The Research On UAV-assisted Secure Transmission Mechanism In Cognitive Radio Network

The fifth generation mobile communication(5G)network has been gradually deployed for commercial purposes,promoting the rapid development of new technologies and new services.Spectrum efficiency is a key efficiency index in 5G networks.As an indispensable and limited precious resource,wireless spectrum has not been fully utilized in most application scenarios.Cognitive radio(CR)can effectively improve the utilization efficiency of spectrum resource through the application of a variety of spectrum sharing methods.Because of the openness of wireless signals,the information transmission in CR network may be maliciously eavesdropped by illegal users.Therefore,the secure transmission issues in CR networks should be further investigated in combination with the communication requirements of typical 5G scenarios.Unmanned aerial vehicle(UAV)has the characteristics of flexible deployment and strong line-of-sight(LOS)link,and combines with artificial noise(AN)technology,which provides a solution to realize the secure transmission in CR network.As a jammer to transmit AN,UAV can effectively interfere with illegal eavesdroppers.In order to achieve secure transmission for CR system,it is necessary to deploy the position of UAV and allocate wireless resources according to the requirements of actual scenarios,so as to enhance the interference impact on illegal eavesdroppers and reduce the interference impact on legitimate users as far as possible.In this thesis,AN transmitted by UAV is introduced to achieve secure transmission,and the overlay and underlay methods for spectrum sharing are combined to carry out research on typical scenarios.In this thesis,a secure transmission scheme based on spectrum sensing and resource allocation for UAV is proposed in UAV-assisted overlay CR network.In the overlay spectrum sharing method,the UAV determines the current access status of the primary channel through spectrum sensing,and decides to act as a friendly jammer or a secondary transmitter.At the same time,the power splitting ratio is introduced to configure the transmission power of the UAV,In this scenario,the spectrum sensing time,power splitting ratio and the UAV’s deployment position are optimized jointly with the secrecy rate of CR system as the optimization objective.In the process of solving,an adaptive inertia particle swarm optimization(A-PSO)algorithm is adopted to solve the formulated problem.Simulation results show that the proposed scheme achieves better secure transmission performance compared with the existing secure transmission schemes in CR network.In this thesis,a dynamic allocation scheme for transmission power based on marginal utility(MU)is proposed in UAV-assisted underlay CR network.It is found through research that when the UAV acts as an assisted jammer in the secondary network,the increment of primary secrecy rate decreases with the increase of the transmission power of the secondary network,and the corresponding model is established as the MU.In particular,the main research is the secure transmission performance for primary user.The transmission power of the secondary network is designed to be dynamic allocation according to the change law of the MU,and the position of the UAV is optimized to maximize the secrecy rate of the primary user.In the process of solving the problem,a dichotomous precision linear search(D-FLS)algorithm is adopted.Simulation results show that the proposed scheme can effectively improve the performance of secure transmission for the primary user by reducing the impact of MU compared with the two existing schemes.