With increasing advancement of wireless communication systems and development of new applications with high data rate requirements in fifth generation wireless communication systems and beyond, the data traffic on cellular networks will increase significantly. On the other hand, the extension of the concept of Internet of things(IoT) in wireless communication networks is possible only by easy and global access to wireless communications. Therefore, the design of next generation wireless communication networks requires the definition of innovative solutions to improve existing cellular networks as well as the possibility of communications in all situations, even in the event of unforeseen events. The use of unmanned aerial vehicle(UAV) is considered as a proposed solution to improve wireless communication networks. Specifications of UAVs including fast deployment and 3D location adjustment, have defined a variety of applications for them in next generation wireless communications systems. One of the roles for UAVs is to use them as an aerial base station(UAV-BS). Compared to the terrestrial type, the aerial base station has higher flexibility and ease of use in different conditions. However, the adjustable height and characteristics of the aerial wireless communication channel, have made the three-dimensional location designation of the UAV-BS as an important challenge in the use of this type of base station. In this thesis, we study the three-dimensional location of UAV-BS in the system without terrestrial base station by maximizing the coverage of users and due to the limitation of its transmission power. For this purpose, we first separate the height dimension from the other two dimensions of the UAV-BS location and obtain its optimal value by a method based on maximizing the coverage radius of this type of base station in different urban environments. Then determining the UAV-BS horizontal location is expressed in the form of an optimization problem with the aim of maximizing user coverage. This problem is non-convex and NP-hard in terms of complexity. Therefore, a suboptimal numerical method is proposed to solve it. In this method, by changing the discrete binary variable to a continuous variable, the problem is solved numerically by satisfying the constraints of the transmission power limitation and the UAV-BS location range. After solving this problem, by determining the appropriate range for the continuous variable, the users' coverage and the UAV-BS horizontal location are determined. The simulation results show the performance of this system and the effectiveness of the UAV-BS maximum transmission power and the required data rate of users. Unmanned Aerial Vehicle, Unmanned Aerial Vehicle Base Station, Aerial Wireless Communication Channel, User’ Coverage