Recently, we provided high-speed mobile Internet and mobile communications to the upper sections of the Elbrus ski slopes. Now the signal there reaches a height of 5100 meters. And it was not the easiest installation of equipment - the installation took place within two months in difficult mountain climatic conditions. Let's tell how it was.
Builders adaptation
It was important to adapt the builders to high mountain conditions. Check-in installers took place two days before the start of work. Two overnight stays in one of the climbers' houses did not reveal any tendency to mountain sickness (nausea, dizziness, shortness of breath). On the second day, the installers began light work to prepare the site. Technological breaks were arranged twice, lasting 3-5 days each, when the builders descended onto the plain. Re-adaptation was easier and faster (a day was enough). Of course, sudden changes in the weather dictated their conditions. For example, self-heating heaters had to be purchased in addition to ensure normal working conditions for the installers.
Site selection
At the stage of selecting a site for the construction of a base station, first of all, it was necessary to take into account the specific meteorological conditions of the highlands. First of all, the site must be ventilated. This should not create windward and leeward snow drifts that prevent access to the site. To fulfill these conditions, it is important to identify the direction of the prevailing wind, from which the air flow most often comes to the area + its strength.
Long-term meteorological observations have given these average values of the wind rose (%). The dominant direction is highlighted in red.
As a result, it was possible to pick up a small ledge, which can be reached without much difficulty in the most snowy period. Its height is 3888 meters above sea level.
Installation of BS equipment
The lifting of materials and equipment was carried out on snowcats, since wheeled vehicles were useless due to the onset of snowfalls. During daylight hours, the snowcat managed to rise no more than twice.
Smaller equipment was delivered by cable car. Work began at sunrise. It is possible to predict the weather on the slope of Elbrus, but with a small degree of probability. In the clearest weather, a cloud may appear over the peaks (as they say, Elbrus put on a hat). Then it can either melt, or in an hour turn into fog, snow, wind. When the weather worsens, it is important to cover the tool and materials in time so as not to dig out later.
When designing, the "site" was raised above the ground by almost three meters, pouring soil. This was done so that the site would not be covered with snow and there would be no need for its regular rolling with snowcats.
The second task was to securely fix the structure of the "site", since the wind speed at the altitude of the base station reaches 140-160 km/h. Taking into account the high center of mass, the height of the structure and its windage, it was decided not to be limited to concreting pipe racks into the pit. Moreover, during the development of soil for the installation of supports, very hard rocks came across, so it was only possible to go deep by a meter (under normal conditions, deepening occurs by more than two meters). I had to additionally mount gabion-type weights (a grid with stones - see the first photo).
The design parameters of the base station on Elbrus turned out to be the following: base width - 2,5 * 2,5 meters (we proceeded from the dimensions of the heating cabinet in which the equipment had to be installed). Height - 9 meters. They raised it so high that the station was ventilated and it was not covered with snow. For comparison, flat base stations do not rise to such a height.
The third task was to provide sufficient structural rigidity necessary for the stable operation of radio relay equipment in strong winds. To do this, the structure was reinforced with cable stretch marks.
It was no less difficult to ensure the thermal regime of the equipment. As a result, all station equipment that receives and transmits a radio signal was placed in a special protective box, which ensures uninterrupted operation of the station in any weather conditions. Such so-called Arctic containers are designed for the harsh conditions of the Arctic - increased wind loads and negative temperatures. They can withstand temperatures down to -60 degrees with high humidity.
Do not forget that during operation the equipment also heats up, so a lot of effort has been spent on ensuring normal thermal conditions. Here we had to take into account the following factors: a very low atmospheric pressure (520 - 550 mm Hg) significantly impairs the heat transfer of air. In addition, technological openings immediately freeze, and snow fills into the room through any gap, so it is impossible to use heat exchange systems of the “freecooling” type.
As a result, the area of wall insulation and the mode of operation of the heating cabinet were selected empirically.
I also had to resolve the issue with the ground loop and lightning protection. The problem is the same as that of colleagues in the northern regions on permafrost. Only here we had bare rocks. The resistance of the circuit fluctuates slightly depending on the weather, but is always 2-3 orders of magnitude higher than the allowable one. Therefore, along with the power supply, it was necessary to pull the fifth wire to the electrical substation of the cable car.
Base station specifications
Taking into account the wishes of the Ministry of Emergency Situations of the Russian Federation, in addition to the base station of the 3G range, the project provided for the construction of a 2G BS. As a result, we received high-quality UMTS 2100 MHz and GSM 900 MHz coverage of the entire southern slope of Elbrus, including the main climbing route up to the bend (5416 m) of the saddle.
As a result of the work, two base stations of a distributed type were mounted on the site, consisting of a base frequency processing unit (BBU) and a remote radio frequency unit (RRU). The CPRI interface is used between the RRUs and the BBUs to connect the two modules with optical cables.
GSM standard - 900 MHz - DBS3900 manufactured by Huawei (PRC).
WCDMA standard - 2100 MHz - RBS 6601 manufactured by Ericsson (Sweden).
Transmitter power is limited to 20 watts.
The base station is powered by cable car power networks - there is no alternative. When the power is turned off, the operational personnel turn off the 3G base station and only one 2G sector remains, looking towards Elbrus. This helps to always stay in touch, including rescuers. Backup power is enough for 4-5 hours. Ensuring access for personnel to repair equipment should not be a problem when the cable car is in operation. In case of emergencies and increased urgency, snowmobile lifting is provided.
Author: Sergey Elzhov, Technical Director of MTS in the KBR
Source: habr.com