On the Performance of Fluid Antenna Systems under Block-Diagonal Correlation Model

2026-07-21

AI Summary

This study investigates the performance of single-transmit multiple-receive fluid antenna systems over block-diagonal correlated channels, with a focus on enhancing reliability and spectral efficiency through port selection combined with maximal ratio combining (MRC) within spatially constrained environments. By partitioning ports into independent blocks, the proposed scheme selects the strongest port within each block and applies MRC across blocks. The outage probability is derived using convolution and characteristic function techniques, while tight approximations of ergodic rate are established via Gamma distribution matching and Jensen’s inequality. Theoretical and simulation results demonstrate that the system achieves a diversity order approximately equal to the total number of ports, and that increasing either the number of ports or blocks significantly improves performance. Notably, the proposed approach attains outage performance comparable to or better than conventional MRC with fewer combining branches, and the block-wise strategy affects only coding gain without compromising diversity gain.

Abstract

Fluid antenna systems (FASs) have recently emerged as a promising reconfigurable antenna technology for future wireless networks, owing to their unique ability to exploit fine-grained spatial channel variations within a compact aperture. In this paper, a single-input multiple-output (SIMO) FAS employing maximum-ratio combining (MRC) is investigated under the block-diagonal correlation model, where the ports of FAS are partitioned into independent blocks and the strongest port within each block is selected for MRC combining. Exact outage probability (OP) expressions are first derived in both convolution and characteristic-function forms. To gain further insights, closed-form high-SNR asymptotic expressions are developed, from which the diversity order is shown to approximate the number of ports. This result reveals that block partitioning influences only the coding gain and can therefore be optimized without compromising the diversity performance. For the ergodic rate (ER), a Gamma-matching approximation together with a tighter Jensen-based approximation is derived in closed form. Simulation results corroborate the analytical framework and demonstrate that: i) increasing either the number of ports or the number of blocks improves the system performance; ii) the diversity order depends solely on the number of ports; and iii) the proposed SIMO-FAS achieves comparable or superior outage performance to conventional MRC receivers despite employing fewer combining branches.

Problem

• Fluid Antenna Systems
• Block-Diagonal Correlation
• Outage Probability
• Diversity Order
• Ergodic Rate

Innovation

• Fluid Antenna System
• Block-Diagonal Correlation
• Maximum-Ratio Combining
• Outage Probability
• Diversity Order