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arxiv: 2602.20039 · v2 · submitted 2026-02-23 · 📡 eess.SP

On the Spatial Consistency of Sub-Terahertz Channel Characteristics for Beyond-6G Systems

Hossein Amininasab , Huda Farooqui , Dmitri Moltchanov , Sergey Andreev , Michele Polese , Mikko Valkama , Josep M. Jornet This is my paper

Pith reviewed 2026-05-15 19:59 UTC · model grok-4.3

classification 📡 eess.SP
keywords sub-terahertzspatial consistencychannel modelingray tracingbeyond-6Gdelay spreadindoor hallK-factor
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The pith

In an indoor hall at 140-150 GHz, sub-terahertz channel characteristics such as delay spread remain nearly constant over distances of tens of centimeters.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper investigates whether sub-THz wireless channels vary over wavelength-scale distances or stay similar over much larger spans, which would ease ray-tracing computations for beyond-6G systems. It reports a measurement campaign in an indoor hall environment at 140-150 GHz, sampling channel properties at receiver separations from 2.5 mm up to 1 m. The results show that delay spread, angular delay spread, and K-factor change only slightly over multiple tens of centimeters. This stability allows coarser spatial grids in line-of-sight regions while requiring finer sampling or interpolation where scattered paths dominate.

Core claim

Channel characteristics including delay spread, angular delay spread, and K-factor change only slightly over multiple tens of centimeter distances in the considered InH environment at 140-150 GHz, implying that the mesh grid can be in the range of 10-50 wavelengths along stable LoS directions while a finer resolution is needed in regions not dominated by LoS.

What carries the argument

Large-scale measurement campaign at 140-150 GHz in an indoor-hall environment that samples channel metrics at separations from 2.5 mm to 1 m and compares them to identify regions of quantitative similarity.

If this is right

  • Ray-tracing mesh grids can span 10-50 wavelengths along stable line-of-sight paths without significant loss of accuracy.
  • Finer spatial sampling remains necessary in areas dominated by scattered components.
  • Advanced interpolation techniques become essential when using grids coarser than the observed consistency scale.
  • Computational effort for precise sub-THz channel modeling drops substantially in line-of-sight dominated indoor halls.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same consistency pattern could simplify beamforming and handover planning in sub-THz networks if it holds across multiple environments.
  • System-level simulators for beyond-6G could adopt adaptive grid sizes that switch between coarse LoS and fine non-LoS regions.
  • Further campaigns at slightly different frequencies or in larger halls would test whether the 10-50 wavelength rule generalizes.

Load-bearing premise

The single indoor-hall environment and the 140-150 GHz measurement campaign are representative of typical beyond-6G sub-THz scenarios and the observed consistency extends to other indoor settings and distances.

What would settle it

A new measurement campaign in a different indoor or outdoor sub-THz environment that records large changes in delay spread or K-factor over distances shorter than 10 cm.

Figures

Figures reproduced from arXiv: 2602.20039 by Dmitri Moltchanov, Hossein Amininasab, Huda Farooqui, Josep M. Jornet, Michele Polese, Mikko Valkama, Sergey Andreev.

Figure 1
Figure 1. Figure 1: Block diagram of the NU channel sounder and the equipment in use [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: Measurement points along the cross-shaped trajectory. Black circles [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: K-factor, RMS delay spread, and RMS angular spreads versus position [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Pairwise directional PDP spatial autocorrelation between measurement [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
read the original abstract

Ray tracing is a versatile approach for precise sub-terahertz (sub-THz, 100-300 GHz) channel modeling when designing new mechanisms for beyond-6G cellular systems. Theoretically, wireless channels may exhibit variations over wavelength distances. In the sub-THz band, close-to-millimeter wavelengths thus require extremely large computational efforts for ray-tracing modeling. However, in practice, channel characteristics may remain quantitatively similar over much larger distances, which can drastically decrease computational efforts. The aim of this study is to experimentally characterize the degree of spatial consistency in sub-THz channel characteristics. To this end, we performed a large-scale measurement campaign in the 140-150 GHz frequency band in an indoor-hall (InH) environment and characterized the channel at separation distances from 2.5 mm up to 1 m. Our results show that channel characteristics including delay spread, angular delay spread, and K-factor change only slightly over multiple tens of centimeter distances. This implies that, in the considered InH environment, the mesh grid can be in the range of 10-50 wavelengths (at 145 GHz) along stable line-of-sight (LoS) directions, while a finer resolution is needed in regions not dominated by LoS. For coarser grids, advanced interpolation is required to capture rapidly varying scattered components.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript reports results from a 140-150 GHz measurement campaign conducted in a single indoor-hall (InH) environment. Channel parameters (delay spread, angular delay spread, and K-factor) were characterized at spatial separations ranging from 2.5 mm to 1 m. The central finding is that these parameters vary only slightly over distances of multiple tens of centimeters, which the authors interpret as permitting ray-tracing mesh grids of 10-50 wavelengths along stable LoS paths while requiring finer resolution or interpolation for scattered components.

Significance. If the observed spatial consistency generalizes beyond the single measured environment, the result would allow substantially coarser spatial sampling in ray-tracing models for sub-THz beyond-6G systems, reducing computational cost while preserving accuracy in LoS-dominated regions. The work is experimental rather than theoretical and supplies no machine-checked proofs or parameter-free derivations.

major comments (2)
  1. [Abstract and conclusion] The recommendation that mesh grids of 10-50 wavelengths suffice along LoS directions rests entirely on data from one indoor-hall geometry at 140-150 GHz with maximum separation 1 m. Other indoor or outdoor geometries, surface materials, or link distances could produce faster spatial decorrelation of the same parameters, undermining the grid-size guidance for general beyond-6G use. This assumption is load-bearing for the practical claim.
  2. [Abstract] The abstract states that a 'large-scale measurement campaign' was performed but supplies no quantitative information on the number of distinct locations, number of frequency points, statistical tests used to quantify 'only slightly' changes, or uncertainty analysis. Without these details the support for the quantitative claims cannot be verified.
minor comments (1)
  1. [Abstract] The abbreviation 'InH' is used without an initial definition; it should be expanded on first appearance.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for the constructive comments on our manuscript. We address each major comment point-by-point below, indicating where revisions will be incorporated.

read point-by-point responses

  1. Referee: [Abstract and conclusion] The recommendation that mesh grids of 10-50 wavelengths suffice along LoS directions rests entirely on data from one indoor-hall geometry at 140-150 GHz with maximum separation 1 m. Other indoor or outdoor geometries, surface materials, or link distances could produce faster spatial decorrelation of the same parameters, undermining the grid-size guidance for general beyond-6G use. This assumption is load-bearing for the practical claim.

    Authors: We agree that the measurements were performed in a single indoor-hall (InH) environment. The abstract and conclusions already qualify the 10-50 wavelength grid recommendation as applying specifically 'in the considered InH environment'. To strengthen this, we will add an explicit limitations paragraph noting that other geometries, materials, or distances may exhibit faster decorrelation and that the guidance is data-driven for this setting rather than universal. We will also tone down any broader phrasing in the abstract to avoid implying general beyond-6G applicability without further validation. revision: partial

  2. Referee: [Abstract] The abstract states that a 'large-scale measurement campaign' was performed but supplies no quantitative information on the number of distinct locations, number of frequency points, statistical tests used to quantify 'only slightly' changes, or uncertainty analysis. Without these details the support for the quantitative claims cannot be verified.

    Authors: We accept this criticism of the abstract. While the full manuscript details the campaign (multiple positions with separations from 2.5 mm to 1 m, 140-150 GHz band, and analysis of delay spread, angular delay spread, and K-factor variations), the abstract will be revised to include concise quantitative elements: the number of distinct locations sampled, frequency sampling points, the statistical methods (e.g., variance analysis or hypothesis testing) used to establish that changes are slight, and associated uncertainty measures. This will make the support for the claims verifiable from the abstract alone. revision: yes

standing simulated objections not resolved
  • The results are confined to one indoor-hall environment at 140-150 GHz with maximum 1 m separation; we cannot provide data or analysis demonstrating that the observed spatial consistency holds in other geometries, outdoor settings, or different materials without additional measurement campaigns.

Circularity Check

0 steps flagged

No circularity in experimental measurement study

full rationale

This paper reports results from a direct measurement campaign in a single indoor-hall environment at 140-150 GHz, with channel parameters (delay spread, angular delay spread, K-factor) extracted at physical separations from 2.5 mm to 1 m. The central claim—that these parameters vary only slightly over tens of centimeters—is an empirical observation drawn from the collected data, not a derivation, fitted model, or self-referential definition. No equations, ansatzes, uniqueness theorems, or self-citations are invoked to reduce the reported consistency to prior inputs by construction. The study is therefore self-contained against external benchmarks and receives the default non-circularity finding.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on empirical observations in one indoor environment; no free parameters, invented entities, or additional axioms beyond standard domain assumptions about propagation are introduced.

axioms (1)
  • domain assumption The chosen indoor-hall environment and 140-150 GHz band are representative of beyond-6G sub-THz scenarios.
    The study is confined to a single InH setting and frequency range.

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