轨道电路多音调频信号的数字解调方法

Digital Demodulation Method for Multi-tone FM Signal in Track Circuit System

针对新型数字编码轨道电路传输的窄带多音调频信号,提出利用FIR高通数字滤波器进行多音调频信号数字解调的方法。FIR高通滤波器幅频响应曲线中过渡带局部具有近似线性的特点。对采样率为10 kHz,过渡带为800 Hz至3 800 Hz的10阶FIR高通滤波器幅频响应曲线过渡带局部进行线性拟合。利用其中具有高度线性特性的部分对轨道电路窄带多音调频信号进行幅频变换,从变换结果的幅度包络中得到调制信号信息。对调制信号进行频谱分析,得到原始的列车控制编码信号。仿真结果表明,高通FIR数字滤波器鉴频特性线性度高,所需FIR滤波器阶数少,实现方法简单,在0 dB信噪比、14 dB信干比环境下能够很好地恢复原始调制信号。

A demodulation method for narrowband multi-tone FM signal based on high-pass FIR filter in new type digitally coded track circuit system is proposed. Frequency responses of some high-pass FIR filters are partially linear in their transition bands. A linear fitting algorithm is applied to the frequency response of a 10-order high-pass FIR filter with 10 kHz sample rate and a transition band from 800 Hz to 3 800 Hz. The transition band of the filter is used for frequency discrimination and recovering the modulating signal. The digital train control codes can be further attained from spectrum analysis result of the modulating signal. Simulation shows that the method does not need high order FIR filter and has high linearity and low computation complexity. It can easily recovered the modulating signal with 0 dB SNR and 14 dB SIR. The train control codes are finally obtained through spectrum estimation algorithm.