FedPeel: Peeling Stabilized Layers for Robust Heterogeneous Federated Learning

Proxy model-based heterogeneous federated learning enables clients with diverse architectures to collaborate through a shared lightweight intermediary. However, current methods aggregate and distill proxy knowledge in a structure-agnostic manner, ignoring layer-wise convergence dynamics, conflating shared and client-specific information, and transferring knowledge without assessing its reliability. These oversights jointly cause model oscillation, drift, and negative transfer. We propose FedPeel, a framework that makes the aggregation pipeline aware of the internal structure of model parameters. Rather than updating the proxy monolithically, FedPeel selectively aggregates only the layers that have stabilized, decouples their frequency-domain representations to separate generalizable patterns from personalized details, and modulates knowledge transfer intensity on a per-sample basis according to teacher confidence. Theoretical analysis establishes an O(1/T ) convergence rate. Experiments on image, text, and audio benchmarks show that FedPeel consistently outperforms state-of-the-art methods in both accuracy and communication efficiency.