{"id":"ebb1b43d-d2a9-4670-89e6-d2a298217eb8","arxiv_id":"2501.15917","paper_version":1,"verdict":"REJECT","confidence":"MODERATE","novelty_score":3.0,"correctness_risk":"high","formal_verification":"none","parameter_count":3,"one_line_summary":"RIS element delays cause aperture-fill-time bit errors that grow with array size and symbol rate, and the proposed correlation alignment only helps when the transmitted waveform is known in advance.","lead":"A simulation study of RIS-assisted QPSK links shows that larger arrays and faster symbols raise bit error rates through element-delay-induced inter-symbol interference. The paper also proposes a cross-correlation alignment method that beats pilot alignment only when the receiver already knows the transmitted signal.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Algorithm 3's optimal matching uses the full transmitted QPSK waveform as the correlation reference; without this genie-aided information, the claimed BER reduction over pilot alignment is unsupported.","rationale":"Both the abstract and Section VI claim a novel alignment algorithm that significantly reduces BER. The verification of this claim rests on Algorithm 3's use of the complete original signal S(t) as the correlation reference. That signal is not known to a real receiver; the only known portion is the small pilot. Using the full random data as a template is equivalent to a genie-aided bound, not an implementable receiver. The comparison is also asymmetric: the baseline uses a two-bit pilot, while the proposed method uses the entire data sequence, so the length of the reference, rather than the alignment strategy, could explain the improvement. Without a like-for-like comparison, the central claim of improved BER is not established. The qualitative observation that larger arrays and higher symbol rates increase ISI is plausible and supported by the delay-spread mechanism, but that part alone does not justify the paper's primary contribution. The reader's verdict of REJECT is consistent with this concern; no change is needed.","tokens_in":7408,"tokens_out":5116,"duration_ms":52760,"concrete_test":"Re-run the delay-sweep experiments of Section V/VI with Algorithm 3 modified so that the correlation template is only the known pilot bits (e.g., the first two bits) instead of the full S(t), keeping all other simulation parameters and the pilot-alignment baseline unchanged; if the optimal-matching BER curves no longer lie significantly below the pilot-alignment curves, the claimed advantage depends on unavailable knowledge of the transmitted waveform.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The strongest claim includes the assertion that the proposed optimal matching alignment algorithm significantly reduces BER relative to pilot-based alignment. Algorithm 3 defines F(τ) = ∫R*(t)S(t+τ)dt and chooses the time shift maximizing this cross-correlation, where S(t) is the complete originally-transmitted QPSK waveform, including all random data bits. In a practical link the receiver does not have S(t); only a short pilot (the first two bits, per Algorithm 1) is available. The paper's comparison to 'pilot-based alignment' therefore gives the proposed method access to the very data the receiver is trying to recover, while restricting the baseline to a two-bit pilot. This is not a fair algorithmic comparison: the gain shown in Fig. 17 may simply reflect the much longer, information-bearing reference sequence. Since this alignment algorithm is a central contribution (abstract, Section VI, conclusions), the headline improvement is unsupported. Secondary issues (single 200-bit trials, no released code) compound the problem, but this genie-aided reference is the load-bearing flaw.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript proposes a joint simulation framework for RIS-assisted wireless communication that combines array-level antenna modeling with end-to-end communication signal processing. Using QPSK as an example, the authors simulate signal generation, modulation, propagation, RIS phase adjustment, multi-channel delay, reception, alignment, demodulation, and decision, and they report BER results as functions of SNR, array size, baseband symbol frequency, and emission angle. The main claims are that larger arrays and higher baseband frequencies increase aperture-fill-time-induced inter-symbol interference and BER, and that a proposed 'optimal matching' alignment algorithm based on cross-correlation with the original transmitted waveform substantially reduces BER relative to a pilot-based alignment baseline.","tokens_in":7628,"tokens_out":3097,"duration_ms":31840,"significance":"If the claims were valid, the paper would offer a useful simulation methodology for RIS links that captures physical element delays rather than idealizing the RIS as a point scatterer, and it would quantify an aperture fill time effect that is often neglected in communication-level RIS models. The paper also has the merit of attempting an end-to-end validation against a known AWGN QPSK result. However, the central positive claim about the alignment algorithm is undermined by an unfair comparison that gives the proposed method access to the full transmitted waveform, and the analytical formulation contains dimensional inconsistencies. The work is therefore a potentially interesting simulation study, but its headline conclusions are not currently supported by the evidence presented.","major_comments":[{"comment":"The optimal matching alignment algorithm computes the cross-correlation F(tau) between the merged received signal R(t) and S(t), where Algorithm 3 explicitly lists the 'Original QPSK Signal: S(t)' as an input and the baseline pilot method uses only the first two bits as a pilot. In a real link the receiver does not know the full transmitted data waveform, so the proposed method is given genie-aided information that the pilot-based baseline lacks. The BER reduction shown in Fig. 17 is therefore a consequence of this information asymmetry rather than a demonstrated algorithmic advantage, and the abstract's and conclusions' claim that the proposed algorithm 'significantly reduces BER' is unsupported.","section":"Section VI, Algorithm 3 and Fig. 17"},{"comment":"Equation (1) begins with a delayed signal s(t - tau_mn) and then replaces s(t) by exp(j 2 pi f_c t), which mixes a real passband representation with a complex exponential notation; for a QPSK signal with I/Q modulation, s(t) should be a real passband waveform, and the reduction to h * s(t) is not justified without a clear complex-baseband conversion. Equation (2) further adds a phase phi^Q_mn (which is 0 or pi in Eq. (4)) to a time delay tau^Path_mn, which is dimensionally inconsistent; this needs to be reformulated with a common unit or with an explicit frequency conversion before the analytical framework can be assessed.","section":"Section II, Eqs. (1) and (2)"},{"comment":"All reported BER values are obtained from single random bitstreams of length 200 bits. For example, the 25.5% and 21% BER values are single-sample estimates with a standard deviation of roughly 3-4 percentage points, and the claim of 'no BER' for the small-delay cases cannot be distinguished from the finite-sample floor. The paper therefore does not provide statistically reliable evidence for the quantitative BER trends, and this weakens the central aperture-fill-time claim.","section":"Section V and Figs. 14-15"},{"comment":"The verification against the theoretical QPSK AWGN BER is performed with a 1x1 array, which by construction eliminates all element-dependent delays and phase adjustments that are the subject of the RIS model. The agreement in Fig. 10 thus validates only the noise generation, demodulation, and decision chain; it does not validate the RIS delay and phase processing steps that distinguish this framework from a conventional baseband AWGN simulator.","section":"Section III"}],"minor_comments":[{"comment":"There is a spelling error: 'dicision' should be 'decision' in the phrase 'alignment, dicision, and post-processing'.","section":"Introduction"},{"comment":"The caption contains a typo: 'Uniform Linear Aarry' should be 'Uniform Linear Array'.","section":"Fig. 13 caption"},{"comment":"The declared output of Algorithm 3 is 'Original QPSK Signal: S(t)', but the algorithm actually returns the aligned received signal R'(t); the output specification should be corrected.","section":"Algorithm 3"},{"comment":"The term 'intertwined function' is nonstandard; the operation defined in Algorithm 3 is a cross-correlation, and using standard terminology would improve clarity.","section":"Section VI"},{"comment":"The sampling time dt in Eq. (5) is not defined in the text, and the relationship between the number of delayed sample points and the physical propagation delay should be stated explicitly.","section":"Section II, Eq. (5)"},{"comment":"No code or pseudocode details are provided for the channel propagation and signal merging steps, and several MATLAB-like functions such as 'circshift' and 'finddelay' are used without formal definitions; since reproducibility is claimed, a code release or a complete algorithmic description would be needed.","section":"General"}],"recommendation":"reject","confidential_remarks":"The paper's central algorithmic claim is invalid as presented because the optimal matching method is tested with knowledge of the full transmitted waveform while the baseline is limited to a two-bit pilot. This is not a presentation issue but a design flaw in the comparison that directly affects the headline conclusion. The dimensional inconsistency in Eq. (2) and the single-stream BER estimates are additional load-bearing problems. Even with revision, the main claim would require a fundamentally different evaluation protocol, so the manuscript is not suitable for publication in its current form."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The paper has a useful idea—jointly simulating RIS antenna behavior and communication signal processing—and the qualitative trend it reports, that larger arrays and higher symbol rates worsen delay-induced BER, is probably correct. But the central quantitative claim, that the proposed optimal-matching alignment algorithm significantly reduces BER compared to pilot alignment, is not supported, because Algorithm 3 cross-correlates the received signal against the full transmitted QPSK waveform S(t). A real receiver does not have S(t), so the comparison gives the proposed method an unfair advantage while the baseline is restricted to a two-bit pilot. That is load-bearing, and it breaks the headline result.\n\nWhat the paper does well: it packages known components into an end-to-end simulation pipeline, and Section V's illustrations of aperture-fill-time effects on delayed element responses are clear and helpful. The idea of simulating the whole chain rather than idealizing the RIS is worth pursuing.\n\nThe soft spots are not minor. The 1x1 AWGN verification exercises only the noise and decision path, not the RIS delay/phase processing, so it does not validate the parts that matter. Equation (1) treats s(t) as a pure carrier and then identifies it with a QPSK signal, mixing passband and baseband notation; Equation (2) adds a phase angle to a time delay. BER numbers come from single 200-bit streams, so the reported rates (25.5%, 44.5%) have wide confidence intervals. No code or data are released, so the simulation cannot be independently checked.\n\nThe stress-test note is on target. If Algorithm 3 used only the pilot as its reference, the gain in Fig. 17 would likely shrink or disappear. The authors need a fair baseline: a pilot-only or blind alignment method, with the same reference information available to both sides.\n\nThis paper is for readers who want a starting point for system-level RIS simulation, but as it stands it is not a reliable research contribution. I would not cite it, and I would not send it to referees yet. The right move is to ask the authors to fix the comparison, add proper BER statistics, clean up the equations, and provide code before it is referee-ready.","headline":"A plausible qualitative study of aperture-fill-time ISI in RIS links, undercut by a genie-aided alignment comparison and sloppy passband/baseband math.","tokens_in":8138,"tokens_out":2609,"would_cite":false,"duration_ms":27153,"reading_group":"no","serious_thinker":"yes","would_accept_peer_review":false},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"RIS-assisted links gain an aperture-induced ISI: larger arrays and faster symbols raise BER, and matching alignment recovers part of it.","keywords":["Reconfigurable intelligent surface","aperture fill time","bit error rate","inter-symbol interference","QPSK","waveform-level simulation","array size","optimal matching alignment"],"falsifier":"Take the same $100 \\times 1$ ULA simulation and run Algorithm 3 with only a short pilot segment or a decision-directed estimate of the transmitted waveform as the reference, rather than the true $S(t)$; if the BER near three symbol periods of edge delay stays near the reported value, the claim survives, and if it reverts to pilot-alignment levels, the gain is an artifact of knowing the transmitted signal.","tokens_in":1601,"feed_emoji":"📡","tokens_out":2249,"duration_ms":89398,"temperature":0.7,"pith_summary":"This paper claims that reconfigurable intelligent surfaces add a form of self-inflicted multipath: because the elements sit at different distances from the feed and the receiver, a single wideband symbol arrives as many delayed copies, and the timing spread, the aperture fill time, grows with array size and with faster symbol rates. The authors build an end-to-end waveform simulation that starts from QPSK bits and follows the signal through 1-bit phase adjustment, per-element delay, superposition, alignment, demodulation, and decision, and they show BER rises sharply once the aperture delay spread approaches a symbol period. They also propose an alignment step that uses the cross-correlation peak between the merged received signal and the original transmitted waveform, and they report that this optimal matching alignment lowers BER compared with pilot-based alignment. If this is right, RIS link design must treat the surface itself as a delay-spreading channel, not as an ideal phase-shifting mirror.","feed_headline":"Large RIS arrays raise bit errors via aperture fill time","feed_subtitle":"A joint simulation links BER to array scale and symbol rate, and matching alignment cuts the penalty.","key_machinery":"The load-bearing object is the aperture fill time, the time spread across the RIS aperture between the earliest and latest element paths, expressed in sampling intervals via $r_f^{mn} + r_{\\mathrm{eye}}^{mn}$ divided by $c$ and $dt$. The simulation pipeline turns each RIS element into a delayed copy of the same QPSK waveform, applies a 1-bit phase quantization so a $\\pi$ phase state becomes a half-carrier-period circular shift, superposes all element signals, and then estimates a global delay by maximizing the cross-correlation (the intertwined function) between the merged signal and the original transmitted waveform. This machinery converts an antenna-array property into a communication-channel impairment, letting the paper sweep array size, symbol frequency, and emission angle and read off BER as the output variable.","core_discovery":"On the paper's own terms, the central discovery is that a RIS creates a programmable, aperture-induced multipath from its own array: each element's feed-to-element and element-to-receiver distances impose a distinct delay on the same QPSK waveform, 1-bit phase quantization forces some paths to shift by half a carrier period, and the superposition of these delayed copies produces inter-symbol interference at code transitions. The quantitative evidence is a set of waveform simulations: a $100 \\times 1$ ULA at $f_{\\mathrm{symbol}}/f_c = 1/2$ gives 25.5% BER under normal incidence, the same array at $f_{\\mathrm{symbol}}/f_c = 1/20$ gives error-free reception, and steering a $10 \\times 1$ array to 50 degrees gives 21% BER. The authors then show that aligning the merged signal by the peak of its cross-correlation with the transmitted waveform, the intertwined function, shifts the BER-versus-delay curve down substantially relative to pilot alignment, indicating that most of the aperture-fill penalty is recoverable when the reference signal is known.","pith_inferences":["Editorial extension: because Algorithm 3 requires the true transmitted waveform, the reported gain is best read as an upper bound for data-aided processing; a real receiver would need a known preamble or decision-directed estimate to approach it.","Editorial extension: the same aperture delay-spread mechanism should appear in OFDM as carrier-dependent phase rotation and inter-carrier interference, so the QPSK-specific BER result is likely a special case of a broader wideband RIS impairment.","Editorial extension: one testable design rule follows directly from the simulated scaling: for a fixed target BER, the tolerable array aperture shrinks as symbol rate rises and as the output beam steers away from broadside; sweeping these two parameters in one experiment would confirm the claimed equivalence."],"forward_implications":["At fixed carrier frequency, increasing RIS array size raises the maximum element delay, so the aperture fill effect grows and BER rises even at high SNR.","Raising the baseband symbol frequency shortens each symbol period, so the same physical delay spans more symbols; the paper shows $f_{\\mathrm{symbol}}/f_c = 1/2$ with a $100 \\times 1$ array gives 25.5% BER while $1/20$ gives error-free reception.","Steering the output beam to large angles makes edge-element delays asymmetric and multiplies the delay spread; the paper reports 21% BER for a $10 \\times 1$ array at 50 degrees and 44.5% for a $100 \\times 1$ array at that angle.","Optimal matching alignment, which cross-correlates the merged received signal against the transmitted waveform, reduces BER for a given average channel delay compared with pilot-based alignment.","A RIS therefore introduces multipath-like ISI from its own aperture, a distinction from a single-antenna system where multipath comes only from the environment."],"supporting_citations":[{"why":"Supplies the canonical RIS communication system model that the paper's transmission equation builds on.","marker":"[4]"},{"why":"Positions RIS as a controllable wireless environment, the premise for treating the surface as an active channel element.","marker":"[7]"},{"why":"Provides the reflectarray phase-distribution method behind Equation (3) for element phase adjustment.","marker":"[9]"},{"why":"Reviews reconfigurable reflectarrays and array lenses, the class of devices whose 1-bit phase quantization the simulation adopts.","marker":"[10]"},{"why":"Supplies beam-scanning reflectarray design experience that motivates sweeping emission angle as a performance variable.","marker":"[11]"}],"fun_headline_variants":["RIS array delays distort QPSK, matching alignment recovers BER","Aperture fill time sets RIS bit errors, alignment cuts penalty","RIS-induced multipath from element delays boosts BER, matching fixes","Simulation ties RIS BER to array size and symbol rate, alignment wins"],"cache_read_input_tokens":10368,"weakest_assumption_plain":"Algorithm 3's BER reduction is computed with the transmitted QPSK waveform as the cross-correlation reference, so the receiver is assumed to know the exact transmitted signal rather than only a pilot.","fun_headline_variants_meta":{"raw":{"variants":["RIS array delays distort QPSK, matching alignment recovers BER","Aperture fill time sets RIS bit errors, alignment cuts penalty","RIS-induced multipath from element delays boosts BER, matching fixes","Simulation ties RIS BER to array size and symbol rate, alignment wins"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000127,"raw_usage":{"total_tokens":1138,"prompt_tokens":993,"completion_tokens":145,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":609,"completion_tokens_details":{"reasoning_tokens":70}},"tokens_in":609,"tokens_out":145,"duration_ms":2318,"temperature":1.0,"reasoning_tokens":70,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T13:49:32.327122+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Take the same $100 \\times 1$ ULA simulation and run Algorithm 3 with only a short pilot segment or a decision-directed estimate of the transmitted waveform as the reference, rather than the true $S(t)$; if the BER near three symbol periods of edge delay stays near the reported value, the claim survives, and if it reverts to pilot-alignment levels, the gain is an artifact of knowing the transmitted signal.","supporting_citations":[{"cited_title":"Wireless communications through reconfigurable intelligent surfaces,","cited_arxiv_id":null,"evidence_quote":"Supplies the canonical RIS communication system model that the paper's transmission equation builds on."},{"cited_title":"Huang and J","cited_arxiv_id":null,"evidence_quote":"Provides the reflectarray phase-distribution method behind Equation (3) for element phase adjustment."},{"cited_title":"Reconfigurable reflectarrays and array lenses for dynamic antenna beam control: A review,","cited_arxiv_id":null,"evidence_quote":"Reviews reconfigurable reflectarrays and array lenses, the class of devices whose 1-bit phase quantization the simulation adopts."},{"cited_title":"Beam scanning reflectarray antennas: A technical overview and state of the art,","cited_arxiv_id":null,"evidence_quote":"Supplies beam-scanning reflectarray design experience that motivates sweeping emission angle as a performance variable."}],"review_version":1}