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arxiv: 2606.26808 · v1 · pith:PBF3RH4Nnew · submitted 2026-06-25 · 💻 cs.NI

An Experimental Assessment of the Spatial and Frequency Selectivity of Reconfigurable Intelligent Surfaces

Cyrille Morin (MARACAS) , Leonardo S Cardoso (CITI , MARACAS) , Maxime Guillaud (MARACAS) , Ahmad Shokair , Youssef Nasser , Amelie Hennequart , Geoffroy Lerosey This is my paper

Pith reviewed 2026-06-26 02:41 UTC · model grok-4.3

classification 💻 cs.NI
keywords reconfigurable intelligent surfacesRISfrequency selectivityspatial selectivitysecondary linkexperimental measurementFR1 bandchannel phase
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The pith

RIS configurations tuned for one link measurably change power and phase on secondary links even at different carrier frequencies.

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

The paper examines whether reconfigurable intelligent surfaces affect radio links other than the one they are configured to serve. Through controlled experiments in three scenarios on the CorteXlab testbed with a Greenerwave RIS operating in the FR1 band, the authors measure received power and channel phase on a secondary link while the surface is optimized for a primary link. The results indicate that the effect remains substantial outside the RIS nominal frequency range and that separating the carriers does not remove the impact. A reader would care because future dense wireless deployments may place many RIS units near multiple users or services, making unintended cross-link effects a practical concern rather than an edge case.

Core claim

The central claim is that the impact of a RIS configuration optimized for a primary link, in terms of received power and channel phase shift on a secondary link, is significant even outside the nominal frequency range of the RIS and is not mitigated by carrier frequency separation between the two links.

What carries the argument

Experimental comparison of received power and phase on secondary links when a Greenerwave RIS is configured for a primary link, tested across same-frequency and different-frequency cases in three spatial scenarios.

If this is right

  • Frequency separation between links does not protect secondary links from RIS-induced changes in power and phase.
  • Spatial selectivity of the RIS is limited enough that nearby secondary links experience measurable effects.
  • RIS deployments must account for effects on non-targeted links operating on the same or adjacent carriers.
  • Joint configuration of multiple RIS units may be needed to limit cross-link interference.

Where Pith is reading between the lines

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

  • In a dense environment with many uncoordinated RIS units, cumulative effects on secondary links could become harder to predict from single-link tests.
  • Future work could test whether explicit multi-link optimization routines reduce the observed secondary-link impact.
  • The finding suggests that RIS selectivity claims should be validated across a wider range of frequency offsets than the nominal band.

Load-bearing premise

The testbed measurements isolate the RIS configuration effect from other variables such as multipath, hardware imperfections, or uncontrolled environmental changes in the three scenarios.

What would settle it

A repeated measurement in the same testbed setup that shows no measurable change in secondary-link power or phase when the RIS is switched between configurations optimized for the primary link.

Figures

Figures reproduced from arXiv: 2606.26808 by Ahmad Shokair, Amelie Hennequart, Cyrille Morin (MARACAS), Geoffroy Lerosey, Leonardo S Cardoso (CITI, MARACAS), Maxime Guillaud (MARACAS), Youssef Nasser.

Figure 1
Figure 1. Figure 1: Scenarios in which a RIS can negatively impact the communication performance of the secondary link [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Layout of measurements in CorteXlab. Crosses indicate [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: TDMA Scenario, f1 = f2, 1 MHz steps. For all plots, RX1 = 15. Green shade is nominal RIS operation bandwidth V. RESULTS A. TDMA Scenario The first set of results corresponds to the TDMA scenario (f1 = f2) described in Section II-A with RX1 chosen as node 15. Power gain and EVM metrics are presented in Figs. 3(a) and 3(b) respectively. Subplots positions for different choices of RX2 are arranged to correspo… view at source ↗
Figure 4
Figure 4. Figure 4: Multiple Operators Scenario, distribution over all [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Multiband Scenario, Metrics over all f1 vs. f2, RX1 = RX2 [3] C. Pan, H. Ren, K. Wang, et al., “Reconfigurable intelligent surfaces for 6g systems: Principles, applica￾tions, and research directions,” IEEE Communications Magazine, vol. 59, 2021. [4] G. C. Alexandropoulos, D.-T. Phan-Huy, K. D. Kat￾sanos, et al., “RIS-enabled smart wireless environ￾ments: Deployment scenarios, network architecture, bandwidt… view at source ↗
read the original abstract

This work investigates the impact of reconfigurable intelligent surfaces (RIS) on radio links other than the one for which the RIS configuration is optimized. We consider three different scenarios in which a secondary communication link could be affected by a RIS whose configuration is optimized for a primary communication link operating in the vicinity, on the same or on different frequencies. This question is investigated experimentally in the FR1 band, using the CorteXlab radio testbed and a Greenerwave RIS. We show that the impact, in terms of received power and impact on the channel phase of the secondary link, is significant even outside of the nominal frequency range of the RIS, and is not mitigated by carrier frequency separation between the two communication links.

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 / 2 minor

Summary. The manuscript experimentally investigates the impact of a reconfigurable intelligent surface (RIS) on secondary communication links when the RIS phase configuration is optimized for a primary link. Using the CorteXlab testbed and Greenerwave RIS in the FR1 band, the authors examine three scenarios involving same or different frequencies and report that the effects on received power and channel phase of the secondary link remain significant even outside the RIS nominal frequency range and are not mitigated by carrier frequency separation between the links.

Significance. If the measurements include adequate controls to attribute changes specifically to RIS configurations, the results would provide useful empirical data on cross-link interference in RIS-assisted systems, with implications for multi-user deployments and frequency planning in FR1. The real testbed approach adds practical value over purely simulated studies.

major comments (2)
  1. [Experimental Setup] Experimental methodology (likely §3 or equivalent): The description of the three scenarios does not report baseline measurements with fixed or disabled RIS configurations, repeated trials under controlled environmental variation, or statistical tests for hardware drift and multipath, which are required to isolate RIS phase effects from other variables when comparing primary- vs. secondary-optimized settings across frequencies.
  2. [Results] Results and discussion (likely §4): The claim that frequency separation does not mitigate the impact lacks quantitative support such as effect-size comparisons with confidence intervals or p-values between same-frequency and separated-carrier cases; without these, the insensitivity conclusion rests on qualitative observation rather than rigorous attribution.
minor comments (2)
  1. [Figures] Figure captions should explicitly state the number of independent trials and any averaging performed for each power/phase measurement.
  2. [Introduction] Notation for primary and secondary links is clear but could benefit from a table summarizing the three scenarios, carrier frequencies, and RIS nominal band for quick reference.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We appreciate the referee's thorough review and constructive suggestions for improving the experimental rigor and quantitative analysis in our manuscript. We address each major comment below.

read point-by-point responses

  1. Referee: [Experimental Setup] Experimental methodology (likely §3 or equivalent): The description of the three scenarios does not report baseline measurements with fixed or disabled RIS configurations, repeated trials under controlled environmental variation, or statistical tests for hardware drift and multipath, which are required to isolate RIS phase effects from other variables when comparing primary- vs. secondary-optimized settings across frequencies.

    Authors: We agree that explicit baseline measurements are valuable for attributing changes to the RIS configurations. The original experiments included comparisons across different RIS phase settings, which serve as internal controls, but we acknowledge that measurements with the RIS disabled or in a fixed non-optimized state were not detailed. In the revised manuscript, we will add a description of any available fixed-configuration data from the testbed and clarify the steps taken to control for multipath and hardware stability. However, due to limited testbed access time, repeated trials with statistical analysis were not conducted; this will be noted as a limitation. revision: partial

  2. Referee: [Results] Results and discussion (likely §4): The claim that frequency separation does not mitigate the impact lacks quantitative support such as effect-size comparisons with confidence intervals or p-values between same-frequency and separated-carrier cases; without these, the insensitivity conclusion rests on qualitative observation rather than rigorous attribution.

    Authors: We concur that quantitative metrics would provide stronger evidence for the conclusion. We will revise the results section to include effect size calculations and confidence intervals derived from the measured received power and phase data for the same-frequency versus frequency-separated scenarios. This will allow for a more rigorous comparison and support the claim that frequency separation does not mitigate the RIS impact. revision: yes

standing simulated objections not resolved
  • Providing p-values or results from repeated trials under controlled variations, since such repeated experiments were not performed in the original study.

Circularity Check

0 steps flagged

No circularity: purely experimental measurements with no derivations or fitted predictions

full rationale

The paper presents direct testbed measurements of RIS impact on secondary links across scenarios in the FR1 band using CorteXlab and Greenerwave hardware. No equations, derivations, parameter fitting, or predictions are claimed; results are reported as observed received power and phase shifts. No self-citations form load-bearing steps, and no quantities are defined in terms of themselves. The central claim rests on attribution of measured differences to RIS configurations, which is an experimental validity issue rather than a circular reduction. This matches the default case of a self-contained empirical study.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The work relies on standard domain assumptions about RIS behavior and testbed validity rather than new free parameters or invented entities.

axioms (2)
  • domain assumption A RIS can be configured to optimize a primary link without inherent constraints on its effect on other links.
    Implicit in the experimental design of optimizing for one link and measuring others.
  • domain assumption The CorteXlab testbed and Greenerwave RIS produce measurements representative of real-world radio propagation.
    Required for generalizing the observed effects beyond the lab setup.

pith-pipeline@v0.9.1-grok · 5686 in / 1298 out tokens · 53810 ms · 2026-06-26T02:41:25.595053+00:00 · methodology

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Reference graph

Works this paper leans on

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