How is the 4G signal full grid in the high-speed rail tunnel realized?
Release time:
2023-09-25
How is the 4G signal full grid in the high-speed rail tunnel realized?
When the train enters the tunnel, there will be no signal, no phone calls, let alone the Internet. This seems to be common sense, and people seem to be used to it. However, in recent years, with the development of China's high-speed rail, it can be seen that on some high-speed rail lines, such as the Shanghai-Kunming high-speed rail and the Yunnan-Guangxi railway, even in the tunnel, the mobile phone signal is full. You can not only make phone calls, brush Weibo, watch Moments, but also video chat and watch live broadcasts. What the hell is going on here? How did the cell phone signal in the tunnel get full?
1.Where's the signal coming from?
As we all know, to have a signal, there must be a base station and an antenna. However, it is not allowed to install antennas in the tunnel of the high-speed railway, because the speed of the high-speed railway is too fast and there will be a lot of wind when the train passes by. According to the test train, the speed of 350 km/h is equivalent to level 12 wind, and the antenna will be blown down, causing safety accidents. Since the antenna cannot be installed, how does the signal in the tunnel come from?
In the high-speed rail tunnel, signal transmission is realized by hanging a leaky cable on the tunnel wall. The leaky cable not only realizes the antenna function, but also realizes the signal propagation. In order to reduce signal loss, the laying height should be between 2.0-2.8 meters from the rail surface, which is exactly the height of the high-speed rail window. The loss of signal passing through the glass is much smaller than that of passing through the iron sheet. The general construction plan is to lay two leaky cables on the tunnel wall, one at 2.1 meters and the other at 2.6 meters. The two leaky cables are jointly covered by MOMI technology, which can improve the coverage effect, increase the capacity and, more importantly, improve the data download rate.
Two leaky cables and three operator system allocations are shown in the figure below:
Where is the 2. source equipment?
We can make phone calls, surf the Internet and watch movies by receiving signals from leaky cables on the tunnel wall through our mobile phones. However, where does the signal on the tunnel wall come from? That is, where is the base station?
When building high-speed rail, a cavern will be built every 500 meters. On the one hand, it is used to place railway equipment, such as transformers, communication repeater equipment, etc., on the other hand, it is also convenient for railway workers to avoid trains. The source equipment of the operator is installed in the cavity of the railway. It can be simply understood that in the railway tunnel, the operator also has a base station every 500 meters, so as to ensure that the mobile phone signal in the tunnel is also full.
At present, the new high-speed railways in the country will basically consider the coverage of the public communication network. For example, all railways in Yunnan Province that operate mobile units have achieved the coverage of 2G,3G, and 4G signals from three operators. It facilitates the travel of passengers and improves the quality of railway operations.
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