Research On Anti-interference Method Of Time-Frequency Modulation Technology

Short-wave communication is a technology that uses ionosphere to complete communication,because it has the characteristics of low cost,strong anti-destructiveness and flexible networking,and with adaptive technology,error control technology and time-frequency modulation technology in short-wave communication technology.The development of the communication has greatly improved the communication quality of short-wave communication and played an important role in different fields.The time-frequency modulation technology is one of the short-wave communication technologies.Its essence is a code modulation.The carriers of different frequencies are selected according to different combinations of binary symbols,and the signal transmission is completed within the duration thereof.Since the same signal is transmitted with different frequencies in different time slots,the time-frequency modulation technology has the characteristics of diversity and has good anti-fading and antiinterference ability.In this thesis,the in-depth study of time-frequency modulation technology is carried out,and the modulation,demodulation and anti-interference methods of time-frequency modulation are mainly studied.The first is modulation,for the modulation technology of time-frequency modulation,starting from the traditional modulation principle,the principle of generating different time-frequency modulation signals is analyzed.Furthermore,the time-frequency modulation technique under different modulation systems is studied,and the timefrequency modulation technique under phase modulation and the time-frequency modulation technique under space-time coding are mainly studied.Followed by demodulation,the anti-interference method under the demodulation method is studied for different time-frequency modulation and demodulation techniques.Firstly,the interference and fading that affect the communication quality are described.The characteristics of different interference and fading are analyzed.Then the energybased demodulation method and the demodulation method based on the sideband correlation algorithm are studied from the existing demodulation methods.Under these two demodulation methods,the demodulation principle is analyzed,and the existing demodulation method is made to make the existing demodulation method have better anti-interference performance.After that,a new demodulation scheme,ie,an instantaneous frequency based demodulation scheme,is proposed.This scheme can demodulate the signal at a lower signal to noise ratio.Finally,the performance of the three demodulation schemes and their respective application scenarios are obtained through experiments.Finally,the anti-interference method mainly studies the anti-interference method based on cyclic code,convolutional code,Turbo code,anti-interference method based on diversity reception,anti-interference method based on frequency hopping and antiinterference method based on blind source separation technology.Through the experiments under different interference environments,the anti-interference performance improvement of the time-frequency modulation technology by different anti-interference methods is obtained.