| Communication Based Train Control system(CBTC) has been the most advanced in technology and most widely used system in Global urban rail transit signal control system recently.CBTC system mainly used the Wireless local area network(WLAN) based on IEEE802.11 standard for communication, which working frequency band is generally open2.4GHz frequency band and the universal phenomenon is that the system is common to other systems outside, so that it’s likely to be subject to interference by other signals which may affect the normal running of the train, therefore, analyzing the interference of WLAN in CBTC system and researching the corresponding anti-interference measures have vital significance for promoting the development of reliability and safety of CBTC system.This paper firstly introduced the overall structure of CBTC system, which elaborated functions and features of each component. It analyzed their respective advantages and disadvantages by contrast with three kinds of conventional signal coverage, on this basis,this article put forward the research on the internal structure of data communication system(DCS) that the subsystem was applied to the ESS network topology, to be responsible for real-time two-way communication between the car and the ground. Then the paper further analyzed the WLAN wireless channel partitioning mechanism for CBTC system and elaborated the causes of interference.Secondly the paper analyzed propagation characteristics of radio waves in space and had a derivation of the spatial propagation model and the path loss formula for the CBTC system,which was based on typical signal path loss model and combined with the actual situation of CBTC,laid the theoretical foundation for the establishment of the simulation model. Then the paper classified the WLAN interference, and the same frequency interference and adjacent frequency interference are analyzed specially. We calculated the influence factors of inter channel interference and the influence to noise ratio of different working channel on signal so that the mode was more close to the actual situation In the following simulation. At the same time, this paper briefly introduced the characteristics of LTE network interference and WPAN interference, and analyzed its impact on the CBTC system.At length the paper used OPNET software to build simulation platform to analyzed the possible interference in the actual scene, which mainly divided into ground disturbance and interference in the car, and several statistical results were analyzed and compared in order to get the influence degree of the interference and the effect after the optimization measures were taken. Through the detailed analysis of the data, we can reach a conclusion that it is easier to be affected by the outside world when the train is switched on and the degree is greater; the impact of interference in the car is also far greater than the presence of interference on the ground, and vehicle ground communication will be interrupted whenserious, which will endangering traffic safety. On this basis, the paper put forward a variety of practical solution to optimize the CBTC system from the perspective of network type,coverage, interference type, communication protocol, etc. |
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