STAR-RIS-Empowered Heterogeneous Federated Edge Learning With Flexible Aggregation

As a prominent and appealing paradigm, federated edge learning (FEEL) aims to orchestrate collaborative training across a multitude of distributed edge devices without the need for sensitive information transfer. However, device heterogeneity and wireless transmission distortion, which compromise training robustness and efficiency, severely hinder FEEL deployment in real-world applications. To this end, we propose in this article a novel FEEL framework empowered by simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) with flexible aggregation. This framework harmonizes devices to train models with heterogeneous intensity in each communication round, while the deployment of STAR-RIS significantly boosts the quality of wireless aggregation. Here, we emphasize that there may exist a crucial tradeoff between the heterogeneous local training intensity and the transmission quality, particularly when edge devices operate under a limited energy budget. To illuminate this perspective, we rigorously derive a novel explicit upper bound that captures the joint impact of local training accuracy and the mean square error of wireless aggregation on FEEL convergence performance. Our theoretical results indicate that a naive focus on improving the local training accuracy within a constrained energy budget may ultimately detract from overall training performance. This finding sharply contrasts with existing research, which typically aims to accelerate convergence by increasing local training intensity while neglecting the impact of wireless aggregation distortion. To strike the ideal balance, we formulate a mixed-integer nonlinear programming problem to guide the joint design of the beamforming at devices and the base station, the configuration mode of STAR-RIS, and the local training intensity. Comprehensive experiments on representative datasets demonstrate that our proposed framework achieves significant performance improvements compared with existing baselines.