Correction method for detection of the frequencies of railway FSK signals

In order to acquire the information of railway binary frequency-shift keying signals, which include upper/down side frequencies and base low-frequency with high-accuracy, a novel frequency detection algorithm for France UM-71 system is proposed. Combining fast Fourier transform with the ratio correction method, the carrier frequency and the base frequency are obtained. Furthermore, the hardware consumption has been decreased. And it possesses the advantage of simple algorithm and fast operation speed. Comparing with the detection of the base frequency, the upper/down side frequency of railway signal is more difficult. Based on spectrum analysis and the spectrum correction, a new method, which adopts the sliding window, is put forward in this paper. The absolute differences between the upper side frequencies and the down side frequencies obtained are regarded as the criterion for judgment. Then the set of data, in which the maximum absolute value is, is to be the result of the upper/down side frequency. Because the sliding window will go through every stage when the upper/down side frequency changes, therefore, it is not sensitive enough to the position of data which need to be transformed. Using the method mentioned above, the experiment results show that the accuracy requirement of the side frequency is satisfied well.