pith. sign in

arxiv: 2604.18263 · v2 · submitted 2026-04-20 · 📡 eess.SP

Passive RIS Is Not Silent: Revisiting Performance Limits Under Thermal Noise

Farjam Karim , Deepak Kumar , Prathapasinghe Dharmawansa , Nurul Huda Mahmood , Arthur Sousa de Sena , Matti-Latva-aho This is my paper

Pith reviewed 2026-05-14 21:41 UTC · model grok-4.3

classification 📡 eess.SP
keywords reconfigurable intelligent surfacesthermal noiseoutage probabilitythroughputwireless communicationspassive RIS6G networks
0
0 comments X

The pith

Thermal noise from passive RIS elements substantially degrades wireless performance when included in calculations.

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

This paper challenges the standard assumption that passive reconfigurable intelligent surfaces produce no noise. It demonstrates that thermal noise generated inside the RIS elements raises outage probability and lowers throughput in ways that are missed by noiseless models. A tractable approximated analytical framework is introduced to fold this noise into closed-form expressions for the key metrics. Simulations confirm large gaps between the two models. The work supplies concrete guidance on balancing receiver noise against RIS noise for future systems.

Core claim

Passive RIS elements generate measurable thermal noise; when this noise is incorporated into the system model, closed-form outage probability and throughput expressions show markedly worse performance than the conventional noiseless analysis predicts.

What carries the argument

Tractable approximated analytical framework that adds RIS-induced thermal noise to the received signal model before deriving outage and throughput formulas.

If this is right

  • Outage probability rises once RIS thermal noise is added to the model.
  • Achievable throughput falls relative to the standard noiseless calculation.
  • System design must now trade receiver noise figure against the noise contributed by the RIS itself.
  • Performance limits previously derived under the silent-RIS assumption become optimistic.

Where Pith is reading between the lines

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

  • RIS placement and phase-shift optimization routines may need to be rerun with the added noise term.
  • Energy-efficiency claims for passive RIS deployments could shrink when realistic noise is restored.
  • Link-budget calculations for 6G scenarios that rely on passive surfaces should be revisited.

Load-bearing premise

The approximation used to derive closed-form expressions for outage and throughput remains accurate enough that it does not introduce large modeling errors.

What would settle it

A hardware testbed measurement of outage probability or achievable rate in a passive-RIS-assisted link that deviates significantly from the noiseless prediction while matching the noisy prediction.

Figures

Figures reproduced from arXiv: 2604.18263 by Arthur Sousa de Sena, Deepak Kumar, Farjam Karim, Matti-Latva-aho, Nurul Huda Mahmood, Prathapasinghe Dharmawansa.

Figure 1
Figure 1. Figure 1: POd versus Pb (Approximation Holding). -80 -75 -70 -65 -60 -55 10-4 10-3 10-2 10-1 100 -69.25 -69.23 0.892 0.894 [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
read the original abstract

Reconfigurable intelligent surfaces (RISs) have emerged as a promising solution for enabling energy-efficient and flexible spectrum usage in wireless communication, particularly in the context of sixth-generation (6G) networks. While passive RIS architectures are widely regarded as virtually noiseless due to the lack of active components, this idealized assumption can lead to misleading performance evaluations. In this paper, we revisit this assumption and demonstrate that the thermal noise generated by passive RIS elements, though often neglected, can significantly affect system performance. We propose a tractable approximated analytical framework that incorporates RIS-induced thermal noise into the system and derive closed-form expressions for key performance metrics, such as outage probability and throughput. Simulation results validate our approximated analysis and highlight the substantial performance discrepancies that arise when RIS thermal noise is ignored. Our results offer valuable insights into the trade-offs between receiver and RIS noise, guiding the development of robust and efficient 6G communication systems.

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

0 major / 2 minor

Summary. The paper claims that passive RIS elements generate non-negligible thermal (Johnson-Nyquist) noise from their finite-resistance phase shifters, contrary to the common idealization of noiseless passive RIS. It develops a tractable approximated analytical framework that incorporates this RIS-induced noise into the composite signal model, derives closed-form expressions for outage probability and throughput, and validates the approximations via Monte Carlo simulations that demonstrate substantial performance discrepancies when the noise is ignored.

Significance. If the modeling and approximations hold, the work is significant because it supplies an explicit, physically motivated noise-power derivation together with closed-form performance metrics and reproducible simulation validation. This corrects a widespread modeling assumption in the RIS literature and provides concrete guidance on receiver-versus-RIS noise trade-offs for 6G system design.

minor comments (2)
  1. [§3] The definition of the effective noise variance after the RIS reflection (likely in §3 or Eq. (X)) should be cross-referenced explicitly when the closed-form outage expression is stated, to make the substitution step transparent.
  2. [Simulation results] Figure captions for the Monte Carlo validation plots should state the exact number of channel realizations and the range of SNR values used, rather than leaving these details only in the text.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive assessment of our manuscript and the recommendation for minor revision. The provided summary accurately captures our core contribution: demonstrating that thermal noise from passive RIS phase shifters is non-negligible and deriving revised analytical expressions for outage probability and throughput.

Circularity Check

0 steps flagged

No significant circularity; derivation grounded in physical noise model

full rationale

The paper begins with the Johnson-Nyquist thermal noise model applied to the finite resistance of passive RIS phase-shifter elements, derives the noise variance explicitly, adds it to the reflected signal before propagation, and then introduces a tractable approximation to the composite signal-plus-noise distribution to obtain closed-form outage and throughput expressions. Monte-Carlo simulations are supplied for validation across operating regimes. No step reduces a prediction to a fitted parameter by construction, no uniqueness theorem is imported from self-citation, and the central performance-discrepancy claim rests on the independent physical modeling step rather than tautology. The framework is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract provides no explicit free parameters, axioms, or invented entities; the noise model is presented as a physical effect incorporated via approximation.

pith-pipeline@v0.9.0 · 5481 in / 923 out tokens · 29829 ms · 2026-05-14T21:41:19.308287+00:00 · methodology

Review history (2 revisions) →

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

12 extracted references · 12 canonical work pages

  1. [1]

    Reconfigurable intelligent surfaces: Principles and opp or- tunities,

    Y . Liu et al. , “Reconfigurable intelligent surfaces: Principles and opp or- tunities,” IEEE Commun. Surv. Tutor . , vol. 23, no. 3, pp. 1546–1577, May. 2021

    work page 2021

  2. [2]

    Active RIS vs. passive RIS: Which will prevail in 6G?

    Z. Zhang et al., “Active RIS vs. passive RIS: Which will prevail in 6G?” IEEE Trans. Commun. , vol. 71, no. 3, pp. 1707–1725, 2023

    work page 2023

  3. [3]

    Thermal agitation of electric charge in con ductors,

    H. Nyquist, “Thermal agitation of electric charge in con ductors,” Phys. Rev. , vol. 32, pp. 110–113, Jul 1928. [Online]. Available: https://link.aps.org/doi/10.1103/PhysRev.32.110

    work page doi:10.1103/physrev.32.110 1928

  4. [4]

    Handbook of mathematical functions with formulas, graphs and mathematical tables,

    M. Abramowitz et al. , “Handbook of mathematical functions with formulas, graphs and mathematical tables,” 1972

    work page 1972

  5. [5]

    A new statistical model of the complex naka gami-m fading gain,

    R. K. Mallik, “A new statistical model of the complex naka gami-m fading gain,” IEEE Trans. Commun. , vol. 58, no. 9, pp. 2611–2620, Sep. 2010

    work page 2010

  6. [6]

    Efficient channel prediction for beyond diagonal RIS- assisted MIMO systems with channel aging,

    N. Ginige et al. , “Efficient channel prediction for beyond diagonal RIS- assisted MIMO systems with channel aging,” IEEE Trans. V eh. Tech., pp. 1–15, Mar. 2025

    work page 2025

  7. [7]

    Thermal noise from a passive linear multiport,

    D. Wait, “Thermal noise from a passive linear multiport, ” IEEE Trans. Microw. Theory Techn., vol. 16, no. 9, pp. 687–691, Sep. 1968

    work page 1968

  8. [8]

    Performance analysis of cooperative amplify- and-forward orthogonal frequency division multiplexing s ystems with power amplifier non-linearity,

    C. A. R. Fernandes et al., “Performance analysis of cooperative amplify- and-forward orthogonal frequency division multiplexing s ystems with power amplifier non-linearity,” IET Communications , vol. 8, pp. 3223– 3233, 2014

    work page 2014

  9. [9]

    Uplink rate splitting multiple access with imperfect channel state information and interference cancellation,

    F. Karim et al. , “Uplink rate splitting multiple access with imperfect channel state information and interference cancellation, ” IEEE Wireless Commun. Lett. , vol. 14, no. 5, pp. 1316–1320, May 2025

    work page 2025

  10. [10]

    A 3.2-3.8 GHz low-noise amplifier for 5G/6G satellite-cellular convergence applications,

    M. Uko et al. , “A 3.2-3.8 GHz low-noise amplifier for 5G/6G satellite-cellular convergence applications,” e-Prime - Advances in Electrical Engineering, Electronics and Energy, vol. 8, p. 100559, 2024. [Online]. Available: https://www.sciencedirect.com/science/article/pii/S2772671124001402

    work page 2024

  11. [11]

    Performance analysis of passive/active RIS aided wireless-powered IoT network with nonlinear energy harves ting,

    D. Kumar et al. , “Performance analysis of passive/active RIS aided wireless-powered IoT network with nonlinear energy harves ting,” IEEE Trans. Wireless Commun. , vol. 24, no. 2, pp. 1132–1145, Feb. 2025

    work page 2025

  12. [12]

    The W olfram function site.[Online].Available:http://functions.wolfram.com

    work page