  Recently, big data has seen explosive growth in the Internet of Things (IoT).
Multi-layer FL (MFL) based on cloud-edge-end architecture can promote model
training efficiency and model accuracy while preserving IoT data privacy. This
paper considers an improved MFL, where edge layer devices own private data and
can join the training process. iMFL can improve edge resource utilization and
also alleviate the strict requirement of end devices, but suffers from the
issues of Data Reconstruction Attack (DRA) and unacceptable communication
overhead. This paper aims to address these issues with iMFL. We propose a
Privacy Amplification scheme on iMFL (PA-iMFL). Differing from standard MFL, we
design privacy operations in end and edge devices after local training,
including three sequential components, local differential privacy with Laplace
mechanism, privacy amplification subsample, and gradient sign reset.
Benefitting from privacy operations, PA-iMFL reduces communication overhead and
achieves privacy-preserving. Extensive results demonstrate that against
State-Of-The-Art (SOTA) DRAs, PA-iMFL can effectively mitigate private data
leakage and reach the same level of protection capability as the SOTA defense
model. Moreover, due to adopting privacy operations in edge devices, PA-iMFL
promotes up to 2.8 times communication efficiency than the SOTA compression
method without compromising model accuracy.
