New Multi-Domain Transmission Techniques For Wireless Covert Communication

With the rapid development of wireless communication,the security of information transmission has become the focus of attention.Traditional encrypted communication is easy to attract the attention of eavesdroppers.In contrast,covert communication technology hides part of information by hiding it in ordinary information carriers,so that it is not easy to find the information in the transmission process.Covert communication technology based on the physical layer is an important branch.The covert communication technology based on the physical layer can make the eavesdropper unable to intercept information and even unable to distinguish confidential information,which not only improves the confidentiality,but also has a variety of ways and is easy to implement.Therefore,covert transmission technology based on physical layer has attracted extensive attention due to its advantages.In this thesis,for some problems of index modulation(IM)and directional modulation(DM),which are the key technologies in covert communication,a new covert transmission technology is studied based on the existing traditional index modulation and directional modulation.The specific work of this thesis is as follows:First,this thesis introduces the theoretical methods and experimental principles of traditional index modulation technique and directional modulation technique,which are summarized in two parts: developments and research status.Secondly,this thesis introduces two covert transmission techniques based on code index modulation(CIM)and conventional phased-array directional modulation.The bit error rate(BER)performance of the code index modulation technique and the conventional direct-sequence spread spectrum system,and the BER performance of the phased array directional modulation technique and the conventional beamforming system are compared under the additive white Gaussian noise(AWGN)channels.Then,A novel code-domain index modulation(CDIM)communication framework is proposed by using multi-domain combination,which transmits and hides information by combining spreading code and interleaver index.performance of the CDIM system is demonstrated by theoretical analysis and Monte Carlo simulation,and an optimization analysis method using maximum correlation and vector inner product as optimization metrics is proposed,and detection optimization is applied to complex wireless communication scenarios,such as non-Gaussian fading channels,and a maximum likelihood(ML)algorithm and a support vector machine(SVM)-based detection are proposed.Then,based on the previous work,a new code-domain index modulation with directional modulation(CDIDM)combining code domain index modulation and directional modulation is proposed by combining the advantages of directional modulation in angle against eavesdropping.Then the maximum likelihood scheme of expected receiving angle receiver and unexpected receiving angle receiver is given,the average BER boundary is analyzed theoretically and Monte Carlo simulation is performed to verify that the BER performance of the system.It is shown that the proposed scheme is better than that of the conventional system and has good steganography in the direction.Basing on the phased array,the directional modulation technique of the frequency-controlled array is further studied,and the beamforming diagram of the CDIDM system based on the directional modulation technique of the frequency-controlled array is given.Chapter 5 gives a brief summary of the whole thesis and points out the possible research directions in the physical layer covert transmission techniques.