Study Of The Mobile Base Station Assisted Resource Allocation In Cell-free Massive MIMO Heterogeneous Network

With the development and implementation of the fifth generation of mobile communication technology,the number of users and the demand of data flow in the mobile communication system are increasing fast,and it is one of the major problem of the development of the wireless communication system is to provide users with higher quality of communication service.The Cell-Free Massive MIMO system has the advantage of uniform wireless coverage,balanced service quality,and cheap and easy to deploy,can significantly improve the service quality of all the users,has been one of the important research directions in the field of mobile communication.However,the high user density area and the sudden surge of communication service demand bring huge pressure to the Cell＿Free Massive MIMO wireless communication system.With the increase of the UAV load,the UAV mobile base station becomes possible.By taking advantages of the line-of-sight propagation characteristics between the UAV and ground users and the flexible deployment of UAV,a heterogeneous network can be formed with the Cell-Free Massive MIMO system,and the system performance can be improved significantly.In the case of temporary users gathering and the surge of service demand,deploy a UAV mobile base station to assist communication is one of the effective choices to offload data for the Cell-Free Massive MIMO system and improve the service experience of users.The resource allocation scheme including the UAV trajectory and power allocation scheme,is the key factor to determine the performance of the UAV-assisted Cell-Free Massive MIMO system.This problem contains some complex non-convex optimization problems,and is the main content of this paper.Therefore,according to the specific scenarios with different demand,we focus on the problem of designing the UAV trajectory and power allocation algorithm.The specific research and innovation contents of this paper are as follows:In the UAV-assisted Cell-Free Massive MIMO system designed in this paper,based on the consideration of the balance of the user service quality,in order to further improve the wireless coverage rate and service experience of all the users,we design a UAV trajectory optimization and power allocation algorithm.Firstly,according to the position of users in the system,we design a circular UAV flight trajectory determined by three user dense centers to improve wireless coverage performance.And based on the flight trajectory of the UAV,we derived the expression of the achievable user rate.Then according to the expression,combined with the max-min power allocation algorithm in the Cell-Free Massive MIMO system,a power allocation algorithm aimed at maximizing the minimum achievable user rate was designed.The simulation results of the experiment show that the performance of the system we designed is significantly improved compared with the normal Cell-Free Massive MIMO system.Consider of the different of the demand of users service,in order to meet the higher service quality demands of some users,a user scheduling and UAV trajectory optimization scheme is designed based on the UAV-assisted Cell-Free Massive MIMO system.First divide the users according to the demand of the quality service,into high priority users and low priority users,and establish a resource allocation problem for user scheduling and UAV trajectory,in order to accurately cover and improve the communication quality of high priority users.And divide the complex non-convex optimization problem into two subproblems which can be relaxed into convex optimization problems,and we can solve them by a alternately scheme.The results show that the algorithm we designed can effectively improve the communication performance of high priority users.