Privacy Decentralized Online Federated Learning for Smart Healthcare Service Systems

The Smart Healthcare Service Systems (SHSS) aim to integrate decentralized healthcare institutions, intelligent technologies, and end users into a cyber-physical system that enables high-quality medical decision-making. However, the sensitive nature of healthcare data presents significant privacy and security challenges, which hinder effective collaboration among healthcare providers. Moreover, existing research lacks a comprehensive theoretical framework that spans the full pipeline from data acquisition to intelligent decision services. To address these challenges, we propose a theoretical framework for SHSS that systematically analyzes data processing and user demand to establish the goals of secure, stable, and adaptive collaborative learning. Guided by these goals, a Decentralized Online Federated Learning (DOFL) network model is tailored for SHSS, where participating institutions interact through a decentralized federated learning structure. Building on this model, we design DP-DOOR (Differentially Private Decentralized Online Federated Learning with One-Point Residual Feedback), a fully decentralized algorithm that supports row-stochastic communication topologies, accommodating practical limitations where bidirectional synchronization is often infeasible. DP-DOOR ensures data privacy through differential privacy (DP) mechanisms and achieves efficient gradient estimation using a one-point residual feedback (OPRF) approach. Theoretical analysis shows that DP-DOOR provides ϵ-DP guarantees and achieves sub-linear regret. Experimental evaluations on diverse real-world medical datasets under both IID and non-IID settings demonstrate the algorithm’s robustness and effectiveness in enabling secure, decentralized collaboration and enhancing adaptability in dynamic healthcare environments.