Federated multi-task learning (FMTL) has emerged as a promising framework for learning multiple tasks simultaneously with client-aware personalized models. While the majority of studies have focused on dealing with the non-independent and identically distributed (Non-IID) characteristics of client datasets, the issue of task heterogeneity has largely been overlooked. Dealing with task heterogeneity often requires complex models, making it impractical for federated learning in resource-constrained environments. In addition, the varying nature of these heterogeneous tasks introduces inductive biases, leading to interference during aggregation and potentially resulting in biased global models. To address these issues, we propose a hierarchical FMTL framework, referred to as $\mathtt{F}\mathtt{e}\mathtt{d}\mathtt{B}\mathtt{o}\mathtt{n}\mathtt{e}$, to facilitate the construction of large-scale models with improved generalization. $\mathtt{F}\mathtt{e}\mathtt{d}\mathtt{B}\mathtt{o}\mathtt{n}\mathtt{e}$ leverages server-client split learning and gradient projection to split the entire model into two components: 1) a large-scale general model (referred to as the general model) on the cloud server, and 2) multiple task-specific models (referred to as client models) on edge clients, accommodating devices with limited compute power. To enhance the robustness of the large-scale general model, we incorporate the conflicting gradient projection technique into $\mathtt{F}\mathtt{e}\mathtt{d}\mathtt{B}\mathtt{o}\mathtt{n}\mathtt{e}$ to rectify the skewed gradient direction caused by aggregating gradients from heterogeneous tasks. The proposed $\mathtt{F}\mathtt{e}\mathtt{d}\mathtt{B}\mathtt{o}\mathtt{n}\mathtt{e}$ framework is evaluated on three benchmark datasets and one real ophthalmic dataset. The comprehensive experiments demonstrate that $\mathtt{F}\mathtt{e}\mathtt{d}\mathtt{B}\mathtt{o}\mathtt{n}\mathtt{e}$ efficiently adapts to the heterogeneous local tasks of each client and outperforms existing federated learning algorithms in various dense prediction and classification tasks while utilizing off-the-shelf computational resources on the client side.

The metaverse signifies the amalgamation of virtual and tangible realms through human-computer interaction. The seamless integration of human, cyber, and environments within ubiquitous computing plays a pivotal role in fully harnessing the metaverse’s capabilities. Nevertheless, metaverse operating systems face substantial hurdles in terms of accessing ubiquitous resources, processing information while safeguarding privacy and security, and furnishing artificial intelligence capabilities to downstream applications. To tackle these challenges, this paper introduces the UbiMeta model, a specialized ubiquitous operating system designed specifically for the metaverse. It extends the capabilities of traditional ubiquitous operating systems and focuses on adapting downstream models and operational capacity to effectively function within the metaverse. UbiMeta comprises four layers: the Ubiquitous Resource Management Layer (URML), the Autonomous Information Mastery Layer (AIML), the General Intelligence Mechanism Layer (GIML), and the Metaverse Ecological Model Layer (MEML). The URML facilitates the seamless incorporation and management of various external devices and resources. It provides a framework for integrating and controlling these resources, including virtualization, abstraction, and reuse. The AIML is responsible for perceiving information and safeguarding privacy and security during storage and processing. The GIML leverages large-scale pre-trained deep-learning feature extractors to obtain effective features for processing information. The MEML focuses on constructing metaverse applications using the principles of Model-as-a-Service (MaaS) and the OODA loop (Observation, Orientation, Decision, Action). It leverages the vast amount of information collected by the URML and AIML layers to build a robust metaverse ecosystem. Furthermore, this study explores how UbiMeta enhances user experiences and fosters innovation in various metaverse domains. It highlights the potential of UbiMeta in revolutionizing medical healthcare, industrial practices, education, and agriculture within the metaverse.

Wearable health monitoring is a crucial technical tool that offers early warning for chronic diseases due to its superior portability and low power consumption. However, most wearable health data is distributed across different organizations, such as hospitals, research institutes, and companies, and can only be accessed by the owners of the data in compliance with data privacy regulations. The first challenge addressed in this paper is communicating in a privacy-preserving manner among different organizations. The second technical challenge is handling the dynamic expansion of the federation without model retraining. To address the first challenge, we propose a horizontal federated learning method called Federated Extremely Random Forest (FedERF). Its contribution-based splitting score computing mechanism significantly mitigates the impact of privacy protection constraints on model performance. Based on FedERF, we present a federated incremental learning method called Federated Incremental Extremely Random Forest (FedIERF) to address the second technical challenge. FedIERF introduces a hardness-driven weighting mechanism and an importance-based updating scheme to update the existing federated model incrementally. The experiments show that FedERF achieves comparable performance with non-federated methods, and FedIERF effectively addresses the dynamic expansion of the federation. This opens up opportunities for cooperation between different organizations in wearable health monitoring.