GSM and UMTS standard base station maintenance report

Dear Khabravchians, in view of my work for the benefit of the three-letter federal mobile operator, I constantly encounter 2G / 3G radio subsystem equipment and the surrounding infrastructure. Accordingly, during the work of the “Bazovik” there was a desire to share with the public information on how the base station of the radio access network is actually arranged. I won’t give a diagram of the structure of mobile communication networks, because there is enough information on the Internet via GSM and UMTS, but I will demonstrate to you a voluminous photo report of the technical maintenance of the object.





So, the GSM or UMTS radio access network consists of the Nth number of base stations. Base stations (BS) are controlled by a BSC / RNC controlleror several controllers. User traffic and signaling information from the BS and controllers is delivered to the Core Network, which consists of a switch, transcoders , media gateways, access nodes to the packet-switched network , etc.

Thus, the base station and their controllers belong to the radio subsystem, which I directly deal with . The BS placement point is referred to as the site / platform / hardware. Periodically, at certain sites, maintenance work is performed on the BS, power supply system, transport network equipment, fire alarm, automatic fire extinguishing system, antenna mast structures and feeder path.

The power supply system consists of an input shield.





Power supplythree-phase with the possibility of a backup connection from the generator.


Socket for connecting a cable from a mobile generator.

The switchboard contains an electricity meter, additional sockets, surge arresters and machines of various sizes for electricity consumers: air conditioners, working and emergency lighting lamps, uninterruptible power supply (UPS), fire alarm, heater, exhaust ventilation.

The most important elements of the radio access network are powered by a -48 V DC network, although domestic equipment has been designed at -60 V since Soviet times. In the event of a power outage by energy supplying organizations for various reasons, there is a backup of battery power (battery).



At this facility, 3 Coslight 6-gfm-150x batteries are installed, each with a capacity of 150 Ah. By the way, the numbering of the batteries in the photo is made correctly from the positive terminal to the negative. During battery maintenance, a control discharge is performed using a block of load resistors . Based on the results of the discharge, it is concluded whether the battery requires replacement or not.

By the way, about the quality of products from China. When checking the tightening torque of the battery jumper bolts, the following happened.









The conversion of alternating current to direct current and battery content is controlled by an uninterruptible power supply.



In this UPS7-48 / 218-7 (2.0), 4 pulse stabilization units are installed.



On the UPS indicator, we observe a constant voltage with a nominal value of 54.1 V, a load current of 32 A, a charge current of a battery of 0 A and a temperature on a rack with a battery of +18 degrees Celsius (a temperature sensor is necessary for temperature compensation of the battery content).



Behind the UPS cover there are a number of machines, from which wires are drawn to base stations, radio relay stations (RRS), batteries and other direct current consumers. There, on the left, a scarf with contacts for the output of an external alarm signaling a power outage and a battery discharge is visible.

In a specific case, the site was a base station of GSM 900 standard manufactured by Alcatel.





Behind the cabinet door is the main equipment: 10 TRAGE transmitters, 3 AGC9E combiners and one SUMA control board. The BS configuration is described as 4/3/3, which means: 4 transmitters operate on the first sector, 3 on the second and third. Each transmitter is connected to a combiner of the assigned sector. From the combiner go 2 feeders (jumper) to lightning protection and then up to the antenna of the selected sector.



On the upper part of the cabinet there are 2 plinths for external accidents from left to right , a connection plate for the transport network via the A-bis interface (E1 streams), power contacts (blue and black wires) and switches, each on a separate cabinet shelf.



At the top of the BS cabinet there are 6 jumpers (specifically for a three-sector configuration), which are connected through lightning protection to an external feeder path (feeder diameter 7/8 inches).




Lightning protection The



cable entry is hermetically sealed against moisture.



A 19 "rack is installed in the corner. It houses a cross, indoor PPC units and a UMTS base station. The



indoor unit (IDU) of the PPC is connected to the external unit (ODU) by a black 8D-FB feeder. Cables are connected to 2 IDU connectors, each of which outputs 8 E1 streams per cross. The patch cord of port 1 is connected to the transport port of the UMTS base station.



The MDP-34MB-25C relay is capable of transmitting 34 Mbps of traffic, indeed, is not enough.



Below is located the Ericsson RBS 6601 BS of the UMTS standard (3G).



External transmitters are connected by an optical cable to the indoor unit.




Excess optics are neatly wrapped, packaged and mounted on the wall.


View of the hardware from the entrance.


Opposite side.


Kabelrost with the main grounding bus (GZSh).


Empty cable duct, exhaust hood, air conditioning, bottom left shield with automatic devices for external transmitters (RRU) UMTS base.


Supply ventilation box.


Actually skirtings of cross.


Heater and fire extinguishers.

Let's see what is outside the hardware BS. An iron-concrete pole is installed as an antenna-mast support, a separate story can be added about the posts, because they are not designed for real load. In the near future they will be replaced by all-metal supports.



View of the cable entry from the outside. 6 feeders from GSM to antennas, in the corrugation 3 optical cables, 3 black power cables of 3G transmitters, from which thin black grounding cables go to the red bus, a yellow-green wire - grounding of the external PPC unit.

Next, a photo of the external cabling.








Anti-ice protection.


Staircase with safety guard.

At the top of the column is a metal basket with a superstructure, which is closed by a lightning rod.




Pipe-resistant and installed on it sector antenna BS GSM standard.


Sector marking is made for ease of orientation in case of modernization or elimination of accidents.



Antenna connectors with fixed jumpers. Jumpers with a length of 1.5 to 3 meters and a diameter of 1/2 inch.


GSM sector antenna label.


A pair of jumpers from feeders to antenna.


Marking feeders with tags.


Feeder Grounding.


Grounding points of feeders for metal construction.


Pipe-resistant with an antenna and an external PPC unit.


The PPC antenna was tagged.


RRL span, the nodal tower is visible in the distance.


Label on the PPC outdoor unit.



In the upper photo, the leftmost connector is used to connect a voltmeter during alignment (adjustment) of the span, the voltage on this connector is proportional to the level of the received signal from the response relay. The next connector is for connecting the ODU and IDU (outdoor unit & indoor unit) PPC with a coaxial IF cable (intermediate frequency). The connector is sealed against moisture in the cable. The far right point to ground the unit.


Labeling of PPC cables.



Actually fasteners antenna PPC. Two long screws / studs are used for fine adjustment of the RRL span.


Top view of the site.


RRU - remote radio unit of the UMTS standard.



What is connected to the RRU? On the left, a thin optical cable enters from the corrugation into a transmitter inside which a conventional SFP is installedmodule. The next is the power cable (also -48 V, direct current), To the right is a thin cable for connecting to RET (Remote Electrical Tilt) - a device that controls the electrical angle of the sector antenna. Next 2 jumpers to the antenna and a yellow-green ground cable.

It should be explained why antennas with cross-polarization are used in both GSM and UMTS. In fact, there are 2 antennas with different polarization in the case (usually angles of +45 degrees and -45 degrees), so 2 feeders from transmitters are connected. Thus, polarization diversity of the signal received from the subscriber is realized.


Label on the UMTS antenna.


RET at the back.


RET from the front of the antenna.


Top view of the control room (30 m).


Competitors' BS with a climate cabinet in which everything necessary for work is installed.


After finishing work, we close the hatch to the platform from the “vandals”.


We close the fence of the site ...


... we load into the pepelats and go to rest.

I hope this small photo report shows you how the usual base station for mobile communications is built and how, approximately, everything is implemented in hardware. I apologize for the quality of the photo, the shooting was carried out in working order. The post was written for an invite to Habr with the hope of new interesting publications.

PS As an suggestion: “There is no disclosure of corporate information in the post!”
PPS Thank @FakeFactFelis for the invite.

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