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Exact Statistical Characterization and Performance Analysis of Fluid Reconfigurable Intelligent Surfaces

Masoud Khazaee, Felipe A. P. de Figueiredo, Rausley A. A. de Souza, Farshad Rostami Ghadi, Kai-Kit Wong, Luciano L. Mendes, Fernando D. Almeida García

Abstract

Fluid reconfigurable intelligent surfaces (FRIS) extend conventional RIS architectures by enabling physical reconfiguration of element positions, thereby introducing a fundamentally new degree of freedom for controlling spatial correlation and improving link reliability. Despite this promise, rigorous performance analysis of FRIS-assisted wireless systems has remained challenging, as exact statistical analyses of the end-to-end cascaded channels have been unavailable. This paper addresses this gap by providing the first exact closed-form characterization of the end-to-end cascaded channel gain in FRIS-aided systems under general spatial correlation. By exploiting the spectral structure of the FRIS-induced correlation matrix, we show that the channel gain statistics can be represented as a finite linear combination of K-distributions. This unified formulation naturally captures fully correlated, effectively decorrelated, and intrinsically uncorrelated operating regimes as special cases. Building on the derived channel statistics, we further obtain exact closed-form expressions for the outage probability and ergodic capacity. We also conduct an outage-based asymptotic analysis, which reveals the true diversity order of the system. Numerical results corroborate the proposed analytical framework via Monte Carlo simulations, benchmark its accuracy against state-of-the-art approximation-based approaches, and demonstrate that fluidic reconfiguration can yield tangible reliability gains by reshaping the spatial correlation structure.

Exact Statistical Characterization and Performance Analysis of Fluid Reconfigurable Intelligent Surfaces

Abstract

Fluid reconfigurable intelligent surfaces (FRIS) extend conventional RIS architectures by enabling physical reconfiguration of element positions, thereby introducing a fundamentally new degree of freedom for controlling spatial correlation and improving link reliability. Despite this promise, rigorous performance analysis of FRIS-assisted wireless systems has remained challenging, as exact statistical analyses of the end-to-end cascaded channels have been unavailable. This paper addresses this gap by providing the first exact closed-form characterization of the end-to-end cascaded channel gain in FRIS-aided systems under general spatial correlation. By exploiting the spectral structure of the FRIS-induced correlation matrix, we show that the channel gain statistics can be represented as a finite linear combination of K-distributions. This unified formulation naturally captures fully correlated, effectively decorrelated, and intrinsically uncorrelated operating regimes as special cases. Building on the derived channel statistics, we further obtain exact closed-form expressions for the outage probability and ergodic capacity. We also conduct an outage-based asymptotic analysis, which reveals the true diversity order of the system. Numerical results corroborate the proposed analytical framework via Monte Carlo simulations, benchmark its accuracy against state-of-the-art approximation-based approaches, and demonstrate that fluidic reconfiguration can yield tangible reliability gains by reshaping the spatial correlation structure.

Paper Structure

This paper contains 43 sections, 4 theorems, 77 equations, 8 figures.

Table of Contents

  1. Introduction
  2. Related Works
  3. Contributions
  4. Structure and Notation
  5. System Model
  6. Array Geometry
  7. Spatial Correlation and Active-Set Selection
  8. Received Signal Model
  9. Definitions and Performance Metrics
  10. Instantaneous SNR
  11. Instantaneous Channel Capacity
  12. Outage Probability
  13. Ergodic Capacity
  14. Statistical Characterization
  15. Main Results
  16. ...and 28 more sections

Key Result

Theorem 1

The PDF and CDF of $G_0$ can be written as a finite linear combination of $K$-distributions given, respectively, by where $f_K(\cdot)$ and $F_K(\cdot)$ denote the PDF and CDF of a $K$–distribution with shape parameter $k$ and scale parameter $\lambda_i$, given by Furthermore, let $\{\lambda_i\}_{i=1}^{q}$ denote the $q$ distinct strictly positive eigenvalues of $\mathbf{C}=\mathbf{A}\mathbf{A}^{

Figures (8)

  • Figure 1: System model of the FRIS-aided communication system.
  • Figure 2: Element activation patterns for RIS and FRIS.
  • Figure 3: PDF of $G_0$ for different FRIS and RIS configurations with $M_{\mathrm{on}} = 25$.
  • Figure 4: PDF of $G_0$ for different FRIS and RIS configurations with $M_{\mathrm{on}} = 36$.
  • Figure 5: OP versus the average SNR, $\bar{\gamma}$, for different FRIS and RIS configurations with $M_{\mathrm{on}} = 25$.
  • ...and 3 more figures

Theorems & Definitions (8)

  • Theorem
  • proof
  • Corollary 1
  • proof
  • Corollary 2
  • proof
  • Corollary 3
  • proof