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On Performance of RIS-Aided Fluid Antenna Systems

Farshad Rostami Ghadi, Kai-Kit Wong, Wee Kiat New, Hao Xu, Ross Murch, Yangyang Zhang

TL;DR

The paper addresses RIS-aided wireless links to a user equipped with a planar fluid antenna system, with the direct BS–MU path blocked. It models spatial port correlations via a Gaussian copula and applies the central limit theorem to approximate the per-port channel gains, deriving compact OP and DOR expressions for the RIS–FAS setup. Key contributions include closed-form OP and DOR formulas and the finding that enabling a single active FAS port can significantly outperform traditional TAS as the RIS size grows, highlighting a strong RIS–FAS synergy for ultra-reliable low-latency communications (URLLC). The work provides a tractable analytical framework for evaluating RIS-assisted fluid antennas, with implications for designing flexible, low-latency wireless networks.

Abstract

This letter studies the performance of reconfigurable intelligent surface (RIS)-aided communications for a fluid antenna system (FAS) enabled receiver. Specifically, a fixed singleantenna base station (BS) transmits information through a RIS to a mobile user (MU) which is equipped with a planar fluid antenna in the absence of a direct link.We first analyze the spatial correlation structures among the positions (or ports) in the planar FAS, and then derive the joint distribution of the equivalent channel gain at the user by exploiting the central limit theorem. Furthermore, we obtain compact analytical expressions for the outage probability (OP) and delay outage rate (DOR). Numerical results illustrate that using FAS with only one activated port into the RIS-aided communication network can greatly enhance the performance, when compared to traditional antenna systems (TAS).

On Performance of RIS-Aided Fluid Antenna Systems

TL;DR

The paper addresses RIS-aided wireless links to a user equipped with a planar fluid antenna system, with the direct BS–MU path blocked. It models spatial port correlations via a Gaussian copula and applies the central limit theorem to approximate the per-port channel gains, deriving compact OP and DOR expressions for the RIS–FAS setup. Key contributions include closed-form OP and DOR formulas and the finding that enabling a single active FAS port can significantly outperform traditional TAS as the RIS size grows, highlighting a strong RIS–FAS synergy for ultra-reliable low-latency communications (URLLC). The work provides a tractable analytical framework for evaluating RIS-assisted fluid antennas, with implications for designing flexible, low-latency wireless networks.

Abstract

This letter studies the performance of reconfigurable intelligent surface (RIS)-aided communications for a fluid antenna system (FAS) enabled receiver. Specifically, a fixed singleantenna base station (BS) transmits information through a RIS to a mobile user (MU) which is equipped with a planar fluid antenna in the absence of a direct link.We first analyze the spatial correlation structures among the positions (or ports) in the planar FAS, and then derive the joint distribution of the equivalent channel gain at the user by exploiting the central limit theorem. Furthermore, we obtain compact analytical expressions for the outage probability (OP) and delay outage rate (DOR). Numerical results illustrate that using FAS with only one activated port into the RIS-aided communication network can greatly enhance the performance, when compared to traditional antenna systems (TAS).
Paper Structure (9 sections, 2 theorems, 22 equations, 4 figures)

This paper contains 9 sections, 2 theorems, 22 equations, 4 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. Performance Analysis
  4. Statistical Characterization
  5. OP Analysis
  6. DOR Analysis
  7. Numerical Results
  8. Conclusion
  9. Spatial Correlation in Planar FAS

Key Result

Proposition 1

The OP for the considered RIS-aided FAS is given by where $F_{h_{{\mathrm{FAS}}}^2}(r)$ is defined in eq-cdf.

Figures (4)

  • Figure 1: A RIS-aided channel from a TAS BS to a FAS-equipped user.
  • Figure 2: OP versus $P$ (a) for selected values of $M$ and $N$ when $W=1\lambda\times 1\lambda$, and (b) for selected values of $M$ and $W$ when $N=25$.
  • Figure 3: OP versus (a) the number of fluid antenna ports $N$ for a fixed $W=1\lambda\times 1\lambda$, (b) the size of fluid antenna $W$ for a fixed $N=25$, (c) the number of RIS elements $M$ for a fixed $W=1\lambda\times1\lambda$, and (d) the number of RIS elements $M$ for a fixed $N=25$.
  • Figure 4: DOR versus (a) the bandwidth $B$ for a fixed $W=1\lambda\times1\lambda$, (b) the bandwidth $B$ for a fixed $N=25$, (c) the amount of transmitted data $R$ for a fixed $W=1\lambda\times1\lambda$, and (d) the amount of transmitted data $R$ for a fixed $N=25$.

Theorems & Definitions (3)

  • Proposition 1
  • proof
  • Proposition 2