We can often see that "the construction of a foundation station stopped due to the local residents' disturbance", "the signal of the dismantled mobile phone became weak because the base station was near the residential area", and so on. Whether the radiation of the base station has an impact on the human body, and the base station will be dismantled as soon as the construction of the base station is noisy, and so on, the news comes up from time to time. Today, I will give you some information about mobile phone base stations.
electromagnetic radiation
In fact, as long as it is electromagnetic, it will produce radiation, mainly divided into ionization and non ionization. The former refers to high-energy radiation, which can destroy biological tissues and cause damage to organisms, such as X-ray and nuclear radiation. The latter is just a general thermal effect. The household appliance induction cooker commonly used in life uses this principle for heating, which will not damage the molecular bonds of organisms. The radiation generated by the base station belongs to this category, and will not be harmful to human health.
Base station construction
Based on the results of scientific experiments, many international organizations and countries have formulated corresponding standards to specify the human safety limits of electromagnetic radiation. The international standards for electromagnetic radiation can be divided into two camps: North America and Europe, one is the "ICNIRP standard" and the other is the "IEEE standard". China has also formulated relevant standards for this and issued the Electromagnetic Environment Control Limits (GB8702-2014). According to the regulations, the power density in the communication frequency band shall be less than 40 μ W/cm2. Compared with the 900 μ W/cm2 regulated by Europe (1800 MHz), the 1000 μ W/cm2 regulated by the US FCC (1800 MHz) is 20 times and 25 times higher than the former and the latter respectively. If Western physics is a little far away, let's take Hong Kong as an example. The electromagnetic radiation standard (1800MHz) stipulated by the Hong Kong Telecommunications (Telecommunications) Authority is 900 microwatts/square centimeter, and there is still a gap of 20 times, which shows how strict the mainland of China is.
Electromagnetic radiation standards formulated by various countries in the 1800HMz frequency band
How to explain this fixed value? Take the electric hair dryer for example, its power is generally above 1000 watts. Since it is close to the user when in use, its actual radiation can reach 100 microwatts/square centimeter. Some insiders said that, considering that the signals of base stations will overlap each other, the construction of mobile communication base stations now implements the standard of one-fifth of the national standard, that is, less than 8 microwatts/square centimeter. The selected site is particular, and the simple principle can be summarized as follows: comply with the cell plan, the station height is appropriate, the surrounding of the machine room is safe and controllable, the temperature, humidity and power supply of the machine room, and try to reuse the existing site to save costs.
4G band of three major operators in China
Grading Standards for Allowable Radiation Intensity of Environmental Electromagnetic Waves
Now, with the development of 4G network construction, more than 600000 4G base stations will be built this year. The 4G bands of the three major operators in China are all concentrated in the 1750-2655MHz band, with wavelengths between 0.17m-0.12m, belonging to microwave. For microwave electromagnetic radiation, the national standard stipulates that the allowable radiation intensity standard of environmental electromagnetic waves is divided into two levels with the power density of micro watt/square centimeter as the unit as far as possible:
Level I standard: safety zone refers to an area where all people (including infants, pregnant women, the elderly, the infirm and the disabled) who live, work and live for a long time under the electromagnetic wave intensity of the environment will not be affected by any harmful effects.
Level II standard: intermediate zone refers to the area where all people (including infants, pregnant women, the elderly, the infirm and the disabled) who live, work and live for a long time under the electromagnetic wave intensity of the environment may cause potential adverse reactions. In this area, factories and institutions can be built, but residential houses, schools, hospitals and sanatoriums are not allowed.
"Big trees" near the west wall of Beijing Yuanmingyuan
According to the regulations and site selection principles, combined with the relevant factors on the site of the base station, the operator will order the construction. Sometimes it is also built in the shape of a big tree. There is a base station near the west wall of Beijing Yuanmingyuan near the Yanbei Garden of Beida that is disguised as a big tree, and it is much higher than the surrounding trees. If you have the chance to pass by, you can pay attention to the children's shoes.
Base station disguised as external unit of air conditioner
You must have seen such mini base stations
"Community street light" lights up at night
Lawn ornament
Of course, there are also various mini NodeBs in the city that are decorated with various decorations, which cannot be detected without careful observation.
Base station signal coverage
The poor communication of mobile phones can be associated with poor signal coverage or the influence of some shielded signal equipment. It was reported that the residents of a community removed the base station for fear of radiation, and the signals of mobile phones and other communication equipment were affected. The operator had to select a site for reconstruction, but the signals still failed to return to the level before the removal. In fact, the factors affecting them are very complex, which can be simply classified into the following three points:
1. The processing capacity of base stations in cities is limited
In a city, the base station is built in a "small and many" way. The image is represented by images, just like the shape of a cell. The iPhone has the option of "cellular mobile network" in its settings.
The advantage of cellular data network is that it can meet the demand of high-density access. If there is only one big iron tree in the city, it cannot solve the problem of frequency reuse and signal strength attenuation.
2. The coverage of small base stations is limited
The signal coverage radius of a small base station is about 1km, so the signal penetration will be poor if the scale is small. Therefore, a mini base station will be built in some office buildings and subway stations to enhance the signal. At present, most newly installed vertical elevators will be equipped with repeaters to ensure that mobile phone signals will not be disconnected. However, if older elevators are not installed, the signals will not be covered.
3. There is a physical signal blind zone between BTSs
In addition to the reason that the mobile phone signal is not covered and the signal penetration is weak, when the mobile phone is in the node position of a base station, the selection of edge signals of different frequency bands by the mobile phone will cause a decline in the network quality, which is also inevitable.
