High Rate Covert Communication Based On Chaos

With the rapid development of wireless communication technology,it is used more and more widely.However,the information transmitted by wireless channel is subjected to be interfered or intercepted,which causes security risks.Covert communication is an attempt to hide the communication signal,making it difficult for the enemy to perceive the communication signal.Covert communication can be classified into two types: Low Probability of Intercept(LPI)and Low Probability of Detection(LPD),in which LPD is a more commonly used technology,Direct Sequence Spread Spectrum(DSSS)technology or Chirp Spread Spectrum(CSS)technology are the general ways of LPD communication.The spread spectrum communication based on high spreading gain decreases the probability of detection by eavesdropper,however,the trade-off is a low data transmission rate.Chaos is a quasi-random signal generated by deterministic systems,which is sensitive to initial conditions.It has a wide spectrum and is suitable to be used as a spread spectrum signal in spread spectrum communication systems.In this paper,the low detection probability performance of chaotic signals,inverse M sequences and linear frequency modulation signals is compared and analyzed.A communication scheme based on Chaotic Pseudo Orthogonal(CPO)shape forming filter is proposed to improve the data transmission rate.The Chaotic Pseudo Orthogonal Covert Communication(CPOC)system is compared with DSSS system and CSS system in terms of error,communication rate and covert performance by simulation.Finally,the experiment is carried out on the Software Defined Radio(SDR)platform to verify the simulation results.The main research contents of this paper are as follows:First,the basic principles of DSSS system and CSS system are introduced.Then,the characteristics of chaotic signals generated by different methods are analyzed,and the basic characteristics and spread spectrum principle of chaotic pseudo orthogonal signals are explained.The autocorrelation function,spectrum,cepstrum,power spectrum and spectral correlation function of CPO signal,M sequence and linear frequency modulation signal are simulated and analyzed.The LPD performance of CPO signal adopted in this paper is evaluated,and the feasibility and superiority of CPO signal applied in covert communication are verified.Secondly,a chaotic pseudo-orthogonal covert communication system is designed based on the chaotic pseudo-orthogonal shape forming filter,and the encoding and decoding method is proposed.In this system,CPO signal is spread spectrum,and orthogonal frequency division multiplexing modulation is adopted,which solves the problem of periodicity of spread spectrum element and insufficient spectrum of traditional scheme using M sequence.Then,the Additive White Gaussian Noise(AWGN)and multipath channels bit error rate performance of the CPOC and DSSS systems are simulated,and the corresponding communication rates are calculated.The results show that the CPOC system has higher data transmission rate with lower bit error rate.The characteristics of frequency domain and cyclic spectrum of chaotic pseudo-orthogonal covert communication system are compared for DSSS system and CSS system,and the covert performance of CPOC system.Finally,Software Defined Radio is used to verify the communication performance of chaotic pseudo-orthogonal covert communication system in two different environments,including indoor and outdoor.The experimental results show that the communication system designed in this paper has better error performance and higher data transmission rate than the comparison schemes.