FedDAF: Federated Domain Adaptation Using Model Functional Distance

Mrinmay Sen; Sidhant Nair; C Krishna Mohan

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arXiv · 2509.11819

FedDAF: Federated Domain Adaptation Using Model Functional Distance

Mrinmay Sen·Sidhant Nair·C Krishna Mohan

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Abstract

Federated Domain Adaptation (FDA) improves model performance at a target client by collaborating with source clients while preserving data privacy. FDA faces two key challenges: domain shift between source and target data, and limited labeled data at the target, a common constraint when a new site joins a federation before it has accumulated its own labeled data, as in clinical deployments. Most existing methods address domain shift alone, assuming ample target data; those that also tackle data scarcity still fail to prioritize source information according to the target's specific objective. We propose FedDAF, which addresses both challenges through similarity-based aggregation of the global source and target models, using their model functional distance, computed from the angle between their mean gradient fields on target data and normalized via a Gompertz function. The global source model itself is formed using a distance-based weighted average, giving greater weight to source models closer to the target model. Experiments on real-world datasets show FedDAF outperforms existing federated learning (FL), personalized FL, and FDA methods in test accuracy.

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Mrinmay Sen, Sidhant Nair, C Krishna Mohan. 2026-07-09. FedDAF: Federated Domain Adaptation Using Model Functional Distance. https://arxiv.org/abs/2509.11819

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