This is a case study in Europe.
Now the high-speed trains are getting faster and faster, and there are more and more tunnels passing through, but the mobile phone does not have the unstable signal as before. The 4G and 5G signals are still full. Why? ? IT Home has learned that China Railway has conducted popular science on this today, let’s take a look.
Once, why the cell phone signal was intermittent when taking a train
In the past, poor signal on trains was a common occurrence. When trains were traveling in mountainous areas, it would be difficult for them to make phone calls, let alone surfing the web. Why? The reason is more complicated than you think!
01. The train runs too fast, affecting signal transmission
When the train is running at high speed , the signal transmitted between the mobile phone and the signal tower outside the car is relative motion , and the transmitted signal is electromagnetic waves. The electromagnetic wave emitted by the mobile phone moving at high speed in the car and the electromagnetic wave received by the mobile phone do not have the same wavelength, which may exceed the range recognized by the signal tower outside the car and cannot receive the signal. This phenomenon is the “Doppler effect.”
02. Fully enclosed car body structure blocks signals
In order to ensure high-speed driving safety, the high-speed rail car body adopts a fully enclosed structure. Part of the high-speed rail car window glass uses metal coating technology to reduce heat loss. But these coatings will also hinder the entry of electromagnetic signals, and the enclosed metal car body will quickly attenuate mobile phone signals .
03. The signal coverage area keeps switching
When the train is running at a high speed, the mobile phone will quickly switch between different signal coverage areas, so that rapid switching can easily lead to signal loss. According to the person’s movement speed, the time for handover is sufficient. However, on high-speed rail trains, according to the estimation of the switching algorithm time, a switching occurs in 3 to 6 seconds. Such a frequency is a test of system coverage and performance.
Simply put, the mobile phone signal is unstable when taking a train, because the mobile phone is moving too fast and the signal can’t catch up. When the signal arrives, it has been misplaced.
Trivia:
Why is the mobile phone network called “Hive Mobile Network”? The coverage area of each signal tower is a hexagon, and the country’s mobile signal network consists of countless hexagons, just like a honeycomb.
Now, “leaky cable” technology allows signals to shuttle in culverts
In order to keep everyone from dropping on high-speed rail trains, the best distance between the base station and the rails is 100 to 500 meters for signal coverage along the high-speed rail, so that the signal can reach passengers’ mobile phones. The height of the antenna is also particular. It should not be too low or too high. Generally, the antenna is at least 15 meters above the track surface, and the antenna is facing the car window.
Different from ordinary cables, this type of cable periodically has slots of a certain shape on the outer conductor of the metal shield, so it is also called slotted cable, which is equivalent to a small antenna that continuously transmits wireless signals.
At present, many high-speed rail lines have taken the lead in achieving full coverage of mobile phone signals. For example, Zhanghu High-speed Railway, Xicheng High-speed Railway, Hainan Island High-speed Railway and other lines have achieved full 4G signal coverage.
Take the Zhang-Hu high-speed railway (Ulanchabu to the east section of Hohhot) as an example. This line is the first to achieve simultaneous coverage of mobile phone signals during construction. Public wireless network communication equipment is installed in each culvert, which is the communication of the three major operators. equipment.
The communication section of Hohhot is “tailored” according to the changes in the mountainous terrain. Communication optical cables are laid on both sides of the railway line, and communication towers are erected. Through the installation of optical cables and towers, the mobile phone signal is still full even in the 4560-meter Dongtu Village tunnel grid.
Leaky cables are generally laid on the hole wall 2.1 meters and 2.6 meters above the track surface, just aligned with the upper and lower edges of the speeding high-speed rail windows, and radiate the controlled electromagnetic wave energy evenly and effectively along the line before receiving it in.
In the future, look forward to full and seamless coverage of wireless network signals
It is the common goal of railway people to make the travel experience of passengers better. In the future, when passengers take trains, they will not only enjoy the speed of high-speed rail, but also better experience the seamless coverage of wireless networks.
At present, the railway department is speeding up the research and application of 5G technology, speeding up the 5G coverage project, and constantly creating a convenient, warm and comfortable passenger riding environment.
What kind of enjoyment can 5G bring to passengers? In the EMU with a speed of 350 kilometers per hour, 5G users can enjoy smooth communication services. Watching movies online, working in business, and reading news are more efficient and smooth, making the high-speed rail travel experience more beautiful.
In places such as station waiting rooms, passengers can take advantage of the high bandwidth and low latency of 5G to experience VR, AR, cloud games and even 8K video.
The optimization of mobile signals for high-speed trains is a very complicated task. It requires a lot of investment and many technical difficulties, which cannot be separated from the hard work of railway communication engineers.
It is expected that with the empowerment of 5G black technology, the mobile phone signals on the train will get better and better.
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