REVIEW 4 major objections 4 minor 2 cited by
A MIMO ISAC System for Ultra-Reliable and Low-Latency Communications
T0 review · 4 major / 4 minor · reviewed 2026-08-10 · deepseek-v4-flash
Pith's one-line read A sensing-triggered MIMO ISAC scheme with dirty-paper coding promises higher eMBB rates while meeting URLLC and detection constraints.
desk verdict Good premise, but the central rate bound assumes an independence the system model itself breaks. 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 load-bearing mechanism is a two-stage dirty-paper coding (DPC) construction. In a block with no URLLC message, DPC with parameter \(\alpha_{s,1}\) precancels the sensing signal from the eMBB codebook. In a block carrying URLLC, the transmitter first precancels the sensing signal from the eMBB signal with \(\alpha_{s,2}\), then precancels the combined eMBB-plus-sensing interference from the URLLC codeword with \(\alpha_u\) (equations 13–18). This makes the URLLC message see an almost interference-free channel despite riding on top of eMBB and sensing. The companion machinery is finite-blocklength Gaussian approximation: the information densities are shown to converge to Gaussians with means and variances built from the eigenvalues of the channel Gram matrices, so error probabilities are handled with Q-functions and Berry–Esseen corrections rather than asymptotic capacity arguments.
What would settle it
Run a Monte Carlo simulation of the sensing-triggered protocol: generate target echoes under Lemma 1's channel model, apply the likelihood-ratio test with the same false-alarm threshold, and record the set of blocks in which a URLLC message is actually transmitted and decoded. If the empirical joint distribution of this set diverges from the product formula \(P[\mathcal{B}_{\mathrm{detect}} = \mathcal{B}_{dt}] = P_{\mathrm{det}}^{|\mathcal{B}_{dt}|}(1-P_{\mathrm{det}})^{\eta-|\mathcal{B}_{dt}|}\) used in Lemma 3, the eMBB rate bound in Theorem 1 is not the true rate of the protocol at finite blocklength.
Extended reading notes
Core claim
On its own terms, the paper establishes the rate-reliability-detection tradeoff for a bi-static MIMO ISAC system with sensing-triggered URLLC. The central result, Theorem 1 (equation 49), maximizes the upper bound on the eMBB rate, \(R_e \leq C_e - \sqrt{V_e/n}\,$Q^{{-1}}$(\epsilon_e - \Delta_e) - K_e \frac{\log\,n}{n} - \frac{\log\,M_s}{n}\), over the DPC power-splitting parameters \(\beta_u, \beta_{s,1}, \beta_{s,2}\) and \(\alpha_u, \alpha_{s,1}, \alpha_{s,2}\), subject to per-block URLLC error probability at most \(\epsilon_U\) and per-block detection probability at least \(P_D\). This bound is assembled from Lemma 1 (the detection probability expressed through generalized chi-square statistics of the echo), Lemma 2 (the URLLC error probability decomposed into missed-detection, misdecoding, and false-alarm events), and Lemma 3 (the eMBB rate bound conditioned on which blocks were detected as carrying URLLC). The claim that the scheme outperforms power-sharing and time-sharing is that this optimized bound lies strictly above the corresponding bounds of those schemes at the same constraints.
Load-bearing premise
The derivation assumes that whether the UE thinks a URLLC message arrived in a block is an independent coin flip with one fixed probability, even though in the protocol a detection in one block changes how likely the next block carries a URLLC message.
Editorial extensions
If this is right
- If Theorem 1 is correct, the same power budget can serve eMBB, URLLC, and sensing simultaneously, with no orthogonal resource split, so the eMBB rate is not cut by the sensing duty.
- Tightening the URLLC reliability requirement \(\epsilon_U\) lowers the maximal eMBB rate; the paper's numerical curves show the scheme absorbs this loss more gently than power- or time-sharing.
- Raising the required detection probability \(P_D\) also lowers the eMBB rate; at a fixed \(P_D\) the DPC scheme holds a rate margin over both baselines.
- Because URLLC transmissions are triggered by physical detection rather than by an assumed Bernoulli arrival process, the scheme extends to environments where URLLC events are deterministic or unpredictable.
- The detector threshold can be set to meet a desired false-alarm probability while the DPC parameters are re-optimized per block, decoupling sensing robustness from communication reliability.
Reading between the lines
- If block-level detection outcomes are serially correlated because a detection in block \(b\) changes the probability of a URLLC transmission in block \(b+1\), the product-form probability in Lemma 3 may overstate how often the UE's detection set matches the true arrival set; a Markov-chain extension could be tested against the paper's binomial formula.
- The same trigger loop could be inverted: instead of sensing triggering URLLC, a URLLC arrival could be used as a sensing cue, turning the scheme into a communication-driven radar setup.
- One can test DPC gain with imperfect channel state information by treating estimation error as additional interference to be precanceled; the present framework already supplies the SNR-like terms where such error would enter.
- Because the sensing receiver and the base station are linked by an ideal backhaul in the paper, a practical latency budget would need to fold backhaul delay into the trigger decision, turning the current per-block tradeoff into a latency-aware scheduling law.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies a bi-static MIMO ISAC system in which a sensing receiver detects the presence of a target and, upon detection, triggers the transmission of a URLLC message over the next block. The base station employs dirty-paper coding to precancel sensing and eMBB interference, and the authors derive a finite-blocklength rate-reliability-detection trade-off. The central result, Theorem 1, formulates a constrained maximization of an upper bound on the eMBB rate, with constraints on URLLC decoding error and target detection probability. Numerical results compare the proposed DPC-based scheme against power-sharing and time-sharing baselines and claim significant outperformance.
Significance. If the derivations were sound, the paper would offer a useful finite-blocklength framework for a sensing-triggered URLLC traffic model, which is a nontrivial extension of earlier works that assume Bernoulli or deterministic URLLC arrivals. The random-coding structure and the explicit closed-form expressions for the detection probability, URLLC error probability, and eMBB rate bound are a strength. However, the central rate bound relies on an independence assumption that is contradicted by the paper's own system model, and additional load-bearing steps are asserted rather than proved. As a result, Theorem 1 and the numerical comparisons do not currently provide a reliable achievability statement.
major comments (4)
- [Appendix C, Eq. (95)] The binomial formula P[Bdetect = Bdt] = Pdet^{|Bdt|}(1-Pdet)^{eta-|Bdt|} requires the events {b in Bdetect} to be independent and identically distributed across blocks with common probability Pdet. This is not consistent with the system model. In Section II, A_1 = 0 and P(A_b = 1) = P_{b-1,D} for b >= 2, while Lemma 1 shows that P_{b,D} depends on whether b is in Barrival through the factors kappa1 and kappa2 in Eqs. (27)-(29). Hence A_{b+1} depends on A_b through the sensing detection probability, creating serial dependence, and the marginal probability Pdet defined in Eqs. (92)-(94) is not block-invariant because P_{b-1,D} varies with b and with the sensing channel eigenvalues. No conditioning or Markov-chain calculation is provided to replace the product form. Since Ce, Ve, and Delta_e in Eqs. (41)-(48) are weighted by this product, the objective in Theorem 1 and the numerical outperformance claims are not justified.
- [Appendix C, Eq. (100)] The expression for P[Ee,1|Bdetect = Bdt] is not a valid product of probabilities over the intended events. For a block b not in Bdt and not in Barrival, the required event is that no false alarm occurs, whose probability is 1 - P[EU,3]. The numerator in Eq. (100) instead uses P[EU,1](1-P_{b-1,D}) for the non-detected blocks, where P[EU,1] is the missed-detection probability defined in Eq. (37) for blocks in which a URLLC was actually transmitted. Thus the second factor in the numerator applies the missed-detection probability to blocks without a URLLC arrival, which is not the event of interest. This directly affects Delta_e in Eq. (48) and therefore the Q^{-1} inversion leading to the rate bound in Eq. (109).
- [Section III-A, Eqs. (13)-(18)] The admissible-power condition Tr(XX^H) <= nP is asserted at the start of Section III but never proved for the proposed encoding. For a block b not in Barrival, the transmitted signal is X_{b,j} = S^{(1)}_{b,j}(m',s) + (1-alpha_{s,1}) X^{(s,1)}_{b,j}; its squared norm contains the cross term 2(1-alpha_{s,1}) Re<S^{(1)}, X^{(s,1)}>. The DPC condition in Eq. (13) constrains only the norm of S^{(1)} - alpha_{s,1} X^{(s,1)} and does not control this cross term. A similar issue appears for URLLC blocks through Eqs. (16)-(18). Without a proof that the generated codewords satisfy the power constraint, the finite-blocklength achievability bounds and the numerical optimization over beta and alpha in Theorem 1 are not grounded.
- [Section III-B.1, paragraph after Eq. (13)] The paper states, 'For simplicity, we assume that at least one such a codeword exists' for the DPC encoding step. This is a non-trivial covering assumption: for every realization of the message and channel, there must exist an index s such that the precoded codeword falls in the required shell. The failure probability of this event under the random codebook construction is never bounded, and similarly for the index v in the URLLC encoding in Section III-B.2. Because the encoders in Definition 1 must be defined for every message, this assumption is part of the achievability argument and cannot be waived without quantification.
minor comments (4)
- [Section III-C.2, Eq. (25)] In the second term of the information density expression, the density f_{Y_{b,c}|S^{(2)}_b}(y_{b,c}|s^{(1)}_b) should condition on s^{(2)}_b, the codeword used in blocks b in Bdt, rather than on s^{(1)}_b.
- [Appendix C, Eq. (94) and Lemma 3, Eq. (47)] The definition of Pdet is inconsistent between the main text and the appendix: Eq. (47) uses PU,2 as defined in Eq. (32), while Eq. (94) writes (1 - P_{b-1,D})(1 - (1 - tilde{epsilon}_{U,2})^{M_U M_v}) without the division by M_U M_v inside the exponent. Since Pdet enters Ce, Ve, and Delta_e, this discrepancy must be resolved.
- [Abstract] The phrase 'Our numerical analysis show' should be 'Our numerical analysis shows'.
- [Section V] The numerical optimization procedure is described only verbally: it is not stated how the search over (alpha_u, beta_u) is performed, whether the constraints in Eqs. (49b)-(49c) are evaluated for every possible realization of Barrival or only for a stationary/averaged version, or what values are used for the auxiliary codebook sizes M_v and M_s. These details are needed to reproduce the figures.
Circularity Check
No significant circularity: Theorem 1 is derived from the channel model and external finite-blocklength CLT bounds, not from a fitted parameter or a self-citation chain.
full rationale
The paper's central result, Theorem 1's rate-reliability-detection trade-off, is derived from explicit channel-law calculations and standard finite-blocklength random-coding bounds rather than from any quantity fitted to data or defined in terms of the target result. Lemma 1 computes the detection probability from the LRT and generalized chi-square distributions (Appendix A). Lemma 2 upper-bounds the URLLC error using the Berry-Esseen CLT result of MolavianJazi and Laneman [21] and the threshold bound of Polyanskiy, Poor, and Verdú [22], both external standard results. Lemma 3 uses the same external CLT machinery together with a binomial decomposition of the detected-block set; the quantity Pdet in Eq. (47) is computed from the model's detection and error probabilities, not fitted to the eMBB rate. The claimed outperformance over power-sharing and time-sharing is a numerical evaluation of the derived bound, not a re-discovery of an imposed advantage. Self-citations appear in the motivation and in the DPC construction ([15], [18]), but these are not load-bearing: the DPC encoding is defined in the paper itself and the finite-blocklength ISAC framework is only a framing reference. The most serious caveat is that Eq. (95) assumes independent, identically distributed detection events across blocks even though the model's P_{b,D} is block-dependent and serially coupled through the arrival process; that is a modeling-validity or correctness concern, not circularity, since the conclusion is not assumed as an input.
Assumptions & free parameters
free parameters (4)
- DPC and power-splitting parameters alpha_u, alpha_s,1, alpha_s,2, beta_u, beta_s,1, beta_s,2 =
not specified; optimized numerically
- Positive constants K_U, B, K_e, B_tilde =
unspecified
- Auxiliary codebook sizes M_v, M_s =
not specified
- Shell slack parameters zeta_s,1, zeta_s,2, zeta_u =
not specified
assumptions (5)
- domain assumption MIMO memoryless Gaussian quasi-static fading channel with channel state information known at both BS and UE.
- domain assumption The SR and BS can communicate over an interference-free backhaul link, and the UE is outside the sensing range.
- standard math The information density of the power-shell DPC-coded scheme converges to a Gaussian distribution as stated in Lemma 4/5, citing [21, Proposition 1].
- ad hoc to paper For every message realization there exists at least one DPC index s (and v) such that the precoded codeword lies in the required shell D(...,zeta).
- ad hoc to paper URLLC detection events across blocks are independent and identically distributed with a common probability Pdet.
Cite this review
Pith. "Pith review of A MIMO ISAC System for Ultra-Reliable and Low-Latency Communications." pith.science (2026). https://pith.science/paper/7LRSLWST
@misc{pith2026250113025,
author = {Pith},
title = {Pith review of: A MIMO ISAC System for Ultra-Reliable and Low-Latency Communications},
year = {2026},
howpublished = {\url{https://pith.science/paper/7LRSLWST}},
note = {Machine review of arXiv:2501.13025}
}
read the original abstract
In this paper, we propose a bi-static multiple-input multiple-output (MIMO) integrated sensing and communication (ISAC) system to detect the arrival of ultra-reliable and low-latency communication (URLLC) messages and prioritize their delivery. In this system, a dual-function base station (BS) communicates with a user equipment (UE) and a sensing receiver (SR) is deployed to collect echo signals reflected from a target of interest. The BS regularly transmits messages of enhanced mobile broadband (eMBB) services to the UE. During each eMBB transmission, if the SR senses the presence of a target of interest, it immediately triggers the transmission of an additional URLLC message. To reinforce URLLC transmissions, we propose a dirty-paper coding (DPC)-based technique that mitigates the interference of both eMBB and sensing signals. For this system, we formulate the rate-reliability-detection trade-off in the finite blocklength regime by evaluating the communication rate of the eMBB transmissions, the reliability of the URLLC transmissions and the probability of the target detection. Our numerical analysis show that our proposed DPC-based ISAC scheme significantly outperforms power-sharing based ISAC and traditional time-sharing schemes. In particular, it achieves higher eMBB transmission rate while satisfying both URLLC and sensing constraints.
Figures
Forward citations
Cited by 2 Pith papers
-
Blind and Topological Interference Managements for Bistatic Integrated Sensing and Communication
For bistatic ISAC with dispersed receivers and a sensor that does not know the communication messages, BIA and TIM schemes achieve (sDoF,cDoF) tradeoff points that dominate time-sharing.
-
A Comprehensive Survey of 5G URLLC and Challenges in the 6G Era
A broad literature survey of 5G URLLC across PHY, MAC, cross-layer, ML, and security, with a 6G challenges and research directions section.
Reference graph
Works this paper leans on
-
[1]
V . Koivunen, M. F. Keskin, H. Wymeersch, M. Valkama, and N. González- Prelcic, “Multicarrier ISAC: Advances in waveform design, signal pro- cessing, and learning under nonidealities,” IEEE Signal Processing Mag- azine, vol. 41, no. 5, pp. 17–30, Sept. 2024
work page 2024
-
[2]
YOLO: An efficient terahertz band integrated sensing and communications scheme with beam squint,
H. Luo, F. Gao, H. Lin, S. Ma, and H. V . Poor, “YOLO: An efficient terahertz band integrated sensing and communications scheme with beam squint,” IEEE Transactions on Wireless Communications , vol. 23, no. 8, pp. 9389–9403, Aug. 2024
work page 2024
-
[3]
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 Journal on Se- lected Areas in Communications, vol. 40, no. 6, pp. 1728–1767, June 2022
work page 2022
-
[4]
Waveform shaping in integrated sensing and communications,
H. Li, Z. Han and H. V . Poor, “Waveform shaping in integrated sensing and communications,” in Proceedings of the IEEE Military Communications Conference, Washington, DC, USA, pp. 670–671, 2024
work page 2024
-
[5]
Next- generation multiple access for integrated sensing and communications,
Y . Liu, T. Huang, F. Liu, D. Ma, W. Huangfu, and Y . C. Eldar, “Next- generation multiple access for integrated sensing and communications,” Proceedings of the IEEE , vol. 112, no. 9, pp. 1467–1496, Sept. 2024
work page 2024
-
[6]
N. H. Mahmood, I. Atzeni, E. A. Jorswieck, and O. L. A. López, “Ultra-reliable low-latency communications: Foundations, enablers, sys- tem design, and evolution towards 6G,” Foundations and Trends® in Communications and Information Theory , vol. 20, no. 5-6, pp. 512–747, 2023
work page 2023
-
[7]
Joint processing and transmission energy optimization for ISAC in cell-free massive MIMO with URLLC,
Z. Behdad, Ö. T. Demir, K. W. Sung, and C. Cavdar, “Joint processing and transmission energy optimization for ISAC in cell-free massive MIMO with URLLC,” arXiv:2401.10315, 2024
arXiv 2024
-
[8]
P. Qin, Y . Fu, Z. Yu, J. Zhang, and X. Zhao, “URLLC-aware trajectory plan and beamforming design for NOMA-aided UA V integrated sensing, communication, and computation networks,” IEEE Transactions on Vehic- ular Technology, vol. 74, no. 1, pp. 1610–1625, Jan. 2025
work page 2025
Show all 22 references
-
[9]
Joint beamforming and scheduling for integrated sensing and communication systems in URLLC: A POMDP approach,
X. Zhao and Y . -J. Angela Zhang, “Joint beamforming and scheduling for integrated sensing and communication systems in URLLC: A POMDP approach,” IEEE Transactions on Communications , vol. 72, no. 10, pp. 6145–6161, Oct. 2024
2024
-
[10]
An information-theoretic view of mixed-delay traffic in 5G and 6G,
H. Nikbakht, M. Wigger, M. Egan, S. Shamai (Shitz), J-M. Gorce, and H. V . Poor, “An information-theoretic view of mixed-delay traffic in 5G and 6G,” Entropy, vol. 24, no. 5, article 637, 2022
2022
-
[11]
Performance analysis of one-way highway vehicular networks with dynamic multiplexing of eMBB and URLLC traffics,
X. Song and M. Yuan, “Performance analysis of one-way highway vehicular networks with dynamic multiplexing of eMBB and URLLC traffics,” IEEE Access, vol. 7, pp. 118020–118029, 2019
2019
-
[12]
On the coexistence of eMBB and URLLC in multi-cell massive MIMO,
G. Interdonato, S. Buzzi, C. D’Andrea, L. Venturino, C. D’Elia, and P. Vendittelli, “On the coexistence of eMBB and URLLC in multi-cell massive MIMO,” IEEE Open Journal of the Communications Society , vol. 4, pp. 1040–1059, 2023
2023
-
[13]
Joint coding of eMBB and URLLC in vehicle-to-everything (V2X) communications,
H. Nikbakht, E. Ruzomberka, M. Wigger, S. Shamai, and H. V . Poor, “Joint coding of eMBB and URLLC in vehicle-to-everything (V2X) communications,” in Proceedings of the IEEE Global Communications Conference, Kuala Lumpur, Malaysia, pp. 1–6, 4–8 Dec. 2023
2023
-
[14]
Feedback coding of URLLC in vehicle-to-everything (V2X) communications and its secrecy analysis,
J. Wang, G. Xie, D. Xia, and B. Dai, “Feedback coding of URLLC in vehicle-to-everything (V2X) communications and its secrecy analysis,” in Proceedings of the IEEE Wireless Communications and Networking Conference, Dubai, United Arab Emirates, pp. 01-06, 21–24 April, 2024
2024
-
[15]
Dirty paper coding for con- secutive messages with heterogeneous decoding deadlines in the finite blocklength regime,
H. Nikbakht, M. Egan, and J.-M. Gorce, “Dirty paper coding for con- secutive messages with heterogeneous decoding deadlines in the finite blocklength regime,” in Proceedings of the IEEE International Symposium on Information Theory, pp. 2100–2105, Espoo, Finland, 26 June – 01 ...
2022
-
[16]
Writing on dirty paper (Corresp.),
M. H. M. Costa, “Writing on dirty paper (Corresp.),” IEEE Transactions on Information Theory , vol. 29, no. 3, pp. 439–441, May 1983
1983
-
[17]
A broadcast channel framework for joint communications and sensing-part II: Superposition coding,
H. Li, Z. Han, and H. V . Poor, “A broadcast channel framework for joint communications and sensing-part II: Superposition coding,” in Proceed- ings of the IEEE Global Communications Conference , Kuala Lumpur, Malaysia, pp. 7381–7386, 4–8 Dec. 2023
2023
-
[18]
Integrated sensing and communication in the finite blocklength regime,
H. Nikbakht, M. Wigger, S. Shamai, and H. V . Poor, “Integrated sensing and communication in the finite blocklength regime,” in Proceedings of the IEEE International Symposium on Information Theory, pp. 2790–2795, Athens, Greece, 07–12 July, 2024
2024
-
[19]
H. V . Poor, An introduction to signal detection and estimation , Springer Science & Business Media, 2013
2013
-
[20]
Probability of error for optimal codes in a Gaussian channel,
C. E. Shannon, “Probability of error for optimal codes in a Gaussian channel,” The Bell System Technical Journal, vol. 38, no. 3, pp. 611–656, 1959
1959
-
[21]
A finite-blocklength perspective on Gaussian multi-access channels,
E. MolavianJazi and J. N. Laneman, “A finite-blocklength perspective on Gaussian multi-access channels,” arXiv:1309.2343, sep. 2013
2013 arXiv
-
[22]
Channel coding rate in the finite blocklength regime,
Y . Polyanskiy, H. V . Poor and S. Verdu, “Channel coding rate in the finite blocklength regime,” IEEE Transactions on Information Theory , vol. 56, no. 5, pp. 2307–2359, May, 2010
2010
Reviewed August 10, 2026 · model on record in the stance chip above.
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