| Compared with satellite communication and terrestrial wireless communication technologies,Unmanned Aerial Vehicle(UAV)communication is considered to be the 6th generation(6G)mobile communication due to its strong mobility,flexible networking,and moderate cost,which has received extensive attention from academia and industry.This dissertation mainly proposes a solution based on adaptive beamforming for the serious interference and the shortage of spectrum resources in the UAV communication system.The main contributions of the dissertation can be summarized as follows:1.A phase-only beamforming(POB)algorithm based on the desired signal power maximization criterion is proposed.First,for the UAV relay-assisted terrestrial communication network with interference,an optimization problem is established with the UAV interference power lower than the threshold as the constraint and the desired signal power maximization as the optimization goal.Then,considering the limited weight and power of the communication module carried by the UAV,a phase-only beamforming algorithm is proposed,achieved by adjusting phase.Finally,the computer simulations verifie the correctness of the proposed scheme,and quantitatively analyze the effects of the phase disturbance vector,the number of iterations on the signal-to-interference-noise ratio(SINR),and the number of UAV antennas on the achievable rate of the system.2.A beamforming algorithm based on the criterion of maximizing SINR is proposed.First,for the satellite-terrestrial cognitive network based on an UAV relay,the problem of maximizing the SINR of the secondary user under the condition that the transmission power of the UAV relay and the interference power of the primary user are limited is constructed.Then,an iterative beamforming algorithm is proposed under the condition of known secondary user’s statistical channel state information(CSI).Secondly,considering the high computational complexity of iterative-based BF algorithm,another BF algorithm based on zero-forcing(ZF)is proposed in order to reduce the computational complexity of solving the problem.Finally,the simulation results show that compared with the ZF algorithm,the proposed iterative algorithm is more superior in improving the system performance.3.A UAV formation beamforming algorithm based on the maximum sum rate criterion is proposed.Firstly,for the communication system in which the multi-UAV relays adopt the amplification and forwarding strategy to assist the sending user to transmit information,the optimization problem is established with the maximization of the sum rate as the criterion.Then,considering the channel feedback overhead and time-varying characteristics,a beamforming algorithm is proposed under three different CSI situations.Finally,simulation verifies the feasibility and effectiveness of the proposed beamforming scheme,and quantitatively analyzes the impact of user transmit power on the system and rate. |
