FedAL: Black-Box Federated Knowledge Distillation Enabled by Adversarial Learning

--Knowledge distillation (KD) can enable collaborative learning among distributed clients that have different model architectures and do not share their local data and model parameters with others. Each client updates its local model using the average model output/feature of all client models as the target, known as federated KD. However, existing federated KD methods often do not perform well when clients' local models are trained with heterogeneous local datasets. In this paper, we propose Federated knowledge distillation enabled by Adversarial Learning ( FedAL) to address the data heterogeneity among clients. First, to alleviate the local model output divergence across clients caused by data heterogeneity, the server acts as a discriminator to guide clients' local model training to achieve consensus model outputs among clients through a min-max game between clients and the discriminator . Moreover, catastrophic forgetting may happen during the clients' local training and global knowledge transfer due to clients' heterogeneous local data. T owards this challenge, we design the less-forgetting regularization for both local training and global knowledge transfer to guarantee clients' ability to transfer/learn knowledge to/from others. Experimental results show that FedAL and its variants achieve higher accuracy than other federated KD baselines. To address this problem, collaborative learning among multiple clients can be useful for producing models with better accuracy. However, there are several challenges. First, clients have their own local datasets and they may not be willing to share their raw data with others due to privacy concerns [1]. Second, clients on the edge of wireless networks often have different computation and memory resources, resulting in clients with heterogeneous models that have different architectures and parameters. Clients may not want to reveal their model architectures to other clients to further prevent privacy leakage [2], [3]. We refer to a client's model with unknown architecture to other clients as a black-box model. Pengchao Han is with the School of Information Engineering, Guangdong University of Technology, Guangzhou 510006, China. Han's contribution to this work was made when she was a Postdoc research associate at The Chinese University of Hong Kong, Shenzhen, China.