Wireless Transmission Strategy And Performance Evaluation In UAV Communication Systems

Compared with satellite communication and ground cellular communication,UAV communications have shown broad application prospects in the field of future mobile communication,especially in the sixth generation(6G)mobile communication system,due to the advantages of easy deployment and control,flexible networking methods,and moderate cost.The dissertation mainly focuses on the UAV relay communication,proposes the wireless transmission strategy scheme,and further analyze the performance of the system,which provides a theoretical basis and design plan for the future UAV communication systems.The main contributions of this dissertation can be summarized as follows:1.For the multi-UAV realy system based on the threshold-based decode-and-forward protocol,schemes of MRC and MRT at the UAV relay is proposed,and the system outage performance is investigated.By taking path loss into account,the output SNR of the system is obtained firstly.Then,by assuming that both the uplink and downlink experience Rician distribution,the closed-form expression for OP of the considered system with multiple UAVs was derived.Furthermore,the asymptotic OP formula at high SNR is also derived to show the diversity order and array gain of the considered system,which were convenient to reveal the effects of system parameters on the outage performance.Finally,the computer simulations verify the correctness of the theoretical analysis,and reveal the effect of the relay numbers,antenna numbers and the outage threshold on the system outage performance.2.For the multi-source single-destination UAV relay system with multiple co-channel interferers based on the DF protocol,schemes of MRC and MRT at the UAV relay is proposed,and the system outage performance is investigated.By taking path loss into account,the end-to-end output SNR of the system is obtained firstly.Then,based on the SNR expression,the closed-form expression of the OP for the UAV relaying system is derived,where both the uplink and downlink channels undergo Nakagami-m fading while the interference channels experience Rayleigh fading.Finally,numerical results are given to demonstrate the effectiveness of the performance analysis,and reveal the impacts of UAV antenna numbers,co-channel interferer numbers and the outage threshold on the system outage performance.3.For the multi-source multi-destination UAV relay system based on the threshold-based DF protocol,the ergodic sum-rate performance of the system is investigated.By taking path loss into account,the output SINR expression for the considered system is obtained firstly,Then,we propose a statistical channel state information based beamforming scheme to maximize the ergodic rate,where both the uplink and downlink are subject to the correlated Rayleigh fading.Furthermore,the analytical expression of the ergodic sum-rate is derived for the considered system with the proposed scheme.Finally,numerical results are given to demonstrate the validity of the theoretical analysis and the superiority of the proposed scheme,and reveal the effects of the antenna numbers and the SINR threshold on the system performance.4.For the UAV relay system with multiple eavesdroppers based on the thresholed-based DF protocol,the secrecy performance of the system is investigated.By taking path loss into account,the output SINR expressions at UAV relay,destination and eavesdroppers are obtained firstly.Then,we propose a statistical channel state information based beamforming scheme to maximize the secrecy rate,where the the satellite-UAV link undergoes the correlated Rician fading,while the UAV-user link,the UAV-eavesdropper links and the interference links experience the correlated Rayleigh fading.Furthermore,the analytical expression of the SOP and SER are derived.Finally,numerical results are given to demonstrate the validity of the theoretical analysis,and reveal the effects of the antenna numbers and the eavesdropper numbers on the system secrecy performance.