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Finite-blocklength Fluid Antenna Systems With Spatial Block-Correlation Channel Model

Zhentian Zhang, Kai-Kit Wong, David Morales-Jimenez, Hao Jiang, Pablo Ramírez-Espinosa, Chan-Byoung Chae, Christos Masouros

TL;DR

The paper tackles finite-blocklength communications with fluid antenna systems (FAS) under a tractable block-correlation channel model. It derives the exact PDF of the FAS channel strength, develops Gauss–Laguerre quadrature and a Gamma approximation for fast, closed-form statistics, and provides a high-SNR BLER bound for short-packet codes. A Gamma-based simplification and an integral-free BLER expression enable low-complexity performance prediction. Numerical results demonstrate substantial reliability gains of FAS over fixed multi-antenna configurations, with scalable evaluation and practical relevance for ultra-reliable, low-latency links.

Abstract

Massive connectivity with ultra-low latency and high reliability necessitates fundamental advances in future communication networks operating under finite-blocklength (FBL) transmission. Fluid antenna systems (FAS) have emerged as a promising enabler, offering superior spectrum and energy efficiency in short-packet/FBL scenarios. In this work, by leveraging the simplicity and accuracy of block-correlation channel modeling, we rigorously bound the performance limits of FBL-FAS from a statistical perspective, focusing on two key performance metrics: block error rate (BLER) and outage probability (OP). Furthermore, we introduce a novel complex-integral simplification method based on Gauss-Laguerre quadrature, which achieves higher approximation accuracy compared to existing Taylor-expansion-based approaches. Numerical results validate the robustness of the proposed analysis and clearly demonstrate the superiority of FBL-FAS over conventional multiple-antenna systems with fixed antenna placement.

Finite-blocklength Fluid Antenna Systems With Spatial Block-Correlation Channel Model

TL;DR

The paper tackles finite-blocklength communications with fluid antenna systems (FAS) under a tractable block-correlation channel model. It derives the exact PDF of the FAS channel strength, develops Gauss–Laguerre quadrature and a Gamma approximation for fast, closed-form statistics, and provides a high-SNR BLER bound for short-packet codes. A Gamma-based simplification and an integral-free BLER expression enable low-complexity performance prediction. Numerical results demonstrate substantial reliability gains of FAS over fixed multi-antenna configurations, with scalable evaluation and practical relevance for ultra-reliable, low-latency links.

Abstract

Massive connectivity with ultra-low latency and high reliability necessitates fundamental advances in future communication networks operating under finite-blocklength (FBL) transmission. Fluid antenna systems (FAS) have emerged as a promising enabler, offering superior spectrum and energy efficiency in short-packet/FBL scenarios. In this work, by leveraging the simplicity and accuracy of block-correlation channel modeling, we rigorously bound the performance limits of FBL-FAS from a statistical perspective, focusing on two key performance metrics: block error rate (BLER) and outage probability (OP). Furthermore, we introduce a novel complex-integral simplification method based on Gauss-Laguerre quadrature, which achieves higher approximation accuracy compared to existing Taylor-expansion-based approaches. Numerical results validate the robustness of the proposed analysis and clearly demonstrate the superiority of FBL-FAS over conventional multiple-antenna systems with fixed antenna placement.

Paper Structure

This paper contains 10 sections, 18 equations, 5 figures.

Table of Contents

  1. Introduction
  2. System Descriptions
  3. Finite-Blocklength Single Antenna FAS Signal Model
  4. Spatial Block-Correlation Channel Model for Single Antenna $N$-Ports FAS
  5. Main Results
  6. PDF of $|g_{\mathrm{FAS}}|^2$ and BLER under Block-Correlation Model
  7. Simplified PDF of $|g_{\mathrm{FAS}}|^2$ via Gamma Approximation
  8. BLER Approximation
  9. Numerical Results
  10. Conclusion

Figures (5)

  • Figure 1: Illustration of block-correlation model's CDF and the PDF (block diagonal CDF in \ref{['eq:remarkA1']}, the derived PDF in \ref{['eq:pdf_channel_response']} and the corresponding Monte-Carlo samples.) with $N=10,~\mu^2=0.97,~W=0.5$.
  • Figure 2: Illustration of block-correlation model's CDF and the PDF (exact CDF in \ref{['eq:remarkA1']}, exact PDF in \ref{['eq:pdf_channel_response']}, the Gauss-Laguerre-approximated PDF with $N_{\mathrm{GL}}=128$ by \ref{['eq.GL_A']} and the Gamma-distribution-approximated PDF by \ref{['eq.GA_pdf_cdf']}.) with $N=10,~\mu^2=0.97,~W=0.5$.
  • Figure 3: BLER comparison between exact and high-SNR approximation for $\sigma^2=2$, $|g_{\mathrm{FAS}}|^2=1$, $U=100$, and $M=400$.
  • Figure 4: BLER versus SNR with $N=10$ available ports, $L\in\{1,3,5\}$, and $W=1$. All simulations are conducted within block-correlation model and the exact PDF refers to block-diagonal expression in \ref{['eq:pdf_channel_response']} and the approximated PDF refers to the Gamma-approximated expression in \ref{['eq.GA_pdf_cdf']}.
  • Figure 5: BLER versus aperture with $N=50$ available ports, $L\in\{1,3,5,10,20\}$, and SNR $=10$ dB.