{"id":"208262f7-eb2e-4254-97c3-b7781debc1e7","arxiv_id":"2506.19526","paper_version":1,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"low","formal_verification":"none","parameter_count":0,"one_line_summary":"A comprehensive survey of RIS for 6G that integrates use cases, control mechanisms, channel sounding, channel estimation, and standardization and industry perspectives.","lead":"This paper reviews the current state of reconfigurable intelligent surfaces (RIS), flat panels that steer wireless signals around obstacles, and brings together use cases, control methods, channel measurement and estimation, plus standardization efforts. It is a reference for engineers and researchers who want a single map of where RIS stands as 6G development moves forward.","discovery_kind":"review","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The survey's 'latest advancements' and gap claims in channel sounding rest on a self-selected 2022-2024 corpus with no documented search methodology, so comprehensiveness is unverified.","rationale":"The reader's ACCEPT with moderate confidence is reasonable, but the weakest assumption - literature representativeness - is not just an editorial nicety: it is the load-bearing condition for the survey's claim to provide an integrated, up-to-date view. I found no internal mathematical or technical error on spot-checking the path-loss, scattering-gain, and Kronecker formulations. The stated exclusion of RIS optimization (Section I-A) is an honest limitation that narrows 'comprehensive' but does not contradict the four-aspect integration. The most concrete vulnerability is the channel-sounding section: the 2022-2024 window and the resulting scarcity claims (outdoor, mmWave) are central to the paper's update value, yet the absence of a documented search methodology makes the corpus unverifiable. A systematic database check could settle whether key outdoor/mmWave measurement campaigns are missing. Hence I recommend CONDITIONAL rather than ACCEPT: the paper should be accepted with the condition that the authors either supply their search methodology and complete the table, or soften the comprehensiveness/latest-advances claims. If the check shows the corpus is complete, the conditional can be discharged and the ACCEPT stands.","tokens_in":52022,"tokens_out":8164,"duration_ms":88573,"concrete_test":"Run a reproducible query in IEEE Xplore and Scopus: (TITLE-ABS-KEY('reconfigurable intelligent surface' OR 'intelligent reflecting surface') AND TITLE-ABS-KEY('channel sounding' OR 'channel measurement' OR 'field trial')) AND PUBYEAR > 2021 AND PUBYEAR < 2025. Screen all results for experimental campaigns and compare the full set against Table III; if any outdoor, O2I, or mmWave/THz campaign published in 2022-2024 is absent, the paper's gap analysis and 'latest advances' claim require revision.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim is that this survey provides a comprehensive, integrated review, with a specific contribution being the update of RIS channel sounding to 2022-2024 (Section III) and the identification of gaps such as scarcity of outdoor and mmWave measurements. These claims are load-bearing because they motivate the survey's differentiation from [56] and its future-directions section. However, the selection of channel-sounding works in Table III is not accompanied by any description of search strategy, inclusion criteria, or database coverage. The table lists 24 experiments, of which only a handful are outdoor or O2I. Without a systematic and reproducible method, the statement that 'successful experiments on outdoor channel soundings are relatively more limited' and the broader assertion that the 2022-2024 window captures the latest advances cannot be audited. A non-exhaustive selection of favorable studies would preserve the narrative but undermine the survey's value as a reference. This is a correctness risk about the survey's central descriptive claim, not a disagreement with consensus. The same issue affects Table I, where the characterization of prior surveys as fragmented is based on only eight selected surveys.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper is a survey of reconfigurable intelligent surface (RIS) technology for 6G, covering fundamentals and hardware taxonomies, use cases drawn from ETSI GR RIS 001 and the RISE-6G project, control mechanisms and control-channel taxonomies, RIS-assisted channel sounding campaigns from 2022–2024 with associated channel characterization models, channel estimation methods organized by architecture and technique, standardization activities in ETSI/3GPP/ITU and national bodies, and industrial perspectives from operators and vendors. It positions itself as an integrated survey that fills gaps left by prior surveys, particularly by updating channel sounding to 2022–2024 and by adding standardization and industrial viewpoints. The paper contains no new derivations, fitted parameters, or self-referential results; its claims are descriptive and grounded in the cited literature.","tokens_in":52190,"tokens_out":6405,"duration_ms":72159,"significance":"If the reviewed corpus is representative, the survey provides a useful unified reference for RIS researchers and for 6G standardization discussions. Its standardization section is a clear strength: it summarizes current ETSI GR reports, 3GPP release-level considerations, ITU activities, and concrete operator/vendor positions. The compilation of 23 recent channel-sounding experiments in Table III and the taxonomy of channel estimation approaches in Tables IV–VIII are also valuable organizing devices. The equations are attributed to cited sources and appear internally consistent, and there are no fitted parameters or new theoretical claims that would raise circularity concerns. The main caveat is that the survey's 'comprehensive' and 'latest advancements' claims rest on an undocumented selection of literature, so the value of the survey as an authoritative reference depends on a methodological transparency fix that is within the authors' control.","major_comments":[{"comment":"The survey's central update claim—that the 2022–2024 window captures the latest channel-sounding advances and that outdoor and mmWave campaigns remain relatively scarce—rests entirely on the corpus assembled in Table III. However, no search strategy is documented: the text only states that the survey focuses on papers published between 2022 and 2024 because [56] covered earlier works. There is no list of databases, search strings, inclusion/exclusion criteria, or screening procedure, so a reader cannot audit whether omitted works would change the gap claims (for example, only [114] and [115] are exclusively outdoor, while [116]–[120] are mixed-environment campaigns). Please add a reproducible methodology subsection describing the literature retrieval and selection process, and either justify the corpus as complete or soften the 'comprehensive' and 'latest advancements' claims to match the actual selection.","section":"§III.A, Table III"},{"comment":"The positioning claim that prior surveys are fragmented and leave standardization and industrial perspectives underexplored is supported by only eight selected surveys ([54]–[61]), with no documented procedure for identifying or selecting those surveys. This makes the differentiation claim difficult to verify, since other recent RIS surveys may already cover standardization or industrial aspects. Please either document how the comparison set in Table I was chosen or temper the framing to 'among the surveys we compared,' so that the novelty claim is not stronger than the evidence.","section":"§I-A, Table I"}],"minor_comments":[{"comment":"The ETSI document is referred to as 'GS RIS 003' twice in this subsection, while the correct series designation used elsewhere in the paper is 'GR RIS 003'; please correct this typo.","section":"§V-A1"},{"comment":"Several reference numbers appear to be duplicated within the table: [175] appears twice in the single-RIS multi-user MIMO passive-RIS cell, [183] appears in both the conventional and the ML-based lists, and [148] appears in two MISO cells. The authors should verify the intended classification and remove unintended duplicates.","section":"Table IV"},{"comment":"The opening sentence says indoor channel sounding was investigated in [97]–[111], but [112] is then listed among the indoor experiments in the following sentence; include [112] in the initial enumeration or rephrase the sentence.","section":"§III.A"},{"comment":"The sentence defining θt and θr as the 'angle of arrival (AoA) from BS to RIS' and 'angle of departure (AoD) from RIS to BS' is confusing because the AoA is measured at the RIS and the AoD is measured at the RIS; please reword using standard incidence/reflection angle notation consistent with the cited source [119].","section":"§III.B.1, Eq. (2)"},{"comment":"The heading 'Wideband Commmunication' contains a typo, and the phrase 'This factors challenge the accurate extraction' in §IV.C should read 'These factors challenge the accurate extraction.'","section":"§VI.C.2 and §IV.C"}],"recommendation":"major_revision","confidential_remarks":"The manuscript fits the journal's scope and the standardization/industrial sections are genuinely useful. My main reservation is methodological transparency: the load-bearing comprehensiveness and gap claims are not currently auditable because the literature selection for both Table I and Table III is undocumented. If the authors add a reproducible search/selection description and align their claims with the resulting corpus, I would be happy to recommend acceptance."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"This is a solid survey, better than average for the genre. It delivers an integrated view of RIS use cases, control mechanisms, channel sounding, channel estimation, and standardization/industry. The standardization section (ETSI GRs, 3GPP timeline, ITU, national bodies) is genuinely useful and well-organized. Table III, the channel sounding summary, gives a compact at-a-glance comparison of 24 campaigns with setup, frequency, RIS size, tuning element, and substrate. That is a real service.\n\nWhat is new here is not a result but consolidation: the comparative table of prior surveys, the 2022–2024 update on channel sounding, and the added industrial perspective. That is a legitimate increment over the prior surveys it builds on.\n\nThe stress-test note lands. Section III says the survey covers 2022–2024 because [56] covered earlier work, and the text uses that selection to claim outdoor and mmWave measurements are relatively limited. But there is no search strategy, inclusion criteria, or database coverage statement. With 24 entries and no audit trail, “comprehensive” is doing too much work. The scarcity claim might be true, but the survey does not establish it; it is an observation about a convenience sample. The same issue touches Table I, where eight surveys are selected and their “fragmented” nature is presented as fact. This is a moderate weakness: it does not invalidate the survey as a reference, but the authors should soften the gap claims or add a methodology paragraph.\n\nMinor issues: Table IV has a duplicated entry ([175] appears twice), and one ETSI report is called “GS” instead of “GR.” Nothing load-bearing. The equations in Section III are attributed and internally consistent. The channel estimation taxonomy is clear, and the dense tables are usable. Citation patterns look fair.\n\nThis paper is for researchers entering RIS, for standardization people wanting a snapshot, and for anyone needing a quick map of channel sounding and estimation methods. It deserves a serious referee. The right outcome is probably acceptance after minor-to-moderate revision: add a methodology note to Section III, temper the “comprehensive” and gap language, and fix the typos. I would support that.","headline":"Useful, honest RIS survey that earns its place as a reference, but its channel-sounding “gap” claims rest on a non-systematic 2022–2024 selection.","tokens_in":52716,"tokens_out":1749,"would_cite":true,"duration_ms":19891,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The paper claims that reconfigurable intelligent surfaces have matured enough that a single integrated survey—covering use cases, control mechanisms, channel sounding, channel estimation, and standardization—can serve as a unified…","keywords":["reconfigurable intelligent surfaces","6G standardization","channel sounding","channel estimation","RIS control mechanisms","RIS use cases","industrial deployment","smart radio environment"],"falsifier":"A citation-level audit would settle the claim: if a search of the same literature base finds a 2022–2023 survey that already covers standardization and industry efforts in comparable depth, or finds key outdoor or mmWave channel-sounding experiments outside the 2022–2024 window that contradict the summary table, then the paper's central gap argument and its integrated-view contribution would be materially weakened.","tokens_in":51833,"feed_emoji":"📡","tokens_out":5037,"duration_ms":51131,"temperature":0.7,"pith_summary":"This survey sets out to show that reconfigurable intelligent surfaces (RIS) can be understood as one coherent technology rather than a scattering of isolated research threads. It knits together five strands: the use cases described by ETSI and the RISE-6G project, the control architectures that decide how much autonomy a surface has, the channel-sounding campaigns that measure how RIS behaves indoors and outdoors, the channel-estimation methods that recover the cascaded base-station-to-surface-to-user channel, and the standardization and industrial efforts preparing for 6G. A reader who takes the survey at face value comes away with a unified map of where RIS stands and what must happen before deployment. That matters because 6G standardization is approaching and RIS has not yet been standardized.","feed_headline":"One map takes RIS from metasurface physics to 6G standards","feed_subtitle":"Use cases, control, sounding, estimation, and standardization in one reference for 6G.","key_machinery":"The central object is the reconfigurable intelligent surface itself: a planar metasurface of unit cells whose impedance is tuned by diodes, varactors, liquid crystals, or other elements to shape reflected wavefronts via the generalized Snell's law. Throughout the survey, the load-bearing model is the cascaded channel: the BS–RIS–UE link composed of two sub-channels with a diagonal RIS reflection matrix, which all channel sounding and channel estimation techniques ultimately aim to characterize. Around this model, the survey builds its organizing taxonomies—control autonomy (fully controlled, partially controlled, fully autonomous), control channel (explicit in-band or out-of-band, implicit), channel estimation setup (cascaded versus separate), and RIS hardware (passive, active, hybrid).","core_discovery":"The paper's central claim is that previous surveys cover RIS only in fragments, so that use cases, control mechanisms, channel sounding, and channel estimation live in separate literatures, while standardization and industrial perspectives are largely missing. By contrast, this survey claims to provide an integrated treatment: it organizes use cases from ETSI and RISE-6G, classifies control into fully controlled, partially controlled, and fully autonomous modes, tabulates 2022–2024 channel-sounding experiments, organizes channel estimation into conventional and machine-learning families, and traces RIS through ETSI, 3GPP, and ITU standardization timelines plus operator and vendor trials. If correct, it provides a single reference that researchers and industry can use to locate RIS within the 6G standardization process.","pith_inferences":["The survey's staging argument suggests the most probable first standardized RIS form is a network-controlled repeater-like device rather than a fully autonomous metasurface; that is an extension, since the paper itself only presents the network-controlled repeater as a reference point.","Because the survey's path-loss and scattering-loss models assume Gaussian phase roughness and cascaded two-path attenuation, one could test whether those assumptions hold in outdoor dynamic environments; a meta-analysis of the campaigns in its sounding table could quantify model errors across frequency bands.","The classification of channel estimation by hardware type implies a testable trade-off: hybrid RIS with a few active sensing elements should achieve near-full channel-state-information performance at a fraction of active-RIS power, and a direct comparison of estimation error per watt across passive, hybrid, and active RIS would settle it.","The survey's control taxonomy could be turned into a standardization checklist that maps each use case to the required control channel type and autonomy level, which the paper does not explicitly provide."],"forward_implications":["If the survey's synthesis is right, the immediate 6G standardization window (3GPP Rel-20 study item) is the critical moment where RIS either enters the formal specification path or risks the fate of earlier over-engineered relay concepts.","Channel estimation research will need to shift from single-RIS passive setups toward high-mobility and multi-RIS scenarios, which the survey identifies as the least covered areas.","Outdoor and mmWave or sub-THz channel sounding remains too sparse to validate deployment-grade models, so early commercial RIS deployments will likely be indoor, outdoor-to-indoor, or controlled campus settings.","Control architecture will be a key standardization axis: the choice between fully controlled, partially controlled, and autonomous RIS determines signaling, backhaul, and computing requirements.","Machine-learning-based channel estimation, especially with hybrid RIS sensing elements, is a growing route to keep pilot overhead manageable."],"supporting_citations":[{"why":"Supplies the 11 ETSI use cases, deployment scenarios, and the requirements table that anchor Sections II and V.","marker":"[17]"},{"why":"Defines the 14 connectivity and reliability use cases and introduces the RIS orchestrator and external operator entities.","marker":"[88]"},{"why":"Defines the localization and sensing use cases and the role of integrated sensing and communication.","marker":"[89]"},{"why":"Defines the sustainability and security use cases and the intended versus non-intended user distinction.","marker":"[90]"},{"why":"The earlier channel characterization survey that sets the baseline and motivates the 2022–2024 sounding window.","marker":"[56]"},{"why":"The earlier channel estimation survey that this paper extends by covering active and hybrid RIS, high mobility, and multi-RIS deployments.","marker":"[59]"},{"why":"Supplies the fully controlled, partially controlled, and fully autonomous control taxonomy used in Section II-B.","marker":"[94]"},{"why":"Proposes the staged 3GPP Rel-18/19/20 standardization roadmap and the network-controlled repeater comparison that carries Section V-A.","marker":"[279]"},{"why":"Provides the 3GPP TR 38.901 standard channel model used in the path-loss and geometry-based stochastic model formulations.","marker":"[125]"}],"fun_headline_variants":["RIS: complete map from wave physics to 6G standards","One reference spans RIS theory, hardware, and 6G trials","RIS survey unites use cases, control, sounding, and estimation","From metasurface to standardization: the RIS guide","RIS for 6G: integrated survey from fundamentals to field trials"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The survey's added value rests on the assumption that its literature selection is representative—specifically that prior surveys really do omit standardization and industrial perspectives and that the 2022–2024 window captures the latest channel-sounding advances—so a biased or incomplete selection would weaken every gap claim and future direction drawn from it.","fun_headline_variants_meta":{"raw":{"variants":["RIS: complete map from wave physics to 6G standards","One reference spans RIS theory, hardware, and 6G trials","RIS survey unites use cases, control, sounding, and estimation","From metasurface to standardization: the RIS guide","RIS for 6G: integrated survey from fundamentals to field trials"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000974,"raw_usage":{"total_tokens":4102,"prompt_tokens":873,"completion_tokens":3229,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":489,"completion_tokens_details":{"reasoning_tokens":3143}},"tokens_in":489,"tokens_out":3229,"duration_ms":23905,"temperature":1.0,"reasoning_tokens":3143,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T23:06:08.060349+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A citation-level audit would settle the claim: if a search of the same literature base finds a 2022–2023 survey that already covers standardization and industry efforts in comparable depth, or finds key outdoor or mmWave channel-sounding experiments outside the 2022–2024 window that contradict the summary table, then the paper's central gap argument and its integrated-view contribution would be materially weakened.","supporting_citations":[{"cited_title":"Reconfigurable Intelligent Surface Relay: Lessons of the Past and Strategies for Its Success,","cited_arxiv_id":null,"evidence_quote":"Proposes the staged 3GPP Rel-18/19/20 standardization roadmap and the network-controlled repeater comparison that carries Section V-A."}],"review_version":1}