Introduction
Modern wireless communication systems have developed from the first to the fourth generation and have propelled to the fifth generation (5G) to provide advanced wireless services, such as virtual reality, autonomous driving, and Internet of Things (IoT). Enhanced mobile broadband, massive machine-type communications, and ultra-reliable and low-latency communications are the three main scenarios for 5G wireless networks. They require communication systems to have the ability to handle a large amount of wireless data, recognize and dynamically adapt to complex environments, and satisfy the requirements for high speed and accurate processing. Therefore, future wireless communication systems must be highly intelligent.