Research On Transmission Method Of Non-Orthogonal Multiplexing Covert Communication System

In wireless communication networks,due to the broadcast nature of wireless channels,information is prone to eavesdropping or interference by illegal users during the transmission process.The security of information transmission in wireless communication has received widespread attention.In previous studies,the security of information transmission has been addressed using conventional high-layer encryption or conventional physical layer security mechanisms.They safeguard data transfer by key encryption and the physical properties of the wireless channel,respectively,but do not hide the data transmission method.Through the detection of the information transmission process,illegal users in networks can still detect how information is being transmitted.They can then maliciously attack or interfere with the transmission process to prevent information from being transmitted normally.As a result,it is also important to consider how information transfer is hidden.In order to achieve the aim of information security transmission,covert communication technology is based on conventional physical layer security technology.It introduces uncertainty through the detection of illegal users in order to prevent the transmission process from being discovered by illegal users.Transmission systems represented by non-orthogonal multiplexing have been used extensively among a variety of developing communication technologies.Due to its spectrum sharing properties,the non-orthogonal multiplexing communication system makes it possible to transmit multiple signals at once,enabling hiding of the hidden signal and the completion of covert communication.This thesis introduces covert communication technology into the nonorthogonal multiplexing communication system,studies the transmission security issue,and designs a disguised communication transmission method.The major work is as follows:This thesis first examines the two-hop non-orthogonal multiplexing covert communication system’s transmission scenario.In this scenario,the source node uses the relay node to transmit information to the destination node while also trying to transmit covert information in addition to the public information.The relay node decodes and transfers the information after receiving it from the source node and transmitting it on to the destination node.The detector detects whether there is a transmission of information at both phases of transmission by detecting the energy in the transmission scenario.From the viewpoint of the detector,a two-stage joint detection verdict scheme is designed for this particular scenario,and the closed-form expression and the best verdict threshold with the least amount of detection error probability are obtained.Secondly,this thesis proposes an optimal power allocation method under the constraints of public information transmission connection probability and covert performance,aiming at maximizing the effective concealed transmission rate,in order to improve the covert transmission performance of legitimate users.By distributing power between the two phases and between the public and covert information,the system’s effective discreet transmission rate is improved.The simulation results demonstrate that the power allocation strategy can significantly increase the system’s covert transmission rate.The transmission scenario is thus further expanded to multi-hop non-orthogonal multiplexing systems.For the multi-stage joint detection verdict for the detector,the closed-form expression with the lowest detection error probability and the best judgment threshold for each hop are first calculated.Furthermore,the power of public information and covert information at each stage is optimized with the aim of increasing the effective concealed transmission rate under the scenario of satisfying the constraints of public information transmission connection probability and covert performance,and an optimal power distribution method is obtained.The simulation results demonstrate that the optimal power allocation approach suggested can achieve an optimal covert transmission rate while assuring covert performance in the multi-hop nonorthogonal multiplexing covert communication system.Additionally,by choosing the hop number on the assumption of utilizing the best power distribution method,covert transmission performance can be further enhanced with changes in the transmission environment.In conclusion,this study develops covert transmission power allocation technique for twohop and multi-hop non-orthogonal multiplexing covert communication systems and achieves effective covert communication.