A heart-breaking question for holiday travel: Why is the signal on the high-speed rail so poor?

High-speed rail is an important symbol of the modernization of transportation and an important manifestation of a country's industrialization level. In recent years, my country has gradually accelerated the expansion of the high-speed rail network. Today, our country has the most developed high-speed rail network in the world, providing a safe, comfortable and convenient means of transportation for the general public. However, many passengers feel that their mobile phone signals are not very good when riding on high-speed rail, and Internet access is prone to lag. This is also a problem that everyone has to face when traveling by high-speed rail. So why is the network status not good? Let's take a look at the reasons.

High-speed trains have to pass through sparsely populated areas with complex terrain during their journey. Compared with densely populated areas, such areas have poor network coverage. In recent years, the number of base stations in my country has steadily increased, and the probability of network coverage in remote areas has continued to increase, but passengers on high-speed trains still feel that the signal is poor, and the signal is also poor on high-speed trains passing through non-remote areas. In fact, there are three main reasons for this phenomenon:

1. Mobile phones frequently switch between adjacent base stations

The high-speed train travels at a very high speed and can quickly leave the coverage of a base station. At this time, the system will automatically switch base stations. Therefore, you will frequently switch between different base stations while riding the high-speed train, and it is estimated that a switch will occur every 3 to 6 seconds. Such a high frequency is very challenging for the coverage and performance of the base station. If the time to complete the signal switching is insufficient, the mobile phone will not be able to connect to the next signal immediately after losing the original signal, resulting in signal interruption.

2. Doppler effect occurs when mobile phones and base stations are connected

Mobile phone signals are within a certain spectrum. When the high-speed train is running at high speed, the relative motion between the mobile phone and the signal tower will cause the electromagnetic waves emitted by the mobile phone to be inconsistent with the wavelength and frequency just received, thus exceeding the range that the signal tower can identify, so the signal tower cannot receive data. The faster the speed, the more obvious the Doppler effect will be, which will cause frequency changes, especially on high-speed trains with speeds exceeding 200km/h, which will cause more serious signal frequency shifts, ultimately causing weak signals, slow network speeds, and call interruptions.

3. Shielding effect of train body materials on electromagnetic waves

High-speed trains use a fully enclosed body structure, and the train carriages are all made of metal. Enclosed metal objects will attenuate the electromagnetic waves of mobile phones and naturally absorb some signals. And because the high-speed trains are extremely fast, the special glass selected to withstand the ultra-high wind pressure when meeting other trains will also aggravate signal attenuation. In addition, there is a layer of metal coating on the carriage glass to help keep the temperature inside the carriage stable and reduce energy loss, but this also isolates the electromagnetic waves that transmit signals, so there will be a phenomenon that the signal outside the high-speed train station is very good, but the signal becomes worse after entering the high-speed train.

At present, relevant departments are actively promoting the construction of 5G signal coverage quality and capacity along the high-speed rail and in indoor and outdoor areas such as platforms and station halls. For example, on the Guangshan High-speed Railway, which was put into operation on September 26, mobile network coverage has achieved full coverage. In order to ensure the mobile network coverage of the Guangshan High-speed Railway, Guangdong Mobile innovatively uses comprehensive technical solutions such as high-speed rail super cell merging, channel adaptive estimation and correction, and high-gain characteristic antenna extension to carry out joint construction. At the same time, it studies the use of high-speed rail dedicated network networking structure to greatly reduce the signal instability and unsmooth Internet access and calls caused by frequent network switching during high-speed train travel.

Through the integration of "wireless network + high-speed rail", not only can tourists from all over the world experience high-quality voice calls and mobile network services, but it will also accelerate the development of ethnic minority areas and inject new vitality into regional cultural tourism.