•  Cellular communication standards: GSM. GSM operators in Russia

    We all use mobile phones, but rarely does anyone think about how they work? In this article we will try to understand how communication actually works with your mobile operator.

    When you make a call to your interlocutor, or someone calls you, your phone is connected via a radio channel to one of the antennas of the neighboring base station (BS, BS, Base Station).Each base station cellular communications(in common parlance - cell towers) includes from one to twelve transceivers antennas, having directions in different directions in order to provide high-quality communications to subscribers within their range. Experts in their jargon call such antennas "sectors", which are gray rectangular structures that you can see almost every day on the roofs of buildings or special masts.


    The signal from such an antenna is transmitted via cable directly to the control unit of the base station. The base station is a collection of sectors and a control unit. In this case, a certain part of a settlement or territory is served by several base stations, connected to a special block - local zone controller(abbreviated LAC, Local Area Controller or simply "controller"). As a rule, one controller unites up to 15 base stations in a certain area.

    For their part, the controllers (there may also be several of them) are connected to the main block - Mobile services Switching Center (MSC), which, to simplify perception, is usually called simply "switch". The switch, in turn, provides input and output to any communication lines - both cellular and wired.

    If you display what is written in the form of a diagram, you get the following:
    Small-scale GSM networks (usually regional) can use only one switch. Large ones, such as our operators " big three» MTS, Beeline or MegaFon, which simultaneously serve millions of subscribers, use several MSC devices interconnected.

    Let's figure out why we need so much complex system and why can’t you connect the base station antennas to the switch directly? To do this, you need to talk about another term called technical language handover. It characterizes the handover of services in mobile networks on a relay basis. In other words, when you are moving along the street on foot or in a vehicle and talking on the phone, so that your conversation is not interrupted, you should promptly switch your device from one BS sector to another, from the coverage area of ​​one base station or controller local zone to another, etc. Consequently, if the base station sectors were connected directly to the switch, it would have to carry out this procedure of handover of all its subscribers itself, and the switch already has enough tasks. Therefore, to reduce the likelihood of equipment failures associated with its overloads, the design of GSM cellular networks is implemented according to a multi-level principle.

    As a result, if you and your phone move from the service area of ​​one BS sector to the coverage area of ​​another, then this movement is carried out by the control unit of this base station, without touching more “high-ranking” devices - LAC and MSC. If handover occurs between different BSs, then the LAC takes over, etc.

    The switch is nothing more than the main “brain” of GSM networks, so its operation should be considered in more detail. Switch cellular network takes on approximately the same tasks as PBX in networks wire operators. It is he who understands where you are calling or who is calling you, regulates the operation of additional services and, in fact, decides whether you can currently make your call or not.

    Now let's figure out what happens when you turn on your phone or smartphone?

    So you clicked " magic button" and your phone turned on. Your mobile operator's SIM card contains special number, which is called IMSI - International Subscriber Identification Number. It is a unique number for each SIM card not only for your operator MTS, Beeline, MegaFon, etc., but a unique number for all mobile networks in the world! This is how operators differentiate subscribers from each other.

    The moment you turn on your phone, your device sends this code IMSI to the base station, which transmits it further to the LAC, which, in turn, sends it to the switch. At the same time, two additional devices connected directly to the switch come into play - HLR (Home Location Register) And VLR (Visitor Location Register). Translated into Russian this is, accordingly, Home subscriber register And Guest subscriber register. HLR stores the IMSI of all subscribers on its network. The VLR contains information about those subscribers who currently use the network of this operator.

    The IMSI number is transmitted to the HLR using an encryption system (another device is responsible for this process AuC - Authentication Center). At the same time, HLR checks whether a subscriber with a given number exists in its database, and if the fact of its existence is confirmed, the system looks at whether he can currently use communication services or, say, has a financial block. If everything is normal, then this subscriber is sent to VLR and after that gets the opportunity to make calls and use other communication services.

    For clarity, we display this procedure using the diagram:

    Thus, we have briefly described the principle of operation of GSM cellular networks. In fact, this description is quite superficial, because... If we delve into the technical details in more detail, the material would turn out to be many times more voluminous and much less understandable for most readers.

    In the second part, we will continue our acquaintance with the operation of GSM networks and consider how and for what the operator debits funds from our account.

    WCDMA and GSM - communication standards mobile network. Today in Russia the most popular is GSM, in the environment in which most Russian operators. And very rarely, users may hear about WCDMA, for example, when they accidentally noticed the tariffs of WCDMA operators or wanted to buy a phone that only supports this standard communications. For now, GSM is not going to move to Russian market, but some advantages of the WCDMA network make users wonder whether WCMDA or GSM is better. What is the difference between these communication standards and which one is better to choose? Let's try to figure it out.

    What is WCDMA and GSM in a phone?

    It is impossible to explain the difference without talking about the very essence of these standards. Therefore, before we figure out what the difference is, we will consider the WCDMA or GSM standards in more detail.

    Let's start with GSM. This abbreviation stands for Global System for Mobile Communications. And this is the first global digital cellular standard, which is somewhat of a model.

    It was developed by ETSI (Europe) in the 90s, and was based on the principles of TDMA channel division, security, encryption and data transmission. GMS allows you to transmit:

    1. Speech.
    2. Text messages.
    3. Fax.
    4. Data packages (GPRS).

    Also, thanks to this standard, for the first time it became possible to determine the number mobile phone, from which the call is received, forwarding to another number. We must not forget about the possibility of creating a conference call, in which several cell phones can be combined simultaneously, and holding a call in waiting mode. At one time, GSM created a revolution in the field of cellular communications.

    What is WCMDA?

    When talking about WCDMA or GSM and what is the difference between them, it is always appropriate to mention that WCMDA is to some extent an add-on that improves the GSM standard. Or rather, this is how everything was originally intended, but today WCDMA is a third-generation communication standard, which is based on seven international projects. But GSM remained the second generation communication standard (read 2G).

    WCDMA is based on DS-CDMA technology, which, compared to TDMA, is more resistant to interference and has a higher throughput. Phones that operate in the WCMDA environment can perform the same functions as in the GSM standard (voice or digital information), however the quality and speed will be much higher. Therefore, operators supporting WCMDA provide Internet access services for more high speed.

    WCDMA or GSM - what's the difference?

    The most important and key difference is in the technologies used (TDMA and DS-CDMA), that is, in the methods of channel separation. In GSM, the channel separation is temporary, and because of this, the subscriber is allocated a small frequency band for a certain period of time.

    In WCMDA, everything is different: it uses code division of streams, thanks to which information is transmitted between devices over a wide frequency band. As a result, the data transfer speed increases greatly. Hence the name Wideband Code Division Multiple Access.

    This is the main difference between the GSM and WCDMA LTE standards. What is the difference for the user? He will have higher Internet speeds and much less interference when talking. Despite all these advantages, the most popular cellular communication standard is still GSM. But we note that every year there are more WCDMA subscribers, and many telecom operators are gradually switching to this standard in order to provide higher data transfer speeds. Today, uninhabited areas and villages are not covered by the WCMDA network, so residents of such areas do not yet have an alternative to GSM.

    Which one to choose?

    It all becomes obvious now that you know the difference. Both WCDMA and GSM modems will provide Internet access, but at different speeds. Living in a big city, it is more logical to give preference to the WCDMA communication standard due to the higher data transfer speed. At the same time, it is worth understanding that when traveling, the phone will not catch the network in many regions of the country, since WCMDA coverage is scarce today.

    You need to choose between these standards depending on your needs. Generally speaking, GSM is a “cheap and cheerful” type of communication. It will be guaranteed everywhere, even in remote regions. As a bonus, you can highlight the ability to surf the Internet. In the event that fast internet is always at hand and long trips are not planned, then you can safely give preference to the WCMDA standard. However, you should first check whether your phone and mobile operator support it.

    As of November 2007 There were about 168 million mobile subscribers in Russia. Moreover, 85% of them are clients of the Big Three GSM operators - Mobile Telesystems (MTS), Megafon and VimpelCom. Despite the fact that the annual growth rate is constantly decreasing, the penetration level cellular services in Russia as a whole it is 107%, while in the Moscow License Zone (MLZ) this figure was 164%.

    Megafon holds the leadership in the growth of the subscriber base on a nationwide scale, and in MLZ it is inferior in this indicator to MTS. Among federal and regional operators, the highest annual subscriber growth rates are demonstrated by Tele2, NTK, Baikalwestcom and Yeniseitelecom.

    Regional GSM operators that are not part of the Big Three are looking for a way to compete with the market giants. Most independent GSM operators in Russia have appeared in the last few years based on operators of the outdated AMPS standard. All of them in 2001-2002. received licenses from the Ministry of Communications giving them the right to work in GSM standard-1800.
    Now these companies are launching GSM networks one after another, but their subscribers, finding themselves in other regions, are forced to pay $1-$1.5 per minute for roaming communications. Now these companies intend to agree on uniform roaming tariffs for each other, which will allow network subscribers, when moving around the country, to feel no worse than the clients of MTS, VimpelCom and MegaFon, for whom uniform and relatively low tariffs for intranet roaming are one of key advantages"Big Three" operators.

    Open Joint Stock Company Mobile TeleSystems (MTS) is the largest cellular operator in Russia and the CIS countries, serving more than 74 million subscribers. MTS's license portfolio includes most regions of Russia, Ukraine, Belarus, Uzbekistan and Turkmenistan, and the population living in the MTS network coverage area is more than 230 million people.
    The Mobile TeleSystems company was founded in October 1993. On November 19, 1993, MTS received the first license to provide GSM cellular communication services. On May 15, 1994, the first calls were made on the MTS network and already on July 7, 1994, MTS began connecting the first subscribers.
    In June 2002, MTS launched a network in the Republic of Belarus. In March 2003, MTS acquired a controlling stake in UMC, the leading mobile operator in Ukraine.

    OJSC "Megafon"- All-Russian mobile operator of the GSM 900/1800 standard. Formed in May 2002. The licensed territory of OJSC MegaFon covers 100% of the territory of Russia - all 89 constituent entities of the Russian Federation, where 145 million people live. MegaFon is the first all-Russian mobile operator of the GSM 900/1800 standard.

    OJSC "VimpelCom" is a cellular operator in Russia, providing its services under the Beeline brand. Licenses for the provision of cellular communication services of the VimpelCom group of companies cover the territory where 94% of the Russian population lives, including Moscow, the Moscow region and St. Petersburg. The Beeline network operates in 76 constituent entities of the Russian Federation.
    The VimpelCom company was organized on September 15, 1992. In June 1997, the first GSM-1800 network in Russia - "Beeline 1800" - was successfully launched. On October 21, 1998, the company successfully launched the first stage of dual-band GSM networks-900/1800.
    On March 24, 1999, VimpelCom JSC became a member of the GSM Operators Association, which unites companies operating in the GSM-900 and GSM-1800 standards in Russia and a number of CIS countries.

    CJSC "Srednevolzhskaya Interregional Association of Radio Telecommunication Systems" (SMARTS) was founded in May 1991 in Samara. The founders of the company are 95% individuals. Currently, the SMARTS GSM network covers 16 regions of Russia. To date, SMARTS has concluded roaming agreements with almost all Russian networks in 74 regions. The company's global roaming service operates in 78 countries.

    OJSC "Uralsvyazinform" is the largest operator of mobile communications and Internet services in the Ural region. The company operates on the territory of seven constituent entities of the Russian Federation with a total area of ​​1.9 million square meters. km with a population of more than 15 million people

    NSS Nizhny Novgorod Cellular Communications- at the end of June 1995, the company began working with subscribers. In 1999, the company established connections with the world through international roaming.

    OJSC "Sibirtelecom" is the largest operator of telecommunication services in the Siberian region federal district. The company operates on an area of ​​about 5 thousand square kilometers with a population of about 21 million people.

    TELE2, known as Comviq until 1993, was founded in Sweden in 1981. In Russia, TELE2 is the owner of 12 Russian mobile operator companies. Russia's first mobile communication network, TELE2, was launched in Irkutsk on April 1, 2003.

    Did you know that

    (2 Generation) (1G - analog cellular communication, 2G - digital cellular communication, 3G - broadband digital cellular communication switched by multi-purpose computer networks, including the Internet).

    Depending on the number of bands, phones are divided into classes and frequency variations depending on the region of use.

    • Single-band - the phone can operate in one frequency band. Not currently available, but it is possible to manually select a specific frequency range in some phone models, such as the Motorola C115, or using engineering menu phone.
    • Dual Band - for Europe, Asia, Africa, Australia 900/1800 and 850/1900 for America and Canada.
    • Tri-band - for Europe, Asia, Africa, Australia 900/1800/1900 and 850/1800/1900 for America and Canada.
    • Quad Band - supports all bands 850/900/1800/1900.

    Commercial GSM networks began operating in European countries in the middle of the year. GSM developed later than analogue cellular communications and was in many ways better designed. Its North American counterpart, PCS, has grown from its roots to include standards including TDMA and CDMA digital technologies, but for CDMA the potential improvement in quality of service has never been proven.

    GSM Phase 1

    1982 (Groupe Spécial Mobile) - 1990 Global System for Mobile Communications. The first commercial network in January Digital standard, supports data transfer rates up to 9.6 kbps. Completely outdated, production of equipment for it has been discontinued.

    In 1991, GSM “PHASE 1” services were introduced.

    Base station subsystem

    Antennas of three base stations on a mast

    The BSS consists of the base stations themselves (BTS - Base Transceiver Station) and base station controllers (BSC - Base Station Controller). The area covered by the GSM network is divided into hexagonal-shaped cells. The diameter of each hexagonal cell can be different - from 400 m to 50 km. The maximum theoretical radius of a cell is 120 km, which is due to limited opportunity synchronization systems to compensate for signal delay time. Each cell is covered by one BTS, and the cells partially overlap each other, thereby maintaining the possibility of handover to the MS when moving it from one cell to another without breaking the connection ( The operation of handing over a mobile phone (MS) from one base station (BTS) to another when the mobile phone passes the range of the current base station during a conversation, or GPRS session, is called the technical term “Handover”). Naturally, the signal from each station actually spreads, covering an area in the form of a circle, but when crossing, regular hexagons are obtained. Each base has six neighboring ones due to the fact that the planning tasks for station placement included minimizing signal overlap areas from each station. Larger number neighboring stations than 6 - does not bring any special benefits. Considering the boundaries of signal coverage from each station already in the overlap zone, we just get hexagons.

    The base station (BTS) provides signal reception/transmission between the MS and the base station controller. BTS is autonomous and built on a modular basis. Directional base station antennas can be located on towers, rooftops, etc.

    The Base Station Controller (BSC) controls the connections between the BTS and the switching subsystem. His powers also include managing the order of connections, data transfer rates, distribution of radio channels, collecting statistics, monitoring various radio measurements, assigning and managing the Handover procedure.

    Switching subsystem

    NSS consists of the following components.

    Switching Center (MSC - Mobile Switching Center)

    The MSC controls a specific geographic area with BTS and BSC located there. Establishes a connection to and from a subscriber within the GSM network, provides an interface between GSM and the PSTN, other radio networks, and data networks. Also performs the functions of call routing, call management, handover when moving an MS from one cell to another. After the call is completed, MSC processes the data on it and transfers it to the settlement center to generate an invoice for the services provided and collects statistical data. The MSC also constantly monitors the position of the MS using data from the HLR and VLR, which is necessary to quickly locate and establish a connection with the MS in the event of a call.

    Home Location Registry (HLR)

    Contains a database of subscribers assigned to it. It contains information about the services provided to this subscriber, information about the status of each subscriber, necessary in the event of a call, as well as International Identifier Mobile Subscriber(IMSI - International Mobile Subscriber Identity), which is used for subscriber authentication (using AUC). Each subscriber is assigned to one HLR. All MSCs and VLRs in a given GSM network have access to HLR data, and in the case of inter-network roaming, also MSCs of other networks.

    Visitor Location Registry (VLR)

    VLR provides monitoring of the movement of MS from one zone to another and contains a database of moving subscribers located in at the moment in this zone, including subscribers of other GSM systems- so-called roamers. Subscriber data is deleted from the VLR if the subscriber has moved to another zone. This scheme allows you to reduce the number of requests to HLR of this subscriber and therefore the call service time.

    Equipment Identification Registry (EIR)

    Contains the database necessary to establish MS authenticity by IMEI (International Mobile Equipment Identity). Generates three lists: white (approved for use), gray (some problems with MS identification) and black (MS prohibited for use). Russian operators (and most operators in the CIS countries) use only white lists, which does not allow them to solve the problem of mobile phone theft once and for all.

    Authentication Center (AUC)

    Here the subscriber is authenticated, or more precisely, the SIM (Subscriber Identity Module). Access to the network is permitted only after the SIM has passed the authentication procedure, during which a random number RAND, after which the AUC and MS simultaneously encrypt the RAND number with the Ki key for a given SIM using a special algorithm. Then, “signed responses” - SRES (Signed Response), which are the result of given encryption. At the MSC, responses are compared, and if they match, authentication is considered successful.

    OMC (Operations and Maintenance Center) subsystem

    Connected to other network components and provides quality control and management of the entire network. Handles alarms that require personnel intervention. Provides network status checks and the ability to make calls. Performs an update software on all network elements and a number of other functions.

    See also

    • List of GPS tracker models
    • GSM terminal

    Notes

    Links

    • GSMA (The GSM Association)
    • 3GPP - Current level of GSM standardization, free standards (English)
    • 3GPP Specification Numbering Scheme
    • (English)
    • WHO booklet “Building a dialogue about the risks from electromagnetic fields” (pdf 2.68Mb)
    • “WHO Proposals for a Project to Study the Influence of Electromagnetic Fields; Influence of Radio Fields of Mobile Telecommunications on Health; Recommendations to State Authorities"

    GSM technology

    GSM belongs to the second generation networks (2 Generation), although as of 2010 it is conditionally in the 2.75G phase thanks to numerous extensions (1G - analog cellular communication, 2G - digital cellular communication, 3G - broadband digital cellular communication switched by multi-purpose computer networks, including the Internet). Cell phones are available for 4 frequency ranges: 850 MHz, 900 MHz, 1800 MHz, 1900 MHz. Depending on the number of bands, phones are divided into classes and frequency variations depending on the region of use:

    Single-band - the phone can operate on one of the frequencies. Currently not produced, but it is possible to manually select a specific frequency in some phone models, for example MotorolaC115, or using the phone’s engineering menu;

    dual-band (DualBand) _ for Europe, Asia, Africa, Australia 900/1800 and 850/1900 for America and Canada;

    tri-band (TriBand) _ for Europe, Asia, Africa, Australia 900/1800/1900 and 850/1800/1900 for America and Canada;

    quad-band (QuadBand) _ supports all bands 850/900/1800/1900.

    The GSM standard uses GMSK modulation with a normalized bandwidth VT _ 0.3, where B is the filter bandwidth at a level of minus 3 dB, T is the duration of one bit of a digital message.

    Today, GSM is the most common communication standard. According to the GSM Association (GSMA), this standard accounts for 82% of the global mobile communications market, 29% of the population globe uses global technologies GSM. The GSMA currently includes operators in more than 210 countries and territories. Initially, GSM stood for "Groupe Special Mobile", after the name of the analysis group that created the standard. It is now known as the "Global System for Mobile Communications" ( Global System For Mobile Communications), although the word “Communication” is not included in the abbreviation. The development of GSM began in 1982 by a group of 26 European national telephone companies. The European Conference of Postal and Telecommunications Administrations (CEPT) sought to build a common cellular system 900 MHz band.

    GSM's achievements were "one of the most compelling demonstrations of what European industry cooperation can achieve in a global marketplace." In 1989, the European Telecommunications Standards Institute (ETSI) took responsibility for further development GSM. The first recommendations were published in 1990. The specification was published in 1991. Commercial GSM networks began operating in European countries in mid-1991. GSM developed later than conventional cellular communications and was in many ways better designed. Its North American counterpart, PCS, has grown from its roots into standards including TDMA and CDMA digital technologies, but for CDMA the actual increased service capability has never been proven.

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