How Valuable Is Your Data? Optimizing Client Recruitment in Federated Learning

Abstract

Federated learning allows distributed clients to train a shared machine learning model while preserving user privacy. In this framework, an operator recruits user devices (i.e., clients) to occasionally perform local iterations of the learning algorithm on their data. We propose the first work to theoretically analyze the resulting performance tradeoffs in deciding which clients to recruit for federated learning, complementing other works on the selection of recruited clients in each iteration. Specifically, we define and optimize the tradeoffs between both accuracy (training and testing) and efficiency (completion time and cost) metrics. We provide efficient solutions to this NP-Hard optimization problem, and verify the value of client recruitment in experiments on synthetic and real-world data. The results of this work can serve as guidelines for the real-world deployment of federated learning and an initial investigation of the client recruitment problem.