I. Introduction
Industry 4.0 enhances the operational efficiency of the entire manufacturing process by incorporating multiple emerging technologies, including blockchain, Internet of Things, cloud computing, and artificial intelligence [1], [2]. Recently, industrial artificial intelligence (IAI) has attracted widespread attention and has driven the arrival of Industry 4.0 [3], [4]. As a branch of artificial intelligence, deep learning (DL) is widely used to solve data-driven industrial problems in real-world applications, such as smart grid, autonomous driving, and facial recognition [5], [6]. The development of DL-based products often requires large amount of data collected from different IoT devices, which is essential for learning high-quality DL models. Nevertheless, the collection of massive data for centralized training causes serious privacy threats [7], [8]. For example, malicious adversaries can compromise the privacy of IoT devices by eavesdropping industry data uploaded to cloud service (CS) providers (such as Microsoft Azure Machine Learning,
[Online]. Available: https://azure.microsoft.com.
Google Cloud ML Engine[Online]. Available: https://cloud.google.com/ml-engine/.
) [9], [10]. On the other hand, the large scale of current industrial systems, represented by the number of industrial nodes and the amount of data generated, makes such traditional deployment (e.g., centralized training) nontractable [11], [12]. Therefore, it puts new demands on how to effectively and collaboratively implement artificial intelligence in large-scale industrial applications.