In recent years, domestic high-speed rail has been rapidly constructed and developed, and construction efforts have become increasingly intensive. From Harmony to Fuxing , the mileage and number of passengers of high-speed rail have continued to grow, and the speed of high-speed rail has become faster and faster. But at the same time, everyone's experience of using mobile phones on high-speed trains has always been poor. Not only is it difficult to browse web videos, but sometimes even phone calls cannot be made, which greatly affects people's communication efficiency today.
As we all know, the mobile phone signals we use are emitted by the base station and then received by our mobile phones for us to access the Internet and make calls.
Then why is the signal in the high-speed rail relatively poor? Let’s step by step analyze the main factors that affect mobile phone signals when driving on high-speed trains.
. The carriage is well sealed, but the body loss is large.
Everyone has ridden in the high-speed train. The interior of the car is well sealed, and the outer skin of the car is also made of metal, so the shielding effect on external wireless signals is relatively large.
We generally describe the signal shielding effect of different models of vehicles as wear and tear . The figure below lists the cabin materials and wear and tear of different car models. dB is a unit of measurement. Simply put, 20dB roughly means that due to the shielding of the cabin, the signal strength inside the car is attenuated 100 times compared to outside the car.
. The extremely fast speed causes too frequent switching and the Doppler effect of and is obvious.
First of all, the coverage range of the base station may only be 1-2 kilometers, and a train with a speed of 350km/h will pass by in a few seconds. This causes the user's mobile phone to frequently switch between different base stations, which directly affects the Use experience.
Because after the mobile phone arrives at a certain base station, it needs to register at this base station and a series of processes. Because the high-speed train is too fast, the interaction between the mobile phone and the current base station has not been completed, and it is forced to flow to the next base station. This will inevitably affect the transmission of information.
In addition, fast speed will also cause serious Doppler frequency deviation. You must know that each signal has its own frequency. The so-called Doppler frequency shift effect is . When the speed reaches a certain level, the frequency of the signal will undergo an obvious Doppler frequency shift , and it will not be the original frequency. , , which will cause the demodulation performance of the receiver to deteriorate, thus affecting signal transmission and reception.
. The concurrency rate of user communication services is high, causing the base station to be instantly overbusy.
The high-speed rail is very comfortable and safe, and the high-speed rail has multiple carriages connected. It can connect up to 16 carriages, and the 16 carriages can carry about 1,800 passengers. In other words, the high-speed train is very fast. When it passes under a certain base station, the number of users under the base station will suddenly increase, and the load of the base station will increase suddenly, resulting in poor network perception for users. Just like it was a one-way lane, a lot of vehicles came from both front and back, and everyone was stuck on the road.
Of course, there are some other reasons, such as tunnels, hillside terrain obstruction, signal interference, base station failure, etc. All in all, the interior of a moving high-speed train is a relatively complex wireless environment. How to ensure users' network perception under the conditions of high speed, high traffic volume, and high concurrency rate has become a difficult problem. This brings great challenges to the construction and optimization of high-speed rail networks. Brings new levels of difficulty and a series of challenges. #Only experts know#
