FedProto: Federated Prototype Learning across Heterogeneous Clients (2105.00243v4)

Abstract: Heterogeneity across clients in federated learning (FL) usually hinders the optimization convergence and generalization performance when the aggregation of clients' knowledge occurs in the gradient space. For example, clients may differ in terms of data distribution, network latency, input/output space, and/or model architecture, which can easily lead to the misalignment of their local gradients. To improve the tolerance to heterogeneity, we propose a novel federated prototype learning (FedProto) framework in which the clients and server communicate the abstract class prototypes instead of the gradients. FedProto aggregates the local prototypes collected from different clients, and then sends the global prototypes back to all clients to regularize the training of local models. The training on each client aims to minimize the classification error on the local data while keeping the resulting local prototypes sufficiently close to the corresponding global ones. Moreover, we provide a theoretical analysis to the convergence rate of FedProto under non-convex objectives. In experiments, we propose a benchmark setting tailored for heterogeneous FL, with FedProto outperforming several recent FL approaches on multiple datasets.

FedProto: Federated Prototype Learning across Heterogeneous Clients

The paper presents a novel framework, FedProto, designed to address the challenges of federated learning (FL) across heterogeneous clients. In FL, data resides across various clients without centralization, which inherently brings about heterogeneity in data distributions, model architectures, and communication capabilities. Traditional FL methods often rely on gradient-based aggregation, which can falter in the presence of client heterogeneity, leading to suboptimal convergence and performance. This research proposes a prototype-based communication method to counteract such limitations, aiming for both robustness and efficiency in heterogeneous FL scenarios.

Main Contributions

1. Framework Introduction: FedProto departs from traditional gradient-centric FL methods by exchanging class prototypes between clients and a central server. Each client computes local prototypes for each class, which are aggregated at the server to form global prototypes. These prototypes are then communicated back to the clients to regularize local model training.
2. Theoretical Insights: The paper provides a theoretical analysis of FedProto's convergence under non-convex conditions. By employing the concept of prototypes, the authors claim improved convergence rates compared to traditional methods, theoretically supported by detailed derivations grounded in assumptions typical of distributed learning frameworks.
3. Empirical Evaluation: Extensive experiments demonstrate FedProto's performance against existing FL methods like FedAvg, FedProx, and personalized FL strategies. The framework consistently yields higher test accuracy and less variance among clients across datasets such as MNIST, FEMNIST, and CIFAR10.
4. Communication Efficiency and Scalability: Unlike traditional methods that transmit large model gradients, FedProto only requires the transmission of prototypes, significantly reducing communication costs. This is particularly beneficial as model sizes grow large and can facilitate scenarios with limited communication bandwidth.
5. Privacy Considerations: Prototype aggregation provides inherent privacy benefits since it abstracts the data to a representation that cannot easily be inverted to obtain raw input data. This abstraction offers resilience against potential data reconstruction attacks often discussed in gradient-sharing FL systems.

Implications and Future Directions

This exploration opens several avenues for practical implementations and future research:

• Model Heterogeneity: The framework naturally accommodates variation in client-side model architectures. By abstracting representations to prototypes, FedProto allows different clients to operate with tailored models adapted to their hardware capabilities, a crucial feature for real-world applications.
• Class Imbalance and Non-IID Data: By focusing on prototypes, FedProto can dynamically handle non-IID data distributions across clients, which aligns it more closely with real-world data scenarios found in applications like mobile data processing or industry-specific IoT networks.
• Prototype Reliability: Future work could delve into improving prototype reliability under noisy conditions or hostile environments, ensuring consistency and robustness in prototype representations across diverse client hardware and varying data quality.
• Integration with Other Learning Approaches: Combining FedProto with techniques such as transfer learning or continual learning could enhance its adaptability to evolving datasets or tasks, making it a versatile component in dynamic learning ecosystems.
• Expanding to Other Domains: Beyond image datasets, extending FedProto to text, time-series, or multi-modal data can further test and potentially validate its utility across broader application domains like natural language processing in federated settings or distributed sensor networks.

The FedProto framework represents a significant departure from the conventional approach in FL, addressing longstanding challenges in federated settings by leveraging prototype communication. This approach not only expands the toolkit available for managing client heterogeneity but also reinforces the potential of FL as a practical method for privacy-aware distributed learning.