Research On Covert Communication Technology Based On Non-orthogonal Multiple Access

In the context of the rapid development of the mobile Internet,more and more data are transmitted through wireless communication.Due to the broadcast characteristics of wireless communication,the privacy data in wireless communication are facing severe challenges of leakage,once eavesdropped and destroyed,which will cause incalculable losses.In order to solve the privacy and security problems of wireless communication,covert communication,as a physical layer security technology,fundamentally guarantees privacy and security by confusing wardens so that they cannot determine whether covert users have transmitted message.However,in covert communication,the transmit power of covert users is strictly limited,which seriously affects the communication performance of users.In order to realize the efficient utilization of spectrum resources and meet the quality of service(QoS)of multiple users,the non-orthogonal multiple access technology effectively improves the communication performance of users through allocating the same time-frequency resource block to multiple users.And with the further development of short video,virtual reality,HD Live and other services,the performance of uplink communication will become crucial.In order to meet the requirements of modern communication for privacy security and communication rate performance,this thesis provides certain ideas and solutions for realizing covert communication and improving covert message transmission rate for the uplink multiple access communication scenario.The main research work of this thesis are as follows:1.Considering the uplink power-domain non-orthogonal multiple access(PD-NOMA)communication scenario,this thesis proposes a reconfigurable intelligent surface(RIS)-assisted covert communication scheme.This scheme utilizes the uncertainty of RIS phase shift and public user’s cover mechanism to confuse the warden,where the optimal phase matrix of RIS is designed according to the channel state information(CSI)of legal communication links.This work formulates the optimization problem of maximizing the covert rate under the covert requirement and maximum transmit power constraint.Firstly,this work obtains the analytical expression of the total detection error probability(DEP)of the warden,and analyzes the optimal detection performance of the warden.Secondly,this work constructs the optimization objective function and uses the problem decomposition optimization method to obtain optimal solution.The experimental results prove that the RIS-assisted transmission scheme can effectively improve the covert rate while enable covert communication.2.In order to further strengthen the performance of the communication system,this thesis studies the uplink covert communication system based on rate splitting multiple access(RSMA)technology.In this work,the warden only knows the statistical CSI,and which is confused by the joint effect of noise uncertainty and channel uncertainty.This work constructs the problem of maximizing the covert sum rate under the constraints of covert requirement,QoS requirements and maximum transmit power.Since the total DEP analysis expression of the warden in this work is difficult to handle,we adopts the method of numerical search to solve it.Experimental results prove that under the combined effect of the above constraints,RSMA has a significant improvement in covert sum rate compared to PD-NOMA and OMA schemes.