Enhanced Connectivity in Ambient Backscatter Communications via Fluid Antenna Readers

TL;DR

This paper introduces a fluid antenna system at the reader in ambient backscatter communications, enabling dynamic antenna selection to improve data rates without explicit channel estimation, addressing key challenges like path loss and fading.

Contribution

It proposes a novel fluid antenna system for AmBC readers that enhances connectivity by spatial diversity and joint optimization of modulation and antenna position without needing explicit CSI.

Findings

Significant rate improvements over traditional single-antenna systems

Robust performance under imperfect channel observations and energy constraints

Effective antenna port selection via particle swarm optimization

Abstract

Ambient backscatter communication (AmBC) enables ultra-low-power connectivity by allowing passive backscatter devices (BDs) to convey information through reflection of ambient signals. However, the cascaded AmBC channel suffers from severe double path loss and multiplicative fading, while accurate channel state information (CSI) acquisition is highly challenging due to the weak backscattered signal and the resource-limited nature of BDs. To address these challenges, this paper considers an AmBC system in which the reader is equipped with a pixel-based fluid antenna system (FAS). By dynamically selecting one antenna position from a dense set of pixels within a compact aperture, the FAS-enabled reader exploits spatial diversity through measurement-driven port selection, without requiring explicit CSI acquisition or multiple RF chains. The intrinsic rate-energy tradeoff at the BD is also incorporated by jointly optimizing the backscatter modulation coefficient under an energy harvesting (EH) neutrality constraint. To efficiently solve this problem, a particle swarm optimization (PSO)-based framework is developed to jointly determine the FAS port selection and modulation coefficient on an optimize-then-average (OTA) basis. Simulation results show that the proposed scheme significantly improves the achievable rate compared with conventional single-antenna readers, with gains preserved under imperfect observations, stringent EH constraints, and different pixel spacings.