How we built the base station

The terms “base station” and “cell tower” have long and firmly entered our vocabulary. And if the average user remembers these things not so often, then the “cell phone” out of habit is clearly among the top ten. Hundreds of millions of people use cellular communications daily, but very few of them think about how this communication is provided. And of this minority, very few really represent the complexity and subtlety of this communication tool.

From the point of view of most people, the installation of a cellular base station is a very simple matter. It is enough to hang several antennas, connect them to the network - and you're done. But this idea is fundamentally wrong. And so we decided to talk about how many subtleties and nuances arise when installing a base station in a metropolis.

Caution traffic!

To clearly illustrate our story, we have documented in detail the process of installing a cell tower on the roof of a building in Moscow, at ul. Krasnodonskaya, d.19, building 2. This is a two-story detached administrative building. We chose this particular example because at this base station not only a small bracket for mounting the antennas was mounted, but a 5-section tower with a height of 15 m was installed. But let's start in order.

Preparation and design

The installation of the base station begins with the search for a suitable facility. When it is found, a lease is concluded with its owner. The necessary location of the antennas of the future station, the mass of the payload is determined, and based on this, the metal structures are designed. In this case, the bearing capacity of the structural elements of the building itself is taken into account.

For each installed base station, a set of documentation is drawn up (almost 5 cm thick). Among other things, many parameters of the future design are indicated here: its location at the facility, overall dimensions, total weight, location of pivot points, consumed voltage and power, and so on.



Comprehensive information is collected in this folder:

• Project documentation,
• Copies of statements, licenses, certificates and conclusions of conformity for all elements, including nuts and paints;
• Detailed documentation for equipment, metal structures, architectural and construction solutions, lightning protection.
• Sanitary and epidemiological report on the safety of the station for residents of surrounding houses.

Let's get back to our tower. After coordination and approval of the project, a platform and five tower segments were manufactured separately at the plant. Since in this case it was a rather heavy construction, it was necessary to install it on the supporting walls of the building. To do this, holes were cut in the roof and the installation of support beams was carried out. They play the role of a pile foundation for the platform, on which station equipment and a tower with antennas were subsequently mounted. The total weight of the platform was 3857 kg.



The profile, size and number of beams from which the platform is assembled, wall thickness, length of welds, hardware used - all these parameters are calculated based on the mass of the payload, the bearing capacity of the walls of the building, as well as possible wind loads in this region. Of course, these are far from the only criteria, first of all, the tower should provide the ability to install transmit-receive antennas at the required height in the visible range of neighboring base stations. In addition, the design must be rigid enough so that the relay beam is not lost.

Installation of metal structures

The building is small, it does not have a separate exit to the roof, so the team of installers have to climb the fire escape. Its lower part is cut off so that residents of surrounding houses do not climb onto the roof. Unfortunately, this does not stop them too much, so something often disappears from the roofs - spare parts, cables, feeders, etc.

Despite the fact that each station is equipped with an alarm system, the security service does not always have time to arrive on time.

The base station of another mobile operator has already been installed on the roof, but its dimensions cannot be compared to ours.



After the installation of the platform, the sites for the installation of the first section of the tower are prepared:











After the installation of the section, the “tightening of nuts” begins:





The installation of the tower on the studs is done in order to compensate for deviations from the vertical during installation and further operation.



The vertical structure is constantly monitored from two points using theodolites. Moreover, measurements are carried out separately for each section of the tower, and then the measurement log will be included in the set of documents. Subsequently, periodic measurements of the position of the tower are carried out, since under the own weight and weight of the equipment a small spiral-like twisting of the structure (up to 50 mm at 72 m in height) can occur.



A hardware cabinet prepared for installation on the platform:



So, the first section is installed and aligned. Installers are preparing to receive the second section:



The safety and comfort of work is paid a lot of attention not only during installation, but also during further maintenance. The size of the work sites is selected so that the engineers have enough space for work. Enclosed stairs, the openings in the platforms on the tower are closed with hatches to prevent accidental fall. The platform is raised above the roof plane so that in winter the equipment is not swept by snow and not blocked by ice.

Installation of the remaining sections of the tower:







The turn of the hardware cabinet: The







tower is mounted, the last measurements were made using theodolites. Deviations are minimal and strictly within tolerances. The weight of the tower was 2827 kg, and the total mass of all metal structures was 6684 kg.







The colors of the sections are standard: the lower and upper are always red, the intermediate alternate with white. At the top you can see 4 pins, which are a continuation of the tower edges - these are elements of lightning protection.

Equipment

The next step was the installation of all necessary equipment and cabling. Full list of installed equipment:



As a result, the station acquired a rather magnificent appearance, especially in comparison with the building itself:







The station is supplied with voltage of 380 V (3 phases), which is then converted to 48 V. The power is taken with a margin of up to 10 kW. Power is supplied in a separate cabinet.



Open the door of the hardware cabinet. It has a built-in air conditioning (top) and a heater (bottom).



Throughout the year, the cabinet maintains a temperature of 18 ... 20 degrees Celsius. This is necessary for the smooth operation of the equipment and the long service life of the batteries (they are located below).



Batteries are designed to ensure the operation of the station for about a day in case of disconnection of external power.

Above is the switching unit and voltage converter.





Information transfer between system modules and transceivers (about them below) is carried out through fiber optic cables. This is what the connector in the switching unit looks like. In no case should you touch it with your hands, the fiber is very sensitive to damage and pollution.



All base stations of cellular communication are connected to a single information fiber-optic network stretched across Moscow. The white bay under the hardware cabinet is just the cable through which this station is connected.



To the right of the cabinet are the GSM, CDMA, and LTE system modules:







These modules are the heart of the base station, they receive the signal from the antennas and carry out its conversion and compression with further transfer. They are not afraid of rainfall, all connectors are sealed, and the operating temperature range is from +60 to -50.

Under the system modules there are lightning arresters that prevent equipment from burning out in the event of a lightning strike:



To the right above the modules are bays of fiber optic cable, with which they are connected to the transmitters on the tower.



Let's move on to the tower. It has transceivers installed separately for each band (GSM, CDMA and LTE). They amplify the signal from extremely small values ​​to 115-120 dB. From the hardware cabinet, power is supplied to them:





Oblong vertical "boxes" - this is the antenna. They are shielded at the back to protect service personnel from electromagnetic radiation. We rise to the site.



GSM transceiver:





CDMA transceiver:





LTE transceiver:



Fiber optic cables are connected to the transceiver at the edges, power supply is connected in the center:



Grounding is sent to the tower:



Cable connectors and their plugs on the antenna:







Schematic diagram of the base station equipment switching scheme:



We already mentioned that the design and construction of a cellular base station is not at all as simple as it seems uninitiated. There are many nuances that are associated with the specific location of the station. For example, the transmission of a radio signal over a large water surface is deteriorating, although it should be the other way around, because there are no obstacles. But the fact is that an electromagnetic field spreads over the earth’s surface, and a large volume of water works as a kind of capacitor, over which interference with the radio signal is amplified. And there are many such subtleties, therefore the efficiency of the base station directly depends on the professionalism of the designers and installers. For example, from people like this foreman of installers, a highly skilled radio engineer, and just a wonderful person: