Application And Research On Demodulation Of Balise 2FSK Signal Using Chaotic Oscillator And Wavelet Transform

In recent years, with the acceleration of the train running speed,the safety requirements of train running is gettting higher and higher in railway transportation. And a higher requirement for the reliable and complete information transmission between the train and the ground is put forward. As an important equipment of information communication between the train and ground, the balise provides good guarantee for the safe operation of the train. Balise Transmission Module(BTM) is an important component equipment of onboard part of the balise transmission system, and its main function is to filter,demodulate and decode the uplink 2FSK signal transmitted from the ground balise. The performance of BTM has a great impact on the effective transmission of balise message. Hence, it is necessary to study BTM. Therefore, it is an important way to improve the performance of BTM by studying how to remove the noise that is mixed in the transmission quickly and demodulate the message of the balise accurately.This subject studies on the usage of chaos theory to demodulate the balise uplink 2FSK signal under strong noise background. The Duffing oscillator model is the most studied chaotic oscillator model. When the noise and useful signals through chaotic oscillators behave very differently, therefore this advantage can be used to detect the signal and the wavelet transform has the characteristics of multi-resolution analysis, which can be used to effectively remove the noise mixed in the signal. In the dissertation, the advantages of the two are combined to apply into the 2FSK signal demodulation of the balise. And its anti-interference performance is analyzed.Firstly, the equipment composition and working principle of the balise transmission system are described in detail, characteristics of the balise uplink 2FSK signal and existing 2FSK signal modulation, and demodulation methods are analyzed. Because the balise uplink signal is a phase continuous signal, the direct frequency synthesis method is used to modulate the 2FSK signal of the balise. Secondly, the dynamic characteristics of the Duffing oscillator system are analyzed, including the immune characteristics of noise and the sensitivity of initial value. The Duffing oscillator is used to detect weak sinusoidal signal and the influence of different frequency sinusoidal signal and noise on the system are analyzed. Then, combined with the wavelet threshold denoising method, a combined detection model of the 2FSK signal of the balise is built based on the combination of wavelet denoising and chaotic oscillator. The power spectrum entropy method is analyzed and applied to the output state identification of chaotic system. Finally, the simulink model is used to realize the simulation of the signal demodulation of the balise uplink. The uplink 2FSK signal of the balise is simulated and analyzed under the background of noise and downlink signal. Compared with the error rate of the traditional demodulation method, the advantages of this method are verified. The method can reduce the threshold value of the balise signal detection, and has good anti-interference performance.