On the Generalization of Wasserstein Robust Federated Learning

• Published in: arXiv.org
• Main Authors: Tung-Anh Nguyen, Nguyen, Tuan Dung, Long Tan Le, Dinh, Canh T, Tran, Nguyen H
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 03.06.2022
• Subjects: Algorithms; Computer Science - Distributed, Parallel, and Cluster Computing; Computer Science - Learning; Domains; Federated learning; Optimization; Robustness
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2206.01432

In federated learning, participating clients typically possess non-i.i.d. data, posing a significant challenge to generalization to unseen distributions. To address this, we propose a Wasserstein distributionally robust optimization scheme called WAFL. Leveraging its duality, we frame WAFL as an empirical surrogate risk minimization problem, and solve it using a local SGD-based algorithm with convergence guarantees. We show that the robustness of WAFL is more general than related approaches, and the generalization bound is robust to all adversarial distributions inside the Wasserstein ball (ambiguity set). Since the center location and radius of the Wasserstein ball can be suitably modified, WAFL shows its applicability not only in robustness but also in domain adaptation. Through empirical evaluation, we demonstrate that WAFL generalizes better than the vanilla FedAvg in non-i.i.d. settings, and is more robust than other related methods in distribution shift settings. Further, using benchmark datasets we show that WAFL is capable of generalizing to unseen target domains.