Research On Digital Covert Communication Technology Based On Physical Layer

With the rapid development of communication technology,wireless communication networks have become very popular in our lives.However,due to the inherent broadcast line of wireless communication,communication data is easily eavesdropped by eavesdroppers during transmission.Once important data is leaked,it will cause serious harm to society.The traditional method of communication encryption is to encrypt data at the data link layer or higher.However,with the continuous development of computer technology,the computing power is continuously improved,and many traditional encryptions are no longer secure.It is a good idea for us to covertly transfer important information so that eavesdroppers cannot perceive the existence of covert information.This paper is based on the research of digital covert communication technology based on physical layer.The main work of this paper are as follows:1.A novel covert communication system based on AR noise is proposed.In the covert communication system,AR noise is used as a covert signal in the system for transmitting binary data,that is,parameters for determining AR noise using covert information bits.After obtaining the estimated value of the AR noise,the legal receiver can obtain the AR parameter by calculating the correlation coefficient,and then obtain the covert information through the decision.Since AR noise is one of the most common noises in wireless channels,this technique provides good concealment.More importantly,the host system can help covert communication systems to solve problems such as synchronization and channel estimation,so the structure is greatly simplified.The simulation results show that in this communication scheme,the reliability of data transmission is related to the parameters of the AR model and the length of the noise sequence samples.Simply put,the higher the absolute value of the AR model parameters,the lower the bit error rate when the sample length is constant.Similarly,the absolute value of the AR model parameters is unchanged,and the larger the sample length value,the lower the bit error rate.Moreover,due to the existence of the channel coding module,the error rate of the original service data of the host system is not affected.2.A novel covert communication system based on IEEE 802.11 a is proposed.IEEE 802.11 a is a commonly used WLAN physical layer protocol.The research and analysis of IEEE 802.11 a reveals that there is a difference between the subcarriers actually used in IEEE 802.11 a and the available subcarriers provided by OFDM,that is,there are null subcarriers.The subcarrier modulation technique is used in the covert system to modulate the covert information bits to be transmitted into the null subcarriers,and then the subcarriers with the covert information are normally transmitted to the receiving end,and corresponding demodulation techniques are applied to the specific subcarriers.Can solve hidden information.The simulation results show that the inserted covert information has little effect on the original service information and achieves the purpose of covert communication.3.A novel covert communication system based on random noise modulation is proposed in this paper.The correlation coefficient of a joint normal distribution noise sequence is modulated by a binary stream to achieve a covert communication system.Then the joint normal distribution noise is superimposed on the output of the digital modulator of the conventional communication system.At the receiving end,the correlation coefficient is estimated from the received signal and the covert binary stream is recovered by a hard decision.The key issues of the proposed scheme,such as channel estimation and symbol synchronization,are solved by the conventional digital communication system.The bit error rate of the proposed covert communication system is derived theoretically.Simulation results show that the proposed covert system has good bit error rate performance and is consistent with the theoretical derivation.