Research On Resource Optimization Technology Of Cooperative Covert Communication System

With the vigorous development of broadband mobile communication technology,wireless communication has replaced traditional wired communication as the main means for people to interact with information.However,due to the natural broadcasting characteristics of electromagnetic waves,wireless signals are easily eavesdropped and intercepted by illegal eavesdropper,posing great risks to information security.Therefore,anti-interception is one of the core keys to ensuring the security of wireless information transmission.Covert communication technology is a new wirbellos anti-interception communication technology based on an information theory perspective,which can prevent communication signals from being intercepted by unauthorized third parties while ensuring reliable transmission of information.To solve the problem of low communication capacity of traditional covert communication technology,this dissertation studies collaborative covert communication technology,which improves the covert communication capacity of the system through collaborative scheme design and optimal resource allocation.The specific research content and contributions are as follows:The first part of this dissertation mainly investigates the cooperative and covert communication assisted by device-to-device(D2D)relay cooperation.This dissertation investigate a the Lyapunov’s Drift-Plus-Penalty(DPP)algorithm to solve the optimization problem of dynamic relay selection and power allocation for a specific secure area in the system.Since this problem is subject to a time-average constraint on the penalty processes,dynamic relay selection and power allocation can be modeled as an infinite-horizon timeaverage renewal-reward problem.Additionally,simulation results verify that the proposed dynamic selection scheme with power allocation can achieve higher transmission rates than the traditional Branch and Bound(Bn B)and Random Selection(RS)benchmark schemes and simultaneously improve system resource utilization efficiency.The second part of this dissertation mainly investigates the cooperative and covert communication assisted by UAV jammer.This dissertation develop a geometric method(GM)to solve the joint optimization problem of UAV’s trajectory and transmitter power.This method can directly solve the closed form expressions for the flight trajectory of UAV and transmitter’s power through the analysis of the Sphere of Apollonius.Therefore,it is possible to avoid using high computational complexity continuous convex approximation methods to optimize the flight trajectory of UAV.Numerical simulation shows that compared with the continuous convex approximation method,the proposed method can improve the system’s covert communication capacity with lower computational complexity.On the other hand,the simulation results also indicate that as long as the flight time of the UAV is long enough,the UAV can hover at the optimal position in the air for a period of time,and the optimal hovering position is always on the straight line connecting the receiver and the eavesdropper,which provides important theoretical basis for engineering practice,providing important theoretical basis for engineering practice.The third part of this dissertation mainly investigates an extensible covert communication based on closed-loop cooperation of the receiver.This dissertation considers how to covertly transmit multipl emessage transmissions on a physical degraded additive Gaussian white noise eavesdropping channel.Previous studies of this problem mainly focused on the maximum possible number of bits that can be sent over a certain period of time.To attain this maximum,the communication scheme has to be designed in a “one-shot”manner,meaning that it could only be used to convey a single message of a predetermined length; if the transmitter attempts to send more bits,then the probability of it being detected will exceed its permitted value and covert communication cannot be achieved.An extensible covert communication based on closed-loop cooperation of the receiver proposed in this dissertation utilizes the Schalkwijk and Kailath(SK)encoding scheme to achieve covert transmission of multiple messages.In addition,the achievability of the SK encoding scheme proposed in this dissertation has been rigorously proven.