REVIEW 2 major objections 5 minor 1 cited by
Coexistence of Radar and Communication with Rate-Splitting Wireless Access
T0 review · 2 major / 5 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read Splitting an uplink message and decoding it around the radar echo yields a better sensing-communication trade-off than OMA or NOMA coexistence.
desk verdict A rate-splitting ISAC scheme that likely works, but the printed CRLB inequality is backwards and needs fixing before publication. 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 object is the rate-split transmit signal $x(t)=\sqrt{P_{c,1}} s_{c,1}(t)+\sqrt{P_{c,2}} s_{c,2}(t)$, where $s_{c,1}$ and $s_{c,2}$ are independently encoded streams of one user's message, combined with the SIC decoding order $s_{c,1} \to$ radar $\to s_{c,2}$ at the base station. Rate-splitting means the message is split into two parts that are superposed at the transmitter and sequentially decoded at the receiver, giving a continuous set of operating points indexed by $\alpha$. The mathematical engine is the Cramér–Rao lower bound for radar time-delay estimation under Gaussian interference from $s_{c,2}$: the Fisher information step, simplified via the Sherman–Morrison formula and a Cauchy–Schwarz bound, produces the conservative estimator variance in (9), which feeds the REIR bound (13) and the interference term in (12). The closed-form power split (16) follows from setting the derivative of $R_{c,1}+R_{c,2}$ to zero and solves for the DIR-maximizing operating point.
What would settle it
Run the joint receiver with a radar waveform whose spectrum is not flat, for example a pulse-shaped waveform with a non-rectangular envelope, and compare the measured residual interference power after predicted-return subtraction with $P_{\mathrm{r}} |a_{\mathrm{r}}|^2 \gamma^2 B^2 \sigma^2_{\tau_r,\mathrm{proc}}$; a systematic mismatch means equation (4) and the bounds built on it do not correctly describe the scheme.
Extended reading notes
Core claim
The paper's central claim is that inter-functionality interference in an uplink ISAC receiver should be treated as a controllable resource rather than something to be entirely avoided or fixed in a rigid order. The communication user rate-splits its message into two superposed streams; the joint radar-communication receiver decodes the first stream with the predicted radar echo subtracted, estimates the radar time delay while the second stream acts as interference, and then decodes the second stream after removing the estimated echo. The achievable trade-off is described by inner bounds (13) for the ergodic radar estimation information rate and (14) for the ergodic data information rate, parameterized by the power split $\alpha=P_{c,2}/P_c$. The paper shows that as $\alpha$ moves from 0 to 1, this region improves on the OMA- and NOMA-inspired bounds for the system model considered, with $\alpha=0$ exactly recovering the NOMA-inspired bounds, and it gives the closed-form $\alpha^{\mathrm{RS}}_{\max}$ in (16) that maximizes the communication rate.
Load-bearing premise
The whole calculation treats the leftover radar echo after subtracting the predicted return as white noise with power $P_{\mathrm{r}} |a_{\mathrm{r}}|^2 \gamma^2 B^2 \sigma^2_{\tau_r,\mathrm{proc}}$; if real residual echoes are correlated or non-Gaussian, the CRLB and the rate bounds change.
Editorial extensions
If this is right
- The NOMA-inspired coexistence scheme becomes a special case of the RS scheme at $\alpha=0$, so a design already using NOMA-inspired SIC can switch to RS without losing that operating point.
- The closed-form optimal split means the DIR-maximizing point can be computed from the channel gains, radar power, bandwidth, and target process noise without numerical search over $\alpha$.
- Because $\alpha$ controls how much of the communication signal interferes with radar estimation, the scheme gives operators a continuous knob to shift the operating point between sensing accuracy and communication rate.
- The same decoding-and-estimation ordering can be applied to radar parameters other than range, since the CRLB structure carries over, a direct extension the paper states.
Reading between the lines
- The paper analyzes a single communication user; a natural next step is to combine RS with multiple users, where each user's streams could be inserted at different points of the radar estimation chain, though the resulting rate region is not derived here.
- The closed-form split $\alpha^{\mathrm{RS}}_{\max}$ depends on the target's process noise and radar power, so an adaptive implementation that recomputes the split as the target moves would be a practical refinement the paper leaves implicit.
- The flat-spectrum residual-echo assumption is likely the first thing to test experimentally: if real residuals are colored, the CRLB and the claimed region would need correction, but the splitting idea itself would remain applicable.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a rate-splitting (RS)-inspired scheme for an uplink integrated sensing and communication (ISAC) scenario in which a base station simultaneously serves a communication user and estimates a radar target's delay. The communication user splits its message into two streams, and the receiver uses a fixed decoding order sc,1 → radar → sc,2. The authors derive bounds on the ergodic data information rate (DIR) for communication and the ergodic radar estimation information rate (REIR), together with a closed-form expression for the power-split factor α that maximizes DIR. They compare the RS scheme with OMA- and NOMA-inspired baselines and report that RS yields a more favorable sensing–communication trade-off, with the RS curve beginning at the NOMA point for α=0 and extending toward higher DIR at the cost of lower REIR.
Significance. If the bounds are valid, the work is a useful conceptual extension of rate-splitting from digital communication to a framework that treats the sensing signal as a non-orthogonal interferer that is partially decoded and partially noise. The closed-form optimal power split and the explicit recovery of the NOMA case at α=0 are positive features, and the simulation results corroborate the analytical curves. The central qualitative claim—that decoding-order flexibility from message splitting improves the trade-off relative to OMA and NOMA—is plausible and, if properly argued, would be a solid addition to the ISAC literature. However, the technical derivation contains a sign error in the Cramér-Rao step that must be corrected before the inner bounds are rigorously established.
major comments (2)
- [Section II.C, Eqs. (8a)–(9)] The inequality in Eq. (9) is reversed. Equation (8d) is a lower bound on the Fisher information J(τr): J ≥ |ar|^2 Pr ||r'_τr||^2 / (σ_n^2 + |bc|^2 Pc,2). Since the CRLB is the reciprocal of J, the expression on the right-hand side of (9) is an upper bound on the variance, not a lower bound. The correct statement is σ^2_{τr,est} ≤ (σ_n^2 + |bc|^2 Pc,2) / (2γ^2B^2(TB)|ar|^2Pr), assuming the usual unit-energy pulse h with ||h||^2=1. The phrase 'a more pessimistic CRLB' in the text preceding (9) is also inconsistent: a lower bound on J gives an upper bound on the CRLB, not a larger CRLB. This is load-bearing because equations (12), (13) and (14) all use the variance expression from (9). Please correct the direction and rephrase the step as a pessimistic variance assumption (an upper bound on the true CRLB) rather than as the CRLB itself.
- [Section III, Eqs. (13)–(14)] Assuming Eq. (9) is corrected to an upper bound, the derivation of the inner bounds in (13) and (14) must be made explicit. If the authors intend to use the pessimistic variance (the upper bound on the CRLB), they should state that this produces conservative bounds: the actual achievable REIR and second-stream DIR are at least as large as the printed expressions when the receiver uses the true CRLB-achieving estimator. If, instead, they intend to use the true CRLB, the directions and the numerical results in Fig. 3 change, shifting the RS curve northeast and strengthening the claimed advantage over the baselines. Either way, the current derivation does not rigorously establish the inner bounds as written because the chain from (8d) to (13)–(14) relies on a false inequality. Please provide a short, explicit argument that the variance value used in (12) leads to valid inner bounds (or update the bounds to use the true CRLB).
minor comments (5)
- [Section II.C, Eq. (5)–(7)] The text refers to sc,2(t) as an 'unknown random constant amplitude', but sc,2(t) is a time-varying unit-variance communication stream. The subsequent derivation treats sc,2 as a random scalar multiplying a deterministic unit-energy pulse h, which is a specific modeling choice. Please clarify this assumption, e.g., by stating that the communication signal is modeled as a known pulse shape with random amplitude over the radar processing interval.
- [Section III, Eq. (16)] The optimal α is found by setting the derivative to zero, but the paper does not verify that the stationary point is a maximum (second derivative condition) or discuss what happens when multiple stationary points exist. A brief check or a note that the boundary cases were examined would make the derivation complete.
- [References] Reference [9] is incomplete: 'pp. 1–1' lacks the volume and year details. Please complete the bibliographic information.
- [Section IV, Fig. 4] Figure 4 would be clearer with labeled axes and a caption explaining what is plotted (presumably the optimal α as a function of communication range). Currently the y-axis label is missing.
- [General] There are several typographical and typesetting issues, including inconsistent power notation in (15) (e.g., 'P 3 bc' instead of P_bc^3) and a minor grammar error ('communications stream' in Section II.B). A careful proofread is recommended.
Circularity Check
No circularity: the RS inner bounds and optimal power split are derived from stated assumptions; self-citations are background only.
full rationale
The derivation is self-contained and not circular. The received-signal model (2), the residual-echo interference power (4), the Fisher-information step (8a)-(8d), the CRLB expression (9), the REIR definition (10), and the rate bounds (13)-(14) are all obtained by explicit algebra from stated Gaussian assumptions and from the externally cited model of Chiriyath et al. [5]; none of these steps is defined in terms of the quantity it is supposed to predict. The RS bounds reduce to the NOMA bound when Pc,1=Pc and Pc,2=0, but this is an intended consistency check, explicitly noted in the paper as '(18) can be obtained from (13) and (14) as well, by setting Pc,1=Pc and Pc,2=0,' not a derivation of a prediction from its own input. The self-citations [7] and [9] are background references for rate-splitting concepts and are not used to derive the inner bounds or the optimal power split. The only flagged issue is the direction of the inequality in (9): since (8d) lower-bounds the Fisher information, the CRLB should be an upper bound on the estimation variance, so the printed '>=' in (9) appears reversed. This is a correctness issue, not circularity, and correcting it would make the RS bounds conservative rather than self-referential.
Assumptions & free parameters
assumptions (5)
- domain assumption Ideal self-interference suppression at the BS (no residual from the transmitted radar signal)
- domain assumption The residual radar return after canceling the predicted delay is white noise with power Pr|ar|^2 γ^2 B^2 σ^2_{τr,proc}
- domain assumption Perfect SIC of the first communication stream before radar estimation
- domain assumption The second communication stream acts as an unknown Gaussian random constant amplitude when estimating radar delay
- ad hoc to paper The decoding order sc,1 → radar → sc,2 is fixed
Cite this review
Pith. "Pith review of Coexistence of Radar and Communication with Rate-Splitting Wireless Access." pith.science (2026). https://pith.science/paper/HTWQU6XS
@misc{pith2026241113188,
author = {Pith},
title = {Pith review of: Coexistence of Radar and Communication with Rate-Splitting Wireless Access},
year = {2026},
howpublished = {\url{https://pith.science/paper/HTWQU6XS}},
note = {Machine review of arXiv:2411.13188}
}
read the original abstract
Future wireless networks are envisioned to facilitate the seamless coexistence of communication and sensing functionalities, thereby enabling the much-touted integrated sensing and communication (ISAC) paradigm. A key challenge in ISAC is managing inter-functionality interference while maintaining a balanced performance trade-off. In this work, we propose a rate-splitting (RS)-inspired approach to address this challenge in an uplink ISAC scenario, where a base station (BS) serves an uplink communication user while detecting a radar target. We derive inner bounds on the ergodic data information rate for the communication user and the ergodic radar estimation information rate for the sensing target. A closed-form solution is also derived for the optimal power split in RS that maximizes the communication user's performance. Compared to orthogonal multiple access (OMA)- and non-orthogonal multiple access (NOMA)-inspired approaches, the proposed approach achieves a more favorable sensing-communication trade-off by virtue of the decoding order flexibility introduced through splitting the communication message. Notably, this is the first work to employ an RS-inspired strategy as a general framework for non-orthogonal coexistence of sensing and communication, extending its applicability beyond traditional digital-only settings.
Figures
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Forward citations
Cited by 1 Pith paper
-
Interference Management for Integrated Sensing and Communications: A Multiple Access Perspective
A tutorial that classifies the five interference types in integrated sensing and communication (ISAC) and argues, with simulations, that RSMA outperforms OMA, SDMA, and NOMA in managing them.
Reference graph
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Reviewed August 12, 2026 · model on record in the stance chip above.
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