Adaptive Clustered Federated Learning for Clients with Time-Varying Interests

Clustered Federated Learning (FL) addresses heterogeneous objectives from different client groups, by capturing the intrinsic relationship between data distributions of clients. This work aims to minimize the completion time of clustered FL training while guaranteeing convergence, given the following challenges. First, clients’ data distributions are not static since their interests are usually time-varying. Obsolete data may incur training failures, requiring detection of distribution changes at runtime. Second, even with the same distribution, client datasets may have different contributions to model accuracy. Besides, the training data typically arrive at clients dynamically, which brings uncertainties to assessing the quality of client data. Third, the execution environments of clients and networks are often unstable and stochastic, leading to uncertainties in calculating computation and communication time. Given the above challenges, we propose Acct with two innovations: i) change detection: we first model the time-varying interests of clients as piecewise stationary based on practical observations, then apply generalized likelihood ratio detectors to FL for detecting changes in client distributions; ii) client selection: we adopt the multi-armed bandit (MAB) technique to account for the uncertainties in measuring data quality, computation and communication time. Based on the upper confidence bound (UCB) method, we construct a novel “double UCB” policy to adaptively select clients with high data quality and low computation and communication overhead. We rigorously prove the convergence of Acct and sub-linear regret regarding the proposed client selection policy. Finally, we implement Acct using PyTorch and conduct experiments showing that Acct reduces the completion time by almost 18.2% compared with three state-of-the-art FL frameworks.