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A Universal Block Error Rate Bound for Fluid Antenna Systems

Zhentian Zhang, David Morales-Jimenez, Hao Jiang, Christos Masouros

TL;DR

This work addresses finite-blocklength performance in fluid antenna systems by introducing a universal BLER bound for FBL-FAS that applies across diverse port-correlation models. The authors derive a CSI-conditioned bound (Theorem 1), characterize the distribution of the effective FAS gain under simple correlation (Theorem 2), and extend to CSI-agnostic scenarios by integrating over the gain distribution (Theorem 3). They benchmark against a conventional L-antenna receiver and demonstrate through numerical results that the FAS bound remains accurate and that spatial diversity in fluid antennas yields substantial BLER gains, even at short blocklengths. The bound is computable analytically or empirically, enabling model-aware and model-free evaluations, and is supported by reproducible code. Overall, the paper provides a practical, universal metric for evaluating and exploiting finite-blocklength performance in FAS designs, with broad implications for low-complexity, high-diversity wireless architectures.

Abstract

Fluid antenna systems (FASs) offer genuine simplicity for communication network design by eliminating expensive hardware overhead and reducing the complexity of access protocol architectures. Through the discovery of significant spatial diversity within a compact antenna space, FASs enable the implementation of reconfigurable-antenna-based architectures. However, current state-of-the-art studies rarely investigate the impact of finite blocklength constraints on FAS-based designs, leaving a gap in both analytical modeling and the establishment of a solid, universally applicable performance metric for finite blocklength fluid antenna systems (FBL-FAS). In this work, we focus on the study of FBL-FAS and, more importantly, derive a block error rate (BLER) bound that serves as a general and practical performance benchmark across various FAS architectures. The proposed BLER bound is computable both with and without an explicit statistical model, meaning that the BLER performance can be characterized analytically or empirically under model-aware or model-free system scenarios. Moreover, when the statistical model is known, the analytical results derived from the proposed BLER bound exhibit strong alignment with the empirical findings, demonstrating the remarkable simplicity, accuracy, and universality of the proposed BLER bound.

A Universal Block Error Rate Bound for Fluid Antenna Systems

TL;DR

This work addresses finite-blocklength performance in fluid antenna systems by introducing a universal BLER bound for FBL-FAS that applies across diverse port-correlation models. The authors derive a CSI-conditioned bound (Theorem 1), characterize the distribution of the effective FAS gain under simple correlation (Theorem 2), and extend to CSI-agnostic scenarios by integrating over the gain distribution (Theorem 3). They benchmark against a conventional L-antenna receiver and demonstrate through numerical results that the FAS bound remains accurate and that spatial diversity in fluid antennas yields substantial BLER gains, even at short blocklengths. The bound is computable analytically or empirically, enabling model-aware and model-free evaluations, and is supported by reproducible code. Overall, the paper provides a practical, universal metric for evaluating and exploiting finite-blocklength performance in FAS designs, with broad implications for low-complexity, high-diversity wireless architectures.

Abstract

Fluid antenna systems (FASs) offer genuine simplicity for communication network design by eliminating expensive hardware overhead and reducing the complexity of access protocol architectures. Through the discovery of significant spatial diversity within a compact antenna space, FASs enable the implementation of reconfigurable-antenna-based architectures. However, current state-of-the-art studies rarely investigate the impact of finite blocklength constraints on FAS-based designs, leaving a gap in both analytical modeling and the establishment of a solid, universally applicable performance metric for finite blocklength fluid antenna systems (FBL-FAS). In this work, we focus on the study of FBL-FAS and, more importantly, derive a block error rate (BLER) bound that serves as a general and practical performance benchmark across various FAS architectures. The proposed BLER bound is computable both with and without an explicit statistical model, meaning that the BLER performance can be characterized analytically or empirically under model-aware or model-free system scenarios. Moreover, when the statistical model is known, the analytical results derived from the proposed BLER bound exhibit strong alignment with the empirical findings, demonstrating the remarkable simplicity, accuracy, and universality of the proposed BLER bound.

Paper Structure

This paper contains 15 sections, 28 equations, 5 figures.

Table of Contents

  1. Introduction
  2. System Model
  3. Simple Reference Channel Channel
  4. Modified Reference Correlation Model
  5. Fully Correlated Channel Model
  6. Main Results
  7. BLER Upper-Bound for FBL-FAS
  8. Benchmark: Conventional $L$-Antenna System
  9. Numerical Results
  10. BLER under Simple Reference Correlation Model
  11. BLER Comparison under Different Correlation Models
  12. Conclusion
  13. Appendix
  14. Probability of BLER Conditioned on $|g_{\mathrm{FAS}}|$
  15. Derivations of Random Variable $|g_{\mathrm{FAS}}|$'s PDF $f_{|g_{\mathrm{FAS}}|}\left(r\right)$

Figures (5)

  • Figure 1: Illustration of the simplified CDF in \ref{['joint CDF']} and PDF in \ref{['eq:16']} of $|g_{\mathrm{FAS}}|$ with $10^{5}$ Monte-Carlo samples, $\sigma=1$, number of available ports $N=10$ and antenna length constant $W=0.5$.
  • Figure 2: BLER performance versus SNR (dB). Configurations: $U=20$, $M=400$, $W=2$, $N\in\{5,25\}$, $L\in\{1,3,5,10\}$.
  • Figure 3: BLER performance versus port number $N$. Configurations: $U=20$, $M=400$, $W=2$, $\mathrm{SNR}=-15$ dB, $L\in\{1,3,5,10\}$.
  • Figure 4: BLER performance versus number of codeword $U$. Configurations: $M=400$, $\mathrm{SNR}=-15$ dB, $N\in\{50,200\}$, $L\in\{1,3,5,10\}$.
  • Figure 5: BLER performance under different correlation models versus port number $N$. Configurations: $M=400$, $U=20$, $W\in\{5,10\}$, $\mathrm{SNR}=-15$ dB.