Research On Frequency Parameter Detection Of Frequency-shift Track Circuit Base On The Hht Algorithm

With the continuous improvement of the speed of the train, in order to ensure train’s safety, high-speed operation, the train control system needs to get more information from the wayside, so a numerous information are received on the security provided by the railway signal system. Thus, that high-speed trains can accurately receive information from the wayside is particularly critical. At present, railway frequency-shift signal demodulation basically adopts the Fourier transform as the core spectrum analysis method in China, because there are differences between the spectral characteristics of railway frequency-shift signal and its disturbed spectral structure, so the method in identifying the track circuit frequency signal and the interference signal has obvious advantages. However, it only can analyze the signals in the frequency domain or time domain. In recent years, due to the time-frequency analysis method can analyze signal in the time domain, reflects the time-frequency characteristics of the observed signals fully. the internal characteristics of the signal can be understanded intuitively. The article describes characteristic of the railway frequency-shift signal and the signal processing methods used commonly about time-frequency analysis in recent years, including short-time Fourier transform, Wigner-Vill distribution, pseudo-Wigner-Vill distribution, the smoothing Wigner-Vill distribution, the smoothing pseudo-Wigner-Vill distribution, and analyzes their advantages and disadvantages.In order to realize demodulation of railway frequency shift signal accurately and reliably, a frequency shift signal demodulation method is proposed based on the Hilbert Huang Transform (HHT) algorithm, the algorithm is a time-frequency analysis method, can be more intuitive to understand the information features of frequency shift signal in time domain and frequency domain, it has a good analysis of the non-stationary, non-linear signal, and can not be limited by the Heisenberg uncertainty principle, it is suitable for transient signals and so on. And it is a major breakthrough in the Fourier transform-based linear and steady-state spectrum analysis. The specific steps of the HHT algorithm and the computer simulation is presented in this paper. The simulation results show that the HHT algorithm can accurately demodulate the upper frequency and lower frequency, the low frequency modulation frequency and carrier frequency of frequency-shift signal that can also reached technical indicators of a frequency detection parameters, it can demodulate accurately and reliably frequency-shift signal, presents the correctness and feasibility of this algorithm, lay the foundation for further practical application.