解决联邦学习中设备随机参与的收敛问题,无需知道参与概率也能保证效果。
Convergence of Agnostic Federated Averaging
- 提出在非均匀、未知参与概率下仍有效的联邦平均算法优化模型。
- 证明凸损失下收敛速度达标准的 $\mathcal{O}(1/\sqrt{T})$。
- 实验证明其优于传统加权聚合方法,即使已知参与权重也更优。
联邦学习(FL)实现去中心化模型训练,无需集中原始数据。然而实际部署常面临关键挑战:客户端间歇性参与服务器聚合,且参与概率未知,可能带有偏差。现有收敛结果多假设全设备参与,或依赖对参与分布的了解(实际为均匀分布)——这些假设在现实中极少成立。本文刻画了在随机(且可变规模)客户端可用性下,经典无偏联邦平均(FedAvg)算法的优化问题,并严格建立其在凸、可能非光滑损失下的收敛性,达到标准 $\mathcal{O}(1/\sqrt{T})$ 收敛率,其中 $T$ 表示聚合周期。分析首次在一般非均匀随机参与下,为无偏 FedAvg 提供收敛保证,且无需知晓参与分布。我们还通过实证表明,即使服务器已知参与权重,无偏 FedAvg 仍优于常见但次优的加权聚合版本。
原文摘要 · Abstract (English)
Federated learning (FL) enables decentralized model training without centralizing raw data. However, practical FL deployments often face a key realistic challenge: Clients participate intermittently in server aggregation and with unknown, possibly biased participation probabilities. Most existing convergence results either assume full-device participation, or rely on knowledge of (in fact uniform) client availability distributions -- assumptions that rarely hold in practice. In this work, we characterize the optimization problem that consistently adheres to the stochastic dynamics of the well-known \emph{agnostic Federated Averaging (FedAvg)} algorithm under random (and variably-sized) client availability, and rigorously establish its convergence for convex, possibly nonsmooth losses, achieving a standard rate of order $\mathcal{O}(1/\sqrt{T})$, where $T$ denotes the aggregation horizon. Our analysis provides the first convergence guarantees for agnostic FedAvg under general, non-uniform, stochastic client participation, without knowledge of the participation distribution. We also empirically demonstrate that agnostic FedAvg in fact outperforms common (and suboptimal) weighted aggregation FedAvg variants, even with server-side knowledge of participation weights.
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