Towards Class-Balanced Privacy Preserving Heterogeneous Model Aggregation

Heterogeneous model aggregation (HMA) is an effective paradigm that integrates on-device trained models heterogeneous in architecture and target task into a comprehensive model. Recent works adopt knowledge distillation to amalgamate the knowledge of learned features and predictions from heterogeneous on-device models to realize HMA. However, most of them ignore that the disclosure of learned features exposes on-device models to privacy attacks. Moreover, the aggregated model may suffer from the imbalanced supervision caused by the uneven distribution of amalgamated knowledge about each class and show class bias. In this article, to address these issues, we propose a response-based class-balanced heterogeneous model aggregation mechanism, called CBHMA. It can effectively achieve HMA in a privacy-preserving manner and alleviate class bias in the aggregated model. Specifically, CBHMA aggregates on-device models by using only their response information to reduce their privacy leakage risk. To mitigate the impact of imbalanced supervision, CBHMA quantitatively measures the imbalanced supervision level for each class. Based on that, CBHMA customizes fine-grained misclassification costs for each class and utilizes such costs to adjust the importance of each class (more importance to classes with weaker supervision) in the response-based HMA algorithm. Extensive experiments on two real-world datasets demonstrate the effectiveness of CBHMA.