Beijing Metro said that at present, there are no WiFi signals for public use in the platforms and carriages of all subway lines in the city. Passengers use their computer 3G network card or mobile phone to access the Internet, and generally do not interfere with the train signal. The signal system has the function of blocking interference from other signals and has strict protection measures. "
background
Shenzhen Metro's shielding 3G cited controversy
Subway signal
Should use a dedicated frequency
Recently, the Shenzhen Metro temporarily shut down the 3G signals of the Central Ring Line and the Shekou Line, which triggered a controversy about whether the 3G signals will affect the safety of the subway. Industry experts said that because of fear of signal interference, it is unreasonable to shield 3G signals. The key is that subway communications and signals should use dedicated frequencies.
The Shenzhen Metro Central Line and Shekou Line have recently suffered from WiFi interference, and the signal system has been disrupted during train travels many times. On the 16th, the Shenzhen Metro temporarily shut down the 3G data service signal of the Shekou Line and the Huanzhong Line for 24 hours, which caused a widespread controversy.
Will 3G signals affect subway safety? In this regard, independent telecommunications analyst Xiang Ligang said that at present in China's subway construction, most of the subway signals use the CBTC (mobile block system) wireless access point access method, and each subway train will be regularly controlled when it is running. The center sends a train position report, and the control center transmits the position information of the train to other trains in real time. The subsequent running trains can control the speed and separation distance of themselves, thereby improving the system capacity.
"For operational safety, subway communications and signals should use dedicated frequencies, avoiding civil communications and public communications frequencies, but Shenzhen Metro uses the 2.4GHz public frequency band. Then, when passengers treat 3G devices as wireless hotspots to share WiFi signals At that time, if the number of users is large, the transmission power of the WiFi device is large, it may indeed cause interference to the subway communication signal. "Xiang Ligang told reporters that compared to mobile phones, WiFi radiation to the human body, although it lasts longer, but has a long distance and a small frequency , So the radiation effect is also very small. "So, the fundamental solution to the problem is that subway communications and signals should use dedicated frequencies, avoiding civilian communications and public communications frequencies."
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