Structure of the composition of a trunking connection. Trunking communication systems. iDEN provides the capabilities found in today's digital trunking radio systems, namely

). Here the "pioneers of the Russian lands" (SmarTrunk), and yesterday's leaders (MPT 1327), and LTR, and other protocols found their place. Finally, today the domestic consumer is looking at digital trunking, first of all - to the TETRA standard.

Trunk Zoo

Smartrunk

Traditionally, almost all Russian suppliers of trunking communication systems offer SmarTrunk and SmarTrunk II equipment manufactured by SmarTrunk Systems. Its main advantages are low cost, a wide range of subscriber devices, ease of converting conventional radio stations into trunking and "unpretentiousness" in frequencies (they can operate in the ranges 146-174, 403-470, 300-344 and 800 MHz, even cases of SmarTrunk use are known in the range of 33-48 MHz). It is these properties that have become the reason for the widespread use of such systems in Russia (this phenomenon is more precisely characterized by the word "boom"). Industrial enterprises were the first to be tempted to use SmarTrunk, and then there was no talk of compatibility, quality and reliability of communication, expansion possibilities: communication is needed now, and it is cheaper, because there is simply not enough money for "excess". The fact that the miser pays twice was remembered only three years after the start of the operation of such systems.

MPT 1327 systems

Systems based on the pan-European protocol MRI 1327 are also widely represented in our country. Here the most "mass" is the products of the OTE company (after the merger - Marconi Communications), which were exclusively supplied only for Gazprom and implemented practically along the entire technological chain of production and transportation of the product of this natural monopoly. The second place is still firmly held by the family Accessnet production Rohde & Schwarz... Experts appreciate such equipment for its "German quality".

The system "penetrated" into Russia a long time ago Flyed... English firm Flyed Microsystems, who gave it its name, was one of the "progenitors" (together with Motorola and Philips) of the MRI 1327 protocol. without reference to itself. Such controllers are used, say, in the MRT 1327 systems from Motorola and Maxon.

System Actionet firms Nokia until the mid-90s it was actually a monopoly on the Russian market. On its basis, deployed the first in Russia (1989) the MPT 1327 protocol network of the Surgutneftegaz company. First The certificate of the State Committee for Communications of the Russian Federation for the trunking system of the MRT 1327 protocol was received in February 1996 by Nokia, too (although in it Actionet was called a radiotelephone communication system). Finally, in terms of the number of MPT 1327 trunking systems deployed, Nokia ranks first place in the world.

Today, at least 20 Actionet radio networks are in operation in our country (most of which have replaced the Altai system, inheriting its radio frequency ranges - both 300 and 400 MHz). Until the recent fire at the Ostankino tower, they included the commercial Moscow radiotelephone network of the ACBT operator (according to the management of this company, this network will be restored).

A large market share is accounted for by systems Taitnet... They are produced by the company Tait Electronics(New Zealand), which, along with Flyde Microsystems, developed the first MRI systems, and later acquired a license from the latter to produce its trunking controllers.

Basic equipment must also be mentioned. TrunkSwitch(MPT 1327 protocol), which was created by an English company Stanilight and then acquired by the Australian company ADI. TrunkSwitch systems work with almost any subscriber equipment, and at least five of them are deployed across Russia (in Moscow, a commercial network built on the basis of TrunkSwitch is operated by Svyaz Trunk). However, since 1999 the release of this system has been discontinued.

Another rather "old" system of the MRT 1327 standard, which is known by the name of the controller used in it, is also popular in our market - Selectacom... It was developed by the company Ascom, subsequently bought by Bosch and finally resold to Motorola Corporation. This equipment is currently supplied by Vada Communications, as well as other strategic partners of Motorola.

Unfortunately, MRI 1327 remained protocol without acquiring the status standard, therefore, each of its implementation has its own characteristics. And, of course, network deployers try to use the same vendor's hardware to avoid incompatibility issues. At the same time, the difficulties associated with the organization of intersystem connections still remain. For example, at least 12 large MPT systems have been built in Russia, whose pseudo-interaction (communication at the subscriber level, provided by assigning several numbers to each radio station) is achievable with some effort, but actually interaction impossible.

SmartNet, EDACS, etc.

A significant share of the market is made up of systems using control protocols other than MRI. Among those in our country, perhaps, only the following are actually used: belonging to the SmartNet family of Motorola (see "Networks", 1998, No. 6, p. 27), EDACS from Ericsson (see "Networks", 1998, No. 7 -8, p. 62) and a system based on the LTR protocol, the author of the original specifications of which was EF Johnson (now Transcript International), a well-known company in the world of radio equipment.

Among the trunking networks, one cannot fail to mention the multi-zone radio system. SmartZone built on equipment Motorola... It is serviced by the Moscow company "MTK Trunk".

So far, the only operating system in Russia with digital radio access is EDACS(Enchanced Digital Access Convertional System) of the company Ericsson... Its equipment is designed to operate in three frequency ranges (150, 450 and 800 MHz), and for the last two it is certified in Russia. It is possible to operate EDACS in the modes of both simplex communication (transmission and reception are carried out alternately) and one-way. In our country, according to the author, there are five networks based on this system (St. Petersburg, Togliatti, Yekaterinburg, Orenburg and Krasnoyarsk).

Protocol-based radio communication equipment LTR“Historically” companies supply to Russia Kenwood and E.F. Johnson... About a dozen of such radio systems have been installed here, and several years ago their popularity (both in the world and in our country) was quite large. And they owe this to E.F. Johnson - the creator of LTR, which not only made this protocol open (unlike EDACS), but also made every effort to raise it to the rank of an industry standard, at least de facto. The manufactured equipment operates in the ranges of 400, 800 and 900 MHz.

And of course, one cannot fail to mention the system ESAS company Uniden, the control protocol of which is an extended modification of LTR. It is characterized by continuity and full compatibility with LTR. The radio equipment is designed to operate in the frequency ranges 806-825 and 851-870 MHz and is capable of providing duplex communication (transmission and reception of information are carried out simultaneously). The network created on the basis of such devices is operated by Region Trunk.

Of course, this is not a complete list of trunking systems that have found their application in our country, but, according to the author, the most common of them were named.

Frequencies

When choosing subscriber equipment, you need to know which frequency ranges are available to the Russian civilian consumer. Military structures and public security services have fairly large "own" portions of the spectrum and usually do not experience "frequency" difficulties when deploying their radio networks.

In our country, frequencies for analog systems are allocated on the basis of the decision of the State Communications Supervision Authority. To obtain the denominations listed in the decision of the SCRF dated 04/27/98 (protocol No. 6/3 "On the use of the radio frequency bands 300-308 and 336-344 MHz by radio means of land mobile and fixed services for civil use"), the effect of which applies to all legal and individuals, GKRCH is not required to “disturb”. We will quote this decision to remind readers for what purposes these radio frequency bands are allowed to be used:

“... the bands 300-308 and 336-344 MHz are used to create radial, radial-zone systems of land mobile and fixed services for civil use, including using trunking technology for access to radio channels, under the conditions that:

• radio frequency bands 300.0125-300.5125 and 336.0125-336.5125 MHz are used within the coordination zone only for organizing dispatch radio communication with ships and radio communication between ships on the country's inland waterways;
• radio frequency bands 307.0-307.4625 and 343.0-343.4625 MHz are used for the "Transport" train radio communication system on specific railway lines in accordance with the decision of the State Committee for Radio Frequencies of Russia dated July 5, 1993, protocol No. 13/2;
• the radio frequency bands 307.5-308.0 and 343.5-344.0 MHz are used throughout the country by radio means of the regional rural radiotelephone communication networks.

To provide communication services with the help of radio facilities operating at nominal values ​​or parts of the spectrum of any other ranges, in addition to the decision of the State Communications Supervision Service, a special decision of the State Committee for Radio Frequencies is required. Here the main document - "Table of allocation of frequency bands between radio services Russian Federation in the frequency range from 3 kHz to 400 GHz ", in which" all the good things have already been sorted out. " Therefore, when purchasing any equipment, you need to think not seven, but 777 times whether the frequency range for which it is designed is available.

Closer to the subject

Prices

If the equipment of the infrastructure of trunking networks is comparable in cost to that used in cellular communication, then the prices for subscriber devices of such systems simply cannot be compared. Like any non-mass radio equipment, custom trunking radios are far from cheap, especially by Russian standards. Nevertheless, the set of subscriber devices for trunking communication is quite wide and includes not only portable (wearable) radios, but also mobile (transportable) stations, data transmission terminals, as well as stationary radio stations, which are mainly used for organizing dispatch centers. ...

The cheapest (about $ 300) are portable simplex walkie-talkies with limited functions and no numeric keypad. They, as a rule, are used by closed groups of subscribers who have only one opportunity to communicate with the "outside world" - an emergency call to the dispatcher. Most often, this is enough for trunking users.

Simplex stations have numeric keypad for dialing and support at least a dozen functions provided by the trunking system. However, their price is much higher (from about $ 1,000), so they are available only to a few privileged users.

Even more expensive duplex devices(from 1700-2500 for analog and up to 2000-3000 dollars for digital systems), which in appearance are almost indistinguishable from mobile phones, but are still heavier than the latter - mainly due to the impressive weight of the battery (requirements for it in trunking is much higher). Due to the low power of duplex radio stations (1-1.2 W), their communication range is much shorter than that of simplex ones. Note that according to Russian regulations, connection to the PSTN is allowed only if full-duplex communication is provided.

Available in both duplex and simplex mobile devices... Moreover, their performance is quite diverse (sea, automobile, motorcycle, rail, etc.). Sometimes the set of such equipment includes a built-in satellite navigation GPS receiver, which allows determining the coordinates of the subscriber and transmitting them to the dispatcher. The output power of the transmitters of mobile devices is approximately 3-5 times higher than the power of portable equipment, which means that they provide a long communication range.

Stationary radios usually created on the basis of mobile, but differ from them in a large number of accessories and the presence of additional terminal devices. The output power of the transmitters of mobile and fixed radio stations, as a rule, is the same.

A relatively new class of devices for trunking communication are data terminals... In analog systems, these are special radio modems that support a specific radio interface, and in digital systems, ordinary subscriber stations are more often used, equipped with an asynchronous RS-232 data transmission interface. The cost of analog equipment is determined by the degree of "specialty" of the radio communication protocol, since such terminals are a piece of goods. Digital ones cost almost the same as digital trunking "tubes".

The lineup

Although there are not so many manufacturers of basic equipment for trunking communications, this does not impose any restrictions on the release of subscriber devices. Many companies specialize in the manufacture of only custom radio stations, and for a variety of communication systems - SmarTrunk, ESAS, LTR, MPT 1327, etc. (Table 2).

In the "oldest" trunking systems, such as Smartrunk, which are characterized by decentralized control, the subscriber radio station is "obliged" to continuously scan the working channels in the process of searching for a call signal or an idle BS line. The criteria for choosing such a terminal are the scanning speed (no more than 150 ms), the quality of reception / transmission and the cost of the device.

Company Smartrunk took care of expanding the market for its cheap systems and released a special logic module for radio stations of other companies (Alinco, Vertex, Kenwood, Marantz, Telemobile, Kyodo), which controls the main functions of the subscriber station operating in the SmarTrunk system (such as scanning, turning on the transmitter, etc. .). In our country, radio stations with this module, belonging to the HX and GX series (produced with the logo Standard; many of them have Russian industry certificates), as well as for the TK series of production Kenwood... Programming modules (using security code) is performed by either the supplier or the owner of the system.

The huge popularity (despite the high cost) of Motorola radios forced SmarTrunk to create a similar module for these devices. In Russia, for example, in recent years, the GP300, GP400, GP40 and GP50 radio stations have been in great demand, and to a large extent because they can be equipped with a module for working in SmarTrunk systems, of which there are many deployed here. Such organization of production of subscriber radio equipment allows ensuring their compatibility with each other within the SmarTrunk system.

As for duplex communication, in SmarTrunk it is possible only when using mobile devices such as TM-MDT25 (Telemobile), KG-106 (Kyodo), 9200 (Seiki) and some others. The same radio stations, equipped with a module that combines the functions of SmarTrunk control and a telephone interface, can be used as stationary devices for rural telephony. From portable (wearable) radios, for example, dual-band terminals manufactured by Alinco work in duplex mode, but in our country it is not allowed to use the 450 MHz band for reception, and 160 MHz for transmission.

Almost all subscriber devices for SmarTrunk and SmarTrunkII systems comply with the American military standard MIL STD 810 C / D / E, therefore it is quite legitimate to use them in communication systems used by the military, special services, as well as in cases where increased requirements are imposed on communication reliability ( rescue service, offshore oil production enterprises, etc.).

Systems using the controller Flyed, in Russia they are most often equipped with subscriber equipment of production Motorola(GP1200, GM1200, GP600, GM600). Less actively used handheld terminals H70 from Nokia and even less often - T2000 and T3000, produced by a New Zealand firm Tait Electronics... The latter are much more often bought together with infrastructure equipment for systems based on the MPT1327 protocol, which is manufactured by this company. It should be noted that T2000 radios can be supplied with built-in modems for organizing data transfer using the MAP27 protocol.

The choice of manufacturers of subscriber devices for MPT systems the Russian market is wide enough: this is Motorola, Nokia, and no less than a dozen others (perhaps the most famous equipment is Kenwood, Marantz and Maxon).

Subscriber equipment Nokia"Settled down" somewhat apart. The company's products are designed to work not only in Actionet, but also in other trunking networks based on the MPT 1327. At the same time, the use of the ANN numbering plan in Actionet (different from the one prescribed by the MPT 1343 specifications) and extended (compared to the one defined in MPT 1327) verification procedure electronic serial number radio stations so far allow Nokia to “protect” this system from the “presence” of someone else's subscriber equipment (although today ANN is supported by the GP1200, GM1200 and T2000 radio stations). Be that as it may, in the field of duplex radio stations Nokia is the undisputed leader. Her top-of-the-line models H70, H75 (handheld) and R72 are available in the 330 and 450 MHz bands.

List of subscriber devices manufactured Motorola, could take more than one page. The company manufactures portable, fixed and mobile radios for almost all existing trunking systems, excluding, perhaps, those corresponding to the LTR protocol and its versions. These are the already mentioned models of the GP (portable) and GM (mobile) series, as well as the MTS 2000 (for the StarSite system) and the Spectra mobile terminal (for the SmartNet family). In Russia, Motorola sells equipment not only through many distributors and partners, but also independently.

The most famous manufacturer of radio stations on the market for LTR systems - Transcript International... All models (both portable NPSPAC series and automotive Viking) are equipped with microprocessor control and digital frequency synthesizers (operating ranges 821-824 and 822-869 MHz). Mobile devices supplied in two modifications - mounted on the dashboard of the car and remote (installed, for example, in the trunk) with equipment remote control... Transcript also manufactures duplex devices (NPSPAC series, numbers 8605 to 8621, as well as Viking GT 8604 and Viking HT 8600). An additional feature provided by Transcript radios is a user-changeable transmitter output power (1 to 2.5 W).

Marantz also manufactures a whole family of trunking radios for LTR-based systems. In Russia, this equipment with the Standard logo can be purchased for operation in the 450-480 MHz bands (for example, HX482, HX4800) and 800 MHz (HX590 - 592, GX5910). Note that the transmitter power of the HX59x models is 2W, and the GX5910 mobile radio has 15W.

Functions

A typical portable analogue radio only supports group communication functions and therefore does not need a keypad or display. Individual communication requires at least function keys and a memory for storing numbers. Additional "convenience" that can be obtained using the LCD display, keyboard, voice control etc., are usually typical for models with a cost of $ 1,000 or more.

In addition to the inherent trunking capabilities of group and individual communication, as well as the functions of system-wide and emergency calls, almost all systems in one way or another organize connection to telephone networks - both office and PSTN. However, in our country, connection to the PSTN is allowed only when using duplex subscriber radio stations (and there are not so many of them in analog radio networks). In addition, the declared connection in fact turns out to be only providing communication with the PBX or dispatcher. But the most difficult thing in the implementation of this service is the pairing of the numbering plans of the trunking network and the PSTN.

As for the data transfer function, for its implementation it is best to focus on specialized data transfer terminals or radio stations equipped with an RS232 interface. The use of modems in analog radio networks is not a cheap pleasure.

And where is the number

In Europe, people are already beginning to forget about analog communication (largely thanks to the efforts of Dolphin). In our Fatherland, they just look closely at the figure.

In August, the St. Petersburg operator RadioTel, part of the Telecominvest holding, announced the start of the creation of a test zone for trunking digital communications in the TETRA standard. Its launch was scheduled for early September. In Russia, this is already the second experimental area of ​​digital trunking communication: the first was deployed in the St. Petersburg metro, where ELETTRA equipment (TETRA standard) of the transnational Marconi concern was used.

RadioTel intends to use Motorola equipment in the test area. One base station and 20 wearable and car radios... To demonstrate the possibility of TETRA-GSM international roaming, the issue of connecting a BS via a dedicated channel to one of the automatic telephone exchanges in Denmark or Germany is being considered. Testing in St. Petersburg will last for three months, after which Motorola will dismantle the equipment and hand it over to another Russian partner for testing, which has not yet been selected.

RadioTel is the operator of the only EDACS system in Russia with a digital radio access produced by Ericsson. Today its services, according to RadioTel, are used by approximately 1,600 subscribers, including “ Ambulance», Lenvodokanal and the Administration of St. Petersburg. The latter has built on the basis of this network the Unified Operational Trunking Communication System (ECOTR).

Let's hope that the "ice has broken", gentlemen readers, and digital trunking networks will appear in Russia after all. Perhaps, within six months, potential users of this type of communication will be interested in the nomenclature and characteristics of not analog simplex radios, but modern digital trunking "tubes".

The term "trunking" (trunk, bundle, communication channel, trunk) is understood as a method of automatic distribution of a limited number of free channels among a large number of mobile subscribers. This method makes it possible to efficiently use the frequency resource in mobile radio communication systems due to the random access mode to a free channel. So in the system of mobile radio communication "Altai" of domestic production, 8 radio channels of one trunk served about 200 mobile subscribers. This method is currently used in industrial networks (departmental networks) and modern radio networks. common use(cellular networks).

Mobile radio communication systems serving a large number of subscribers over a large area are usually built according to the principle reuse radio frequencies in the territorial zones (cells, sites) of service. Trunking networks usually serve one zone (site) because do not implement the principle of relay transfer of the subscriber from zone to zone, known in cellular networks as roaming. The main idea of ​​trunking, similar to the organization of trunk channels in wired communication systems, lies in the allocation of one, from a limited number of system channels, to each subscriber for the duration of the connection. This, in addition to increasing the efficiency of using the frequency resource of the system, leads to an increase in the confidentiality of the conversation and the quality of the services provided. In a trunking system, a radio channel is not assigned to a specific subscriber, but any free channel at the moment is allocated to him. Therefore, the number of simultaneously served subscribers in the trunking network is equal to the number of channels.

Obviously, dynamic channel allocation requires the inclusion of a channel allocation manager in the system, and each mobile station has technical capability switch to any dedicated channel frequency. If during busy hours (PNH) all channels are busy, then the network does not reject calls, but puts them in a queue for service. Even in the CNN, the channel allocated to a pair of users is not available to another station that requires a connection, which ensures the protection of the listening conversation. Dynamic selection channels also improves the reliability of the network and increases the confidentiality of the conversation. Failure of one of the channels does not interrupt the access of a group of subscribers to network resources, but somewhat reduces the capacity of the network. Increasing network capacity can provide limiting technical means time of connection to the channel (duration of the conversation).

In analog trunking systems, voice messages are transmitted using frequency modulation and multiple access with frequency division channels (FDMA) with a bandwidth of 25 or 12.5 kHz per channel. At digital processing speech signal in linear predictive codecs provides speech transmission at rates 2.4 ... .9.6 kHz in the same frequency band.

Data transmission (message about the state of resources, subscriber status, short telegrams, etc.) in analog systems are usually transmitted via a control channel, and long ones - via a working channel using a modem.

Among the methods of placing stations in the serviced area, two network configurations can be distinguished: single-zone and multi-zone. With a single-zone network, all repeaters are located on the same base station... With the multi-zone option, there are several base stations located in the served area, and communication with remote repeaters is carried out via dedicated communication channels (wired, radio relay)

The distribution of frequency channels between mobile subscribers distinguishes two schemes: centralized and decentralized control. In the first case, trunking networks contain several repeaters interconnected by a single control network. Channel assignment is done at the base station. In systems with de centralized management subscriber stations continuously scan working channels in search of a ringing signal or free channel.

There are several standards of trunking networks. For analog networks, the most important is the standard introduced by the UK Department of Post and Telecommunications, which describes the protocol for exchanging data between a base station (repeater) and mobile stations: MRT 1327 (Ministry Post and Telecommunications). Trunking networks based on the MRT 1327 protocol are characterized by simplicity of technology and maintenance and availability of equipment. Their inherent disadvantages: low spectral efficiency, relatively low protection from listening to a conversation, low frequency reuse factor, low transmission rates.

Closed digital system EDACS (Enhanced Digital Communication System), developed for special purposes by Ericsson, which has rights to equipment and network structure. The advantages of such a system are: short network access time, the ability to transmit data and voice over all channels.

EDACS is available in two versions, wideband (25 kHz channel spacing) and narrowband (12.5 kHz channel spacing), providing:

• - analog transmission of signals;
• - digital transmission of encrypted speech (in a broadband system at a speed of 9600 bps);
• - data transmission (at a speed of 9600 bit / s or 4800 bit / s, depending on the bandwidth);
• - connection to the PSTN network.

The system can function in various configurations depending on the size of the coverage area. The wideband version of the EDACS system can operate in the frequency ranges: 136 ... 174, 404 ... 515 and 806 ... 870 MHz. Narrowband version - in the range 894 .. .941 MHz. EDACS is Ericsson's first step in the transition to a second generation TETRA trunking system.

Trunking system TETRA (Terrestrial Trunked Radio), developed within the European Union, is an open digital system that eliminates the shortcomings of analog systems and brings the range of services provided closer to cellular systems. The developed two families of standards regulate the system parameters for voice and digital data transmission, as well as packet data transmission. When transmitting speech, various connection options are provided:

individual connection; group connection; direct connection; group connection with confirmation; broadcast connection.

Data and voice transmission in digital form is provided, in accordance with accepted standards, at a rate of 7.2 ... 28.8 kbit / s (in the absence of code protection). Circuit-switched digital voice and data transmission is possible at a speed of 4.8 ... 19.2 kbit / s (with minimum code protection). The standard provides for various options packet transmission data point-to-point with or without connections (in standard format). TETRA system architecture for different types connected equipment and types of interfaces and connections is shown in Fig. 1.17

A mobile station is a radio channel terminal equipment (Mobile Termination, radiotelephone) and terminal equipment (Terminal Equipment) that allows the user to transfer data.

Fixed station (Line Station), which includes equipment similar in purpose, but is connected to the control and switching subsystem using a channel

ISDN. The line station can be used in a corporate network as a dispatch station.

The control and switching subsystem (SwMI, Switching and Management Infrastructure) includes base stations (BTS), the main switching center MSC (Main Switching Center), local switches LSC (Local Switching Center) with location registers LR (Local Registers) and the center of switching and operation technical equipment OMC (Operation Maintenance Center).

As you can see (Fig. 1.17), the architecture of the TETRA trunking system allows you to organize connections directly between mobile stations DMO (Direct Mode Operation) without using an internetwork structure.

Using the gateways of the control and switching subsystem of the TETRA trunking network, you can connect to the public data network (PDN), telephone network public PTN (Public Telephone Network), as well as to the public switched telephone network PSTN (Public Switched Telephone Network). TETRA technology allows you to connect to a digital communication network with comprehensive services iSDN (integrated Services Digital Network) and provide high-speed transmission of various types of data: text, voice, video, etc.

At the physical level, the TETRA system has the following characteristics:

• - the bandwidth of the radio channel is 25 kHz;
• - temporary radio access system (TDMA) together with FDMA (four transmission channels

When using more than one timeslot in a frequency channel with a width of 25

kHz to provide data transmission at a speed of 28.8 kbps;

Differential quadrature phase shift keying is applied with a shift of ± l / 4 or ± Zl / 4 (l / 4-DQPSK);

Information in the TETRA standard is transmitted in packets, as in the GSM standard. A packet is the physical content of a single time slot or sub-slot. There is a variety of six packages for various purposes, containing training sequences in the middle. Due to fewer time slots per frame than GSM, data packets are longer and carry more bits.

Digital Trunking iDEN system(Integrated Digital Enhanced Network) is a unique access platform as it combines several different mobile technologies together that are based on enhanced GSM. Services that are integrated into iDEN include a distribution system, duplex telephone connection, data transmission and short message services (SMS). The distribution system has a conference call function, when a group of subscribers can simultaneously participate in a conversation. The list of participants can be programmed for two-way connection or create a specialized mobile radio system SMR (Specialized Mobile Radio), providing connection on frequencies available to a group of channels physically belonging to subscribers localized in a certain area.

The use of TDMA technology ensures that the iDEN system is compatible with cellular systems based on the D-AMPS protocol. The iDEN system in FDD mode separates the transmit and receive channels with a bandwidth of 45 MHz, while occupying a bandwidth of 15 MHz. With a bandwidth allocated for one subscriber channel of 25 kHz, 600 frequency channels can be organized in the operating band, which provides the capacity of such a system 8 times greater than that of a GSM system.

The iDEN system has many characteristics inherent in cellular systems: error correction, batch mode of data transmission, the ability to establish a connection between the subscriber terminal and the PSTN, as well as receive and send faxes, provide access to the Internet.

The term "Trunking (or trunked) communication comes from the English word trunk(trunk) and reflects the fact that the "trunk" contains several channels, and there is no rigid assignment of channels to subscribers. In the literature, you can find various definitions of trunking systems, the common thing for which is the provision of one of the currently free channels to the subscriber. In particular, this class includes:

Radial - zone systems of land mobile radio communication, using automatic distribution of a limited frequency repeater resource among a large number of subscribers;

Systems of mass use, allowing for a limited frequency resource to serve the maximum number of subscribers.

Typical applications for trunking systems are government, departmental, corporate organizations and institutions, such as ambulance service, fire service, law enforcement, security agencies, various commercial structures, etc. constantly monitored by a contingent of subscribers and within a limited territorial zone. Taking into account the specifics of the use of trunking systems, they are sometimes called professional mobile radio systems (PMR - Professional Mobile Radio), or private mobile radio systems - Private Mobile Radio. PMR systems that connect mobile sites to PSTN subscribers are often referred to as Public Access Mobile Radio (PAMR).

Trunking communication systems (TSS) can be built as systems with a single-zone or multi-zone structure. Taking into account the specific nature of the TCC, i.e. the limited number of users of the system, the transition from a single-zone to a multi-zone structure is explained primarily by the expansion of the geographic coverage area of ​​the system, and not by the desire to increase the number of subscribers (subscriber capacity) of the system. When crossing the boundaries of radio coverage, TSS monitors the movement of subscribers, ensures their registration, and assigns them a new frequency channel. However, as a rule, such a transition occurs with the interruption of communication, for the restoration of which the subscribers need to make a second call.

Trunking systems can use both simplex and duplex radio channels, however, in order to simplify and reduce the cost, they often use half-duplex mode of operation, in which the same channel is alternately used for communication from the control center (base station) to the subscriber and in reverse. direction.

The implementation of the principle of equal access to the communication channel can be carried out decentralized or under centralized control. In the first case, the function of finding a free channel is assigned to the subscriber station, which sequentially searches for an unoccupied frequency channel in the entire range allocated to the system. In the second case, the analysis of the occupancy of communication channels is carried out by the base station or directly by the switching center mobile communications... As a rule, the establishment of communication with a sequential scan of the frequency range takes a fairly long time interval. To ensure the efficiency of management in modern TSS, a special channel is provided through which the trunking system is controlled, including the implementation of procedures for establishing and terminating communication.

According to the method of organizing the control channel, TCC is distinguished with a dedicated and distributed control channel. In the first case, as the name suggests, the dedicated channel is used exclusively to control the operation of the system. In the second, during a communication session, control signals are transmitted simultaneously with a speech signal.

In view of the above, the trunking communication system can be represented by a generalized structural diagram (see Fig. 1), where the following designations are used:

MS - mobile station (mobile subscriber);

BS - base station (control center);

UOR - a device for combining radio signals;

Р - repeaters;

CKMS - mobile communication switching center;

PSTN - public telephone network;

DPU - dispatch control center.

Rice. 1 Generalized block diagram of TSS

It should be noted that for TSS the most typical frequency separation of communication channels with individual repeaters at different frequencies. It is also possible to use TCC with the use of broadband repeaters serving all channels at once. The purpose of the rest of the blocks of the structural diagram is obvious and does not require additional comments.

The MRT 1327 standard, developed by the Ministry of Post and Telecommunication (MPT), basically defines a protocol for transferring control and monitoring information (aka signaling information) for terrestrial and mobile radio trunking systems, with information messages being transmitted over analog radio channel. On its basis, the MS (subscriber) radio interface, defined by the MPT 1343 protocol, and the BS radio interface - MRT 1347 were developed. The standards provide for the transmission of information at a rate of 1.2 kbit / s for each of 500 communication channels in the frequency range 201.2125 ... 207 , 4875 MHz (MRT 1347) and 193.2125 ... 199.4875 MHz (MRT 1343), with each duplex channel occupying two 12.5 kHz bands with a spacing of the transmit and receive channels of 8 MHz.

Ericsson has developed a trunking radio communication system called EDACS (Enhanced Digital / Access Communications System). EDACS systems are available in various modifications, and distinguish between EDACS systems, EDACS networks and extended EDACS networks. EDACS systems, interconnected by means of communication node controllers and dispatching control centers, form EDACS networks, which, in turn, with the help of some integrated communication nodes, can be combined into an extended network to cover large areas.

The EDACS system uses two types of radio channels - the working channel and the control channel. The control channel is used to exchange digital signaling information between mobile stations and control devices for the operation of the entire system. Working channels are used to exchange information itself (conversational or data) between mobile stations. EDACS systems and networks are designed for use of both analog and digital stations, providing the transmission of voice signals in digital form. The standard data transfer rate is 9.6 kbit / s for each of the 20 channels of the EDACS system in the frequency ranges 30 ... 300 MHz, 800 MHz or 900 MHz with a communication channel spacing of 25, 30 and 12.5 kHz.

General trends related to the unification and integration of construction and installation systems for identical purposes have led to the development under the auspices of the ETSI (European Telecommunications Standards Institute) of the pan-European TETRA standard (Trans-European Trunked RAdio - Pan-European Trunked Communication System), which has changed its name since April 1997 on Terrestrial Trunked Radio due to its widespread adoption. TETRA-based TCCs represent the next generation of systems of this type following analogue. Unlike the previous ones, in the TETRA standard a complete transition to the digital representation of the transmitted information has been made and not frequency, but time division of channels is used. As a result of these and a number of other measures, the transmission rate in the system reached 36 kbps.

For the TETRA system, two duplex parts of the spectrum are allocated in the frequency band 380 ... 400 MHz with a spacing of radio channels for receiving and transmitting at 10 MHz and a spacing of Adjacent channels at 25 kHz.

Trunking (trunk) systems are a type of mobile communication systems, they are mainly used to provide mobile communication by various departments (Ministry of Internal Affairs, Ministry of Emergencies, etc.). Trunking is understood as a method of free and equal access of mobile subscribers to all channels of the communication network. Trunking system radio communication is a system that provides dynamic provision of a small number of communication channels to a large number of subscribers (correspondents). In such a system, each subscriber can be provided with any of the free channels. The subscriber radio station can send a request for a communication session to all base stations of the network and when the communication channel is released to any of them, it occupies this channel for the duration of the negotiations. This method of communication allows to ensure the probability of denial of service is much lower than in single-channel or multi-channel radiotelephone systems. Structural scheme trunking communication is shown in Fig. 2.4.

Figure 2.4- Structural diagram of trunking communication: RT is a radiotelephone of a trunking communication network, MS is a mobile station of a trunking communication network, BPS is a base transmitting station, TC is a trunking controller, CCS is a communication switching center, PSTN is a public telephone network

The fundamental difference between trunking systems and other mobile communication systems is that frequency channels are not assigned to specific subscribers. The system has its own specific range of operation, which is provided by several frequency channels. The choice of a free communication channel for a session is carried out by the system itself. At the end of the communication session, the same frequency channel can be provided to other subscribers of the system.

The main meaning of the trunking method of organizing communication is that simultaneous communication sessions of a large number of subscribers have a certain probability, therefore the number of operating frequencies can be selected so that the full employment of communication channels is not more than the permissible one. The above can be explained by the timing diagram of the operation of a 4-channel trunking system (Fig. 2.5), in which the occupancy of each of the communication channels is 40-60%. As can be seen from the diagram, the occupancy of each communication channel separately is quite high, and the load of the system as a whole is low (10%). If all communication channels are busy new request is not lost for service, but is queued until a free channel appears.

Figure 2.5- Timing diagram of the trunking communication system

In trunking communication systems, the allocation of a channel to a specific subscriber is carried out in two ways.

The first method involves searching for a free channel and giving a call signal from the mobile subscriber station. Before establishing communication, the mobile station automatically searches for a free channel and attempts to communicate with the base station on each determined channel. At the same time, the main disadvantage of this option is manifested, namely, the duration of the cycle of establishing a communication channel significantly exceeds the same duration with a fixed assignment of channels to specific mobile subscribers... Therefore, their use is effective with a small number of communication channels.

The second method of building a trunking system allows you to search for a free communication channel by the control subsystem of the base station. To solve this problem, a special control channel of the base station is used, through which the functions of establishing, maintaining and terminating communication are provided.

Trunking systems provide such possibilities as automatic switching of an established connection to a working channel in case of a failure of the main communication channel, prompt switching of an operating communication channel to another carrier frequency when strong interference appears.

The simplest existing trunking system is the Smar Trunk II single-zone analogue system operating in the 146 - 174 MHz and 400 - 470 MHz bands. The base station contains one control and fifteen working channels, which provide operation for up to four thousand subscribers.

A more modern analog trunking system is the MPT 1327 equipment with centralized control (Fig. 2.6).

Currently, there is a tendency to move from analog communication systems to digital ones. The fully digital trunking system is the TETRA standard system.

The structure of the complexes of various trunking systems is approximately the same. The modular design of such systems allows them to be built up to the required capacity.

The basic equipment of each channel includes:

Duplex transceiver (repeater);

Trunking controller;

Antenna feeder device.

Subscriber kits are made on the basis of popular radio stations Kenwood, Icom, Alinco, Motorola, Standard, Yaesu, etc. with installed special logic boards that control the radio station and implement certain functions.

The radio stations can be programmed for the functional tasks of the subscribers of this system using special device- programmer.

Various trunking systems provide a similar set of capabilities. For example, both single-zone and multi-zone systems achieve increased communication range. In a single-zone system, this requires an increase in base station transmitter power and the use of more sensitive antennas. In a multi-zone system, the same result is achieved by using multiple base stations with reduced transmitter power. A large number of base stations in a multi-zone system makes it possible to reduce the distance of the subscriber radio station from the base one, which increases the stability of communication. When a subscriber moves to a neighboring area, a handover of communication support from one base station to another is provided, that is, the established connection is not interrupted. Modern trunking systems provide the ability to divide the total number of subscriber radio stations into groups (detachments), within which we will make an individual and group call. Such a system can be applied, for example, within a municipality, by combining several city services into a common radio network, including units of the local fire brigade, emergency rescue teams. Moreover, each service can have a communication network completely isolated from other services, and mutual calls between groups will be programmatically allowed only to specific radio stations.

Trunking systems implement the following types calls:

An individual call can be addressed to any specific radio station, with each radio station assigned a specific set of numbers;

The group call is intended for a predetermined group of subscribers, which has its own identification number;

The general call can be directed to all subscribers of the radio network (group);

An emergency call allows you to interrupt conversations of any subscribers in the radio network;

The priority call provides a connection advantage for the main radios in the corresponding subscriber group;

Sending a status allows a radio station with an alphanumeric display to automatically select messages from the memory corresponding to this status and display it as a line of text;

A radiotelephone call provides a subscriber with an exit from the radio station to the public telephone network, as well as to the network of a private telephone exchange, and his connection to such networks can occur both via a subscriber line and a connecting line. Calling a subscriber of a mobile station of a trunking system from a public telephone network is carried out using additional number;

Call forwarding allows you to transfer it from one radio station to a predefined other radio station;

Direct calling allows the radio to switch to a simplex mode of operation to establish communication with other radios on the network without the involvement of the base station.

Important service functions of modern trunking systems are the ability to transfer data between radio stations and provide wireless access to databases.

Additional functions of these systems include the ability to transmit short alphanumeric messages over the control channel without occupying the working channel, as well as the provision of voice mail.

The essential advantages of a trunking system are individual programming of access to each type of capabilities, setting the maximum call time and subscriber priority, and protection against unauthorized access to the system. In addition, these systems can be used as a transport medium for systems for determining the location of mobile objects and telemetry systems.

The wide proprietary capabilities of trunking systems, the compatibility of their work with various types of telephone networks, make it possible to effectively use these systems to provide operational dispatching communications. Compared to conventional (conventional) radios, their use is limited by more complex operating procedures.

Trunking radio communication networks are widely used to solve the problems of RSChS and civil defense management using a mobile communication component. Such networks, as a rule, include stationary, automobile and portable radio stations of the heads of civil defense of the constituent entities of the Russian Federation, the administrative center, its urban areas, the heads of the civil defense bodies of the constituent entity of the Russian Federation, the administrative center and its districts, members of the commission for the prevention and elimination of emergency situations and ensuring fire safety (KChSPB), chiefs of civil defense services, chiefs of search and rescue teams, duty services of the administrative center. Mutual use of trunking communication networks is based on entering into their databases the general numbering of radio stations of officials and operational groups allocated for use as interacting ones.

Trunking communication is the most efficient type of two-way mobile communication, the most effective for coordinating mobile groups of subscribers. Trunking communication systems are less interesting for individual users (communication between them remains the prerogative of cellular radiotelephone systems); they are more promising and effective for corporate organizations, for group users - for instant communication between groups of users united by organizational principle or simply by interests. Often, traffic (information transfer) is closed mainly within trunking systems, and although subscribers can enter public telephone networks, it is assumed only in exceptional cases. But in principle, the operation of trunking systems is possible both in the local (single-zone, corporate) and in the network (multi-zone, serving individual users) versions.

Trunking communication system (trunk - trunk, trunk) includes a base station (sometimes several) with repeaters and subscriber radio stations (trunk radiotelephones) with telescopic antennas.

The base station is connected to a telephone line and is connected to a repeater with a long range - up to 50–100 km. Trunk radiotelephones are extremely reliable, compact and come in several versions:

l wearable - range of 20–35 km, weight 300–500 g;

l by transport - range of 35–70 km, weight about 1 kg;

l stationary - range of 50–120 km, weight is usually more than 1 kg.

The average possibilities of trunking communication in terms of coverage of the territory are shown in Fig. 26.1.

Rice. 26.1. Possibilities of trunking communication for coverage of the territory

Generally speaking, trunking systems are characterized by equipment made using high tech supported by good service both for the subscriber and for the network operator, equipment that provides full duplex or half-duplex radiotelephone communication with mobile objects, operation in analog and digital modes.

With trunking, a small number of radio channels are dynamically allocated to a large number of users. One channel has up to 50 or more subscribers; since subscribers do not use the phone very intensively, and the base station operates in the concentrator mode (that is, it distributes all radio channels only between the subscribers who have contacted it), the probability of a busy situation is not great (much less than when even several subscribers are rigidly attached to one channel ).

Radiotelephones can work both in the system, being in the coverage area of ​​the base (base) station and through it communicating with any subscriber of the telephone network (including the trunking subscriber), and individually with each other, being both inside and outside the zone base radio stations. In the first case, direct communication between subscribers will ensure a more efficient connection (connection time usually does not exceed 0.3-0.5 s). The possibility of direct communication between subscribers without the participation of a base station is the main, global difference between trunking systems and cellular systems.