Base stations - microcells - on poles. What it is?

Many readers of Habr began to pay attention to the new equipment on masts of lighting. In general, many new boxes appeared on the poles, and you are probably wondering what it is.

That we are hanging new microcells. Here is an installation example:
In the photo, from bottom to top:
  • Power converter (on the right on the pole).
  • The UMTS base station itself in a protective box.
  • Outdoor base station antenna.
  • Radio relay unit for communication with the operator’s platform (BS outgoing channel).


The architecture is standard: the base itself, the transport block, the power supply. Sometimes an antenna is displayed on the top of the column to improve coverage (as in the photo), but more often the antenna is simply built into the base itself.

Other type of equipment


Here is another pillar. This is not our equipment, but it was already discussed on Habré (http://habrahabr.ru/qa/27971/), and identified as "Device for recording street traffic by vehicles", installed by the traffic police of Moscow. Such blocks began to appear in parallel with ours, so they are often confused.



This railway is not related to cellular networks, so I will return to our base stations.

What is inside the microcell?


The base itself when opening the box will look like this:
Here, from right to left, the following blocks are present:
  • A digital unit that processes traffic and sends it to the operator’s website (long white boards).
  • A power supply unit that stabilizes and converts external power into the necessary -48DC (gray block at the bottom of the base).
  • The radio block of the necessary range, for Russia - 2100 MHz.
  • A radio filter for receiving and transmitting a signal from an antenna.


At the same time, these blocks are similar to those used in standard base stations , they are simply placed in a compact case, and are designed for low performance.

For important areas where traffic loss is unacceptable, batteries can be installed in the unit with the power converter, ensuring uninterrupted operation of the base station in the absence of external power, for several tens of minutes or hours. However, in the general case, such batteries are not used, and when the power is cut off, the base station will simply turn off. Since the purpose of such stations is to increase the capacity of the network, it is usually not at peak times, this means that a macro cell nearby will “pick up” the signal - subscribers will continue to talk, and those who used 3G Internet will feel some speed degradation.

How is this BS different from ordinary ones?


Small size, and, as a result, less power and capacity. Typical power of such base stations is 5-10W (37 ... 40 dBm), and for standard base stations - 20W. The number of sectors in a micro base station is usually one, and a maximum of two carrier frequencies in a given sector. The standard macrobase supports 3 sectors and up to 3-6 carriers (depending on the standard) in each sector.

It is possible to achieve small dimensions by sacrificing the most important parameter for any equipment providing wireless communication - the radius of coverage that such a base creates. If a standard base station can under ideal conditions provide a coverage radius of 30 - 35 km, and if additional software options are used, up to 120 km, then the coverage radius of a micro-cell does not exceed 1 kilometer, and then provided that a good antenna is used.

What are they needed for?


This type of equipment is intended, first of all, to increase the capacity of the mobile network in places of local congestion of subscribers, as well as to improve the quality of communication in those places where to do this using conventional databases will be too expensive and not very effective. Therefore, they appear on poles along the roads, providing communication buildings near the road and motorists bored in traffic jams.

Also a common use case for such base stations is shopping malls or productions where the signal from the street is shielded by thick walls, and the number of people and the need for communication are very high. My colleague from Kazan will tell you more about this a bit later, indoor coverage is a separate big topic.

How did the technology evolve?


The need for such small-sized databases was understandable from the very beginning of the development of cellular networks, so these solutions evolved along with the development of the entire industry. The first options for GSM networks were still large and heavy:
Here, in one case, radio transmitters and control units are necessarily combined. The dimensions of each such base are approximately 1.3x0.3x0.5 meters, weight 40-50 kg.

In the future, the engineers thought concentrated on dividing the functionality of the base station, the processor unit is allocated in one case, and the unit responsible for the formation of the radio signal in another, which is just carried out to the antennas. The result was the so-called distributed base stations. These solutions cannot be called micro base stations, but often the equipment that comes across the poles is not a base station, but only a radio module. Here, for example, are RRUs and antennas that are simply placed away from the main units of the base station and connected to them by optical fiber:



In the future, the development of this direction will lead to the integration of the transmitter into the antenna, and the emergence of the so-called active antenna systems. Many equipment manufacturers are talking about them now, and in the very near future, they may appear in the networks of operators:
However, micro base stations are still solutions in which all units are integrated in one building, and their development continues towards further miniaturization. They can be like this:
New devices - only 10 liters in volume, weight - about 10 kilograms. Micro base stations of these new types are now being actively tested, and this year they will appear on the streets of Russian cities.

Practice use


The first generation microcells are widely used in our network, but most often indoors, and not on poles, since the bases are still too big and heavy.

In the photo with a column at the beginning of the topic - RBS3308 of the UMTS standard, it is used in Moscow and in some other large cities quite often.
Variants of distributed base stations using street transmitters connected to a digital unit with an optical cable have become more widespread. There are a lot of such base stations launched in Moscow and Russia.

A related question - for example, new stations are mounted taking into account the “green” BTS Power Saving technology - and these are distributed BSs, where the radio unit is cooled not by the air conditioning in the room or container, but by the surrounding air near the antenna. They are used almost everywhere in Russia except for some southern regions - it is still very hot outside there.

In the future, the number of such base stations will grow steadily, all suppliers will release new generations of micro base stations, with smaller dimensions, weight and power consumption. Already now, VimpelCom network is conducting pilot projects to launch new types of micro base stations, based on which decisions will be made on the large-scale use of new types of bases in a commercial network. In general, they have proven themselves very well, but we have not yet passed the full testing cycle.

Need a foil hat?


The radiation safety from the base station antenna was analyzed in detail in the topic here . In short, we have an output power of the base station of 5-10 watts. The radiation pattern is horizontal. At a distance of about a meter vertically, it is already completely safe in accordance with the stringent (in comparison with western) SanPiN standards. But I would not advise to climb a pole and cuddle with a sector.

Communication when driving in a car


Since the range of microcells is small (maximum up to a kilometer, typically 200-500 meters), for cars moving at high speed, service continuity can be achieved only with careful planning and configuration of all environmental parameters. Seamless interconnect for voice (voice handover) is obtained almost always.

There is another interesting point. For speeds over 120 km / h, depending on the communication standard, negative effects are possible associated with the transit time of signal messages in the operator’s network. There is nothing to do with the Doppler effect, but just know that at a speed of 180 kilometers per hour, you can’t watch streaming video on a 3G network simply because of the physics of the process.

Oh, and what a strange piece of iron on my post in front of the house?


If you suddenly find an incomprehensible piece of iron on a post that cannot be immediately identified, but presumably telecommunication, please attach it in the comments anytime after publication. I am very interested in this topic, so we will try to understand what it is together with colleagues and habrachitechiteli.