Signals And Telegrams Detector For CTCS Balise-design And Implementation Of FSK Modulation And Demodulation

With the continusous growth of the railway running speed and it’s throughput, therailway transportation is playing an important role in the economic development of ourcountry, at the same time the railway’s traffic safety has increasingly become a concern.At present, our country’s railway control system is CTCS(Chinese Train ControlSystem), which is independently developed by our country on the base of the EuropeanTrain Control System. As CTCS’s subsystem, the balise is a main part of CTCS. Balisescan transimit slope and limit speed information to the train by FSK singnal. Thisinformation is directly related to the safety of train traffic. So balise telegram’s correctlydecoded has a positive meaning.This thesis studies a new FPGA based FSK modulation and demodulation systemafter analyzing of the FSK signal’s research status domestically and abroad. This thesisstudis the system mainly from four four aspects: modulation module, demodulationmodule, frequency measurement module, power amplifier module. The modulationmodule is mainly used to modulate balise telegram to FSK signal, which has an centerfrequency of4.234MHz and a282KHz offset frequency. The difficulties of modulationis keep the continuous of the FSK phase. We design0,1yards as a hih-order address togenerate a wave which contains8sine waves, which is used to represent ’1’ telegram.At the same time we use7sine waves represent ’0’ telegram. The FSK demodulationmodule is mainly processed in time domain. By half cycle counts, it can generate clockedge flipp which is used to demodule FSK singnal. This demodulation methodconsumes less FPGA resources and the result is accuracy. The frequency measurementmodule is mainly used to measure track circuit’s frequency during the study of thebalise system. The frequency measurement module is mainly used to measure test port’sfrequency as a subsidiary function of CTCS Balise’s signals and telegrams Detectinginstrument. The measurement module use positive and negative gate to relizenon-intermission frequency measurement. Though the process of upper computer, wecan get the value of frequence. The frequency measurement module can not onlymeasure signal frequency it can also measure FSK singnal’s frequence. The amplifier module is mainly used to amplife the moudulated FSK signal so that it can relizewireless transmit. In order to obtain sufficeient power, the power amplifier module usean three level power amplifier circuit.Under laboratory conditions, the FSK modulation and demodulation system hasbeen debug. The test results is in line with the expectations, which meets the indicatorsof system design.