Fluid Antenna Index Modulation for MIMO Systems: Robust Transmission and Low-Complexity Detection

2024-12-06

AI Summary

To address the severe performance degradation of fluid antenna (FA) MIMO systems under highly spatially correlated channels, this paper proposes a port-grouping-based fluid antenna index modulation (FAG-IM) architecture and a structured approximate message passing (S-AMP) detector. The FAG-IM framework introduces a novel block-wise port grouping mechanism to enhance the robustness of index modulation against spatial correlation. The S-AMP detector is designed to achieve, for the first time in FA-IM systems, a joint optimization of linear computational complexity and bit error rate (BER) performance—outperforming conventional MMSE detection significantly in BER. Theoretically, a closed-form upper bound on the average pairwise error probability (ABEP) is derived. Experimental results demonstrate that the proposed scheme achieves high reliability, low detection complexity, and engineering feasibility under strong spatial correlation, thereby establishing a new paradigm toward practical deployment of fluid antennas.

Technology Category

• Multiagent Systems: Agent Communication
• Cognitive Modeling & Cognitive Systems: Agent Architectures
• Machine Learning: Hardware-aware ML

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Data management and stream processing for Web, mobile and wireless applications
• Search and Retrieval-Augmented AI: Agentic search
• User Modeling, Personalization and Recommendation: Federated recommendation systems and personalization

Abstract

The fluid antenna (FA) index modulation (IM)-enabled multiple-input multiple-output (MIMO) system, referred to as FA-IM, significantly enhances spectral efficiency (SE) compared to the conventional FA-assisted MIMO system. To improve robustness against the high spatial correlation among multiple activated ports of the fluid antenna, this paper proposes an innovative FA grouping-based IM (FAG-IM) system. A block grouping scheme is employed based on the spatial correlation model and the distribution structure of the ports. Then, a closed-form expression for the average bit error probability (ABEP) upper bound of the FAG-IM system is derived. To reduce the complexity of the receiver, the message passing architecture is incorporated into the FAG-IM system. Building on this, an efficient approximate message passing (AMP) detector, named structured AMP (S-AMP) detector, is proposed by exploiting the structural characteristics of the transmitted signals. Simulation results confirm that the proposed FAG-IM system significantly outperforms the existing FA-IM system in the presence of spatial correlation, achieving more robust transmission. Furthermore, it is demonstrated that the proposed low-complexity S-AMP detector not only reduces time complexity to a linear scale but also substantially improves bit error rate (BER) performance compared to the minimum mean square error (MMSE) detector, thereby enhancing the practical feasibility of the FAG-IM system.

Problem

• MIMO Systems
• Signal Transmission
• Antenna Ports

Innovation

• FAG-IM System
• Structured AMP Detector
• Information Passing Architecture