Cooperative Unmanned Aerial Vehicle Base Station Placement In Air-to-ground Communication Systems

With the continuous development and improvement of unmanned aerial vehicles(UAVs)technology,UAVs,used as the wireless infrastructure,have attracted expanding attention.Compared with the fifth-generation mobile communication(5G)facilities which take the ground base station as the backbone of the network,UAVs have more powerful flexibility.Combining UAVs with 5G communications systems can not only provide stable and reliable services for remote or disaster areas,but also effectively solve the congestion problem caused by communication hot-spots in an emergency situation.However,the introduction of UAVs also brings new challenges for 5G communication systems.On the one hand,the characteristics of UAVs are different from which of traditional infrastructure.It is necessary to reasonably assign the functions of UAVs in the network according to its working characteristics.On the other hand,the deployment of UAVs is quite different from the traditional ground infrastructure,and the network layout needs to be optimized for the unique attributes of the UAV.Therefore,this paper studies the deployment of cooperative UAV base stations(UAV-BS)in the air-to-ground(A2G)communication systems.Firstly,this paper studies the types of UAVs suitable for 5G communication system and the logical functions of UAVs in the network and proposes the framework of cooperative UAV A2 G communication system compatible with 5G network.According to the characteristics of existing UAVs and the form of the access layer of 5G independent networking,this paper designs a distributed MIMO(distributed multiple-input multiple-output)A2G communication system with UAV-BS as the backbone of the network.Based on the framework of the A2 G communication system,this paper proposes a user grouping method to reduce the size of MIMO system.The user grouping strategy of maximizing system throughput and connection rate is designed based on the difference of user requirements under two important scenarios.Simulation results show that compared with the centralized UAV deployment method,the proposed method can provide about two orders of magnitude additional system capacity when making a single floating-point operation.Compared with the traditional user grouping method,this scheme has obvious advantages in system throughput rate,system connection rate and the number of UAVs needed.In addition,based on the above framework,this paper proposes a UAV deployment strategy to maintain the stable operation of the communication network by minimizing the transmission power.Considering the computational complexity of multi-dimensional deployment,a circular deployment strategy was designed,and the optimal circular parameters and the required transmission power were obtained by using particle swarm optimization(PSO)algorithm.Compared with the traditional method,the proposed method shows lower transmission power at different service area radius and user density.Finally,the main contributions are summarized,and future work are proposed.