Research On Separation Of FM Spread Spectrum Mixed Signal Based On Time Varying Filter

With the rapid development of information technology in modern society,while pursuing the efficient transmission of information,more and more attention has been paid to the security and concealment of information transmission.Based on the spread spectrum signal as a carrier of concealed information delivery,this paper builds a model of concealed information delivery and studies the reception of concealed information with high performance.The main contents are as follows:Aiming at the Underlay mode of cognitive radio,a mixed signal concealment communication transmission system using spread spectrum signal as secondary user(SU)signal and FM signal as primary user(PU)signal is proposed.Simulation shows the performance of FM spread spectrum mixed signal system transmitting hidden information.Aiming at the problem of separating the received signal of FM spread-spectrum mixed signal,an algorithm based time-varying filter is proposed.By calculating the instantaneous phase of the mixed signal,an adaptive time-varying filter is used to filter the mixed signal's FM signal to achieve signal separation and interference suppression effect.Its performance is verified by computer simulation.By analyzing the characteristics of the cyclic spectrum of the DSSS signal,an algorithm of using the cyclic spectrum to detect the spread spectrum signal in the mixed signal is proposed.Aiming at the problem of whether the spread spectrum signal exists in the frequency range of the current carrier frequency under the condition that the carrier frequency of the spread spectrum signal is unknown,an algorithm based on adaptive time-varying filter and cyclic spectrum feature analysis is proposed.Firstly,The time-varying filter separates the FM signal and then performs cyclic spectrum analysis on the mixed signal after the interference suppression to determine whether the DS signal exists or not.According to the cyclostationary signal spectrum characteristics to determine whether the mixed signal contains the DS signal,the simulation results verify the performance of the algorithm.The results show that the proposed algorithm can effectively determine whether there is a spread spectrum signal in the mixed signal,and it is still feasible in the case of high jam-to-signal ratio.Based on GNU Radio and the USRP,the paper also develops the FM Spread-Spectrum mixed-signal sending and receiving simulation.Through the simulation test,the feasibility of the system is verified.