Research on demodulation of balise uplink signal based on constant modulus algorithm

In the process of balise uplink signal transmission, the transmission signal is vulnerable to unknown electromagnetic interference, which leads to the increase of demodulation signal error rate and balise message error, which affects the train operation efficiency. In order to reduce the influence of electromagnetic interference on signal transmission, firstly, the signal transmission characteristics of balise uplink are analyzed. Secondly, according to the characteristics of uplink signals, the cost function based on Constant Modulus Algorithm (CMA) blind equalization algorithm is used, and the steepest descent method is used to optimize and update the equalizer weights, so as to equalize the uplink signals and reduce the interference of noise signals to useful signals. Finally, the variation of demodulation bir error rate (BER) indifferent signal-to-noise ratio (SNR) environments and during train operation after adding CMA algorithm to the balise transmission system is simulated and analyzed. The simulation results show that the demodulation method with CMA equalization has a lower bit error rate than the envelope detection method and the coherent demodulation method in different SNR environments. When the SNR is greater than or equal to 6dB, the demodulation BER with CMA equalization is much lower than that of the envelope detection method and the coherent demodulation method. The demodulation BER with CMA equalization is stable when the train speed changes, and far below 10 -6 , which meets the railway test standard. The content of this paper can provide theoretical reference for the application of balise in complex electromagnetic environment.