Research On Covert Transmission Schemes For Wireless Communication Networks

Due to the broadcast nature of wireless channel.information is vulnerable to eavesdropping and interference by illegal users during transmission.Thus information security has become a topic of concern to researchers.Traditional encryption technology and physical layer security technology ensure secure transmission through key encryption and physical characteristics of wireless channel,respectively.However,the two methods can only guarantee the security of information content to the greatest extent,but cannot protect the information transmission process.Illegal users can maliciously interfere and destroy the communication process according to the circumstances of information transmission.Therefore,to conceal the information transmission process is equally important.Covert communication technology is designed to establish a reliable link between legal sender and receiver to ensure that the information transmission event itself is not discovered by illegal users,thus ensuring the information security.This paper first studies the realization of covert communication,and then proposes covert transmission schemes for specific communication scenarios.The main work is as follows:First,the impact of node selection on system performances is studied.Specifically,when there are multiple cooperative relays or jammers,the closed-form expression of minimum detection error probability is derived separately,and the optimal relay selection and jammer selection are respectively proposed with the constraint of minimum detection error probability to maximize the covert transmission rate.Simulation results show that the relay selection and the jammer selection scheme can effectively improve the covert transmission rate of the legal link.For example,the relay selection scheme is used.When the Jamming power is 15dB,the covert transmission rate obtained by the proposed relay selection scheme is better than the reference plan increased by 14.7%.Second,covert transmission schemes for specific communication scenarios where the detector adopts two-phase detection are designed.In the existing research,illegal detectors usually use single-phase detection to determine whether legitimate users are transmitting,but the research on detection and transmission scheme design for two-phase transmission scenarios is not deep enough.Therefore,this paper studies the j oint detection scheme and its countermeasures in this scenario.Firstly,a joint decision making criterion is proposed,and the corresponding minimum detection error probability is derived.Simulation results show that the joint detection scheme can effectively improve the detection performance compared with single-phase detection.Based on that,a single-node jamming scheme is proposed.Under the condition that the minimum detection error probability is subject to a certain constraint,the optimal total transmission power is given to obtain the maximum covert transmission rate.Next,a covert communication method is proposed in a wireless communication network with multiple jammers.The optimal transmission power of the source and the relay under the constraint of minimum detection error probability is obtained and a jammer selection scheme is proposed to maximize covert transmission rate.Simulation results show that the proposed method can effectively resist the impact of two-phase joint detection,and can obtain a higher covert transmission rate than traditional ways.For example,when the Jamming power is 15dB,due to the best power allocation and the selection of two-phase best jammer,the covert transmission rate obtained in this paper is 3.37%higher than that of the equal power allocation scheme,and is 43.7%higher than that of random Jammer selection scheme.In summary,this thesis designs covert transmission schemes for specific transmission scenarios which can obtain perfect covert performances.