I. Introduction
With the advancement of mobile computing technology and the Internet of Things (IoT), industrial digitization and intelligence are rapidly progressing [1], [2], [3]. Intelligent applications in mobile edge computing (MEC) systems are supported by widely deployed edge devices (e.g., sensors) [4], [5]. As the number of sensors deployed increases, the data collected grows exponentially, resulting in a larger accumulation of data at the network edge (e.g., gateways and switches) [6], [7]. However, the network bandwidth burden is an obstacle to uploading data to the cloud for centralized learning [8], [9], [10]. Federated learning (FL) [11] emerges as a solution, allowing edge devices to train machine learning models collaboratively without transmitting private data to the parameter server. As such, FL has many promising applications in IoT, such as human activity recognition [12], [13], fault diagnosis [14], [15], [16], [17], and augmented reality [18].