An adaptive FL framework that employs a hybrid contribution evaluation mechanism as the core principle for client selection and resource management is proposed and demonstrates that the proposed framework outperforms existing FL baselines in terms of training efficiency, data utilization, and fairness.
Abstract
Federated Learning (FL) enables collaborative model training across decentralized data silos while preserving data privacy. However, client selection strategies in conventional FL processes typically rely on single-dimensional evaluation metrics, which fail to capture data diversity and overlook the dynamic nature of client contributions, particularly in domains characterized by sparse and heterogeneous data, such as healthcare and drug discovery. These limitations ultimately hinder the global model's generalization ability and reduce training efficiency. To address these challenges, this paper proposes an adaptive FL framework that employs a hybrid contribution evaluation mechanism as the core principle for client selection and resource management. The proposed approach quantifies each client's effectiveness by integrating two complementary dimensions: (i) a performance-based evaluation that measures the immediate impact of a client's update on the global optimization trajectory, and (ii) a coverage-based evaluation that estimates data diversity in the latent embedding space without exposing raw data. By combining these two criteria, the hybrid mechanism ensures that highly contributive clients are preferentially selected while preventing the permanent exclusion of any participant, thereby maintaining a balanced trade-off between efficiency and fairness. Experimental results demonstrate that the proposed framework outperforms existing FL baselines in terms of training efficiency, data utilization, and fairness.
Federated learning (FL) offers a promising approach to privacy-preserving clinical risk prediction, but its deployment remains limited by restricted data sharing, client heterogeneity, class imbalance, and the lack of realistic tabular electronic health record (EHR) benchmarks. Synthetic data generation may alleviate data scarcity, yet its integration with federated optimisation has received limited systematic study. We propose SynPre-FL, a unified framework combining high-fidelity synthetic EHR generation with synthetic-pretrained FL for robust prediction under non-IID conditions. A latent autoencoder-diffusion model generates privacy-preserving synthetic cohorts, which are used to warm-start federated training. This pretraining is followed by heterogeneity-aware optimisation using class-balanced local objectives, proximal regularisation, and adaptive server aggregation. Post-hoc calibration and federated-safe explainability support reliable and interpretable risk estimates. Experiments show that the synthetic generator preserves univariate, bivariate, and multivariate structure while protecting against membership-inference and reconstruction attacks. The generated data achieve strong downstream utility under TSTR, TRTS, and model-based evaluations. Across federated settings with 5, 10, and 15 heterogeneous clients, SynPre-FL consistently improves robustness and scalability over baseline methods, especially under severe non-IID fragmentation. Calibration improves probability reliability, while SHAP analysis produces stable and clinically coherent feature attributions across federation sizes. SynPre-FL therefore provides a practical and reproducible framework for combining synthetic data with FL to enable privacy-aware, interpretable, and robust clinical prediction from distributed tabular EHR data.
Akarsh K. Nair, Muhammad Arifur Rahman, N. Shopland et al.· 0 citations
In smart healthcare scenarios, patient data are distributed across different medical institutions. Due to privacy protection and data security constraints, such data cannot be directly shared, which consequently affects the training performance of medical image models. Federated Learning (FL) enables collaborative model training among multiple parties without exchanging raw data, allowing models to leverage multi-source data to improve overall performance and generalization capability. However, under non-independent and identically distributed (non-IID) conditions, significant discrepancies among client data can lead to unstable convergence and performance degradation during training. Personalized Federated Learning (PFL) alleviates this issue to some extent. Nevertheless, existing methods mostly rely on coarsegrained parameter partitioning, which fails to capture internal parameter heterogeneity and lacks effective modeling of inter-client similarity, thereby limiting the effectiveness of collaboration. We propose a personalized federated learning framework, FedSCF, which models client heterogeneity at the parameter level. Specifically, a relative perturbation-based sensitivity evaluation is designed to identify critical parameters for personalized modeling, while the remaining parameters participate in cross-client sharing. The overlap of critical parameter masks is utilized to characterize inter-client similarity, enabling the construction of a dynamic collaboration structure. An adaptive threshold is further introduced to select collaborative neighbors, allowing clients with similar data distributions to form stable collaboration relationships. During the aggregation stage, a dual-path strategy is developed to jointly learn globally shared knowledge and personalized features, and a mask-guided parameter-wise fusion mechanism is employed to complete model updates. Experimental results on the Kvasir and Dermoscopic datasets demonstrate that FedSCF outperforms current state-of-the-art methods under heterogeneous data settings.
Mingjun Wei, Rongyang Xu, Qian Zhang et al.· Engineering Research Express· 0 citations
Federated learning (FL) enables collaborative model training across distributed clients while keeping data local. A central challenge is determining which client updates are beneficial for aggregation with respect to each client's target domain. Existing methods typically address this problem in parameter space by comparing model parameters or gradients. However, parameter-space similarity can be a poor proxy for predictive behavior, especially under heterogeneous, non-IID data. Consequently, updates that are misaligned with a client's target domain, including those caused by heterogeneous data or malfunctioning clients, may degrade local model performance. We propose Local Inference Guided Aggregation for Heterogeneous Training Environments to Yield Enhancement Through Agreement and Regularization (LIGHTYEAR), a federated learning framework that performs update selection in function space. LIGHTYEAR uses an NTK-based agreement score to characterize predictive behavior and determine a personalized aggregation set for each client. By relating model parameters to local predictive responses, the Neural Tangent Kernel (NTK) provides a more expressive criterion for update selection than parameter-space similarity alone. Because function-space information is not available before aggregation in conventional centralized FL, LIGHTYEAR uses a peer-to-peer (P2P) topology in which clients exchange updates directly and evaluate incoming models on private validation data. Each client selects only updates that are beneficial for its own target domain and aggregates them using a regularized rule that improves stability under heterogeneity. Across five datasets and nine baseline methods, LIGHTYEAR consistently outperforms centralized FL baselines and existing P2P approaches.
Mirko Konstantin, S. Zachow, Anirban Mukhopadhyay· 0 citations
Federated learning (FL) is a practical framework that can train models on distributed user data while guaranteeing data privacy; however, due to heterogeneity in which each user has a different data distribution, problems frequently arise where both global and personalization performance deteriorate simultaneously. This dissertation presents methodologies for building efficient personalized models by identifying which strategies are effective in the global training stage and by showing how to preserve global knowledge while securing user-specific performance during local adaptation. First, we show that as data heterogeneity increases, the collapse of feature vectors is a more fundamental bottleneck than classifier weights, and propose a method that directly mitigates the discrepancy in representation magnitude between local and global models. Second, we analyze that a training approach that strengthens local alignment can induce forgetting of global knowledge (e.g., categories not observed locally), and propose a method that achieves both local alignment and global knowledge preservation by combining feature distillation based on the global model's feature vectors. Third, in federated personalized reward model learning with preference heterogeneity, we empirically verify the conventional belief that"increasing the number of global models yields better initialization,"and we show that when sufficient local fine-tuning is allowed, a single global initialization can instead provide stronger personalization performance. This study redefines the role of global initialization under data and preference heterogeneity and provides practical training strategies that simultaneously satisfy global knowledge preservation and personalization.
Federated Active Learning (FAL) addresses the dual challenges of data privacy and label scarcity, where the absence of a global data view introduces additional hurdles for coordinated query selection. We study cross-silo FAL in the low-budget regime, where annotation decisions are most critical. We characterize, both theoretically and empirically, a heterogeneity reversal: in low-budget settings, homogeneous (IID) data requires stronger coordination to avoid redundant queries, whereas heterogeneous data naturally promotes diversity; this trend reverses at higher budgets. Thus, in contrast to the standard federated learning (FL) narrative where heterogeneity is a primary challenge, we show that IID settings are more challenging for query selection in FAL. Motivated by these findings, we propose a new FAL framework that utilizes federated representation learning to align client data in a shared embedding space. This enables the server to perform globally coordinated active selection over optionally obfuscated client embeddings, while annotation remains local to each client. Although our framework operates in the more challenging low-budget regime, it achieves performance that surpasses existing FAL methods even when they are given substantially larger annotation budgets, demonstrating the value of centralized coordination under privacy constraints.