| As an irreplaceable means of transportation for large and medium-sized cities in China,urban subway has been built at an extremely fast rate in recent years.The Communication Based Train Control(CBTC)system can rely on two mechanisms,including the Wireless Local Area Network(WLAN)that has been in service for many years and the LTE for Metro(LTE-M)communication technology under development.However,due to WLAN's technical limitations and the openness of the frequency band,the interference problem faced by the CBTC system is becoming more and more serious.After applying LTE-M,it will also face the same frequency and adjacent frequency interference brought by other systems.Therefore,in order to ensure the stable operation of the CBTC system,it is necessary to analyze the interference coexistence problem under the two technologies.This paper firstly tests the CBTC system based on WLAN technology,builds a hardware device environment to capture air interface data,analyzes the interference source and clarifies the interference mechanism to propose solutions.Next,the interference coexistence problem under LTE-M technology is analyzed.Combined with the spectrum division rules of the 1.8 GHz band by 3GPP,the new co-frequency and adjacent-frequency interference sources are clarified.Firstly,the deterministic calculation method is used to derive the laying limit of the same frequency interference source McWiLL,and the simulation is carried out to verify that the theoretical safety isolation meets requirement of the throughput loss.Then propose a guard band boundary field strength model suitable for LTE-M to weaken the co-frequency interference,analyze the field strength limit of the interference source at the specified common boundary,the influence on the signal transmission of the vehicle equipment on the subway line,and propose critical conditions for the interference.Finally,the adjacent interference of LTE FDD mobile terminal uplink and GSM base station downlink are analyzed.Deterministic calculations are carried out in different urban environments to obtain theoretical reference values for network planning and construction.Ensure the safe operation of the subway by setting parameters such as frequency band and safety isolation.Based on the urgent need of the development of urban subway in China,this paper conducts on-the-spot test of interference sources for CBTC system based on WLAN technology.And analyzes the interference of the co-frequency and adjacent-frequency interference problems that may be faced after the application of LTE-M technology in actual construction.Coexistence scenarios and anti-interference schemes are proposed to provide theoretical basis for related research. |
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