Now that technology is so advanced, why is the cell phone signal sometimes interrupted when the train enters the tunnel?

Now the technology is so developed, sometimes the mobile phone signal will be interrupted when the train enters the tunnel, because the equipment in the tunnel fails, which makes it impossible to run. The signal coverage and tunnel coverage of high-speed railway are mainly covered by leaky cable, and the biggest reason for using leaky cable coverage is the incident angle of high-speed railway. The biggest difficulty of high-speed rail signal coverage lies in the closure of high-speed rail cars.

The high-speed rail we are riding now is made of metal, usually aluminum alloy and stainless steel. Glass is also a special kind of glass, which has good sealing performance. The signal of our mobile phone is transmitted by radio waves. However, compared with ordinary carriages, high-speed railways have to face the problem of large penetration loss of wireless signals. The high penetration loss in the carriage will directly affect the received signal strength of the mobile phone in the carriage, which is a challenge that high-speed rail coverage needs to face.

Obviously, the incident angle is small, which can cover the deeper part of the tunnel, but the penetration loss of the car is great, and the cell phone signal in the car will be poor. However, if the incident angle is large, the wireless signal will be blocked by the mountain outside the tunnel and cannot cover the carriage. Therefore, for high-speed railway coverage, tunnels need to use a special power distribution system, and this system uses expensive leaky cables. In fact, regarding the signal coverage along the high-speed rail, the three major operators have always regarded it as a "political mission", especially willing to spend money, and there are many special optimizations for high-speed rail every year. Give the highest attention to this field. The leaked cable needs a source end, and usually the RRU of the source end is also hung on the wall of the tunnel.

In a word, now we pass through some tunnels, and the cell phone has no signal. This is usually because the equipment covering the tunnel has no time to deal with this problem. If you go through the tunnel and look carefully, you will see the cable leaking in the tunnel. Generally speaking, the hanging height of the leaked cable is roughly the same as the height of the carriage. It is said that the three major operators are reluctant to spend money on high-speed rail signal coverage, but all three operators have some dissatisfaction.