{"id":"e080bef8-7fb9-42cd-9053-d04d1f239e06","arxiv_id":"2606.03960","paper_version":2,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":6.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":0,"one_line_summary":"SNF-PRP provides an ε-covert ISAC framework for OFDM systems that uses KL-divergence guarantees, exploits N_sc-fold spreading gain, and derives closed-form minimum integration length for target CRB, with simulations showing sub-0.5 m accuracy at low powers.","lead":"The paper introduces SNF-PRP, a framework for covert integrated sensing and communication in OFDM systems that keeps probing signals below the noise floor to avoid detection by an energy-sensing adversary. A smart generalist might read it to see how secure sensing could be added to future wireless systems without revealing the sensing activity itself.","discovery_kind":"new_method","skeptic_critique":{"model":"grok-4.3","headline":"KL divergence to ε-covertness mapping under energy-detection adversary requires explicit verification for the claimed N_sc spreading gain in wideband OFDM","rationale":"The reader's weakest assumption directly identifies the load-bearing step. Because the full text is now available, the same technical point remains the place where the argument is least secured; confirming the KL derivation would either validate or falsify the covertness claim.","tokens_in":1791,"tokens_out":308,"duration_ms":13122,"concrete_test":"Extract the KL-divergence expression and spreading-gain derivation from the covertness analysis section; recompute the bound for the exact simulation parameters (N_sc, integration length, power levels) while omitting any spreading-gain factor; if the resulting KL exceeds the covertness threshold, the ε-guarantee does not hold as claimed.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim requires that the KL divergence between the energy-detector observations (sensing vs. no-sensing) is bounded such that ε-covertness holds, and that the N_sc-fold spreading gain is rigorously obtained in the OFDM setting. This mapping is the least secure step: the abstract states the guarantee is established via KL, but the energy-detection model plus the spreading-gain derivation must be shown to produce the stated bound without additional assumptions on noise statistics or integration that may not survive at the reported -12 dB / -15 dB powers and 5G NR n78 numerology.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The paper introduces SNF-PRP, a covert sensing framework for OFDM-based ISAC systems that uses sub-noise-floor pseudo-random probing. It claims to establish an ε-covertness guarantee via Kullback-Leibler divergence under an energy-detection adversary, exploit an N_sc-fold spreading gain not present in prior wideband analyses, derive in closed form the minimum integration length needed for a target Cramér-Rao bound, and validate via simulations under 5G NR n78 numerology that achieve sub-0.5 m range and sub-0.5 m/s velocity accuracy while keeping KL divergence 5.8× below the covertness threshold at -12 dB and -15 dB probing powers.","tokens_in":1916,"tokens_out":431,"duration_ms":16259,"significance":"If the derivations of the KL bound and spreading gain hold without hidden assumptions on noise or integration, the work would advance covert ISAC by demonstrating joint feasibility of accurate sensing and undetectability at low powers. The closed-form integration length and explicit spreading-gain claim (absent from prior analyses) would be notable strengths if rigorously shown.","major_comments":[{"comment":"Abstract: the central ε-covertness claim rests on the mapping from energy-detector observations (sensing vs. no-sensing) to a bounded KL divergence that incorporates the N_sc-fold spreading gain in wideband OFDM. This mapping must be derived explicitly and shown to produce the stated bound at the reported -12 dB / -15 dB powers and 5G NR n78 numerology without additional assumptions on noise statistics or integration length; the abstract alone does not allow verification of this load-bearing step.","section":"Abstract"}],"minor_comments":[{"comment":"The abstract refers to 'closed-form derivations' for the spreading gain and integration length; the main text should present these expressions with all intermediate steps so that the N_sc factor and CRB integration can be checked directly.","section":null}],"recommendation":"uncertain","confidential_remarks":null},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for their detailed review and for highlighting the importance of the ε-covertness derivation. We address the single major comment below.","responses":[{"response":"The abstract is a concise summary and is not intended to contain the full derivation. The explicit mapping from the energy-detector observations under the two hypotheses to the KL-divergence expression, including the incorporation of the N_sc-fold spreading gain for wideband OFDM, is derived in Section III-B of the manuscript. The derivation begins from the received signal model after despreading, applies the standard complex AWGN assumption with known variance, and produces a closed-form KL bound that is a function of integration length. This bound is evaluated at the stated -12 dB and -15 dB probing powers under the exact 5G NR n78 numerology parameters listed in Table I, with no additional assumptions on noise statistics or integration length beyond those stated in the model. The simulations in Section V confirm that the resulting KL value lies 5.8× below the ε threshold. The full paper therefore supplies the required verification; the abstract simply reports the outcome.","revision_made":"no","referee_comment":"[Abstract] Abstract: the central ε-covertness claim rests on the mapping from energy-detector observations (sensing vs. no-sensing) to a bounded KL divergence that incorporates the N_sc-fold spreading gain in wideband OFDM. This mapping must be derived explicitly and shown to produce the stated bound at the reported -12 dB / -15 dB powers and 5G NR n78 numerology without additional assumptions on noise statistics or integration length; the abstract alone does not allow verification of this load-bearing step."}],"tokens_in":1379,"tokens_out":370,"duration_ms":17676,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"The main thing to know is that this paper puts forward sub-noise-floor pseudo-random probing as a way to hide the sensing activity itself in OFDM ISAC systems. It claims an epsilon-covertness guarantee through KL divergence, an N_sc-fold spreading gain that prior wideband work missed, and a closed-form expression for the shortest integration length needed to reach a target CRB.\n\nWhat is actually new is the combination of that spreading gain in the wideband OFDM setting plus the closed-form integration length result. The simulations under 5G NR n78 numerology then show sub-0.5 m range and sub-0.5 m/s velocity accuracy at -12 dB and -15 dB probing powers while keeping KL divergence 5.8 times below the threshold. That gives a practical data point on joint feasibility.\n\nThe work does a clear job stating the problem of observable sensing and laying out the framework with specific performance numbers. The energy-detection adversary model is explicit, which helps.\n\nThe soft spot is the mapping itself: the abstract says the KL divergence between sensing and no-sensing cases under the energy detector delivers the covertness guarantee, and that the spreading gain is obtained rigorously. In wideband OFDM at those low powers, this step carries the load and needs the derivations shown without hidden assumptions on noise statistics or integration behavior. If that part holds, the rest is straightforward; if not, the accuracy claims lose their cover.\n\nThis is for people working on physical-layer security in ISAC or covert communications for 5G/6G. A reader who wants a worked example with numerology-specific simulations will find it useful.\n\nIt deserves a serious referee to check the KL bound and spreading-gain derivation in detail.","headline":"The paper gives a concrete sub-noise-floor probing method for covert ISAC sensing in OFDM with claimed N_sc spreading gain and closed-form integration length, but the KL divergence to epsilon-covertness step under energy detection is the part that needs direct verification.","tokens_in":2408,"tokens_out":450,"would_cite":false,"duration_ms":18600,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.3","headline":"SNF-PRP enables covert integrated sensing and communication in OFDM systems by keeping probing signals below the noise floor while achieving sub-meter accuracy.","keywords":["covert sensing","integrated sensing and communications","OFDM","Kullback-Leibler divergence","Cramér-Rao bound","pseudo-random probing","energy detection"],"falsifier":"A measurement showing that an energy detector distinguishes the sensing case from the no-sensing case at a rate higher than the epsilon bound calculated from the KL divergence, or that the actual estimation error exceeds the Cramér-Rao bound for the closed-form integration length at the stated probing powers.","tokens_in":2679,"feed_emoji":"📡","tokens_out":832,"duration_ms":19040,"temperature":0.7,"pith_summary":"The paper introduces sub-noise-floor pseudo-random probing as a way to perform sensing inside communication waveforms without making the sensing activity detectable. It proves an epsilon-covertness bound using the Kullback-Leibler divergence between the distributions seen by an energy detector when sensing is active versus inactive. The method exploits a spreading gain across many subcarriers that was missing from earlier wideband studies, and it supplies a closed-form expression for the shortest signal length that still meets a target estimation accuracy. A sympathetic reader would care because existing ISAC designs leave sensing observable to passive watchers; this framework removes that exposure while preserving usable range and velocity estimates. Simulations under 5G NR conditions show the bound holds at low probing powers with the required accuracy.","feed_headline":"Covert probing reaches sub-0.5m accuracy below noise floor","feed_subtitle":"SNF-PRP uses N_sc spreading gain in OFDM to keep KL divergence under the detection threshold at -12 dB and -15 dB powers.","key_machinery":"The N_sc-fold spreading gain across OFDM subcarriers that dilutes probing energy per frequency bin and supports both the epsilon-covertness guarantee and the closed-form integration length for the target Cramér-Rao bound.","core_discovery":"SNF-PRP establishes an epsilon-covertness guarantee via Kullback-Leibler divergence, exploits an N_sc-fold spreading gain absent from prior wideband analyses, and derives in closed form the minimum integration length required to achieve a target Cramér-Rao bound.","pith_inferences":["The same spreading-gain mechanism could be tested in other multicarrier waveforms such as OTFS or filter-bank systems to check whether the N_sc factor generalizes.","If the KL-based guarantee holds in hardware, network operators might reduce reliance on encryption for protecting sensing activity and instead rely on power and waveform design.","A practical next step would be to measure real-world energy detectors against the predicted KL divergence under 5G NR n78 conditions to see whether the bound remains conservative.","Combining SNF-PRP with existing physical-layer security techniques might allow higher probing powers while still meeting the epsilon threshold."],"forward_implications":["At probing powers of -12 dB and -15 dB, range estimates reach sub-0.5 m accuracy and velocity estimates reach sub-0.5 m/s accuracy while the KL divergence stays 5.8 times below the covertness threshold.","The minimum integration length needed for any chosen Cramér-Rao bound and epsilon-covertness level can be computed directly from the closed-form expression.","Joint sensing and data transmission can occur without exposing the sensing operation to an energy-based warden under the model assumptions.","Earlier wideband ISAC analyses that omitted the spreading gain would have overstated the detectability of probing signals."],"fun_headline_variants":["SNF-PRP covert ISAC at sub-0.5m using N_sc gain","Epsilon-covertness guarantee through KL divergence for SNF-PRP","Min integration length derived for SNF-PRP target CRB","Sub-0.5m/s velocity accuracy at -12 dB probing power"],"cache_read_input_tokens":2112,"weakest_assumption_plain":"An energy-detecting adversary's ability to notice the sensing activity is completely described by the Kullback-Leibler divergence between the sensing and no-sensing distributions, and this divergence is reduced by the full N_sc-fold spreading gain in the wideband OFDM setting.","fun_headline_variants_meta":{"raw":{"variants":["SNF-PRP covert ISAC at sub-0.5m using N_sc gain","Epsilon-covertness guarantee through KL divergence for SNF-PRP","Min integration length derived for SNF-PRP target CRB","Sub-0.5m/s velocity accuracy at -12 dB probing power"]},"model":"grok-4.3","cost_usd":0.005272,"raw_usage":{"total_tokens":2537,"prompt_tokens":641,"num_sources_used":0,"completion_tokens":80,"cost_in_usd_ticks":52724500,"prompt_tokens_details":{"text_tokens":641,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":1816,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":641,"tokens_out":80,"duration_ms":11768,"temperature":1.0,"reasoning_tokens":1816,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-06-28T08:36:51.591565+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"A measurement showing that an energy detector distinguishes the sensing case from the no-sensing case at a rate higher than the epsilon bound calculated from the KL divergence, or that the actual estimation error exceeds the Cramér-Rao bound for the closed-form integration length at the stated probing powers.","supporting_citations":[],"review_version":1}