Study On Disturbance Injection Technology And Test Platform For BTM Susceptibility Test

Automatic Train Protection(ATP)is an important system to ensure the safety of the high-speed trains,in which a Balise Transmission Module(BTM)play a role to perform communicating between the vehicles and the ground equipment.During the train driving,the BTM receives the information from the balises which installed between the tracks.Every model of BTM equipment must have passed the EMC compliance tests before their enrollments,but in these tests the immunities to defend differential mode disturbances are not taking into consideration.However,transmission faults caused by received disturbances from the antenna cannot be avoided during the BTM operation.Therefore,it is necessary to design a test platform for BTM susceptibility,which can test and evaluate the susceptibility that faced to the radiated disturbance.The test bench should have the abilities to simulate the RF behavior of a real balise(a virtual balise),generate arbitrary disturbance waveforms,and mix the signal and disturbance at any ratio,to perform the minimum required Signal to Interference Ratio test and other functions.It also need to realize the communication and control towards the BTM device under test.Based on the diagram of the balise transmission system,the roles of the interfaces,the uplink communication process,and the modulations are analyzed,and the possible disturbances sources to these units or processes are discussed.A series of on-site measurement results of disturbances are shown for demonstration.The principle of the test platform is proposed base on the analysis of the BTM workflow and susceptibility test requirements.The hardware platform and software development environment are also determined.The first step of the test is also the main idea of the test platform that is to generate and mix the virtual balise's RF signal and the interference signal,which samples are generated by a computer program and then synthesis by a Direct Digital Waveform Synthesizer(DDWS).Secondly,the RF signal(and disturbance)are radiated by a magnetic loop antenna and received by the DUT's Cell Antenna Unit(CAU),and then are transmitted to the BTM for demodulating and decoding.Finally,the BTM upload its received results to the test platform via serial communication,and a closed test loop is constructed.The RF link parameters are also monitored simultaneously to help make a decision.In this design,the generation module of the useful signal and the useless signal is realized by same program and same hardware,the test platform also play a role as DUT's upper computer,which means to perform automatic tests is available.The main functions of the test platform includes RF-link calibration,receive sensitivity test,minimum required signal-to-interference ratio test under different interference conditions,and so on.In this thesis,a series of verifications were performed by tested a certain model of BTM equipment in the laboratory.During the tests,the damped oscillation noise,the single-frequency noise,the amplitude-modulated wave,and the field-acquired disturbance were applied separately,and the test results are discussed and analyzed.The link calibration proofs that the link loss increases as the distance between the loop antenna and the CAU antenna increases,and the loss curves under different distances shows nearly parallel patterns.The test results also show that different disturbances affect the balise's receive characteristics differently.The wide-band disturbance collected in the field has the most influence on the transmission of the balise system,followed by the damped oscillation and the amplitude modulation wave disturbance.Although the single-frequency noise has the least influence,the BTM is sensitive to it if the frequency is in the receiver's work band.The DUT still needs a positive signal-to-interference ratio to operate normally.