Research On Wireless Security Transmission Techniques For UAV Communications

Recently,Unmanned aerial vehicle(UAV)communications have widely been used in both military and civilian applications.Different from the traditional terrestrial wireless communications,UAV-enabled wireless communications possess significant advantages,such as controllable mobility,on-demand deployment and high probability of Line-of-Sight(Lo S)air-toground communication links.However,the high probability of Lo S air-to-ground communication links also cause UAV communications to suffer from more stringent security issues than the conventional terrestrial wireless communications.In this work,we first study the communication security in the context of UAV networks from the perspective of physical layer security to improve the communication security of UAV networks.Considering that the wireless physical security focuses on protecting the transmission content of the transmitter from being intercepted by illegal eavesdroppers,and once the malicious node detects the transmission behavior of the transmitter,it may cause its location information be exposed,which makes the network still exist communication security issues.Thus,we then further study the communication security of UAV networks from the perspective of covert communication to hide transmission behavior of the transmitter,in order to achieve a high-level communication security.The specific work and main contributions are as follows:(1)A secure transmission scheme based on directional modulation(DM)technique is proposed to address the communication security of UAV relay SWIPT system.According to the error model of the direction angle from the UAV relay to eavesdropper,an approximation analytical expression of the artificial noise(AN)covariance matrix of the steering vector is derived.Based on this,we formulate an optimization problem that maximizes the average secrecy rate subject to the minimum energy requirement at the energy node and the total power constraint at the UAV relay.We first propose a one-dimensional search scheme to obtain the optimal information beamforming matrix and AN covariance matrix.Then,the maximizing Signal-toLeakage-AN-Noise-Ratio(SLANR)and successive convex approximation(SCA)schemes are developed to achieve low-complexity suboptimal solutions.Simulation results show that the performance of the SCA scheme is very close to that of the one-dimensional search scheme in terms of its average secrecy rate.In addition,compared to the zero forcing(ZF)scheme,the developed maximizing SLANR and SCA schemes provide significant performance improvements.(2)In the presence of multiple legitimate users and multiple eavesdroppers,we develop a secure transmission design scheme in the context of a dual UAV cooperative network.We first formulate a max-min average secrecy rate optimization problem to guarantee the fairness among all ground users.Considering that the optimization variables in the formulated optimization problem are closely coupled,which leads to the optimization problem difficult to tackle directly.As such,then we decompose it into a trajectory subproblem and a transmit power subproblem.Finally,an alternating iterative algorithm based on SCA is proposed to design the trajectory and transmit power of UAV base station as well as the trajectory and AN transmit power of UAV jammer.Simulation results show that the secrecy rate performance of the considered system can be significantly improved by introducing UAV jammer.(3)In order to prevent the confidential information transmitted by the scheduled sensor node(SN)from being intercepted by other unscheduled SNs,a full-duplex(FD)UAV generates AN to interfere with other SNs when it gathers critical information from the scheduled SN.We first derive the analytical expressions of the reliability outage probability(ROP)and the secrecy outage probability(SOP),based on which we formulate a max-min average secrecy rate optimization problem.We note that the formulated optimization problem is a mixed-integer non-convex optimization problem.To solve this problem,we employ the first-order restrictive approximation technique and penalty method to transform the problem into a generalized nonlinear convex programming(GNCP).In order to reduce the computational complexity,we further convert the GNCP into a standard second-order cone programming(SOCP).Finally,we introduce a penalty successive convex approximation(P-SCA)algorithm to jointly design the UAV's trajectory and AN transmit power as well as the redundancy rate and SN scheduling.Simulation results show that the proposed algorithm can efficiently solve the formulated mixed-integer non-convex optimization problem and UAV trajectory design can further improve the max-min average secrecy rate performance of the considered system.(4)We study covert transmission technique to hide the transmission behavior of the UAV,in order to further improve the communication security level of UAV networks.Under the assumption that UAV cannot perfectly achieve the location information of legitimate user Bob and warden Willie,we first derive the optimal detection threshold and the corresponding minimum detection error probability from the perspective of Willie.We then derive a lower bound on the average minimum detection error probability from the perspective of UAV.Based on this,we formulate an optimization problem that maximizes the covert transmission rate,which is subject to the transmission outage probability constraint and covertness constraint together with UAV related constraints.Finally,we develop a SCA algorithm to jointly design a robust trajectory and transmit power for UAV.Simulation results show that the UAV always chooses a trajectory that is farther away from the Willie and jointly design the UAV's trajectory and transmit power can significantly improve the covert transmission rate.(5)In UAV data collection networks,hiding the transmission behavior of ground SNs can effectively protect their privacy information.A FD UAV gather critical information from a scheduled SN and generate AN with random transmit power to interfere with the unscheduled SNs' detection.We first analyze the false alarm probability and miss detection probability,based on which we derive the optimal detection threshold and the corresponding minimum detection error probability.We then formulate a max-min average transmission rate optimization problem,which is subject to covertness constraint and SN scheduling constraint as well as UAV transmit power constraint and mobility constraint.Finally,we develop a P-SCA algorithm to jointly design the UAV's trajectory and AN transmit power together with the SN scheduling.Simulation results show that the proposed joint design scheme achieves a better covert transmission rate than the fixed UAV trajectory design scheme,and the UAV's AN transmit power achieved by P-SCA scheme is dominated by the distance from the UAV to the strongest detector among the unscheduled SNs.