Research Of Track Signal Demodulation

Automatic Train Control (ATC) system is one type of important and fundamental technical equipment that can guarantee the train operation with high speed and high efficiency. With the train speed and control precision continuously improved, the demand of safe information for train control is also rapidly increased. The new generation of Digitized ATC (ATC-D) system based on the Digital Encoded Track Circuit (DETC) has been developed and put into use widely in the world. By adopting digital modulation/demodulation or multi frequency FM modulation/demodulation or Frequency Shift Keying (FSK) technology, the digitization of integral process including data's transmission, receiving and processing is achieved. As such, this type of system represents the mainstream in the present railway signal area in the world Since China hasn't master this kind of technology as yet, the research on ATC-D has become very significant and urgent.The phase of FSK signal transmitted in Frequency-shift track circuit is continuous. However, by studying the characteristics of FSK signal, it is very difficult to realize the demodulation of FSK signal's upper and down side frequencies only through the analysis of FSK signal's Fourier transform spectrum. One of this paper mainly study's the method of the demodulation of FSK signal based on Time-Frequency Analysis. It analyzes Wigner-Ville Distribution (WVD), which is a common method of Time-Frequency Analysis. The conclusion is acquires the result that SPWVD can realize the reliable and high precise demodulation of FSK.A kind of FM(Frequency Modulate) signal, upon whose carrier frequency, a combine of 27 possible audio frequencies are modulate. Its spectrum is rather complicated, and because of this, decode directly through modulated signals is not suitable. The key technique of decoding is described as the frequency estimation of the signal which has been modulated. The Instantaneous Frequency (IF), which is estimated by Hilbert transform, can be considered from a number of the signals superimposed. As the interval between every two signal is only 0.64Hz, and it is a real-time system as train control system. So how to improve the resolution in a short time as the subject of the thesis. The arithmetic of ZOOM FFT is put forward. By the theoretical analysis and computer simulation, it can be proven that ZOOM FFT can realize the high precise detection of spectrum of IF signal.These work provide some recommendable design idea realizing digital signal demodulation used for train control. It is very helpful for developing Chinese domestic ATC-D system. In the end, the author not only draw a concise conclusion but also make a prospect of ATC technology development orientation and trend.