Research On Key Technologies For The Physical Layer Security In UAV Communications

Compared with ground wireless communication,unmanned aerial vehicle(UAV)communication has the advantages of high flexibility and low cost.It is not subjected to the basic communication infrastructures in disaster areas,and can quickly provide reliable communication in a large range for emergency and disaster areas.At the same time,it can quickly cover hot areas and divert services.It shows a wide application prospect in many fields such as communication,detection,search and so on.However,due to the openness of wireless channel,the information transmitted by UAV as relay is easy to be intercepted,cusing a risk of information leakage.Therefore,privacy and security issues have become one of the key issues in UAV communication.The main contributions of this paper are outlined as follows:1.Considering a satellite-multi-UAV relay selection system under the amplify-and-forward protocol,a secure relay selection scheme based on Q-learning(QL)is proposed for satelliteground fusion cooperative transmission.First,in the presence of an eavesdropper,the output signal-to-noise ratio expressions of the user and the eavesdropper at the receiving end are obtained respectively.Then,the parameters of QL algorithm are initialized,the Boltzmann selection strategy is introduced to use the probability scheme to select relay.Finally,power allocation is performed between the selected relay node and the source node to obtain the optimal transmission power.The simulation results show that compared with the random relay selection algorithm,the proposed Q-learning relay selection strategy greatly improves the system performance.2.Assuming multiple legitimate users and a single eavesdropper in the downlink transmission system of multi-antenna UAV communication,two secure beamforming schemes are proposed on the basis of known eavesdropper statistics channel state information.By maxmizing the secure rate of the system,a zero forcing beamforming scheme is firstly proposed,giving the closedform solutions of the beamforming weight vector and power allocation factor.The second scheme is based on the criterion of maximizing the enhanced signal to noise ratio of the system under the condition of total transmit power limit.A fractional programming combined with alternative direction method of multipliers(ADMM)is proposed to design the beamforming weight vector and power allocation factor.Simulation results show that,compared with the zero forcing algorithm,the ADMM algorithm can effectively improve the security performance of the system.3.The performance of UAV downlink convert communication system is analyzed,in both eavesdroppers and warden are considered at the same time.Firstly,the eavesdropper judges whether the UAV is communicating or not through the binary hypothesis test.Meanwhile,the false alarm probability and missing detection probability of the warden are obtained by using energy detection method.Then,the optimal detection threshold is derived based on the criterion of minimizing the error probability.Finally,under the constraints of total detection error probability and total transmission power,the covert capacity of the system is obtained.The correctness of the theoretical analysis is verified by simulation.In addition,the influence of different power allocation schemes and total transmission power is analyzed,and a method to improve the covert capacity is discussed.