Current 4G - the fourth-generation wireless communication, which exists in most countries, represents an advance of the previous 3 generation wireless communication. However, there are some challenges and limitations, associated with an explosion of wireless devices, which cannot be accommodated by 4G. Increasing the proliferation of smart devices, the development of new multimedia applications, and the growing demand for high data rates are among the main problems of the existing 4G system. As a solution, the wireless system designers have started research on the fifth-generation wireless systems. 5G will be the paradigm shift that could provide with ultra-high data rate, low latency, an increase of the base station capacity, and the improved quality of services. This paper is a review of the changes through the evolution of existing cellular networks toward 5G. It represented a comprehensive study associated with 5G, requirements for 5G, its advantages, and challenges. We will explain the architecture changes – radio access network (RAN), air interfaces, smart antennas, cloud RAN, and HetNet. Furthermore, it discussed physical layer technologies, which include new channel modes estimation, new antenna design, and MIMO technologies. Also, it discussed MAC layer protocols. The article included three kinds of technologies: heterogeneous networks, massive multiple-input and output, and millimeter-wave. Finally, it explained the applications, supported by 5G, new features, various possibilities, and predictions.