{"id":"cbc51ed5-111e-41d4-98a2-2a1e7fe57e15","arxiv_id":"2506.13490","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"In a two-user pinching-antenna system, TDMA with per-time-slot PA placements can require less transmit power than NOMA for symmetric user rates, while NOMA beats FDMA.","lead":"This paper compares three multiple-access schemes, NOMA, FDMA, and TDMA, in a two-user pinching-antenna system, minimizing transmit power for given rate targets. The notable finding is that with user-specific antenna placements, TDMA can beat NOMA when user rates are symmetric, while NOMA still beats FDMA.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"TDMA-over-NOMA conclusion rests on an optimal TDMA baseline versus a heuristic NOMA/FDMA baseline with no quantified optimality gap.","rationale":"In good faith, the paper's derivations of the NOMA power expressions and the TDMA formulation appear internally consistent, and the TDMA optimality claim is backed by a prior published lemma. The central question is whether the numerical comparison is fair. The reader identified exactly this issue in weakest_assumption: TDMA is optimal while NOMA/FDMA are solved heuristically. I see no internal contradiction in the NOMA algorithm, but the asymmetry in solution quality is a correctness risk rather than a mere consensus disagreement. The proposed global-optimization benchmark would settle whether the reported TDMA advantage persists when NOMA is given a stronger solver. Since the reader's verdict is already CONDITIONAL and this concern is the same one that motivates that condition, no verdict adjustment is needed.","tokens_in":8671,"tokens_out":8213,"duration_ms":86299,"concrete_test":"For N=4 and the Section IV setup (L=15 m, d=3 m, f_c=28 GHz, gamma_k=3 bps/Hz), replace the SCA/fine-tuning NOMA solver with an independent global optimizer: run a multi-start search (e.g., differential evolution or dense grid over PA position vectors satisfying (8c)-(8d)) evaluating the exact NOMA objective (10) including phases, and record the best feasible transmit power over at least 10^4 starts and 100 random user drops. If the best NOMA power remains above the Lemma 1 TDMA power for all drops, the TDMA-over-NOMA claim is supported; if any drop gives NOMA power below TDMA, the paper's comparison is not established.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's headline claim that TDMA requires less transmit power than NOMA for symmetric rates (Abstract; Section IV, Fig. 2) is obtained by comparing the provably optimal TDMA solution (Lemma 1, from [10]) with NOMA and FDMA solutions from the two-stage SCA-plus-fine-tuning heuristic in Section III-A. The NOMA problem (8)-(10) is non-convex in the PA positions because of coupled large-scale path loss and phase-alignment terms. The coarse SCA stage (17)-(20) optimizes only a relaxed large-scale path-loss surrogate, and the fine-tuning stage in Section III-A2 is a local search that explicitly relaxes the exact phase-alignment constraint (15) for both users. No optimality gap, convergence certificate, or comparison against a global search is reported for NOMA/FDMA. Consequently, the crossover at N>=4 in Fig. 2 and the symmetric-rate comparison in Fig. 3 could be artifacts of a suboptimal NOMA solver rather than a fundamental property of NOMA in PASS. The paper's own text acknowledges that TDMA incurs extra deployment overhead (Section IV), but the unquantified NOMA suboptimality is the more direct threat to the central claim in the ideal setting the paper studies.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper considers a fundamental two-user pinching-antenna system (PASS) under three multiple-access schemes: NOMA, FDMA, and TDMA. For each scheme, a transmit-power minimization problem is formulated subject to user rate requirements. For NOMA and FDMA, the paper develops a two-stage algorithm that first solves a large-scale path-loss surrogate via successive convex approximation and then fine-tunes PA positions for phase coherence. For TDMA, it invokes a globally optimal PA placement from prior work that deploys PAs symmetrically around each user with equal spacing. Numerical results show that PASS significantly outperforms conventional antenna systems, NOMA consistently outperforms FDMA, and TDMA outperforms NOMA for symmetric user rate requirements when the number of PAs N≥4.","tokens_in":8909,"tokens_out":11243,"duration_ms":109426,"significance":"If the conclusions are substantiated, the finding that time-switched per-slot PA reconfiguration (TDMA) can beat power-domain NOMA in a two-user PASS under symmetric rate targets is non-obvious and useful for system design; it would also add a new data point to the ongoing discussion of NOMA versus OMA in flexible-antenna systems. The problem formulation is clean, the power expressions are derived carefully, and the SCA subproblem is convex and solvable. The paper provides reproducible numerical experiments and a clear deployment guideline from Fig. 4. However, the central comparison is currently undermined by an asymmetry in solution quality between the proven-optimal TDMA baseline and the heuristic NOMA/FDMA baseline.","major_comments":[{"comment":"The central conclusion that TDMA requires less transmit power than NOMA for N≥4 (Fig. 2) and at equal rate targets (Fig. 3) is obtained by comparing the globally optimal TDMA solution of Lemma 1 (from [10]) with NOMA and FDMA solutions from the heuristic two-stage algorithm of Sec. III-A, for which no optimality gap or convergence certificate is given. Because the NOMA solver may be substantially suboptimal, the reported crossover could be an artifact of the solver rather than a fundamental property of PASS with NOMA. The authors should either quantify the performance of the NOMA/FDMA algorithm (e.g., by comparing against an exhaustive grid search or a global optimization method in the small-N regime) or explicitly frame the conclusion as \"TDMA outperforms the proposed NOMA algorithm\" in the abstract and in Sec. IV.","section":"Sec. IV, Figs. 2-3"},{"comment":"The fine-tuning stage does not enforce the exact phase-alignment constraint (15) for both users; as the paper itself states, a single uniform PA spacing cannot maximize channel gains for both users simultaneously. The algorithm searches a restricted segment to minimize the surrogate objective (20), but it does not verify whether the refined positions satisfy (15) for either user or whether the actual objective (10) is improved. Consequently, the transmit powers reported for NOMA and FDMA in Figs. 2 and 3 are not certified to correspond to achievable channel gains |v_k|^2 used in the objective, so the comparison with TDMA is not an apples-to-apples comparison of achievable performance.","section":"Sec. III-A2, Eqs. (15)-(24)"},{"comment":"The NOMA problem (10) is solved for a fixed SIC order (λ1=0, λ2=1) without including the corresponding ordering condition |v1|^2 ≥ |v2|^2. Since the PA placement is part of the optimization, the solution may violate this condition, in which case the power expressions in (9) do not represent a valid NOMA transmission. The exhaustive search over the two SIC orders mentioned in the text does not resolve this unless each subproblem enforces the channel-gain inequality. Please add the ordering constraint or explicitly verify the ordering for the reported optimized solutions.","section":"Sec. II-A, Eq. (10)"}],"minor_comments":[{"comment":"The word \"fine-tuning\" is misspelled as \"fine-turning\" in the abstract, in the header of Sec. III-A, and several times in the body text.","section":"Abstract and Sec. III-A"},{"comment":"The symbol δ is used both for the minimum PA spacing (λ/2) and for the relative offset x_p^n - x_p^c in the fine-tuning procedure; this dual use is confusing and should be resolved with distinct symbols.","section":"Sec. IV"},{"comment":"In problem (17), the constraint list \"(8b),(8c)\" appears to be a typo; the rate constraint (8b) is no longer present after the transformation, so it should be \"(8c),(8d)\" as in (20d).","section":"Eq. (17)"},{"comment":"The labels T1 and T2 are not defined in the caption; please define them as the two TDMA time slots.","section":"Fig. 4 caption"},{"comment":"The sentence \"both of them yield similar characteristics\" is vague; please clarify what is similar between the two SIC orders and why an exhaustive search over the two orders is sufficient. Also, the hat notation in bΔx and bΔx′ (Eqs. (23)-(24)) is not defined.","section":"Sec. II-A and Eqs. (23)-(24)"},{"comment":"The parameter \"n_neff\" should be typeset as n_eff for consistency with the notation introduced in Sec. II.","section":"Sec. IV"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the journal's scope and addresses a timely question on pinching-antenna multiple access. The main issue is the fairness of the algorithmic comparison: the TDMA-over-NOMA conclusion currently depends on comparing an optimal baseline with an uncharacterized heuristic. A reasonable revision path is to (i) add a small-N exhaustive/global search to validate the crossover for N=2,...,6, (ii) explicitly state the feasible-set or ordering constraints in the NOMA subproblem, and (iii) temper the abstract claim to reflect the algorithmic nature of the comparison. If the authors can do this, the paper could become a solid contribution."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Dear colleague,\n\nTwo things to know. First, the paper actually delivers a new result: a three-way comparison between NOMA, FDMA, and TDMA in a two-user pinching-antenna system, with the specific finding that TDMA beats NOMA when users demand symmetric rates, because each time slot can place all PAs optimally for one user. This is a genuinely useful design insight for the PASS subfield. Second, the headline is built on an asymmetric baseline: TDMA uses the provably optimal PA placement from prior work [10], while NOMA and FDMA use a two-stage SCA plus local phase fine-tuning with no optimality gap established. The crossover in Fig. 2 could be an artifact of a suboptimal NOMA solver rather than a fundamental property. That concern is the main soft spot, and it is addressable.\n\nWhat the paper does well: the system model is clean, the SIC power derivation is careful, the SCA subproblem is convex, the complexity is stated, and the PA deployment visualizations in Fig. 4 give intuitive design rules — NOMA wants asymmetric PAs, FDMA splits clusters, TDMA focuses per slot. The paper also explicitly acknowledges the implementation overhead of TDMA. Credit is given appropriately to [8] and [10] for the phase alignment and the TDMA optimal placement.\n\nWhere it is soft. The NOMA/FDMA algorithm is heuristic, and the paper never benchmarks it — no exhaustive search for small N, no grid search, no optimality gap. Because the comparison treats the TDMA solution as globally optimal and the NOMA solution as 'high-quality,' the quantitative crossover claims are not like-for-like. The abstract states the TDMA-over-NOMA result without this caveat. Second, the numerical figures show single simulation runs; there are no error bars or multiple channel realizations, so we don't know if the crossover is stable across user positions. Third, the fine-tuning explicitly relaxes the exact phase alignment constraint, so the channel gain achieved is not guaranteed to be near the coherent-combining upper bound. None of these are fatal; all are fixable with additional experiments and caveats.\n\nWho this is for: researchers working on pinching-antenna systems, particularly those interested in multiple access. It deserves a serious referee. I'd send it to review with a specific request: add a benchmark for the NOMA solver (even a small exact search) and report statistics over user drops. With those, the TDMA-over-NOMA result would be either confirmed or qualified in a meaningful way.","headline":"A useful three-way comparison in pinching-antenna systems, but the TDMA-over-NOMA headline rests on a provably optimal TDMA baseline versus a heuristic NOMA baseline, so the central quantitative claim needs a stronger NOMA benchmark before it's fully convincing.","tokens_in":9450,"tokens_out":2957,"would_cite":true,"duration_ms":28574,"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":"For two equal-rate users, TDMA with per-slot antenna placement uses less transmit power than NOMA once four or more pinching antennas are deployed.","keywords":["pinching-antenna systems","multiple access","NOMA","pinching beamforming","transmit power minimization","time-division multiple access","successive convex approximation","flexible antennas"],"falsifier":"Run the same two-user power-minimization problem with an exact global solver for NOMA and FDMA at $N=6$ with equal target rates; if the resulting NOMA transmit power falls below the TDMA value, the reported ordering is an artifact of the heuristic. Alternatively, measure the energy and switching time required to move the pinching antennas between the two TDMA slot positions and add them to the power budget; a large enough overhead invalidates the practical ranking.","tokens_in":8442,"feed_emoji":"📡","tokens_out":6721,"duration_ms":59886,"temperature":0.7,"pith_summary":"This paper asks which multiple-access scheme a two-user pinching-antenna system (PASS) should use: non-orthogonal multiple access (NOMA), frequency-division multiple access (FDMA), or time-division multiple access (TDMA). It sets up power-minimization problems in which pinching-antenna positions along a dielectric waveguide are optimized so that each user's target rate is met with the least transmit power. The central finding is that when the two users demand the same rate, TDMA can beat NOMA once at least four pinching antennas are active, because TDMA lets each time slot place its own antenna cluster around the user being served. The paper also finds that NOMA always needs less power than FDMA and that PASS greatly outperforms conventional fixed-antenna baselines.","feed_headline":"TDMA beats NOMA in pinching-antenna downlinks","feed_subtitle":"With symmetric user rates, per-slot antenna placement cuts transmit power below NOMA once at least four pinching antennas are active.","key_machinery":"The central mechanism is the time-switching feature of PASS: under TDMA, each time slot can use its own antenna-position vector $\\mathbf{x}_{p,k}$, so the array is redeployed to serve each user in turn. For a single-user slot, the optimal placement is to cluster all $N$ pinching antennas symmetrically around the user's $x$-coordinate with equal spacing $\\Delta$, a closed-form result the paper takes from prior work. For NOMA and FDMA, by contrast, one shared placement must balance the two users' channels, and the paper handles the resulting non-convex problem with a two-stage algorithm: a successive-convex-approximation stage that fixes coarse positions by minimizing large-scale path loss, followed by a fine-tuning stage that shifts antennas on a wavelength scale so their phases combine constructively at both users. The phase-alignment constraint $\\phi_k^n - \\phi_k^{n-1} = 2m_k\\pi$ is what makes constructive beamforming possible, and the first-order Taylor approximation of the phase around neighboring antennas is what allows the fine-tuning step to be computed.","core_discovery":"For a single-waveguide PASS with N pinching antennas serving two users, the paper argues that the best multiple-access choice is not fixed: it depends on how symmetric the users' rate demands are. When the rate targets are equal or close, time-division multiple access with per-slot pinching-antenna placement is more power-efficient than NOMA for N≥4, because each TDMA slot can position the full antenna array to maximize the channel gain of exactly one user. When rate targets are asymmetric, NOMA regains the advantage, since its shared resource block exploits the disparity in channel conditions. The paper also establishes that NOMA consistently requires less transmit power than FDMA under the same PASS setup, and that PASS itself yields large power savings relative to a conventional single antenna or a fixed-position array.","pith_inferences":["A fair reader might infer that the NOMA and FDMA power curves are upper bounds, since the two-stage algorithm is heuristic; a better NOMA solver could narrow or close the reported gap at $N \\ge 4$.","Because the TDMA analysis ignores the cost of moving pinching antennas between slots, an energy-aware comparison with switching overhead included could favor NOMA for short time slots or slow reconfiguration.","The results suggest a practical hybrid: use TDMA with per-slot antenna clustering for symmetric traffic and switch to NOMA with a shared asymmetric placement when user rates diverge.","A testable extension would be to derive an optimality gap or a global-search benchmark for the NOMA phase-alignment problem, turning the numerical ordering into a provable one."],"forward_implications":["For symmetric user rate requirements in a two-user PASS downlink, orthogonal access via TDMA can be more power-efficient than NOMA once $N \\ge 4$, so NOMA is not automatically the best multiple-access scheme for pinching-antenna systems.","NOMA still beats FDMA in this setting, so among the two orthogonal schemes the choice matters: time-splitting exploits PASS's reconfigurability, while frequency-splitting does not.","PASS-based beamforming can sharply reduce required transmit power relative to a conventional single antenna or a fixed-position array with the same number of elements.","When user rate targets are asymmetric, NOMA's spectrum-efficiency advantage over orthogonal access reappears, so the multiple-access choice should adapt to traffic symmetry.","The optimal TDMA deployment guideline is simple: in each slot, place the pinching antennas symmetrically around the served user with equal spacing, then refine the phases."],"supporting_citations":[{"why":"Supplies the closed-form optimal single-user pinching-antenna placement (Lemma 1) and the phase-refinement step that the TDMA solution relies on.","marker":"[10]"},{"why":"Supplies the Euclidean-distance expression and the first-order Taylor approximation of the phase that drive the fine-tuning stage.","marker":"[8]"},{"why":"Supplies the convex-optimization machinery used to solve the successive-convex-approximation subproblems for NOMA and FDMA.","marker":"[9]"},{"why":"Supplies the in-waveguide channel model with guided wavelength $\\lambda_g = \\lambda/n_{\\mathrm{eff}}$ used in the phase expressions.","marker":"[6]"}],"fun_headline_variants":["Rate symmetry decides: TDMA or NOMA in PASS","PASS downlinks: TDMA beats NOMA when rates match","Pinching antennas: NOMA for skew, TDMA for equal rates","For symmetric rates, TDMA trumps NOMA in PASS","NOMA wins asymmetric, TDMA symmetric in pinching systems"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The comparison's conclusion depends on treating the TDMA solution as optimal while the NOMA and FDMA solutions come from a heuristic without a proven gap, and on assuming that reconfiguring the antennas between time slots costs no power or time; if the heuristic is far from optimal or reconfiguration overhead is material, the TDMA-over-NOMA result could reverse.","fun_headline_variants_meta":{"raw":{"variants":["Rate symmetry decides: TDMA or NOMA in PASS","PASS downlinks: TDMA beats NOMA when rates match","Pinching antennas: NOMA for skew, TDMA for equal rates","For symmetric rates, TDMA trumps NOMA in PASS","NOMA wins asymmetric, TDMA symmetric in pinching systems"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000197,"raw_usage":{"total_tokens":1330,"prompt_tokens":880,"completion_tokens":450,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":496,"completion_tokens_details":{"reasoning_tokens":362}},"tokens_in":496,"tokens_out":450,"duration_ms":4728,"temperature":1.0,"reasoning_tokens":362,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T20:00:53.085096+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run the same two-user power-minimization problem with an exact global solver for NOMA and FDMA at $N=6$ with equal target rates; if the resulting NOMA transmit power falls below the TDMA value, the reported ordering is an artifact of the heuristic. Alternatively, measure the energy and switching time required to move the pinching antennas between the two TDMA slot positions and add them to the power budget; a large enough overhead invalidates the practical ranking.","supporting_citations":[],"review_version":2}