Research on Co-frequency Interference of CBTC Signal Based on IEEE 802.11

Communication-based train control (CBTC) systems adopt the wireless local area networks (WLAN) technology based on IEEE 802.11 protocol. The popularity of WiFi and other devices makes the 2.4 GHz co-frequency interference problem CBTC faced worse. In this paper, the reasons causing the CBTC systems to break in an emergency are analyzed: The co-frequency interference is too strong for the receivers to work properly; multiple users cause the CBTC signal's failure to access the channel or descending in performance of the receiver. Furthermore, field data test was designed and carried out on the subway line. After troubleshooting by analyzing the relevant parameters such as the number of packets, throughput, signal strength, etc., we find the amount of users requesting to connect to the Access Point (AP) “EN” during rush hours is extremely high, which results in more heavy co-frequency interference and degradation in performance of the receiver. Regarding this serious situation, we propose improvement methods to guarantee the normal operation of CBTC systems.