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Advanced Channel Coding Designs for Index-Modulated Fluid Antenna Systems

Elio Faddoul, Ghassan M. Kraidy, Constantinos Psomas, Ioannis Krikidis

TL;DR

This work investigates index-modulated transmissions in fluid antenna (FA) systems, enabling data transmission via both port indices and signal symbols with a single RF chain. It derives a closed-form BER bound for IM-FAs under spatial correlation, introduces a spatial set-partition coding (SPC) scheme to spatially separate FA ports, and extends to turbo-coded modulation that protects both spatial and signal bits, complemented by mutual information analysis and EXIT-based low-SNR insights. The paper provides tight PEP and WEF-based BER bounds, a numerical capacity expression, and extensive simulations showing substantial gains for coded IM-FAs, particularly in highly correlated, confined FA environments. Collectively, these results establish a complete framework for coded index-based modulation in FA systems, highlighting practical coding strategies to enhance reliability and efficiency in next-generation wireless networks.

Abstract

The concept of fluid antennas (FAs) has emerged as a promising solution to enhance the spectral efficiency of wireless networks, achieved by introducing additional degrees of freedom, including reconfigurability and flexibility. In this paper, we investigate the use of index-modulated (IM) transmissions within the framework of FA systems, where an FA position is activated during each transmission interval. This approach is motivated by the common characteristics exhibited by FAs and IM transmissions, which entails the use of a single radio-frequency chain. From this perspective, we derive a closed-form expression for the bit error rate of IM-FAs considering spatial correlation, and demonstrating superior performance compared to conventional IM systems. To enhance the performance of IM-FAs in correlated conditions, channel coding techniques are applied. We first analyze a set partition coding (SPC) scheme for IM-FAs to spatially separate the FA ports, and provide a tight performance bound over correlated channels. Furthermore, the spatial SPC scheme is extended to turbo-coded modulation where the performance is analyzed for low and high signal-to-noise ratios. Our results reveal that through the implementation of channel coding techniques designed for FAs and IM transmission, the performance of coded IM-FAs exhibits notable enhancements, particularly in high correlation scenarios.

Advanced Channel Coding Designs for Index-Modulated Fluid Antenna Systems

TL;DR

This work investigates index-modulated transmissions in fluid antenna (FA) systems, enabling data transmission via both port indices and signal symbols with a single RF chain. It derives a closed-form BER bound for IM-FAs under spatial correlation, introduces a spatial set-partition coding (SPC) scheme to spatially separate FA ports, and extends to turbo-coded modulation that protects both spatial and signal bits, complemented by mutual information analysis and EXIT-based low-SNR insights. The paper provides tight PEP and WEF-based BER bounds, a numerical capacity expression, and extensive simulations showing substantial gains for coded IM-FAs, particularly in highly correlated, confined FA environments. Collectively, these results establish a complete framework for coded index-based modulation in FA systems, highlighting practical coding strategies to enhance reliability and efficiency in next-generation wireless networks.

Abstract

The concept of fluid antennas (FAs) has emerged as a promising solution to enhance the spectral efficiency of wireless networks, achieved by introducing additional degrees of freedom, including reconfigurability and flexibility. In this paper, we investigate the use of index-modulated (IM) transmissions within the framework of FA systems, where an FA position is activated during each transmission interval. This approach is motivated by the common characteristics exhibited by FAs and IM transmissions, which entails the use of a single radio-frequency chain. From this perspective, we derive a closed-form expression for the bit error rate of IM-FAs considering spatial correlation, and demonstrating superior performance compared to conventional IM systems. To enhance the performance of IM-FAs in correlated conditions, channel coding techniques are applied. We first analyze a set partition coding (SPC) scheme for IM-FAs to spatially separate the FA ports, and provide a tight performance bound over correlated channels. Furthermore, the spatial SPC scheme is extended to turbo-coded modulation where the performance is analyzed for low and high signal-to-noise ratios. Our results reveal that through the implementation of channel coding techniques designed for FAs and IM transmission, the performance of coded IM-FAs exhibits notable enhancements, particularly in high correlation scenarios.
Paper Structure (19 sections, 47 equations, 10 figures, 1 table)

This paper contains 19 sections, 47 equations, 10 figures, 1 table.

Table of Contents

  1. Introduction
  2. System Model
  3. Channel Model
  4. Index-Based Modulation for FAs
  5. BER Analysis of IM-FAs
  6. Spatial SPC for IM-FAs
  7. Spatial SPC Design
  8. BER Analysis of the IM-FA system with SPC
  9. Turbo-Coded IM-FAs
  10. Turbo-Coded Design
  11. Mutual Information Analysis of IM-FAs
  12. BER for High SNRs
  13. EXIT for Low SNRs
  14. Numerical Results
  15. Conclusion
  16. ...and 4 more sections

Figures (10)

  • Figure 1: Transceiver structure for the proposed IM-FA system.
  • Figure 2: Spatial SPC design for the IM-FA.
  • Figure 3: Turbo-coded design for the considered IM-FA system.
  • Figure 4: Impact of the spatial correlation and the number of FA ports on the BER.
  • Figure 5: Performance comparison between the IM-CA and IM-FA systems for different $k$.
  • ...and 5 more figures

Theorems & Definitions (4)

  • proof
  • proof
  • proof
  • proof