FedSOL: Stabilized Orthogonal Learning with Proximal Restrictions in Federated Learning
Authors: Gihun Lee, Minchan Jeong, Sangmook Kim, Jaehoon Oh, Se-Young Yun

Federated Learning (FL) aggregates locally trained models from individual clients to construct a global model. While FL enables learning a model with data privacy it often suffers from significant performance degradation when clients have heterogeneous data distributions. This data heterogeneity causes the model to forget the global knowledge acquired from previously sampled clients after being trained on local datasets. Although the introduction of proximal objectives in local updates helps to preserve global knowledge it can also hinder local learning by interfering with local objectives. Inspired by Continual Learning (CL) we adopt an orthogonal learning strategy to balance these two conflicting objectives. However we observe that directly negating the proximal gradient in the local gradient significantly undermines local learning. To address the problem we propose a novel method Federated Stabilized Orthogonal Learning (FedSOL). FedSOL is designed to identify gradients of local objectives that are inherently orthogonal to directions affecting the proximal objective. Specifically FedSOL targets parameter regions where learning on the local objective is minimally influenced by proximal weight perturbations. Our experiments demonstrate that FedSOL consistently achieves state-of-the-art performance across various scenarios.