Base stations: how it all began

    The first fossil remains of base stations of the family of mobile telesystems in the Moscow region date back to 1994. These were real dinosaurs - huge and with a small volume of brain functional. Outwardly, they looked like a big refrigerator, they worked only in one standard and in one frequency range. The first MTS base station in Moscow operated in the GSM standard and only in the frequency range of 900 MHz.


    What did the “dinosaurs” of cellular communications consist of and how have they evolved to this day will tell the expert of the department of architecture of the radio access network of MTS Konstantin Luchkov. His nickname is Luchkov. We give him the floor.

    Hello! Let's look into this “refrigerator” right away.


    Power supplies, control boards and a transport card are mounted on the top shelf. A little lower, in the “freezer compartment”, transceivers and duplexers are stacked.
    And here is a typical small-sized (but very cozy) "kitchen" of those times in which our "dinosaur" lived.


    The "kitchen" was densely packed with telecommunication equipment. This and the power system, air conditioning, rack with transport equipment (for example, radio relay equipment). Each of these systems, commensurate in size with the BS, was a separate cabinet. By the way, each “kitchen” had a table and a chair (on the left in the photo).


    But back to our “dinosaur”. Thick feeders (two fingers thick) stretched from the top cover of the base station, which exited the container to the antennas. The typical length of the feeder path was about 70 meters; two feeders were connected to each antenna (a diversity reception was used). There were three antennas in a typical single-band station. That is, six feeder paths were laid at the first stations, and later (with the advent of the new GSM1800 range) six more.


    One of the main disadvantages of using feeder paths was the loss of signal power, which is directly proportional to the length of the feeder path and the used frequency range. These shortcomings pushed the evolution of base station equipment to a new round of development.

    Ten years after the appearance of the first cellular base station in the Moscow region, in 2004, critical changes took place in the telecommunication environment. A new interface for the interaction of the controller with the BS radio modules - CPRI (Common Public Radio Interface) has appeared.

    Chapter 2. The Present

    The old "refrigerators" were replaced by a new type of base station - with distributed architecture. They did not need bulky feeder tracks. The base station broke up into a system module (BS brain) the size of an office manager’s case and a transceiver (aka RRU - remote radio unit), interconnected via an optical line through the CPRI radio interface. From the feeder there were only rudiments in the form of short jumpers (1-3 meters) connecting the transceiver with the antenna. In addition to existing GSM, UMTS and LTE standards have been introduced. There were outdoor-performance base stations, for which accommodation was no longer required a room (“kitchen”).


    Distributed BS turned out to be much more adapted to life. They became smaller and easier to place. Electricity consumption has decreased, since power losses in the feeder have disappeared. There is a new functionality.

    Until a certain time, the work of each standard required its own equipment - separate transceivers (RRU), separate system modules (SM), separate antennas. After almost another ten years, in 2013, the Ministry of Communications of Russia allowed technological neutrality, which allowed to implement the LTE standard at frequencies GSM900 / 1800. It should also be noted that even earlier, in 2011, GSM / UMTS900 technical neutrality was allowed. The requirements for the equipment of the base station were new, which needed to be met - the size of the stations was reduced, and the brainfunctional grew.

    Transceivers have learned to support the work in three standards: GSM / UMTS / LTE. Now a typical case is the simultaneous operation of the transceiver in two standards, for example, in GSM / LTE1800. This mode of operation is called RF-sharing.

    Then there was a need for simultaneous work in different standards of system modules. This functionality is called single RAN (single radio subsystem equipment for several standards) and it has already been implemented on the MTS network.

    The emergence of new standards (such as LTE), as well as more sophisticated functionality has led to increased requirements for synchronization accuracy. The accuracy of the phase (it is also temporary) synchronization was required, which immediately affected the composition of the base station. A GPS / Glonass satellite synchronization module was added to its composition.

    A new subspecies of compact base stations has appeared - small cell. It is a compact base station no larger than a shoe box, combining a system module, a transceiver, a GPS / Glonass module and, as a rule, an antenna.


    The compactness of the small cell allowed MTS to install stations almost anywhere: in subway cars, cafes and office buildings. By the way, if desired, each MTS subscriber can buy a compact base station. The station will automatically connect to the core of the network when connected to the Internet.

    Chapter 3. The Future

    The bright future of cellular communications is the 5G standard (you can read more about it here ). Base stations will inevitably have to change again, since the 5G standard implies the use of higher MIMO orders, which makes it impossible to connect the transceiver to the antenna through a jumper. Too many jumpers will be needed: 16, 32, and maybe 64. The radio module will be integrated into the antenna. Such a solution is called an active antenna system (AAS).


    In appearance, AAS is indistinguishable from a conventional cellular antenna, but look at how many elements of the base station are inside it.


    The base station, implemented on the AAS solution, is now a system module (SM) connected to the “antenna” (to AAS). A hybrid option is also possible when the active antenna system includes several active ranges (several transceivers of active ranges) and at the same time supports the connection of several passive ranges. Moreover, for passive ranges, separate RRUs are used that are not part of the active antenna system.

    But this evolution of base station equipment, for sure, will not stop there. One of the possible scenarios in the future may be the transition to the cloud architecture of the base station equipment. Perhaps one day we will be able to completely abandon the use of the system module. At the base station, there will be only one unit left - an active antenna system with integrated system module functionality, which will be connected via an optical transport line to the core of the network.

    In conclusion, I want to proudly note that MTS is at the forefront in 5G testing and is already actively using on the network:

    • BS 5G-ready equipment;
    • BS cloud-ready equipment;
    • AAS equipment (a network of several cities in Russia is fully implemented on AAS).

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