Physical Layer Security Based Covert Capacity Study In Covert Wireless Communication

The covert wireless communication protects not only the content of the information but also the very existence of the transmission itself,and it is widely used under open air in anonymous communication,underwater communication and military communication.Low power of signal transmission used in covert wireless communication will limit the single-hop transmission distance due to signal fading.Defining the covert capacity is the premise and foundation of the wide application of covert wireless communication,and its solution and optimization have become one of the major bottlenecks in realizing covert wireless communication.Based on the physical layer security and information theory method,this thesis focuses on the achieving methods of two hop one/two way covert wireless communication against transmission detection and one hop covert wireless communication against transmission detection and eavesdropping.In addition,the theoretical solution method of covert capacity and the optimization scheme of covert rate are proposed,where the specific research works are as follows.Aiming at the problem of single-hop transmission distance limitation in covert wireless communication,based on the research idea of single-hop covert wireless communication,a two-hop one-way covert wireless communication model is proposed.By analyzing the constraint conditions of signal transmission power,the covert capacity asymptotic value of two-hop one-way transmission is obtained.Furthermore,a two-hop two-way covert wireless communication model is extended to obtain the corresponding detection schemes and covertness schemes based on the different relay prior knowledge of the warden.Based on the scenarios of different time-slot schemes under the two-way transmission modes with three different time slots(4,3 and 2),the asymptomatic value of covert capacity obtained by theoretical analysis is given,which enriches the theoretical foundation system of two-hop covert wireless communication.In order to prevent the passive attacks of transmission detection and message eavesdropping in covert wireless communication,a single-hop covert wireless communication model is proposed to resist the two security threats.The model is based on the physical layer security technology such as artificial noise and transmission power allocation,and the constraint conditions of covert capacity in hiding transmission detection and message eavesdropping are obtained respectively through theoretical analysis.In this thesis,a method for solving covert capacity under two constraints is given to obtain the quantitative index which is helpful to improve covert rate is obtained,and the optimal result of covert rate is achieved.Based on the proposed covert capacity solution method,this thesis verifies the correctness of the covert constraint conditions derived from theoretical derivation that is when the transmission limit is set to the number of channel uses n as covert capacity (?9)),such that the probability of the transmission is very low,and the covert wireless communication can be achieved.Moreover,through numerical analysis and simulation,the results of numerical simulation method are consistent with the theoretical analysis conclusion.The numerical results also show that under the covert wireless communication against two security threats scenario the covert rate is positively correlated with the total transmission power,power allocation coefficient and probability of transmission.