Research On Satellite Overlap Covert Communication Technology Based On Chaos Shift Keying Modulation

Information leakage in modern warfare is fatal.Nowadays,most of the information need to be transmitted by satellites,and satellite channels are open.Therefore,high-performance satellite covert communication technology is particularly important.Traditional satellite covert communication mostly uses direct sequence spread spectrum,but with the development of signal detection and estimation technology,this technology has been completely deciphered.The chaotic shift keying technology that integrates spread spectrum and modulation has the advantages of noise-like,non-periodic and unpredictable,and is very suitable for the transmission of hidden information.Overlapping communication is to parasitic a signal on other carriers for confidential transmission.Therefore,consider combining the two for the transmission of concealed information.Using the noise-like characteristics of the chaotic shift keying modulation technology,the concealed signal modulated by the chaotic shift keying modulation is superimposed on the satellite service signal,and the service signal is used as a cover carrier for secondary concealment,which can greatly improve the concealment of information transmission.Therefore,the study of satellite overlay and covert communication technology based on chaotic shift keying modulation has important theoretical value and application prospects.First,analyze the mutual interference between satellite service signals and covert signals.According to the conditions of covert signal transmission,select the frequency division multiple access(FDMA)type service signal suitable for superposition,and analyze the covert signal versus service signal from the aspects of carrier-to-noise ratio,effective omnidirectional radiation power and power spectral density.The interference and the interference of the service signal to the covert signal,so as to deduce the capacity of the covert signal that can be superimposed under the condition of not affecting the service signal transmission.Secondly,relying on FDMA type satellite service signals,design a satellite overlay concealment scheme based on differential chaos shift keying(DCSK)modulation,and complete the evaluation of concealment.Aiming at the shortcomings of insufficient reliability of chaotic shift keying modulation,a multivariate low-density parity-check(LDPC)code is introduced,and its manifestation,check matrix construction method and coding algorithm are explained.Compare and analyze the modulation techniques of chaos shift keying(CSK),DCSK and frequency modulated differential chaos shift keying(FM-DCSK).Build an LDPC-DCSK coded modulation system model,propose a multi-element LDPC-DCSK-based satellite overlap concealment scheme,and simulate and evaluate the concealment of the transmitted signal from two aspects: power spectral density and factor.Finally,separate the mixed signal and complete the performance evaluation.Aiming at the proposed satellite overlap concealment scheme,a separation algorithm based on auxiliary information is derived,and its separation effect is evaluated.For the separated concealed signal,the soft demodulation algorithm and the fast Fourier transform-based belief propagation decoding algorithm in the mixed logarithmic domain are studied to complete the demodulation and decoding.The overall performance evaluation and analysis of the satellite overlap concealment scheme based on multiple LDPC-DCSK and LDPC-FM-DCSK are carried out.