Research On Multi-antenna Transmission Technology For UAV Spectrum Sharing System

In recent years,due to the advantages of low cost,flexible movement and easy operation,UAV has been widely used in military and civil fields.At the same time,the research of UAV Communication Technology has become a hot direction in the field of wireless communication.Compared with the traditional cellular communication network,UAV has more advantages in dealing with complex communication scenarios.However,the current situation of the shortage of spectrum resources can not meet the rapid growth of data traffic demand,and the static spectrum allocation mechanism leads to the spectrum resources are not effectively utilized.Therefore,how to improve the communication performance of UAV network under the limited spectrum resources and improve the spectrum utilization is particularly important.In this context,this thesis mainly studies the multi antenna transmission technology for UAV dynamic spectrum sharing system.The main contents and innovations of this thesis are as follows:Firstly,this thesis considers the dynamic spectrum sharing system of UAV Communication Network and ground cellular network,in which UAV communication nodes are equipped with multiple transmitting antennas,and spectrum sensing technology is used to detect the spectrum holes of ground communication network,so as to transmit information.In this scenario,two schemes of transmit antenna selection and transmit beamforming are proposed.The closed-form expression of outage probability of UAV Communication in hybrid channel environment of Rician and Rayleigh is derived,and the outage performance of the two schemes is compared.The simulation results show that with the increase of the number of antennas and signal-to-noise ratio,the outage probability of transmit antenna selection scheme and transmit beamforming scheme will decrease,and transmit beamforming scheme can obtain better outage probability performance.Secondly,the multi antenna UAV spectrum sharing communication network with feedback limited is considered in this thesis.The receiver quantifies the channel state information and transmits it to the UAV transmitter through the limited feedback channel for precoding.However,the quantization error will inevitably occur in the channel quantization process.In this scenario,a multi antenna precoding scheme based on channel quantization error is proposed,the difference between information transmission rate and feedback overhead rate is defined as effective transmission capacity,and the channel quantization bits are optimized by maximizing the effective transmission capacity.The simulation results show that the effective transmission capacity of the proposed multi antenna precoding scheme is better than that of the traditional maximum ratio precoding scheme,and there is an optimal quantized bit number to maximize the effective transmission capacity of the proposed scheme.Finally,this thesis considers the multi antenna UAV spectrum sharing communication network with eavesdropping attack,in which the UAV transmitter can improve the transmission reliability by increasing the transmission power,but the eavesdropping channel capacity also increases,and the physical layer security performance is sacrificed.In this scenario,two schemes of transmit antenna selection and transmit beamforming are used to improve the security and reliability tradeoff performance of multi antenna UAV spectrum sharing communication network.The outage probability and intercept probability of the two schemes are derived under the hybrid channel environment of Rician and Rayleigh,and the security and reliability tradeoff performance of the two schemes is compared.The simulation results show that with the increase of the signal-to-noise ratio and the number of antennas at the transmitter of UAV,the security and reliability tradeoff performance of the transmit antenna selection scheme and the transmit beamforming scheme will be improved,and the transmit beamforming scheme will obtain better security and reliability tradeoff performance.