Research On Highly Energy Efficient And Secure Transmission Of Full Duplex UAV Base Station

In recent years,unmanned aerial vehicles(UAVs)have become a research hotspot in the field of wireless communication due to their low cost,wide coverage,strong adaptability to complex terrain,and the absence of communication blind zone.Especially,the UAVs can be used as the air base stations(BSs)to enhance traditional ground cellular network services quality,reduce the deployment cost of communication facilities,and build fast communication channels in disaster areas,effectively making up the inherent shortcomings of terrestrial communication systems.Despite the above advantages,the energy consumption and security issues of UAVs have become bottlenecks in their practical applications due to the limited airborne batteries and the potential wireless eavesdropping threats.Therefore,improving the energy efficiency and security of the communication systems have important theoretical and practical significance for the application of UAV BSs.At present,most of the researches on UAV BS communication system are only focus on energy efficiency or security,and there is no joint optimization research on both of energy efficiency and security.To handle this problem,this thesis focuses on the balance of energy efficiency and security to the full-duplex(FD)UAV BS.The main contents are listed as follow:(1)According to the characteritics of the air-to-ground link of the UAV BS and its flight power consumption,the signal model,channel model and power consumption model of the full-duplex UAV BS uplink communication system were constructed,and the secrecy energy efficiency(SEE)of the UAV BS communication system was proposed.Based on this,in response to the diverse needs of UAV base station(BS)tasks,the global secrecy energy efficiency(G-SEE)and weighted sum secrecy energy efficiency(WS-SEE)indicators of the UAV BS communication system were defined,and optimization models with the UAV BS signal transmission power and trajectory as optimization variables were established respectively.(2)To solve the problem of maximizing the G-SEE maximization problem of the UAV communication system,we firstly recasted the original non-convex problem into an equivalently form by introducing auxiliary variables,and then approximated the equivalently form into a convex problem by jointly using difference of two-convex functions(D.C.),successive convex approximation(SCA)and Dinkelbach’s methods.A convergence-well iterative algorithm was designed to obtain the approximate optimal solutions of the UAV transmit power and trajectory.Finally,we also proposed a second order cone programming(SOCP)-based approximate iterative algorithm to reduce the computational complexity.Numerical results verified the effectiveness of the proposed algorithm and its SOCP-based approximation algorithm.(3)For the WS-SEE maximization problem of the UAV communication system,the block coordinate descent method was applied to equivalently decompose the original optimization problem into two sub-problems,i.e.,the transmit power optimization and the trajectory optimization.To solve these two sub-problems,we proposed a SCA-based approximation approach to transform the original non-convex sub-problems into its convex forms and further designed a two-layer iterative optimization algorithm to jointly optimize the sub-problems.The proposed iterative algorithm can effectively obtain the approximate optimal solutions of WS-SEE maximization problem with few iteration numbers.In addition,an approximate iterative algorithm based on SOCP was also proposed to improve the computational efficiency.Finally,the numerical results verified the effectiveness of the proposed algorithm and its SOCP-based approximation,and shown that the WS-SEE maximization scheme can effectively improve the SEE of UAV compared with the G-SEE maximization scheme in a specific task period,better meetting the diverse needs of tasks.