FedBN: Federated Learning on Non-IID Features via Local Batch Normalization

TL;DR

FedBN introduces a local batch normalization technique to improve federated learning performance under feature shift non-iid data distributions, demonstrating faster convergence and superior results over existing methods.

Contribution

This work presents FedBN, a novel federated learning approach that uses local batch normalization to handle feature shift non-iid data, improving convergence and accuracy.

Findings

FedBN outperforms FedAvg and FedProx on non-iid data.

FedBN achieves faster convergence rates.

Empirical results validate the effectiveness of local batch normalization.

Abstract

The emerging paradigm of federated learning (FL) strives to enable collaborative training of deep models on the network edge without centrally aggregating raw data and hence improving data privacy. In most cases, the assumption of independent and identically distributed samples across local clients does not hold for federated learning setups. Under this setting, neural network training performance may vary significantly according to the data distribution and even hurt training convergence. Most of the previous work has focused on a difference in the distribution of labels or client shifts. Unlike those settings, we address an important problem of FL, e.g., different scanners/sensors in medical imaging, different scenery distribution in autonomous driving (highway vs. city), where local clients store examples with different distributions compared to other clients, which we denote as feature shift non-iid. In this work, we propose an effective method that uses local batch normalization to alleviate the feature shift before averaging models. The resulting scheme, called FedBN, outperforms both classical FedAvg, as well as the state-of-the-art for non-iid data (FedProx) on our extensive experiments. These empirical results are supported by a convergence analysis that shows in a simplified setting that FedBN has a faster convergence rate than FedAvg. Code is available at https://github.com/med-air/FedBN.