Research On Blind Receiving Technology Of Frequency Hopping Communication Under The Strong Interference Environment

Frequency hopping(FH)communication has been widely used in the field of military communications with its excellent anti-jamming performance.As a non-cooperative recipient,the blind receiving system of FH communication can obtain communication parties' information without any prior knowledge by FH signal analysis.However,there are many kinds of interference signals in the electromagnetic environment,which will cause great difficulties in the process of FH signal blind reception,especially FH signal's frequencies have overlapped with interference.Moreover,the de-hopping technology also plays an important role in non-cooperative FH signal blind reception.In this thesis,the researches about blind receiving technology of FH communication include three parts: research on FH signal blind detection under the strong interference environment,research on FH signal blind parameter estimation under the strong interference environment and research on non-cooperative FH signal synchronous de-hopping.In the part of FH signal detection,a detection method based on time-frequency analysis is studied under the strong interference environment.To preprocess the received signal,three different methods of interference removing are researched according to the characteristics of interference signals.A new method based on time-frequency matrix segmentation is proposed to eliminate power-stabilized fixed-frequency interference when FH signal's frequencies have overlapped with interference.Finally,FH signal detection is achieved by successful extraction of time-frequency features.In the part of FH signal parameter estimation,a method based on time-frequency image information is proposed when FH signal's frequencies have overlapped with interference and fixed-frequency signal's power is constantly changing.Firstly,a FH period estimation method based on image center of gravity is studied.Secondly,a threshold value is set to eliminate fixed-frequency interference after binary processing and morphological refinement,and the eliminated FH fragments are successfully completed.Finally,the parameters of FH signal are validly estimated by using a complete time-frequency distribution curve.In the part of non-cooperative FH signal de-hopping,a FH signal synchronization analysis algorithm and a carrier frequency difference analysis algorithm are researched.The received FH signal will be synchronized with local carrier signal by adjusting estimated start time and the de-hopped signal will be suitable for demodulation by adjusting estimated hopping frequencies.Finally,the performances of the algorithms are verified by experiment.