Fluid Reconfigurable Intelligent Surface Enabling Index Modulation

2026-03-12

AI Summary

This work addresses the limited degrees of freedom and performance of conventional reconfigurable intelligent surfaces (RIS) stemming from fixed element positions. To overcome this, it proposes a fluid reconfigurable intelligent surface (FRIS) by integrating fluid antennas with RIS for the first time, enabling dual spatial–phase reconfigurability through joint control of element positions and reflection phases. Building upon this architecture, two novel index modulation schemes—FRIS-RSM and FRIS-RSSK—are developed. A bit error rate (BER) analysis framework tailored to double-Rayleigh cascaded channels is established using the moment-generating function (MGF) method combined with a strongest-link selection strategy. Simulation results demonstrate that the proposed schemes significantly reduce BER, exhibit excellent agreement with theoretical analysis, and maintain manageable computational complexity through an efficient two-stage low-complexity list detection algorithm.

Technology Category

• Intelligent Robots: Multimodal Perception & Sensor Fusion
• Search and Optimization: Mixed Discrete/Continuous Search
• Machine Learning: Feature Construction/Reformulation

Application Category

• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications
• Security and Privacy: Large-scale security measurements

Abstract

Fluid reconfigurable intelligent surfaces (FRIS) enable joint position and phase reconfigurability by integrating fluid antennas (FA) with conventional reconfigurable intelligent surfaces (RIS). In this paper, we propose a novel FRIS-based index modulation (IM) framework that exploits the additional spatial degrees of freedom introduced by FRIS element-position reconfiguration. Based on this framework, two transmission schemes are developed, namely FRIS-assisted receiver spatial modulation (FRIS-RSM) and receiver spatial shift keying (FRIS-RSSK), where information bits are conveyed through receiver-antenna index selection. The proposed framework supports both continuous and finite-bit phase control while accounting for FRIS-side spatial correlation. To balance detection complexity and bit error rate (BER) performance, a two-stage reduced-complexity list detector is proposed. For performance analysis under double-Rayleigh cascaded fading with strongest-link selection, tractable post-selection statistics are developed for both continuous-phase and quantized-phase FRIS and incorporated into a moment-generating-function (MGF)-based framework to derive unconditional pairwise error probability (UPEP) and union-bound BER expressions. Simulation results demonstrate significant BER gains over conventional RIS-assisted schemes and verify the accuracy of the analysis.

Problem

• Fluid Reconfigurable Intelligent Surface
• Index Modulation
• Spatial Degrees of Freedom
• Bit Error Rate
• Double-Rayleigh Fading

Innovation

• Fluid Reconfigurable Intelligent Surface
• Index Modulation
• Spatial Modulation
• Reduced-Complexity Detection
• Double-Rayleigh Fading