Transmission Strategy Of Coverage Enhancement For B5G Mobile Platforms In Wireless Communication Scenarios

The industry of unmanned aerial vehicles(UAVs)has been growing rapidly in recent years.Thanks to the advantages of low cost and flexibility,UAVs can be dynamically deployed in various 5G and B5G communication scenarios.However,when the UAVs are utilized to complement the coverage of the terrestrial communcaions,the problems of the adjacent ground base station(GBS)interference and UAV transmission link blockage will degrade the communication performance of the UAVs.Multi-antenna technology brings new design freedom for interference suppression between UAV and GBS,and the deployment of reconfigurable intelligent surface(RIS)and its passive beamforming can effectively resist blocking.Motivated by the above observations,in the thesis,we study the interference suppression beamforming for UAVs supplementing ground communication coverage,and also the joint robust beamforming for UAV and RIS.The main contributions of the thesis can be summarized as follows:1.To address the problem of the interference from GBS when UAV collects information from ground terminals,this thesis proposes a joint optimization method of GBS transmit beamforming and UAV receive beamforming based on the principle of minimum mean square error.The proposed method can effectively guaranteethe quality of service(QoS)of cellular users,reduce the interference to UAV,and also improve the sum rate of UAV uplink data acquisition and GBS downlink transmission.2.To address the problem of the interference from GBS when UAV collects information from ground terminals,this thesis further proposes an interference suppression beamforming shceme for UAV and GBS according to the transmission priority of the UAV and GBS.Specifically,proposed strategy uses the decomposition of the correlation channel matrix to obtain the UAV receive beamforming space and the GBS interference guidance space,and optimises the UAV receive beamforming and the GBS transmission beamforming in the corresponding space respectively.As a beneficial result,the propsed scheme can further guarantee the QoS of cellular users,reduce the interference to UAV,and also improve the sum rate of UAV uplink data acquisition and GBS downlink transmission.3.The joint beamforming design is also a critical issue for RIS-assisted UAV to bypass blocking and start downlink transmission.This thesis proposes a joint robust beam design scheme under the assumption of non-perfect channel state information(CSI).The proposed scheme transforms the problem of the coupled UAV robust beam and RIS discrete phase shift optimization into two non-convex sub-problems,which are further optimized based on an efficient iterative optimization algorithm.As a beneficial result,a robust UAV-RIS beamforming design with a low computational complexity is achieved.