Research On Simulation About On-board Balise Transmission Module

As the key equipment of the balise system, BTM(Balise Transmission Module) mainlycomplete the functions about balise packet such as filtering, demodulation, decoding and soon, and the merits of its performance directly affects the rapidity and stability about thetransmission of packets in balise system. Based on the brief analysis on the working principleof the balise system, filtering and demodulation methods of BTM are further researched, theadaptive demodulation method based on adaptive filtering algorithm is puts forward, andsimulation is carried out by MATLAB simulation software. The main research content iscompleted as follows:Firstly, the working principle of the balise system is introduced briefly. The LinesideElectronic Unit, the Balise and the On-board BTM are mainly included in the Balise System.BTM controls Onboard Antenna to send27.095MHz high frequency continuouselectromagnetic energy to the ground. The balise is activated by the high frequencyelectromagnetic energy, then modulates the packets to2FSK(2Frequency Shift Keying)signal and launches out in the form of packet frames when the train through it. The packetsare received by Onboard Antenna and transmitted to BTM. After filtered, demodulated anddecoded by BTM, the balise packets are sent to ATP(Automatic Train Protection).Secondly, filtering and demodulation methods of BTM are further researched. TheNon-coherent Demodulation Method is one of the tranditional methods for BTM to modulatebalise packet frames, which is usually carried out after filtering out noise by a band-pass filter.Band-pass filter can merely filter out noise outside the fixed frequency band, but can’t filterout noise within the desired frequency band. When setting the frequency range, the widerfrequency band leads to the worse filtering effect, the narrower frequency band causesdamage to the desired signal, so the choice of frequency band is not easy to grasp. Theadvanced Adaptive Filtering Algorithm in the communication field is introduced in this paper.Two kinds of carrier frequency of balise packets are tracked respectively through two singlefrequency trackers, and balise packets are demodulated by comparing judgment. TheAdaptive Demodulation Method has better tracking ability and anti-interference performanceof desired signal by using adaptive filter, and can overcome the disadvantages of traditionalmethods.Finally, the Adaptive Demodulation Method of BTM is verified by MATLAB simulationsoftware. To simulate modulation and transfer process of actual balise packets by usingMATLAB simulation software, a set of balise packets are modulated and white Gaussiannoise is added to them, then balise packets are received though adaptive demodulation. In theend, the error rate of adaptive demodulation and non-coherent demodulation are compared by using MATLAB in order to assess the effect of the Adaptive Demodulation Method. Theresult shows that the Adaptive Demodulation Method is far superior than the traditionalNon-coherent demodulation Method.