Balancing Accuracy and Integrity for Reconfigurable Intelligent Surface-aided Over-the-Air Federated Learning

TL;DR

This paper introduces a framework that optimizes reconfigurable intelligent surfaces and beamformers to enhance accuracy and integrity in over-the-air federated learning, addressing model obscurity and channel uncertainties.

Contribution

It proposes a novel joint optimization framework for RIS, beamformers, and model integrity in AirFL, considering both perfect and imperfect channel information.

Findings

Achieves comparable accuracy to ideal FL under perfect CSI.

Improves accuracy with small or moderate receive antennas under imperfect CSI.

Balances model accuracy and integrity effectively in AirFL systems.

Abstract

Over-the-air federated learning (AirFL) allows devices to train a learning model in parallel and synchronize their local models using over-the-air computation. The integrity of AirFL is vulnerable due to the obscurity of the local models aggregated over-the-air. This paper presents a novel framework to balance the accuracy and integrity of AirFL, where multi-antenna devices and base station (BS) are jointly optimized with a reconfigurable intelligent surface (RIS). The key contributions include a new and non-trivial problem jointly considering the model accuracy and integrity of AirFL, and a new framework that transforms the problem into tractable subproblems. Under perfect channel state information (CSI), the new framework minimizes the aggregated model's distortion and retains the local models' recoverability by optimizing the transmit beamformers of the devices, the receive beamformers of the BS, and the RIS configuration in an alternating manner. Under imperfect CSI, the new framework delivers a robust design of the beamformers and RIS configuration to combat non-negligible channel estimation errors. As corroborated experimentally, the novel framework can achieve comparable accuracy to the ideal FL while preserving local model recoverability under perfect CSI, and improve the accuracy when the number of receive antennas is small or moderate under imperfect CSI.