Research On Demodulation Method Of Balise Uplink Singal Based On Duffing Oscillator

With the increasing speed of rail transport,the on-board train equipment relies progressively on intermittent transponder to provide information.The transponder,an important equipment of information transmission between the train and ground,provides security guarantee for train operation.The key part of the transponder transmission system is the balise transmission module,which mainly generates high-frequency electromagnetic energy to activate the ground transponder and deals with the information transmitted on the ground transponder.A further study on balise transmission module is necessarily needed due to the critical role the balise transmission module plays in the transmission of the transponder message.However,there are many interference factors,such as the high frequency electromagnetic energy of 27.095 MHz on the downlink which is sent by the balise transmission module antenna of train on-board equipment and received by the ground transponder,strong electromagnetic interference as well as the noise from time,affecting the information transmission of balise uplink signal in the complex electromagnetic environment of high-speed railways and resulting in the abnormal operation of the train.Therefore,the improvement of the balise transmission module is necessary so that the interference above will be stemmed.The demodulation of the balise uplink signal under the noise as well as the 27 MHz signal interference was studied in this thesis by establishing a chaotic Duffing oscillator model.The Duffing oscillator was used to detect the signal because of its sensitive dependence on initial conditions.Ensemble empirical mode decomposition has better local adaptability,which means that the signal can be decomposed from the characteristics of itself.That's how the interference in the signal will be eliminated effectively.The interference immunity of the system was analyzed through the demodulation of the balise uplink signal with the method combining Ensemble Empirical Mode Decomposition and Duffing oscillator system in this thesis.Firstly,the principle of the transmission system of the transponder was concretely analyzed and in terms of the modulation and demodulation method of the signal.By comparing the signal modulation methods,the direct digital frequency synthesis method was selected to modulate the balise uplink signal.Secondly,it was analyzed that the sensitive dependence of the initial conditions of the Duffing oscillator system and the influence of noise on the Duffing oscillator system.Then,the principle of Ensemble Empirical Mode Decomposition algorithm was studied,and combining with Duffing oscillator system and which was the balise uplink signal detected.The state of Duffing oscillator system was identified through the power spectrum entropy method after comparing and analyzing the system status discriminant method.Finally,the Simulink simulation model of the balise uplink signal was established to analyze the demodulation of the balise uplink signal under the noise and high frequency electromagnetic energy interference.By comparing the bit error rate,it was found that the bit error rate of Ensemble Empirical Mode Decomposition and Duffing oscillator detection methods was significantly lower than the traditional coherent and non-coherent demodulation methods under the same signal to noise ratio.