Heterogeneity For The Win: One-Shot Federated Clustering

In this work, we explore the unique challenges-and opportunities-of unsupervised federated learning (FL). We develop and analyze a one-shot federated clustering scheme, k-FED, based on the widely-used Lloyd's method for k-means clustering. In contrast to many supervised problems, we show that the issue of statistical heterogeneity in federated networks can in fact benefit our analysis. We analyse k-FED under a center separation assumption and compare it to the best known requirements of its centralized counterpart. Our analysis shows that in heterogeneous regimes where the number of clusters per device (k') is smaller than the total number of clusters over the network k, (k' <= root k), we can use heterogeneity to our advantage-significantly weakening the cluster separation requirements for k-FED. From a practical viewpoint, k-FED also has many desirable properties: it requires only one round of communication, can run asynchronously, and can handle partial participation or node/network failures. We motivate our analysis with experiments on common FL benchmarks, and highlight the practical utility of one-shot clustering through use-cases in personalized FL and device sampling.