| In order to ensure the accuracy,continuity and real-time requirements of the communication process,the communication measures with strong anti-interference are widely studied.Frequency hopping communication refers to the information communication with narrow-band carrier at both ends of the transceiver according to the predetermined pseudo-random change pattern under the condition of simultaneous synchronization.Because of the inherent characteristics of FH communication technology,it has the advantages of good confidentiality,low interception rate,strong anti-interference ability and easy networking.This makes it widely used in the field of mobile communication,modern radar,sonar and other electronic systems.However,the wide application of FH communication technology also brings more severe challenges to radio monitoring.In the military information electronic warfare,it is very important for us to search,intercept and break the real-time transmission information of the other party,or to interfere with it to ensure the confidentiality of our communication content.At the civil level,the data monitored by non partners play a very important role in radio spectrum management and illegal radio activities.When the other party adopts frequency hopping technology,because there is no cooperation agreement between signal transmission and signal reception,the receiver can not get the modulation mode,signal structure and other relevant information of the received signal,and then can not intercept the other party's information or interfere with the other party's signal.In order to solve this kind of problem,based on the received FH signal,this paper further explores the acquisition of the basic parameters of the acquired signal,and then lays the foundation for the realization of the interception or interference of the other party's FH signal.Firstly,this paper summarizes the basic principle of FH communication system,combs the basic knowledge of FH signal,summarizes the advantages and disadvantages of various FH signal research methods,summarizes the key and difficult points in the process of FH signal monitoring,and establishes the mathematical model of FH communication system,which provides a theoretical basis for the subsequent research of FH signal detection and parameter estimation.Secondly,all kinds of time-frequency methods of FH signal are studied,linear and non-linear time-frequency analysis methods are studied in theory and simulation experiments,the time-frequency distribution performance of all kinds of time-frequency analysis is compared and summarized,and the parameter estimation method of FH signal based on time-frequency analysis is studied.Then,in view of the unknown noise energy,a blind estimation method of FH signal characteristic parameters based on time-frequency graph correction is proposed.Based on the spectrum of FH signal obtained by STFT time-frequency analysis,threshold correction is added to improve the accuracy of FH signal parameter estimation.Using the method of energy detection to get the adaptive threshold to detect the noise and filter the noise,and complete the correction of the time-frequency map.According to the modified time-frequency chart,the method of two times estimation and the method of constructing frequency correction term with signal DFT transformation coefficient are used to estimate the signal jump time and carrier frequency,that is,the DFT transformation coefficient of two positions before and after the peak value is used to obtain the more accurate estimation value of carrier frequency.Finally,the effectiveness and applicability of this method are verified by simulation experiments. |
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