobe term are not visually balanced, and in Appendix A the phrase 'the main peak[k, p] = (0,0)' should be '[k,p]=(0,0)' for consistency.
Circularity Check
No significant circularity: the SINR and power-allocation derivations are self-contained given the paper's explicit model assumptions.
full rationale
The paper's central derivations do not reduce to their inputs by construction. The MF SINR in Eq. (22) is obtained in Appendix A by direct expansion of the ambiguity-function kernel, Parseval's identity, and a clearly stated uniform-offset approximation for undesired monostatic scatterer offsets (after Eq. 53). That approximation turns the per-offset sidelobe powers into an averaged value rho_bar_MF, which is a modeling assumption about scatterer statistics, not a fitted input or a definitional restatement of the SINR. The RF SINR in Eq. (25) is likewise derived from the reciprocal-filter weight and elementary symbol moments. Propositions 3 and 4 are KKT-derived closed forms for the denominator surrogates, and Propositions 5 and 6 are explicit optimizations for symmetric benchmarks. The references to the authors' prior work [13], [15], [17] supply constellation-moment and BER-threshold building blocks that are independently introduced in Eq. (4) and are not the paper's novel multi-cell interference result. The skeptical concern that the uniform-offset averaging makes Eq. (22) an average rather than a per-bin SINR is a legitimate robustness caveat, but it concerns the fidelity of an explicit assumption, not circular reasoning. No fitted parameter is relabeled as a prediction, no uniqueness theorem is imported from self-citation, and no load-bearing ansatz is smuggled in via a self-reference. The derivation chain is therefore not circular; at most it relies on minor, non-load-bearing reuse of the authors' earlier, independently derivable moment/threshold results.
Axiom & Free-Parameter Ledger
axioms (9)
- domain assumption On-grid DD model: paths within CP with integer sample-spaced delays and Doppler aligned to the processing grid.
- ad hoc to paper Uniform-offset/maximum-entropy sidelobe model: relative DD offsets of undesired monostatic paths are uniformly distributed over non-peak bins.
- domain assumption Path phases are independent random phases; path powers are fixed.
- domain assumption Full-band RF with P_n>0 on all N subcarriers.
- domain assumption Inter-cell interference profiles and path powers are known over the design interval.
- domain assumption Beyond-CP analysis: integer excess delay d in {1,...,N-1}, at most one-symbol ISI, and no Doppler/CFO on quasi-static inter-cell links.
- domain assumption Symmetric homogeneous twin-BS abstraction for spectrum-overlap results.
- domain assumption Masked-RF active-tone-pattern sidelobes are ignored.
- domain assumption Communication thresholds Gamma_j taken from standard BER-vs-SINR curves of the selected constellations.
read the original abstract
Future integrated sensing and communication (ISAC) networks are expected to operate in dense multi-cell environments, where multiple base stations (BSs) share their time-frequency resources for communication and sensing. In such scenarios, the delay--Doppler (DD) sensing performance is strongly affected by random finite-alphabet orthogonal frequency-division multiplexing (OFDM) symbols, power allocation, receive filtering, and interference. This paper develops a modulation- and receive-filter-aware framework for the sensing-interference management in multi-cell OFDM-ISAC systems. Starting from a discrete-time OFDM sensing model, we derive closed-form signal-to-interference-plus-noise ratio (SINR) expressions for each range--Doppler bin under matched filtering (MF) and reciprocal filtering (RF). The analysis reveals distinct interference structures: MF depends on fourth-order constellation moments and power-overlap terms, whereas RF is governed by inverse-symbol-power and ratio-type interference terms. Based on these expressions, we obtain sensing-oriented power allocation structures, including a ramped water-filling solution for MF and a square-root allocation rule for RF. Furthermore, we jointly optimize the finite-alphabet constellation selection and power allocation under realistic communication and power constraints, and obtain tractable mixed-integer convex formulations for both MF and RF. Additionally, we study spectrum-overlap coordination in multi-cell scenarios and reveal the distinct MF/RF preferences for shared and orthogonalized tones. Furthermore, we extend the interference model to inter-cell propagation delays exceeding the cyclic prefix (CP), and show how the resultant delay violation redistributes the nominal interference spectrum into a delay-distorted effective spectrum...
Figures
Reference graph
Works this paper leans on
-
[1]
On the road to 6G: Visions, requirements, key technologies, and testbeds,
C.-X. Wanget al., “On the road to 6G: Visions, requirements, key technologies, and testbeds,”IEEE Communications Surveys & Tutorials, vol. 25, no. 2, pp. 905–974, 2023
2023
-
[2]
Integrated sensing and communications: Towards 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: Towards dual-functional wire- less networks for 6G and beyond,”IEEE J. Sel. Areas Commun., vol. 40, no. 6, pp. 1728–1767, Jun. 2022
2022
-
[3]
Integrated sensing and communications: Recent advances and ten open challenges,
S. Luet al., “Integrated sensing and communications: Recent advances and ten open challenges,”IEEE Internet Things J., vol. 11, no. 11, pp. 19 094–19 120, 2024
2024
-
[4]
Joint radar and communication design: Applications, state- of-the-art, and the road ahead,
F. Liuet al., “Joint radar and communication design: Applications, state- of-the-art, and the road ahead,”IEEE Trans. Commun., vol. 68, no. 6, pp. 3834–3862, Jun. 2020
2020
-
[5]
An overview of signal processing techniques for joint communication and radar sensing,
J. A. Zhanget 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, 2021
2021
-
[6]
A survey on fundamental limits of integrated sensing and communication,
A. Liuet al., “A survey on fundamental limits of integrated sensing and communication,”IEEE Commun. Surveys Tuts., vol. 24, no. 2, pp. 994–1034, Nov. 2022
2022
-
[7]
Toward millimeter-wave joint radar communi- cations: A signal processing perspective,
K. V . Mishraet al., “Toward millimeter-wave joint radar communi- cations: A signal processing perspective,”IEEE Signal Proces. Mag., vol. 36, no. 5, pp. 100–114, Sep. 2019
2019
-
[8]
Device-free sensing in OFDM cellular network,
Q. Shi, L. Liu, S. Zhang, and S. Cui, “Device-free sensing in OFDM cellular network,”IEEE J. Sel. Areas Commun., vol. 40, no. 6, pp. 1838– 1853, Jun. 2022
2022
-
[9]
Integrated sensing and communication signals toward 5G-A and 6G: A survey,
Z. Weiet al., “Integrated sensing and communication signals toward 5G-A and 6G: A survey,”IEEE Internet Things J., vol. 10, no. 13, pp. 11 068–11 092, 2023
2023
-
[10]
Random ISAC signals deserve dedicated precoding,
S. Luet al., “Random ISAC signals deserve dedicated precoding,”IEEE Trans. Signal Processing, vol. 72, pp. 3453–3469, 2024
2024
-
[11]
Next-generation MIMO transceivers for integrated sensing and communications: Unique security vulnerabilities and solutions,
K. Han, C. Masouros, T. Riihonen, and M. G. Amin, “Next-generation MIMO transceivers for integrated sensing and communications: Unique security vulnerabilities and solutions,”Proceedings of the IEEE, pp. 1– 34, 2026
2026
-
[12]
On ambiguity function shaping for broadband constant-modulus signals,
M. A. Chitre, J. Tian, and H. Vishnu, “On ambiguity function shaping for broadband constant-modulus signals,”Signal Processing, vol. 166, p. 107224, 2020
2020
-
[13]
Reshaping the ISAC tradeoff under OFDM signaling: A probabilistic constellation shaping approach,
Z. Duet al., “Reshaping the ISAC tradeoff under OFDM signaling: A probabilistic constellation shaping approach,”IEEE Trans. Signal Process., vol. 72, pp. 4782–4797, 2024
2024
-
[14]
Probabilistic constellation shaping for OFDM ISAC signals under temporal-frequency filtering,
——, “Probabilistic constellation shaping for OFDM ISAC signals under temporal-frequency filtering,”arXiv preprint arXiv:2510.12204, 2025
arXiv 2025
-
[15]
Constellation design in OFDM-ISAC over data payloads: From MSE analysis to experimentation,
K. Han, K. Meng, A. Chatzicharistou, and C. Masouros, “Constellation design in OFDM-ISAC over data payloads: From MSE analysis to experimentation,”arXiv preprint arXiv:2510.13101, 2025
arXiv 2025
-
[16]
Sensing with communication signals: From information theory to signal processing,
F. Liu, Y .-F. Liu, Y . Cui, C. Masouros, J. Xu, T. Xiao Han, S. Buzzi, Y . C. Eldar, and S. Jin, “Sensing with communication signals: From information theory to signal processing,”IEEE J. Sel. Areas Commun., vol. 44, pp. 1–30, 2026
2026
-
[17]
Constellation selection and power control for OFDM-based ISAC: From theory to prototype,
K. Meng, K. Han, C. Masouros, and F. Liu, “Constellation selection and power control for OFDM-based ISAC: From theory to prototype,”IEEE Trans. Signal Process., pp. 1–16, 2026
2026
-
[18]
MIMO-OFDM ISAC waveform design for range-doppler sidelobe suppression,
P. Li, M. Li, R. Liu, Q. Liu, and A. Lee Swindlehurst, “MIMO-OFDM ISAC waveform design for range-doppler sidelobe suppression,”IEEE Trans. Wireless Commun., vol. 24, no. 2, pp. 1001–1015, 2025
2025
-
[19]
Sensing-oriented adaptive resource allocation designs for OFDM-ISAC systems,
P. Li, M. Li, R. Liu, Q. Liu, and A. L. Swindlehurst, “Sensing-oriented adaptive resource allocation designs for OFDM-ISAC systems,”IEEE Trans. Signal Processing, vol. 73, pp. 5121–5135, 2025
2025
-
[20]
Learning-based constellation design for uplink bi-static integrated sensing and communication,
J. Huet al., “Learning-based constellation design for uplink bi-static integrated sensing and communication,”IEEE Trans. V eh. Technol., vol. 74, no. 8, pp. 13 219–13 224, 2025
2025
-
[21]
Joint optimization of geometric and probabilistic constellation shaping for OFDM-ISAC systems,
B. Geiger, F. Liu, S. Lu, A. Rode, and L. Schmalen, “Joint optimization of geometric and probabilistic constellation shaping for OFDM-ISAC systems,” inProc. IEEE JC&S, Jan. 2025
2025
-
[22]
Probabilistic constellation shaping for OFDM-based ISAC signaling,
Z. Du, F. Liu, Y . Xiong, T. X. Han, W. Yuan, Y . Cui, C. Yao, and Y . C. Eldar, “Probabilistic constellation shaping for OFDM-based ISAC signaling,” in2023 IEEE Globecom Workshops (GC Wkshps), Kuala Lumpur, Malaysia, 2023, pp. 509–514
2023
-
[23]
Constellation design for integrated sensing and com- munication with random waveforms,
X. Yanget al., “Constellation design for integrated sensing and com- munication with random waveforms,”IEEE Trans. Wireless Commun., vol. 23, no. 11, pp. 17 415–17 428, 2024
2024
-
[24]
Cooperative ISAC networks: Performance analysis, scaling laws, and optimization,
K. Meng, C. Masouros, A. P. Petropulu, and L. Hanzo, “Cooperative ISAC networks: Performance analysis, scaling laws, and optimization,” IEEE Trans. Wireless Commun., vol. 24, no. 2, pp. 877–892, 2025
2025
-
[25]
Network-level ISAC design: State-of-the-art, challenges, and opportunities,
K. Han, K. Meng, X.-Y . Wang, and C. Masouros, “Network-level ISAC design: State-of-the-art, challenges, and opportunities,”IEEE J. Sel. Top. Electromagn. Antenn. Propag., vol. 1, no. 1, pp. 65–83, 2025
2025
-
[26]
Cooperative ISAC networks: Opportunities and challenges,
K. Meng, C. Masouros, A. P. Petropulu, and L. Hanzo, “Cooperative ISAC networks: Opportunities and challenges,”IEEE Wireless Commu- nications, vol. 32, no. 3, pp. 212–219, 2025
2025
-
[27]
Toward seamless sensing coverage for cellular multi-static integrated sensing and communication,
R. Li, Z. Xiao, and Y . Zeng, “Toward seamless sensing coverage for cellular multi-static integrated sensing and communication,”IEEE Trans. Wireless Commun., vol. 23, no. 6, pp. 5363–5376, 2024
2024
-
[28]
Isac from the sky: UA V trajectory design for joint communication and target localization,
X. Jing, F. Liu, C. Masouros, and Y . Zeng, “Isac from the sky: UA V trajectory design for joint communication and target localization,”IEEE Transactions on Wireless Communications, vol. 23, no. 10, pp. 12 857– 12 872, 2024
2024
-
[29]
Deployment optimization of dual- functional uavs for integrated localization and communication,
Z. Yang, S. Bi, and Y .-J. A. Zhang, “Deployment optimization of dual- functional uavs for integrated localization and communication,”IEEE Transactions on Wireless Communications, vol. 22, no. 12, pp. 9672– 9687, 2023
2023
-
[30]
3D multi-target localization via intelligent reflecting surface: Protocol and analysis,
M. Huaet al., “3D multi-target localization via intelligent reflecting surface: Protocol and analysis,”IEEE Trans. Wireless Commun., 2024
2024
-
[31]
Networked sensing with AI- empowered interference management: Exploiting macro-diversity and array gain in perceptive mobile networks,
L. Xie, S. Song, and K. B. Letaief, “Networked sensing with AI- empowered interference management: Exploiting macro-diversity and array gain in perceptive mobile networks,”IEEE J. Sel. Areas Commun., pp. 1–1, Apr. 2023
2023
-
[32]
Sensing-secure ISAC: Ambiguity function engineering for impairing unauthorized sensing,
K. Han, K. Meng, and C. Masouros, “Sensing-secure ISAC: Ambiguity function engineering for impairing unauthorized sensing,”IEEE Trans. Wireless Commun., vol. 25, pp. 5386–5400, 2026
2026
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.