Track communication

In the modern business world, more and more attention is paid to the means of mobile communications: chapels, cellular and satellite communications, personal communicators and similar devices. In fact, in order to be competitive, modern companies need to constantly maintain communication with their customers, and, not less important, between employees of their organization. Recently, some mobile operators offer so-called "corporate" tariffs (for example, the MTS corporate program), which are just intended to create a "virtual telephone network" for employees of the company. However, such programs are not the cheapest solution to the problem of communication, but fortunately, not the only possible.

For the company that decided to "connect" their mobile employees, there is an alternative solution - the use of a trunk connection. Perhaps, many readers of the phrase "trunk communication" see for the first time. Indeed, transit communication systems are now paying less attention than even to paging systems. To some extent, this is due to the fact that the canan communication systems are primarily intended primarily for use by large organizations, and not mass users. Despite this, this technology has its advantages and deserves to be considered under this article.

So, what is hiding behind the term "trunk system"? No matter how paradoxically, we use it every day, without even thinking about it. It is on the principle of trunking that the effect of modern PBXs is based. Let's follow what happens when you are trying to call the home phone, let's say to your friend. You take off the phone, wait for the "Line Free" signal, then dial the number and wait for the answer. All other actions perform PBX: It chooses one of the free communication channels and commutes (connects) your telephone with a friend's telephone. At the end of the conversation, the line that was used is released and becomes available for use by other people. As you guesses, the number of communication lines is limited and knowingly less necessary to connect all telephone sets in the city. Thus, the PBX controls the distribution of a limited number of lines between a large number of subscribers. It is assumed that the situation is when all subscribers suddenly decide to contact each other at the same time, will not arise. Therefore, it is necessary to correctly calculate the minimum required number of communication channels, so that there are no problems associated with their lack during the work. This issue is effectively solved using the mathematical theory of mass maintenance systems.

Fig. 1. In the trunk telephony, the subscriber simply dials the number, and the PBX distinguishes the free line by conversation.

What is a trunk radio system?

Rank radio systems are the systems of mobile radio communications, which are based on the same principles as the usual telephone networks. In other words, in the trunk radio system, there is a limited number of radio channels (as a rule, from two to twenty), which, as needed is allocated to the central controller to negotiate.

Fig.2. In trunk radio systems, the subscriber requests a conversation permission, and the central controller (consisting of several repeaters) highlights the channel by which you can talk.

In conventional radio communications systems, the user has to manually remap to free radio channel, in the trunk communication systems this work takes on a central controller, which himself highlights two radio stations free channel. Thus, the user needs to simply dial the number of the called subscriber, the rest system will make it itself. The trunk system can be given the following definition: automatic and dynamic distribution of a small number of channels among a large number of radio users.

Fig.3. The loading diagram of the five-channel trunk system. Lower chart shows cases blocking when all five channel channels are occupied.

Areas of application of trunk radio systems.

Now, knowing the basic principles of the work of trunk systems, let's talk a little about the areas of their application and the benefits of use. Application areas are large commercial and government organizations, such as auto inspectors, various repair services, companies specializing in industrial mountaineering (maintenance of high-rise buildings) and so on. The trunk communication system can be deployed both in a large city and in a remote, lumpy point, which is especially relevant in the conditions of our country. Trunk systems effectively use the bands of the frequencies isolated by them, provide a high level of privacy (there are even means to encode speech in the process of its transfer), reliable, provide a large number of service functions. Finally, almost the greatest advantage is that the organization can itself become the owner of a trunk radio system, eliminating itself from the subscription fee and traffic payments.

Types of trunk radio communications.

It is time to figure out the types of trunk communications. Various companies and organizations developed a huge number of trunk communication formats, many of which are incompatible with each other. In the United States, the most popular formats are Privacy Plus, developed by Motorola, Logic Trunked Radio - LTR, manufacturer - E.F. Johnson, as well as SmartRunk II from SmartRunk Systems, previously known as SELECTONE. It is also necessary to note the project IDEN company Motorola, which offers a digital transform format. In Europe, the MPT1327 standard was widely widespread, developed in England for general radio radio. Now this standard has become popular in Asia, Australia, Latin America. Currently, in Europe, work is underway to create a new European digital trunk system protocol - TETRA (TRANS EUROPEAN TRUNKED RADIO).

In Russia, the most well-known protocols are SmartRunk II, MPT1327, LTR.

If you classify trunk systems by number of subscribers, then three groups can be distinguished:

• small, in which the number of subscribers does not exceed 300 people. When building such systems, SMARTRUNK II protocol is used;
• average whose number of subscribers does not exceed 3000 people. Most often, the LTR standard is applied when creating such systems;
• large, with the number of subscribers exceeding 3000 people. In this case, MPT 1327 protocol is most often used.

MPT1327 and Tetra refer to the class of open protocols, while LTR, Smartnet, etc. - To the class of closed, "branded", however, those and others work under the two basic principles that we consider in the next part of the article.

Comparison of trunking methods.

Currently, there are two methods for managing trunk systems. The first is the distributed control, the second - control over the dedicated channel.

The method of the selected channel has several disadvantages compared to the method of distributed control. One of them is that when using a dedicated channel, all requests are carried out with its participation, therefore, it is necessary to somehow avoid collisions for data transmission. Another disadvantage is that the system with a dedicated channel must process requests consistently, and as the download and reduction of the number of available channels increases, the number of queries is growing exponentially, so that mobile devices are forced to fight each other in one channel.

One of the advantages of a distributed control method is that access can be obtained by any free channel at the moment. Repeators define a free channel and transmit this information in a data stream that exists with voice information. This means that each repeater supports its data stream and processes all requests on its channel. Treatment of collisions is made by mobile devices, which provides parallel call processing.

Another advantage of the method of distributed control is that voice data is transmitted over all channels, while in the method of the dedicated channel control channel, as a rule, cannot be used in a similar way. The figure shows the speed of blocking the five-channel system in comparison with the speed of blocking the four-channel system (one channel is used to control). It can be seen that the time of blocking the five-channel system is significantly less.

Fig.4. Comparing time blocking.

As a rule, in trunk systems, idle time (time between two adjacent transmissions) is not used in negotiations. The channel is held only for transmission time, and the time between transmissions can be used by other challenges. And only when conducting telephone conversations, the canal is kept constantly.

Some trunk systems use idle time in negotiations during high load periods. This allows the caller to the subscriber to almost always answer the call without fear to be blocked. An obvious disadvantage of this approach is an increase in the total transmission time and, consequently, an increase in the probability of locks and the waiting time of other subscribers.

Access priority is a parameter defining who the first will receive access to a busy system. Most systems with a dedicated control channel use a method that allows all mobile devices to attempt to access, but refuses to provide a channel with devices with a lower priority level. In distributed control systems, the priorities of all mobile devices are the same, and none of the devices can access the system while the channel is busy. When the channel is released, the access to it receives that apparatus that first will try to take line.

Mobile devices used in trunk communication systems must be programmed to work at a certain frequency (usually 800 or 900 MHz); Many features (for example, a channel selection, channel checking before transmission) are performed automatically.

With each repeater, up to 250 codes IDs can be associated. ID Code and home repeater number form a mobile device address on the network. Thus, in a system containing 20 repeaters, the maximum number of subscribers is 5000. The ID code can be assigned to either one mobile device or several.

Structural diagram of the base station for the canon radio system.

Figure 5 shows the block diagram of the base station in the case of using one channel.

The repeater consists of a repeater intended for receiving subscriber radio stations, gain and transmission, and a trunk channel controller that performs control functions.

Duplex filter is a device that allows you to use one antenna for receiving and transmission. In principle, nothing prevents the use of two different antennas for reception and transmission, but in this case there may be a situation where in some places it will be possible, but the transfer is not possible or vice versa. In addition, the transmitter radiated power affects the receiver, so if there are two antennas, they need to be installed at a sufficient distance from each other.

The power source is intended for the repeater. As a rule, it allows you to move to the battery when the power is turned off.

The considered scheme is quite simple and effective, but in real conditions of one trunk channel is not enough. Therefore, systems containing two or more channels are used. The figure shows a system diagram containing four independent channels. As can be seen, the main difference from the previous version lies in the antenna-feeder path, where two more devices appear: a receiving plug-in and combine.

The receiving dumpup provides the same input signal for each repeater in the system, as if the repeater was connected directly to the antenna.

The combiner is a device that allows you to combine the outputs of a certain number of transmitters without interference with each other.

Also, a source of uninterrupted nutrition was also made, which is simply obliged to be present in the system, for the lack of communication in emergency circumstances can lead to unpredictable consequences.

The considered system is easy to expand, that is, in the case of proper design, the number of channels can be increased quite painlessly.

Overview of radio telephone models.

Currently, equipment for base stations and subscriber devices for trunk radio communications systems produces a large number of companies. Of these, Motorola, Nokia, Ericsson, SmartRunk Systems and others use the greatest fame. For example, consider several models of radio telephones produced by Nokia.

Nokia H85.

Nokia H85 - light (weight of only 345 g with battery, output power 1 W in duplex mode), a convenient radiotelephone for use in MPT 1327 systems. The device has a large high-contrast alphanumeric display (contains 3 lines of 10 characters) with voltage level indicators Battery fields and charges. Access to numerous functions and configuration of the device is carried out using the menu. H85 supports individual and group calls, calls on a common telephone network. The memory of the radio telephone is capable of preserving up to 99 names and subscriber numbers. There is also one programmable button that can be assigned or the most frequently dialing number or the emergency call number.

This device provides a wide selection of accessories, including a charger from the cigarette lighter and the holder to the dashboard. There are two types of charger: desktop and hiking.

Nokia R40.

Nokia R40 is a universal half-duplex radio station for users of trunk systems (weight 1.8 kg, output power 10 (15) WT). The radio station meets the specifications of the MPT 1327 and MPT 1343 standard, in addition, the R40 supports the MAP 27 data interface.

The radio station can be used both in the automotive and desktop. The Cu 43 alphanumeric console has 22 keys and three-stricter LCD display per 100 characters and allows you to perform all possible call types in the radio network. Additionally, the console allows you to receive and transmit status messages and data. A screen menu is used to control the station. In memory you can store up to 43 names and numbers of subscribers.

CU 45 communicator has a built-in digital LCD display, microphone and loudspeaker. Management is carried out using the four function keys.

Through the MAP 27 interface, peripheral devices can be connected to the radio station, such as a data transfer modem.

Nokia R72.

Nokia R72 is a radiotelephone to work in MPT 1327/1343 networks (weight of 1.8 kg, 10 W output power in duplex and 15 W in half duplex mode). The radio telephone in addition to the speech link provides the possibilities of transmitting and receiving coded messages and data.

The phone is convenient to use in the car. When the charging wire is connected to the cigarette lighter socket, the battery is automatic charging. The phone has a memory of 97 names and subscriber numbers, and also allows you to program up to nine speed dial numbers. In addition, the phone has a number of other features, among them the transfer of tonal signals to connect to the telephone network equipment, using the code order number (ESN) and blocking codes to protect against unauthorized access.

You may notice that the R72 looks like the same as the famous Nokia 720 - a mobile phone for use in NMT 450 networks. Yes, and the names of these two devices show that they have a lot in common.

Conclusion.

Having determined the main purpose of the trunk radio, having considered and comparing its standards, having studied the principles of building a central controller and finally familiarized with some models of radio stations, we have received a general idea that such a trunk radio system is. It should be noted that at present they continue to actively develop, new standards and equipment are being developed. The number of translated and commissioned transmission systems is growing every year. Of course, they have a future.

For those who have thought about the topic, I give references to some resources on the Internet on tricks. At the end of the article, the glossary of terms used in describing the transmission radio systems is also provided.

Links.

http://members.dingoblue.net.au/~activemedia/trnklinks.htm is a collection of references to resources dedicated to trunk systems.

http://www.sotovik.ru/analit.htm - library on the cellular, contains a very large amount of mobile materials, including a section dedicated to trunk systems.

Glossary.

Base station - A group of repeaters connected to one data bus and located in one place.

Homemade repeater - All radio stations in the Tank Radiocommunication System have one of the repeaters located on the base station as a "home". The radio station monitors this repeater to receive calls and receive information about which repeaters are free.

Duplex - The mode in which you can simultaneously speak and listen (that is, to receive and transmit).

Controller (central controller) - A computer that provides the collaboration of all repeaters. Each repeater contains the controller. Between themselves, they are combined with the data bus.

Mobile device - Receiveter installed in the car or portable radio station.

Repeater - A device that accepts and relays a radio signal. If you use a five-channel trunk system, you will need five repeaters. At the same time, one repeater can only serve one conversation.

Simplex - The mode in which either the transfer is possible or the reception.

Trankung - Automatic and dynamic distribution of a small number of channels among a large number of radio stations.

Managing Channel - One of the radio channels, which is used to communicate with all mobile devices and for sending out the service information.

The transmission radio communication systems, which are radially zone systems of mobile VHF radio communications, carrying out the automatic distribution of communication channels of repeaters between subscribers, are the class of mobile communication systems, oriented, primarily on the creation of various departmental and corporate communication networks, which provide for active application of the regime communication subscribers in the group. They are widely used by power and law enforcement structures, public security services of various countries to ensure the relationship of mobile subscribers among themselves, with stationary subscribers and telephone subscribers.

There are a large number of different standards of transit-on mobile radio communication systems (SPR-OP), differing from each other by voice information transmission (analog and digital), type of multiple access (MDCH - with frequency separation of channels, MDWC - with temporary separation of channels or CDMA - C code separation), a way to search and destination channel (with decentralized and centralized control), type of control channel (dedicated and distributed) and other characteristics.

Currently in the world, and in Russia, previously widely extended analog infrared radio communications systems, such as SmartRunk, MPT1327 protocol (Accessnet, Actionet, etc.), Motorola system (Startsite, Smartnet, SmartZone), systems with distributed systems Control channel (LTR and MULTI-NET firm EFJOHNSON CO and ESAS firm UNIDEN). MPT1327 systems received the greatest distribution, which is explained by significant advantages of this standard compared to other analog systems.

It should be said that in Russia, most large trotanking networks are built on the basis of MPT1327 standard equipment. The heads of companies involved in equipment supply and system integration in the field of professional radio communications noted that most of the tasks of the tasks of the operational speech bond fae into their customers are solved quite effectively with the help of the MPT1327 analog systems.

Digital standards of trunking radio communications have not yet received such widespread in Russia, but now we can talk about their active and successful implementation.

At the same time, the circle of users of digital trunking systems is constantly expanding. Russia also appears large customers of professional radio systems, which require the transition to digital technologies. First of all, these are large departments and corporations, such as RAO UES, Ministry of Transport, MPS, Sibneft and others, as well as power structures and law enforcement agencies.

The need for a transition is due to the benefits of digital trunking in front of the analog systems, such as a large spectral efficiency due to the use of complex modulation types of signal and low-speed spectrum algorithms, increased capacity of communication systems, alignment of the quality of speech exchange throughout the base station's service area due to the use of digital signals in combination With noise-resistant coding. The development of the global market for trotting radio communication systems is characterized by a wide introduction of digital technology. The leading global manufacturers of trunking equipment equipment announce the transition to digital radio standards, providing for either the issue of fundamentally new equipment, or adapting analog systems to digital communication.

Digital trunking systems compared to analogue have a number of advantages by implementing the requirements for increased efficiency and communication security, providing broad data transmission opportunities, a wider range of communication services (including specific communication services for the implementation of special requirements of public security services), opportunities for organizing interaction Subscribers of various networks.

1. High response efficiency. First of all, this requirement means the minimum possible time for establishing a communication channel (access time) with various types of compounds (individual, group, with telephone network subscribers, etc.). In conventional communication systems in transmitting digital information that requires time synchronization of the transmitter and receiver, it takes a larger time to establish a communication channel than an analog system. However, for trinting radio communications systems, where information exchange is mainly made through the base stations, the digital mode is comparable by access time with analog (and in analog, and in digital radio systems, as a rule, the control channel is implemented on the basis of digital signals).

In addition, in digital transcription radio communications systems, various communication modes that increase its efficiency are simply implemented, such as direct mode (direct) communication between moving subscribers (without using a base station), open Canal mode (allocating and securing frequency resources of the network for a certain group of subscribers to keep them in the future negotiations without performing any installation procedure, including without delay), emergency and priority challenges, etc.

Digital Digital Radiocommunication Systems are better adapted to various data transmission modes, which provides, for example, law enforcement officers and public security services, wide possibilities for prompt information from centralized databases, transfer the necessary information, including images from occupants, organizations of centralized dispatching systems Mobile objects based on satellite radio navigation systems. These systems allow consumers of the oil and gas complex to use them as transport not only for voice transmission, but also for transmission of telemetry and television management.

2. Data transfer.Digital Digital Radiocommunication Systems are better adapted to various data transmission modes, which provides digital networks with wide possibilities for prompt information from centralized databases, transmitting the necessary information, including images, organizing centralized dispatching systems for the location of mobile objects based on satellite radio navigation systems. The data transfer rate in digital systems is significantly higher than in analog.

Most radio communication systems based on digital standards are implemented for short and status messages, personal radio communications, facsimile communication, access to fixed communication networks (including TCP / IP protocols).

3. Communication security. Includes the requirements for ensuring the secrecy of negotiations (eliminating the possibility of extracting information from communication channels to someone, except for an authorized recipient) and protection against unauthorized access to the system (eliminating the possibility of capturing the management of the system and attempts to bring it out of order, protection against "twins" and t. n.). As a rule, the main communication safety mechanisms are encryption and subscriber authentication.

Naturally, in digital radio systems compared to analog systems, it is much easier to ensure communication security. Even without adopting special measures to close information, digital systems provide an increased level of negotiation protection (analog scanning receivers are unsuitable for listening to negotiations in digital radio systems). In addition, some of the digital radio standards provide for through code encryption, which allows the use of original (i.e., the speech closing algorithms developed by the user).

Digital transit radio communication systems allow you to use a variety of subscriber authentication mechanisms: various identification keys and SIM cards, complex authentication algorithms that use encryption, etc.

4. Communication services. Digital trunking systems implement a modern level of service to subscribers of communication networks, providing automatic registration of subscribers, roaming, data flow control, various priority call modes, call forwarding, etc.

Along with the standard network service functions, on requests for law enforcement agencies, the requirements for digital transcription radio communications often include requirements for specific communication services: a call mode coming only with the sanction of the system dispatcher; mode of dynamic modification of user groups; The remote inclusion mode of radio stations for acoustic listening of the situation and so on.

5. The possibility of interaction. Digital radio communications systems that have a flexible subscriber addressing structure provide ample opportunities for creating various virtual networks within the same system and for the organization, if necessary, the interaction of subscribers of various communication networks. For public safety services, the requirement to ensure the possibility of interaction between units of various departments to coordinate joint actions in emergency situations: natural disasters, terrorist acts, etc.

The most popular, which earned international recognition by the standards of digital transcription radio communications, on the basis of which in many countries the communication system is deployed:

• EDACS.developed by Ericsson;
• Tetra.developed by the European Institute of Communication Standards;
• APCO 25.developed by the Association of Official Representatives of Communication Services of Public Security;
• Tetrapoldeveloped by Matra Communication (France);
• iDEN,developed by Motorola (USA).

All these standards meet modern requirements for trinting radio communications. They allow you to create various configurations of communication networks: from the simplest local one-room systems to complex multi-zone systems of the regional or national level. Systems based on standard data provide various transmission modes (individual communications, group communication, broadcast call, etc.) and data (switched packets, transmitting data switched data, short messages, etc.) and the ability to organize communication with various systems for standard interfaces (with a digital network with integration of services, with a public telephone network, with a PBX, etc.). In the radio communications systems of these standards, modern methods of recycperement are used, combined with effective methods of noise-resistant encoding of information. Radiochenflow producers ensure compliance with their MIL STD 810 standards on various climatic and mechanical influences.

2. General information on digital transcription radio

2.1. SystemEDACS.

One of the first standards of digital transcription radio communication was EDACS (Enhanced Digital Access Communication System), developed by Ericsson (Sweden). Initially, he only provided for the analogue transmission of speech, but later a special digital modification of the EDACS Aegis system was developed.

The EDACS system works in accordance with the closed branded protocol that meets the safety requirements for transcription radio communications, which have been developed by a number of mobile equipment manufacturers in conjunction with law enforcement agencies (APS 16 document.

Digital EDACS systems were produced on the frequency ranges 138-174 MHz, 403-423, 450-470 MHz and 806-870 MHz with frequency data 30; 25; and 12.5 kHz.

In EDACS systems, the frequency separation of communication channels using high-speed (9600 bps) of a highlighted control channel, which is intended to exchange digital information between radio stations and system management devices. This ensures high efficiency in the system (the establishment of a communication channel in a single-room system does not exceed 0.25 s). The information transfer rate in the working channel also corresponds to 9600 bits / s.

Speech coding in the system is performed by compression of a pulse-code sequence at a rate of 64 kbps, obtained using an analog-digital signal conversion with a clock frequency of 8 kHz and a bit of 8 bits. The compression algorithm that implements the adaptive multi-level coding method (Ericsson's development) provides dynamic adaptation to the individual characteristics of the voice speech and forms a low-speed digital sequence that is subject to noise-resistant encoding, bringing the digital stream speed to 9.2 kbps. Next, the formed sequence is divided into packets, each of which includes synchronization and control signals. The resulting sequence is transmitted to the communication channel at a speed of 9600 bits / s.

The main functions of the EDACS standard that ensures the specifics of public security services are various call modes (group, individual, emergency, status), dynamic call priority management (up to 8 priority levels), dynamic modification of subscriber groups (regrouping), remote shutdown radio stations (with rare or radiochetus).

EDACS Standard Systems provide radio accessivity in digital and analog mode, which allows users at a certain stage to use the Old Radiocommunication Technory Park.

One of the main tasks of the development of the system was to achieve high reliability and fault tolerance of communication networks based on this standard. This goal was achieved, which is confirmed by reliable and sustainable operation of communication systems in various regions of the world. High fault tolerance is ensured by the implementation of distributed architecture in the equipment of the EDACS system and the stirring principle of distributed data processing. The basic communication network station retains performance even in case of refusal of all repeaters, except one. The last workable repeater in this case, in the original state, works as a control channel relay, when calling, processes them by assigning their own frequency channel, after which it switches to the operating channel relay mode. When the base station controller fails, the system switches to an emergency mode, in which some network functions are lost, but partial performance is preserved (repeaters operate autonomously).

In the EDACS system, it is possible through the encryption of information, however, due to the closed protocol, it is necessary to apply either a standard defense algorithm offered by Ericsson, or to coordinate with it the possibility of using its own software and hardware modules that implement the original algorithms that must be compatible with the EDACS system protocol.

To date, a large number of EDACS standards networks are deployed in the world, including multi-zone communication networks used by the public security services of various countries. In Russia, about ten networks of this standard operates, the largest network of communications in Russia in Moscow, which includes 9 base stations. At the same time, the ERICSSON does not work on improving the EDACS system, stopped supplying the equipment to deploy new networks of this standard and only supports the operation of existing networks.

2.2 Tetra system

TETRA is a standard of digital transcription radio, consisting of a number of specifications developed by the European Institute of ETSI telecommunications standards (European Telecommunications Standards Institute). Standard Tetra was created as a single pan-European digital standard. Therefore, until April 1997, the Abbreviation Tetra meant the Trans-European Trunked Radio Trans-European Tranking Radio. However, due to the greatest interest shown to the standard in other regions, its territory is not limited to Europe. Currently, TETRA is decrypted as ground trunked radio (Terrestrial Trunked Radio).

Tetra is an open standard, i.e. it is assumed that the equipment of various manufacturers will be compatible. Access to TETRA specifications are free for all stakeholders who have entered the Association "Memorandum of Understanding and Promoting Tetra Standard" (Mou Tetra). The Association, which at the end of 2001 included more than 80 participants, combines developers, manufacturers, testing laboratories and users of various countries.

The Tetra standard consists of two parts: Tetra V + D (Tetra Voice + Data) - a standard for an integrated speech and data transmission system, and Tetra PDO (Tetra Packet Data Optimized) - a standard describing a special version of the trunking system, oriented only to data transmission .

The Tetra standard includes wireless interface specifications, the interfaces between the Tetra network and the digital network with the integration of services (ISDN), the public telephone network, the data network, the established PBX, etc. The standard includes a description of all basic and additional services provided by networks. Tetra. Local and external centralized network management interfaces are also specified.

Tetra's radio interface involves working in a standard frequency grid in 25 kHz increments. The required minimum duplex separation of the radio channels is 10 MHz. Some frequency subbands can be used for TETRA standard systems. In Europe, the ranges of 380-385 / 390-395 MHz are enshrined in the countries of the Safety Services, and the ranges 410-430 / 450-470 MHz are provided for commercial organizations. In Asia, a range of 806-870 MHz is used for TETRA systems.

In the TETRA V + D standard systems, the multiple-separation (MDWR) of communication channels is used. At one physical frequency, up to 4 independent information channels can be organized.

Messages are transmitted by multicone duration 1.02 s. The multicode contains 18 frames, one of which is control. The frame has a duration of 56.67 ms and contains 4 time intervals (Time Slots). In each of the time intervals, information is transmitted to its temporary channel. The time interval has a length of 510 bits, of which 432 are informational (2 blocks of 216 bits).

In Tetra Standard Systems, the relative phase modulation of type P / 4-DQSK (Differrential Quadrum Phase Shift Keying) is used. Modulation speed - 36 kbps.

To convert speech in the standard, a codec with a Celp-type conversion algorithm is used (Code Excited Linear Prediction). The speed of the digital stream at the codec output is 4.8 kbps. Digital data from the output of the speech codec is subjected to block and convolutional coding, interleaving and encryption, after which information channels are formed. The bandwidth of one information channel is 7.2 kbps, and the speed of the digital information flow of data is 28.8 kbps. (At the same time, the total rate of symbol transmission in the radio channel due to additional service information and the control frame in the multicadron corresponds to the modulation rate and is equal to 36 kbps.)

Tetra standard systems can operate in the following modes:

• transkding communication;
• open channel;
• direct communication.

In mode transkding Communication The serviced territory overlaps the zones of the basic transceiver stations. The TETRA standard allows you to use on systems only a distributed control channel and organize its combination with a dedicated frequency control channel. When operating a network with a distributed control channel, the service information is transmitted either only in the multi-meter control frame (one of 18), or in a specially selected temporary channel (one of the 4 channels organized at one frequency). In addition to the distributed communication network, a dedicated frequency control channel can be used, specially intended for exchanging service information (the maximum communication services are implemented).

In mode with an open channel A group of users has the ability to establish a connection "One item - a few items" without any installation procedure. Any subscriber by joining the group may at any time use this channel. In the open channel mode, the radio station operates in a two-frequency simplex.

In mode direct (direct) communication There are two- and multipoint connections on radio channels that are not associated with the network control channel, without transmitting signals through the basic transceiver stations.

In Tetra Standard Systems, mobile stations can operate in T.N. Dual Watch Mode ("Dual Watch"), which provides applications from subscribers working both in trunking and direct communication.

To increase service areas in Tetra standard, it is possible to use subscriber radio stations as repeaters.

Tetra provides users with a number of services that are included in the standard of the European Police Association (Schengen Group), collaborating with the ETSI Technical Committee:

• challenge authorized by the dispatcher (the mode in which the calls come only with the sanctions of the dispatcher);
• priority access (in the case of the overload of the network, the available resources are assigned in accordance with the prioritization scheme);
• priority challenge (assigning calls in accordance with the prioritization scheme);
• priority interruption call service (interruption of call service with low priority, if the system resources are exhausted);
• selective audition (interception of the incoming call without affecting the work of other subscribers);
• remote audition (remote inclusion of a subscriber radio station for transmission for listening to the following subscriber);
• dynamic regrouping (dynamic creation, modification and removal of user groups);
• identification of the caller.

The TETRA standard provides two levels of security transmitted:

• the standard level that uses the radio interface encryption (information protection level is provided similar to the GSM cellular system);
• a high level using end-to-end encryption (from the source to the recipient).

TETRA radio interface protection means include subscriber and infrastructure authentication mechanisms, traffic confidentiality due to pseudoimeman flow and specified information encryption. Specific additional information protection is provided by the possibility of switching information channels and control channels in the process of maintaining a communication session.

A higher level of information security is a unique requirement of special user groups. Cell-cutting encryption provides speech and data protection anywhere in the communication line between stationary and mobile subscribers. The TETRA standard sets only an interface for through encryption, thereby ensuring the possibility of using original information protection algorithms.

It should also be noted that in the TETRA standard due to the use of the method of temporary separation of channels (HDDW) of communication in all subscriber terminals there is an opportunity to organize communication in the full duplex mode.

Tetra is deployed in Europe, North and South America, China, Southeast Asia, Australia, Africa.

The development of the second stage of the standard is currently being completed (Tetra Release 2 (R2)), aimed at integrating with mobile networks of the 3rd generation, a cardinal increase in the data transfer rate, transition from specialized SIM cards to universal, further increase in the efficiency of communication networks and expansion Possible zones of service.

In Russia, Tetra equipment is offered a range of companies - system integrators. Several pilot projects of TETRA networks have been implemented. Under the auspices of the Ministry of Communications, the system project "The Federal Network of Moving Tetra Radio Communication" is carried out, called Tetrarus. In 2001, the Russian Tetra Forum was created, the tasks of which include the promotion of TETRA technology in Russia, the organization of information exchange, promoting the development of national production, participation in the work on the harmonization of the radio frequency spectrum, etc. In accordance with the decision of the SCPP of 02.07.2003 The use of the TETRA standard is recognized as promising "... in order to provide communication bodies of state administration of all levels, defense, security, law enforcement, the needs of departments and large corporations."

2.3. APCO 25 system

The APCO 25 standard has been developed by the Association of Official Public Security Services Communication Services (Association of Public Safety Communications Officials-International), which combines users of communication systems operating in public security services.

The work on the creation of the standard was started at the end of 1989, and the latest documents to establish the standard were approved and signed in August 1995 at the International Conference and ApCo exhibition in Detroit. Currently, the standard includes all major documents defining the principles of constructing a radio interface and other system interfaces, encryption protocols, speech coding methods, etc.

In 1996, it was decided to divide all standard specifications into two stages of implementation, which were marked as phase I and phase II. In mid-1998, the functional and technical requirements for each of the phases of the standard were formulated, emphasizing the new phase II capabilities and its differences from Phase I.

The fundamental principles of developing the APCO 25 Standard, formulated by its developers, were the requirements:

• to ensure the smooth transition to the means of digital radio communications (i.e., collaboration capabilities at the initial stage of basic stations of the standard with subscriber analog radio stations used at present);
• to create an open systemic architecture to stimulate competition among equipment manufacturers;
• in ensuring the possibility of interaction between various public security services, when conducting joint activities.

The standard architecture of the standard supports both trotking and conventional (conventional) radio communications systems in which subscribers interact with each other or in direct communication mode, or through a repeater. The main functional block of the APCO 25 standard system is a radio method, defined as a communication network, which is based on one or more base stations. At the same time, each base station must support a shared radio interface (CAI - Common Radio Interface) and other standardized interfaces (intersystem, with TFP, with a data transfer port, with a data transfer network and network control).

The APCO 25 standard provides for the possibility of working in any of the standard frequency ranges used by mobile radio communications systems: 138-174, 406-512 or 746-869 MHz. The main access method to communication channels - frequency (MDCH), however, on the Ericsson application to Phase II, includes the possibility of using multiple access to the APCO 25 of the APCO 25 of the APCO 25 of the Channels.

In phase I, the standard step of the frequency mesh is 12.5 kHz, in phase II - 6.25 kHz. At the same time, with a 12.5 kHz strip, four-position frequency modulation according to the C4FM method at a speed of 4,800 characters per second, and with a 6.25 kHz strip, a four-position phase modulation with the smoothing of the CQPSK phase is smoothing. The combination of these modulation methods allows the identical receivers to be used at different phases, supplemented by various power amplifiers (for phase I - simple amplifiers with high efficiency, for phase II - amplifiers with high linearity and limited width of the emitted spectrum). In this case, the demodulator can process signals according to any one of the methods.

Speech information in the radio channel is transmitted by the frames of 180 ms, grouped 2 frames. For speech coding, the IMBE codec is used in the standard, which is also used in the INMARSAT satellite communication system. Coding speed - 4400 bits / s. After noise-resistant encoding of voice information, the speed of the information flow increases to 7,200 bits, and after the formation of speech frames by adding official information to 9600 bits / s.

The subscriber identification system laid in the APCO 25 standard allows you to address at least 2 million radio stations in one network and up to 65 thousand groups. At the same time, the delay when establishing a communication channel in the subsystem in accordance with the functional and technical requirements for the APCO 25 standard should not exceed 500 ms (in the mode of direct communication - 250 ms, when communicating through the repeater - 350 ms).

The APCO 25 systems in accordance with the functional and technical requirements should provide 4 levels of cryptocams. A streaming method encrypting information using nonlinear encryption sequence formation algorithms is used. When using Special OTAR mode (over-the-air-re-keying), encryption keys can be transmitted by radio channel.

Due to the fact that the main method of access to communication channels in APCO - MDIR, currently there are no terminals that would ensure the work of the subscriber in the full duplex mode.

Despite the fact that APCO is an international organization whose representation is located in Canada, Australia, the Caribbean region, American firms supported by the US government play a major role in promoting this standard. The participants of the public sector of the Association include FBIs, the US Department of Defense, the Federal Committee of Communications, the Police of the United States, the Secret Service and many other state organizations. As manufacturers of equipment of the APCO 25 standard, such leading firms as Motorola (main standard standard), E.F.Johnson, Transcrypt, Stanlite Electronics and others have already been stated. Motorola has already presented its first system based on the APCO 25 standard, which has the name ASTRO.

Specialists of the Ministry of Internal Affairs of Russia are the greatest interest in this standard. The pilot network (not yet trotanking, and the conventional radio communications) on the basis of two base stations was deployed by the Ministry of Internal Affairs of Russia in Moscow in 2001. In 2003, a dispatch radio network of a 300 subscribers was deployed in St. Petersburg to the 300th anniversary of the city in the interests of various strength structures.

2.4. Tetrapol system

Work on the creation of a standard Tetrapol digital trinting radio communication was launched in 1987, when Matra Communications entered into a contract with French gendarmeria for the development and commissioning of the RUBIS digital radio network. The communication network was put into operation in 1994. According to Matra, today the network of French gendarmerie covers more than half of the territory of France and serves more than 15 thousand subscribers. In the same 1994, Matra created its Tetrapol Forum, under the auspices of which the Tetrapol PAS specification (Publicly Available Specifications) were developed, which define the standard of digital transit radio communications.

The TetraPol standard describes the digital transcription system of radio communication with a dedicated control channel and the frequency method of separating communication channels. The standard allows you to create both single-room and multi-zone communication networks of various configurations, ensuring the possibility of direct communication between moving subscribers without using the network infrastructure and relaying signals on fixed channels.

TETRAPOL standard communication systems have the ability to operate in the frequency range from 70 to 520 MHz, which, in accordance with the standard, is defined as a set of two subbands: below 150 MHz (VHF) and above 150 MHz (UHF). Most of the radio interfaces for these subband systems is general, the difference is to use various methods of noise-resistant encoding and code interleaving. In the subband UHF, the recommended duplex separation of reception and transmission channels is 10 MHz.

The frequency disposal between adjacent communication channels can be 12.5 or 10 kHz. In the future, it is supposed to transition to the separation between channels of 6.25 kHz. In the TetraPol standard systems, the strip width is supported up to 5 MHz, which provides the ability to use on the network 400 (with a separation of 12.5 kHz) or 500 (with a separation of 10 kHz) radio channels. In this area, each zone can be used from 1 to 24 channels.

The speed of information transmission in the communication channel is 8000 bits / s. Information transmission is organized by 160 bits long frames and a duration of 20 ms. Frames are combined into a supercader duration 4 C (200 frames). Information is subjected to complex processing comprising convolutional coding, interleaving, scrambling, differential coding and final formatting of the frame.

In TETRAPOL standard systems, GMSK modulation with BT \u003d 0.25 is used.

To convert speech in the standard, a codec with a retractation algorithm that uses the analysis method through RPCELP synthesis (Regular Pulse Code Excited Linear Prediction) is used. The transformation rate is 6000 bits / s.

The standard defines three basic communication modes: trunking, direct communication mode and relay mode.

IN network mode (or transcription mode) The interaction of subscribers is carried out using basic stations (BS), which distribute communication channels between subscribers. At the same time, the control signals are transmitted on a separate specifically dedicated for each BS of the frequency channel. In direct communication mode, the exchange of information between moving subscribers is made directly without the participation of the base station. IN repeater modecommunication between subscribers is carried out through a repeater that has fixed transmission and reception channels.

In TetraPol Standard systems, 2 main types of information exchange are supported: voice and data transmission.

Speech communication services Allow the following types of calls: broadcast call, call open channel installation, group call, individual call, multiple call using the list of subscribers, emergency call.

Data transfer services Provide a range of application-level services supported by the functions embedded in radio terminals, such as mezabonent messaging in accordance with the X.400 protocol, access to centralized databases, access to fixed networks in accordance with TCP / IP protocol, transfer facsimile messages, sending files, Transferring personal call signals, transmit short messages, transmitting status calls, supporting the transmission mode of the object received using the GPS receivers on the location of the object, transmitting video images.

The TetraPol standard provides standard network procedures providing a modern subscriber service level: dynamic rearrangement, subscriber authentication, roaming, priority call, subscriber transmitter management, subscriber's profile management (remote change in the parameters of the subscriber radio terminal laid in it during programming), etc.

TetraPol provides users with a number of additional services, which, along with the provision of service services, make it possible to effectively implement specific communication networks of public security services and law enforcement agencies. Such services include the access priority (providing preferred access to the system when overloading radio communication channels); priority call (call assignment in accordance with the prioritization scheme); Priority scanning (providing a user belonging to several groups, the possibility of receiving calls from subscriber any of the groups); a call authorized by the dispatcher (the mode in which the calls are received only with the sanction of the communication network manager); call forwarding (unconditional redirection of a call to another subscriber or forwarding in case of employment of the called subscriber); Connecting to the call (the inclusion of the mode in which one user interacting with the other can make a member of the third subscriber's connection); selective listening (interception of the incoming call without affecting the work of other subscribers); remote listening (remote inclusion of a subscriber radio station for transmission to listen to the situation at the subscriber); identification of the caller (definition and mapping on the caller identifier called the caller); "Double observation" (the possibility of a subscriber radio terminal operating in the network mode, to receive messages and in direct communication) and many others.

Due to the fact that from the very beginning, the TetraPol standard was focused on ensuring the requirements of law enforcement agencies, it provides for various communication safety mechanisms aimed at preventing threats such as unauthorized access to the system, listening to negotiations, creating intentional interference, traffic analysis specific subscribers, etc. Committed to the number of mechanisms include:

• automatic web reconfiguration (periodic redistribution of communication network resources (change in configuration) by setting and canceling open channels, dynamic rearrangement, reassign communication channels network manager, etc.);
• system Access Control (Control control of communication network equipment through smart cards and password systems);
• through code encryption (providing the possibility of protecting the transmitted information at any point of communication line between subscribers);
• subscribers authentication (Automatic or required by the subscriber authentication of subscribers);
• using temporary identifiers of subscribers(replacement of unique identification numbers of subscribers on aliases, connected with each new communication session);
• imitation of activity of radioabonents (mode of support for constant traffic during a negotiation break by sending the BS on the signal communication channels that are difficult to distinguish from information);
• remote disable radio terminal (the ability to disable the subscriber radio terminal network manager);
• distribution of keys by radio channel (Ability to transfer to the network manager to the network to subscribers by radio channel).

TetraPol standard systems are widely used in France. Apparently, not without supporting the government of the domestic manufacturer, except for the RUBIS network of the National Gendarmerie, the TetraPol system is operated by the French police (Acropol system) and railway service (IRIS system).

The TetraPol standard is popular in some other European countries. Based on this standard, the Madrid and Catalonia Police Communications Network, the Security Divisions of the Czech Republic, the airport service in Frankfurt. The Special Communication Network MatraCom 9600 is deployed in the interests of the Berlin Transport Enterprise. Communication network radio stations will be installed on more than 2,000 businesses. In addition to radio communications, the network involves the function of determining the location of vehicles.

In 1997, Matra Communications won a tender for creating a digital radio system for the Royal Thaja Police. The contract is part of the order for the modernization of a police radio network, which will unite 70 police stations. It is assumed to use the most modern possibilities of the system, including access to a centralized database, email, through information encryption, location. There is also information on the deployment of several systems in two other countries of Southeast Asia, as well as in the interests of the Mexico City Police.

In our country, the TETRAPOL standard system is not yet used. Currently, FAPSI implies the deployment of a given standard in Russia of the experimental area of \u200b\u200bthe Infanging radio.

2.5. SystemiDEN.

Iden technology (Integrated Digital Enhanced Network) was developed by Motorola in the early 90s. The first commercial system based on this technology was deployed in the US by Nextel in 1994

From the point of view of the status of the IDEN standard, it is possible to characterize as a corporate standard with an open architecture. This means that Motorola, maintaining all the rights to modify the system protocol, along with that license to manufacture the system components to various manufacturers.

This standard was developed for implementing integrated systems providing all types of mobile radio communications: dispatch communication, mobile telephony, text messaging and data packets. IDEN technology is focused on the creation of corporate networks of large organizations or commercial systems providing services to both organizations and individuals.

When implementing dispatch networks of mobile radio communications, IDEN provides the capabilities of a group and individual call, as well as a call signaling mode, in which in the event of the subscriber's unavailability, the call is remembered in the system, and then transmitted to the subscriber when he becomes available. The number of possible groups in IDEN is 65535. The connection time during a group call in the half-duplex mode does not exceed 0.5 s.

IDEN systems provide telephone organization capabilities in any directions: Mobile subscriber - Mobile subscriber, Mobile subscriber - TFP subscriber. Telephone communication is completely duplex. The system provides the possibility of voicemail.

IDEN system subscribers have the ability to transmit and receive text messages to their terminals, as well as transmit data (in switching mode at a speed of 9.6 kbps, and in packet - up to 32 kbps), which provides the possibility of organizing facsimile and electronic Mail, as well as interact with fixed networks, in particular with the Internet. Batch data transfer supports TCP / IP protocol.

The IDEN system is based on the MDW technology. In each frequency channel, 6 speech channels are transmitted in a width of 25 kHz. This is achieved by dividing the frame with a duration of 90 ms for time intervals of 15 ms, in each of which information is transmitted.

For speech coding, a codec is used according to the VSELP type algorithm. The information transfer rate in one channel is 7.2 kbps, and the total digital stream rate in the radio channel (by using noise-resistant coding and adding control information) reaches 64 kbps. Such a high speed of information transmission in a 25 kHz strip can be achieved due to the use of 16-position quadrature modulation M16-QAM.

The standard uses the standard for America and Asia the frequency range 805-821 / 855-866 MHz. IDEN has the highest spectral efficiency among the considered digital trunking standards under consideration, it allows you to place in 1 MHz to 240 information channels. At the same time, the dimensions of the coating zones of base stations (cells) in IDEN systems are less than in systems of other standards, which is explained by the low power of subscriber terminals (0.6 W for portable stations and 3 W - for mobile).

The architecture of the IDEN system has features characteristic of both trunking and cellular systems, which emphasizes IDEN orientation to maintain a large number of subscribers and intensive traffic. When creating commercial systems for servicing various organizations or enterprises in the system, up to 10,000 virtual networks can be created, each of which can be up to 65,500 subscribers, combined with 255 groups. At the same time, each of the groups of subscribers can use the entire communication zone provided by this system.

The first commercial system, deployed in 1994 by Nextel, is currently nationwide and has about 5,500 sites and 2.7 million subscribers. In the US there is another network, the operator of which is Southern Co. IDEN networks are also deployed in Canada, Brazil, Mexico, Colombia, Argentina, Japan, Singapore, China, Israel and other countries. The total number of IDEN subscribers in the world today exceeds 3 million people.

In Russia, IDEN systems are not deployed and there is no information about the development of projects of networks of this standard.

3. Brief Comparative Analysis of Digital Radiocommunication Standards

3.1. Specifications and functionality

Generalized information about EDACS, TETRA, APCO 25, TETRAPOL, IDEN standards and their technical specifications are presented in Table 1.

Table 1.

Characteristics Risty Standard (Systems) Communication Tetrapol Standard Developer Ericsson (Sweden) Matra Communications (France) Status Standard corporate rative open open corporate rative corporate native architecture Texture Maintenance Radioche manufacturers Nokia, Motorola, Oote, Rohde & Schwarz Motorola, E.F.Johnson Inc., Transcrypt, Adi Limited Matra, Nortel, CS Telecom Possible range working frequencies, MHz 138-174; 403-423; 450-470; 806-870 138-174; 403-423; 450-470; 806-870 138-174; 406-512; 746-869 805-821/ 855-866 Details of each frequency channels, kHz 12,5 (data transfer) Effective frequency band On one speech Channel, kgz. Modulation type C4FM (12.5 kHz) CQPSK (6.25 kHz) GMSK. (Bt \u003d 0.25) The method of speech coding and the speed of the recreation showing adaptive multi- Level coding (convert Towing 64kbit / s and Compression up to 9.2 kbps) Celp. (4.8 kbps) Imbe. (4.4 kbps) Rpcelp. (6 kbps) (7.2 kbps) Information transfer rate in the channel, BIT / S. 7200 (28800 - when transferring 4 information channels on one physician frequency) 9600 (up to 32K when transmitting data in batch mode) Installation time communication channel, with 0,25 (in the same-room system) 0.2 C - with induction. call (min); 0.17 C - with a group call (MIN) 0.25 - in direct communication; 0.35 - in relay mode; 0.5 - in radio Subsystem no more than 0.5 no more than 0.5 Separation method Communication channels MDW (using frequency separation in multizone systems) Channel view Control dedicated selected or distributed (depending on the configuration network gourats) dedicated dedicated Dedicated or distributed divided (depending on the configuration network gourats) Capabilities encryption information standard corporate algorithm Through encryption 1) standard algorithms; 2) end-to-end encryption 4 levels of information security 1) standard algorithms; 2) end-to-end encryption no information

The functionality provided by the systems of the digital transit radio communications standards is presented in Table 2.

Table 2.

Communication system functionality Support for basic call types (individual, group, broadcast.) Exit to TFP Full duplex subscriber terminals Data transfer and access to centralized databases Direct communication mode Automatic registration of mobile subscribers Personal challenge Access to fixed IP networks Transfer status messages Transfer short messages Support for location data transfer from the GPS system Fax communications Ability to install an open channel Multiple Access using the list of subscribers Availability of standard signal relay mode Availability of "Double Surveillance"

Note: (N / s - no information)

Considering the technical characteristics and functionality of the presented transcription standards, it can be noted that all standards are high (relative to this class of mobile radio systems) technical indicators. They allow you to build various communication network configurations, provide a variety of speech and data transmission modes, connection with PSTN and fixed networks. In the radio communication tools, the standards are used effective methods of recycling and noise-resistant information encoding. All standards provide high efficiency.

It can be noted that compared to other EDACS standards has a slightly smaller spectral efficiency. In addition, some specialists note that the EDACS standard does not use digital modulation methods, which makes it possible to talk about it as a standard in which digitized voice information is transmitted over an analog communication channel.

According to the functionality, the EDACS standard is also as a certain extent inferior to the remaining three standards, since it was developed a little earlier. TETRA, APCO 25, TETRAPOL and IDEN standards specify a wide range of standard communication services provided by level compared to each other. (As a rule, the list of services provided is determined when designing a specific system or radio network.)

3.2. Performing Special Requirements for Public Security Radiocommunication Systems

Information on the presence of some specific communication services, focused on using representatives of public security services, is presented in Table 3. The IDEN standard is not considered here, since this standard was designed without taking into account the special requirements of public security services. Currently, only certain information about the ongoing attempts to adapt systems of this standard to special requirements appear.

Table 3.

Special communication services Tetrapol Access priority System of priority calls Dynamic regrouping Selective audition Remote audition Caller Identification Challenge authorized by the dispatcher Transfer keys by radio channel (OTAR) Imitation of subscribers' activity Remote disabling subscriber Subscribers authentication

Since the standards presented in the table were developed in the interests of public security services, they all ensure the fulfillment of most requirements for special communication systems, which can be seen in Table 2. The presented digital standards provide high efficiency (access time for all systems - not more than 0 , 5 seconds and provide for the possibility of increasing the fault tolerance of radio networks due to flexible architecture. All standards allow you to implement information protection: For TETRA and TETRAPOL systems, standards provide for the possibility of using both a standard encryption algorithm and original algorithms due to end-to-end encryption; In EDACS systems, you can use a standard corporate algorithm or specifically to coordinate with the company the possibility of applying your own protection system; In accordance with the functional and technical requirements for APCO 25, 4 levels of information security should be provided (of which only one can be intended for exported applications).

When considering a list of special communication services provided by each standard, it can be noted that Tetra, APCO 25, TetraPol standards provide a compaable level of special services, and EDACs are somewhat smaller. The IDEN standard is not provided to fulfill special requirements.

3.3. Radio frequency spectrum resources

The presence of radio frequency spectrum resources (RFS) to deploy the radio system is the most important criterion for choosing a system or another. In this case, the most promising standards that provide the ability to build communication networks in the widest range.

EDACS systems are implemented in the ranges of 138-174, 403-423, 450-470 and 806-870 MHz, and there is information about the operating radio networks in all bands.

Tetra systems assume the use of the following ranges: 380-385 / 390-395, 410-430 / 450-470 MHz and 806-870 MHz.

APCO 25 systems in accordance with the functional and technical requirements provide the ability to work in any of the ranges allocated for mobile radio communications.

The TetraPol standard limits the upper frequency of its systems at 520 MHz.

IDEN standard systems function only in the 800 MHz band, which limits their use to build a specific circle of systems.

It should be noted that the allocation of radio frequency spectrum resources for building digital transit radio communication systems is most realistic in the 400 MHz band.

3.4. Standard Status (Open / Closed)

When choosing a radio standard, it is necessary to take into account the information on whether the standard is open or corporate (closed).

Corporate standards (EDACS and TETRAPOL) are the property of their developers. The acquisition of equipment is possible only at a limited range of manufacturers.

Open standards to which Tetra and APCO 25 include the creation of a competitive environment, attracting a large number of manufacturers of basic equipment, subscriber radio stations, test equipment for issuing compatible radio resources, which helps to reduce their cost. Access to standards specifications is provided to any organizations and firms entered into the relevant Association. Users who choose an open radio standard are not dependent on the only manufacturer and can change equipment suppliers. Open standards enjoy support from state and law enforcement structures, large companies in many countries of the world, and are also supported by the world's leading manufacturers of the element and nodal base.

Conclusion

A brief comparative analysis of data of data standards for digital trunking radio communications on the main considered criteria allows you to make certain conclusions about the prospects for their development both in the world and in Russia.

The EDACS standard has practically no development prospects. Compared to other standards, it has less spectral efficacy and less broad functionality. Ericsson does not plan to expand the capabilities of the standard and practically turned the production of equipment.

The IDEN standard does not provide many special requirements, as well as despite high spectral efficiency, limited to the need to use the 800 MHz band. It is likely that the systems of this standard have a certain potential and will still be deployed and operated, especially in North and South America. In other regions, the prospects for deploying systems of this standard look dubious.

The TetraPol standard has good technical indicators and sufficient functionality, however, the same as EDACS and IDEN standards do not have the status of an open standard, which can significantly restrain its development in technical terms, as well as in terms of the cost of subscriber and stationary equipment.

Tetra and APCO 25 standards have high technical characteristics and broad functionality, including the performance of special requirements of power structures, have sufficient spectral efficiency. The most important argument in favor of these systems is the presence of open standards status.

At the same time, most experts tends to believe that the digital transmission radio market will be conquered by the Tetra standard. This standard enjoys wide support of most major world manufacturers of equipment and communication administrations of various countries. Recent events in the domestic market of professional radio communications make it possible to conclude that in Russia this standard will get the most widespread.

So, when choosing a commercial transmission operator, users should pay attention not only for the license of the Ministry of Communications, but also on some "passport" network data. First of all, they include supported communications protocols, which can be divided into open and "branded". Open protocols allow any company to organize the issue of basic and subscriber equipment, but the developer of the "branded" protocol is the only manufacturer of the appropriate devices.

The openness of the protocol causes the occurrence of competitive manufacturers, thereby increasing the performance of infrastructure equipment, and systems differ in the market differing in functionality and cost. If there are many proposals of subscriber devices, the consumer gets the ability to choose a radio station park depending on the required price / quality ratio. But the main thing - does not occur his life binding to the equipment of a particular company. For example, for use in the network, organized on the basis of an open protocol of type MPT-1327 (there are many types of its varieties), it is allowed to use the technique of most radio equipment manufacturers. On the contrary, only Ericsson devices are able to work with the "branded" protocol, and the Actionet standard "understands" only the Nokia technique.

Service zone

According to the principles of the organization, a transcriptional bond is similar to cellular. Each basic station "covers" a specific area. The coverage area (read - the zone of competence) is called the site (in cellular communication - cell). To ensure sustainable communication in all points of service area, its solid coating is necessary. One base station is physically unable to perform this condition: in the zone will definitely have "holes", where the radio station will not be able to receive a signal. For example, it will not be possible to organize a steady bond near some reinforced concrete buildings, and to exit the "Radiothenia" site, the user will have to go into the structure or move to open space. Therefore, at least three base stations are needed for a continuous coating.

The quality and reliability of communication is determined not only by the number of transmitters, but also places thereof, the height of the antenna suspension, as well as the technical parameters of the base stations. The easiest way to check the quality of communication provided by a specific operator is to take subscriber equipment for testing in working conditions for a while.

Frequency

In Russia, several frequency ranges were allocated for commercial transmission systems: 136 - 174, 403 - 470, 470 - 520 and 800 MHz. The user needs to remember that the lower the frequency on which the operator works, the greater the range. On the other hand, the higher the frequency, the smaller the distance between the base stations and better the quality of communication. The optimal option may be the range of 478 - 486 MHz. Previously, this section of the frequency spectrum was reserved for the 22nd TV channel, but several years ago it was put up for a tender, and now it is distributed between the five Moscow radio operators. This range is free from the impact of transmitters of paging companies and other sources of interference.

Service and maintenance

Who will install and connect subscriber equipment? If the operator offers the user to independently mount the radio station in the car or directs it to this purpose to another company, then, most likely, he simply decided to save on the remuneration of technical personnel. Then the question of service guarantees remains open. In addition, who knows what other ways he is trying to minimize its expenses.

Prices for all operators are approximately the same. They consist of two components - one-time payment at the time of connection and monthly subscription fee. One-time payment is made from the price of the radio station and the necessary accessories (85-90% of the total), the cost of registration of permits (2-3%), network connections (4-6%) and the installation of the radio station (4-6%).

Subscriber equipment can be bought, rent, arrange in leasing (with the possibility of redemption in a year). In addition, some companies buy out old equipment at a residual value. Its price goes to credit a one-time payment for a new connection.

In Moscow, transcription services have more than 15 operators. Many companies supply equipment and engage in local (conducted) networks. So the customer can always choose a firm that is able to fully satisfy its urgent needs.

AMT. This is one of the first commercial radio telephone operators in Russia. The MPT-1327 AMT network is built on the basis of Nokia equipment. The zone of its action includes the territory of Moscow and the Moscow region at a distance of 50 km from the Moscow Ring Road, as well as the Moscow region of Solnechnogorsk, Dubna and their surroundings. The services of the company are calculated both by individual consumers (radiotelephones) and on corporate customers (virtual departmental networks of radio communications). The system uses duplex and half-duplex radio stations. In addition to voice communication, data transfer is supported. There is a full-fledged access to the public telephone network, roaming is provided with regions.

ASVT ("Rusaltai"). The Russian Network is built on the basis of Nokia ACTIONET equipment. The leading base station is located on the Ostankino Tower, and 10 others are deployed in the Moscow region to ensure its full coating and partial coating of adjacent areas. While network services are positioned as a radiotelephone, that is, the client receives a radiotelephone with a direct Moscow number. However, in contrast to the cell phone provided by the company, the subscriber device is capable of working in half duplex mode, which is used in the transponder transaction. In the RUSALTAY network, it is not added (both in cellular communication), and the secondary billing, which, at a similar value of the airtime, allows subscribers to significantly reduce costs.

"Radiotel". This largest operator of trotting communications in the North-West, and in Russia, is included in the Telecominvest group. Radiotel is the only St. Petersburg mobile operator, providing construction of hierarchical communication systems for corporate users, a trotting link with the possibility of accessing GTS, emergency connection with the "ambulance" (03), duty officers of the city administration and civil defense management services and Emergency situations. The coverage area of \u200b\u200bthe Radiotel network includes the entire St. Petersburg and the nearest suburbs. Terminal equipment is made and supplied by Ericsson and Maxon Corporations. In early 1996, the company created its own dispatching service "Petersburg Taxi 068", currently serving in the city more than 50% of taxi calls by phone.

In 1999, commissioned by one of the St. Petersburg fuel fuel companies "Radiotel" developed a project "Transfer of data for receiving payments on plastic cards of basic payment systems". The created system of multifunctional and allows you to solve several problems, including the task of ensuring transaction security.

In 1999, Radiotel became the winner of the tender for the organization of trunking communications for the service of "ambulance" and put 350 units of equipment. Today, every ambulance car in St. Petersburg has become informed by this company.

"MTK-Trank". The MTK-Trank network is built on the basis of Motorola's Smartzone equipment. Six sites provide a confident relationship in the capital and at a distance of at least 10 km from the Moscow Ring Road for Portable and at least 50 km from the Moscow Ring Road. The network is focused on collective users (organizations), which are characterized by high personnel mobility and arbitrary distribution of employees throughout the territory of Moscow and the region. Each client highlights its own virtual network. Group and personal calls are carried out throughout the radiocrying zone from any subscriber radio station without additional manipulations and switching. There are options for establishing communication outside the network coverage area in Talk-Arround mode (direct channel), as well as exit from the subscriber station to the public telephone network.

"Radiolesing". This is the first operator in Moscow a commercial trotnet network. Under the trademark TransLink several networks are combined:

Local networks in the range of 160 MHz (on "direct" simplex channels);
Pseudotranscing network SmartRunk II (since 1992);
MRT-1327 MP-1327 multi-zone, built on the basis of Fylde Microsystems.

Currently there are five base stations (22 channels), which support a confident relationship within 50 km from the Moscow Ring Road.

"RegionTrans". The company provides radiotelephone services in Moscow and the Moscow region, as well as in the regions of Central Russia. The first of the ESAS protocol based on the ESAS protocol, operating in the 800 MHz range, was commissioned in 1997. Now in Moscow there are six base stations, which ensures confident reception within the city feature for portable subscriber stations and in the near Moscow region - for automotive devices. A distinctive feature of the regional services is the development of professional business solutions, which take into account the specific requirements of customers. For example, a software and hardware complex "Taxi Dispatch Service" has been created for a major Moscow taxi.

"Center-Telko". The urban integrated system of radiotelephone communication "System Trank" is deployed in accordance with the Decree of the Moscow Government of October 29, 1996. The network is based on EDACS equipment, thereby ensuring high security channels and the reliability of the system in any extreme situations. Four base stations support the functioning of portable stations in Moscow and the nearest Moscow region (4-7 km from the Moscow Ring Road), and automotive - within 50 km from the Moscow Ring Road. In addition to the traditional radio communications networks in the TRAC system network, digital data transmission services and location of objects are provided.

Operators of monononon transitnets

BTT. EF Johnson equipment works in the BTT network. Its feature is that along with the repeater, it uses a network of remote receivers associated with the base station with dedicated wired lines. Subscriber terminals are characterized by high reliability.

"Softtnet". The system "Softtnet" was created to provide operational dispatch communication. This was precisely the choice as the LTR transit protocol. The main users are services in need of unified management, such as a taxi, cargo delivery, collection, security services, etc. The dignity of this network is the availability of an operational communication channel with the Moscow City Salvation Service provided to subscribers for free.

Pseudotransking networks

MCS ("Mobile Communication Systems"). MCS is one of the first trotting networks based on the SmartRunk-II protocol - it was deployed back in 1994. The basic equipment DX-RADIO (USA) is located on the 269th and 325th marks of the Ostankino television, which provides a coverage area within a radius of 80-90 km. Together with the "Center-Telco" MCS enters the urban integrated system of radiotelephone communication (GISRS), established by the decree of the Government of Moscow.

Currently, the Mobile Communication Systems Company provides all the carriers of dangerous goods (fuel, oil, acid, etc.) by voice communications, state control sensors and GPS. A single dispatching point is in GOCM GU. Graduation and duplex services are provided, access to the telephone network, data transmission and GPS. There is a possibility of local work (without repeater) on simplex frequencies throughout Moscow and Moscow region. Free provision of equipment to a potential customer for testing in real conditions is not excluded.

"Lansky". The SMARTRUNK-R mobile radiotelephone system is operated in Moscow since 1995. The Moscow network segment consists of two basic stations with a total capacity of 11 radio channels operating in the range of 430-450 MHz. Due to the separation of base stations (BS No. 1, it is located in the area of \u200b\u200bM. Alekseevskaya, and BS №2 - not far from m. "Belyaevo") is ensured uninterrupted communication within the Moscow Ring Road and partly in the near Moscow region.

Since 1999, the company has been operating with mobile radiotelephone communications systems in Orel, Kursk, Belgorod and Tambov. The work of subscribers of the Moscow Transknding Network in the above-mentioned cities is possible when replacing their terminals at the Lansky office on equipment compatible with regional trunking systems. A similar possibility is provided to subscribers of regional networks.

"Everlink". The one-mono-room pseudotranscling compound system based on the E-Trunk protocol provides sustainable reception on portable radio stations within Moscow and mobile - within a radius of up to 30 km from the Moscow Ring Road. Telephony services are not provided. The license applies to Moscow and the Moscow region, which allows users to offer consumers a direct channel (communication with portable radio stations up to 2 km in conditions of any building).

Pavel Dmitriev, Network, №10 / 2002

Section 4 Mobile Transcording Systems

Lecture No. 23.

What is the "trunk"? Let's try to figure out what is hiding behind this "fashionable" word? Here is the translation of "Anglo-Russian Dictionary on Radioelectronics" 1987 of the publication:

Trunk (trunk) - connecting line; Main line of communication; link

Trunking (trunking) - group education

The 1999 electronic dictionary "PROMT" is more "formed":

Trunking - provision of free channels

Trunked Radio System - Radio System with Automatic Redistribution of Channels

As can be seen from the translation, nothing special for the word "trunk" does not lick. Total "Automatic Channel Provision".

Trank principles are used already over 70 years in telephony. Any automatic telephone exchange, mini PBX, Cellular communication uses the trunking. We are all practically daily using trunking. Although not many of us are guessing that when we raise the phone and type the phone ... We use trunking. After all, it would be a non-disabilities to allocate a separate line to each telephone subscriber, especially a long-distance. We all allocate a line for the conversation only at the time of the communication session. With the rest of the time (free from our conversations) other users are serviced.

Imagine the situation when residents, suppose one of the districts of Tashkent at the same time would decide to call their friends. What would happen in this case? And nothing. They simply could not do it, since the number of telephone lines (between PBX) is limited and at the same time can conduct communication sessions a completely defined number of subscribers (how much specifically is the topic of a separate conversation).

Now imagine that all telephone sets are replaced by radio stations, and wired lines for radio frequency channels. As you probably guessed, we got a trunk - a radio system with automatic provision of free channel.

Several explanations

Trank systems do not regulate:

access to the telephone network;

the use of duplex ("I say and listen" at the same time, as in telephony);

huge range;

highest service;

free access;

and much more...

They simply allow you to communicate with each other without thinking about technical intricacies and physical problems. You are talking - the equipment works. Works so that you can talk.

More scientifically, the essence of the trunk connection is that the subscriber is not fixed in a specific channel, but has equal access to all channels in the system. And what to use for a communication session solves special control equipment. When requesting a subscriber, the system automatically provides the subscriber free channel.

About terminology

In Russian publications, the words "trink" and "trunking systems" were established. Let us leave these turns on the conscience of translators and linguists. In our opinion, the word "trunk" and "trunk systems" is more complicated in pronunciation and easier in writing. As a rule, their use does not cause ambiguous understanding. Therefore, in the future, we will mainly use "our" wording.

Myths and reality

Ten reasons for cooling the heat of optimists and raising the spirit of pessimists regarding the "wonders" of a trunk connection:

The trunk is not a miracle, but the development process of radio communications.

The trunk does not replace the cell phone, does not replace the pager ... the trunk does not replace anything at all, but complements.

Transit, which means: comfortable, flexible, expandable, universal, reliable, complicated, dear ...

Trunk systems are used to communicate between radio stations and once again by radio stations, and not between radio stations and telephone lines.

Rank systems can a lot, but not all.

Trunk systems are a lot, and what to choose - depends on the tasks.

If the trunk system does not solve the task, it means that this is an incorrect task.

If you could not choose a suitable trunk system, then you do not need a trunk system.

There are many suppliers, and there is little money - do not pay twice.

Do not flatter yourself! Trust the choice of specialists.

And if seriously, what advantages of trunk systems compared to traditional, so-called, "ordinary" communication networks, with cellular telephony, with personal radio program systems (pajing)?

Definitely answer this question is quite difficult. Like any systems, there are both advantages and disadvantages.

Perhaps the main advantage of trunk systems is the possibility of integrating different services with various needs within the same network with minimal (compared to other radio systems) material costs.

Advantages of trunk networks

Compared to cellular systems:

the ability to communicate simultaneously with several subscribers (group calls);

high efficiency establishing a compound (0.2-1 s);

organization of queues to the resources of the system during employment and automatic connection after accessing the possibility of access;

access to the system based on priorities and emergency provision of a communication channel to a subscriber with a higher priority;

less deployment and operation costs.

Compared to the "ordinary" radio communications systems:

saving frequency resources;

higher level of service - individual calls, priorities, integration with other networks;

the ability to transfer digital data;

coating with a bond of large areas thanks to the multi-zone configuration.

Compared to personal radio calls (Peyding):

double-sided communication;

the ability to transfer short messages (similar paging) on \u200b\u200btrunk channels using existing equipment.

This is not a complete list of existing advantages. And yet the trunk is not a panacea from all troubles. Along with the trunk systems there are a number of users who are needed by a cell phone for different reasons, someone has enough chapel, and a number of users do (and will do) "ordinary" communication systems.

It is necessary to clearly imagine that the trunk is not a universal solution of the whole set of radio communication tasks. In anyone, even the "trunk" state still remains a number of problems that are solved by other communication systems that have nothing to do with trunk.

The disadvantages of trunk systems include:

low profitability with a small number of subscribers;

relatively high cost of equipment (compared with "ordinary" radio communications systems);

the need for interpasic communication lines (wired, radio frequency, radio relay, fiber optic) and, as a result, complication and rise in price of deployment *;

the need for professional service.

* It is worth noting that for the coverage of large territories, most radio communications systems require multi-zone implementation and, of course, interband lines.

Classification of trunk systems

Tranking systems can be classified according to many features, for example, according to the transmitted data format (analog, digital), by type of protocols (LTR, MPT 1327, SmartRunk II), according to the number of served zones (single or multi-zone), according to the radio channel representation methods (" Transmissions "or" Transcang Messages "), according to the methods of control of base stations (centralized or distributed), by type of control channels (dedicated or distributed), etc.

We will not dwell on a detailed classification of trunk systems, especially since there is no single and generally accepted technique in this area. We will try to characterize modern trunk systems, describe their capabilities, note the most important points that you should pay attention to when choosing.

Architecture of trunking systems

Transkding systems are called radial-zone systems of ground mobile radio communications that automatically distribute the communication channels of repeaters between subscribers. This is a rather general definition, but it contains a set of features that combine all transking systems, from the simplest SmartRunk to modern Tetra. The term "trunk" comes from English trunking, which can be translated as "combining into a bundle".

Single-Mono Systems

Figure 67 Structural diagram of a single-distance transking system

The main architectural principles of truncording systems are easily viewed on the generalized structural scheme of the one-mono-one trotting system shown in Fig. 67. The infrastructure of the trunking system is represented by the base station (BS), which, in addition to radio frequency equipment (repeaters, a radio signal combining device, antenna, also includes a switch, control device and interfaces of various external networks.

Repeater. Repeater (RT) - a set of transceiver equipment serving one pair of carrier frequencies. Until recently, in the overwhelming majority TCC, one pair of carriers meant one traffic channel (CT). Currently, with the advent of the TETRA standard and EDACS Protocall systems, providing for a temporary seal, one RT can provide two or four CTs.

Antennas. The most important principle of constructing trunking systems is to create radiocrying zones as large as possible. Therefore, the antennas of the base station are usually placed on high masts or structures and have a circular orientation chart. Of course, at the location of the base station on the edge of the zone, directed antennas are used. The base station can have both a single transceiver antenna and separate antennas for receiving and transmitting. In some cases, several receiving antennas can be placed on one mast to combat fading caused by multipath distribution.

The radio signal combining device allows you to use the same antenna equipment for the simultaneous operation of receivers and transmitters on several frequency channels. Repeaters of truncording systems operate only in duplex mode, and the separation of reception frequencies and transmission (duplex separation), depending on the operating range, is from 3 MHz to 45 MHz.

The switch in the one-mono-axis trotting system serves all its traffic, including the connection of mobile subscribers with a public telephone network (TFOP) and all calls associated with data transfer.

The control device provides the interaction of all base station nodes. It also processes calls, authenticates callers (Verification of "Your Alien"), maintaining call queues and making records in the time-based payment database. In some systems, the control device adjusts the maximum allowable connection duration with the telephone network. As a rule, two regulation options are used: reducing the duration of the connections to the predetermined clock of the highest load, or adaptive change in the connection duration depending on the current load.

The TFP interface is implemented in trunking systems in various ways. In low-cost systems (for example, SmartRunk), the connection can be made using two-wire dial-up lines. More modern TCCs have a direct did (Direct Inward Dialing) in the interface to the PSTN, which provides access to the transcription network subscribers using a standard PBX numbering. A number of systems use a digital ICM connection with PBX equipment.

One of the main problems when registering and using trunking systems in Russia is the problem of their conjugation with TFP. With outgoing calls for trinting subscribers in the telephone network, the complexity lies in the fact that some trunking systems cannot dial the number in decadane mode by subscriber lines in electromechanical PBX. Thus, it is necessary to use an additional tone set conversion device in the decades.

The incoming relationship from TFP subscribers to radioabonents is also problematic but a number of reasons. Most trotking networks are associated with a telephone network using two-wire subscriber lines or E & M lines. In this case, after a dialing of the TFT number, the radioabonent number is required. However, after a complete dialing of the subscriber lipping and closure of the loop, the trunking system control device is considered to be established, and the further set of the numbers in the pulse mode is difficult, and in some cases it is impossible. The "click" in the SmartRunk II system does not guarantee the correctness of the impulse donabe, since the quality of the "pulses-click" coming from the subscriber line depends on its electrical characteristics, length, etc.

To get out of the current situation in the Laboratory of IVP, together with ELTA-R specialists, a telephone interface (T) ELTA 200 was developed to conjugate trinting communication systems of different types with TFP. Such an interface allows you to match the transit-on communication systems and PSTN on digital channels (2.048 Mbps), three-wire connecting lines with a decade set of numbers, as well as four-wire CTC channels with system alarm systems of various types when interconnected with departmental telephone networks.

The connection to the TFOP is traditional for the TCC, but recently the number of applications involving PD increasingly increases, and therefore the presence of an interface to the SCP also becomes mandatory.

Terminal maintenance and operation (TEE terminal) is located, as a rule, at the base station of a single-room network. The terminal is designed to monitor the state of the system, carrying out the diagnosis of faults, accounting for tariff information, making changes to the subscriber database. The overwhelming majority of manufactured and developed truncording systems have the ability to remotely connect the TEO terminal through TFP or UCP.

Dispatch remote. Optional, but very characteristic elements of the infrastructure of the trunking system are dispatcher consoles. The fact is that the trunking systems are used primarily by those consumers whose work does not do without a dispatcher. These are law enforcement services, ambulance, fire protection, transport companies, municipal services.

Dispatcher consoles can be included in the system by subscriber radio channels, or connect via dedicated lines directly to the base station switch. It should be noted that several independent communication networks can be organized within a single trunking system, each of which can have its own dispatch console. Users of each such networks will not notice the work of the neighbors, and that is no less important, they will not be able to interfere with the work of other networks.

Subscriber equipment of trunking systems includes a wide range of devices. As a rule, half-duplex radio stations are the most numerous, because It is they who are most suitable for work in closed groups. For the most part, this is a radio station with a limited number of functions that do not have a numeric keypad. Their users tend to have the opportunity to contact only subscribers within their working group, as well as send emergency calls to the dispatcher. However, this is quite enough for most consumers of communication services of trunking systems. The half-duplex radio stations with a wide range of functions and a numeric keypad are available, but they, being somewhat more expensive, are intended for a narrower privileged number of subscribers.

In trunkding systems, especially designed for commercial use, duplex radio stations are also applied, rather reminiscent of cell phones, but possessing much greater functionality compared to the latter. Duplex radio stations of truncording systems provide users with a full connection with TFP. As for group work in the radio network, it is produced in half duplex mode. In corporate trunking networks, duplex radio stations are used primarily for the highest management personnel.

Both half-duplex and duplex trunking radio stations are manufactured not only in portable, but also in the automotive execution. As a rule, the output power of transmitters of automotive radio stations is 3-5 times higher than that of portable radio stations.

The relatively new class of devices for trunking systems are data terminals. In the analog trotking systems, data terminals are specialized radio models that support the corresponding radio interface protocol. For digital systems, it is more characteristic of embedding the data transfer interface into subscriber radio stations of various classes. The automotive data terminal sometimes includes a GPS satellite navigation receiver (Global Positioning System), designed to determine current coordinates and subsequent transmission to their dispatcher on the remote.

In trinting systems, stationary radio stations are also used, mainly to connect dispatching remote controls. The output power of stationary radio stations transmitters is approximately the same as auto radio stations.

Multi-zone systems

Early standards of trunking systems did not provide for any mechanisms for the interaction of various zones of service. Meanwhile, consumer requirements have increased significantly, and although equipment for single-room systems is still produced and successfully sold, all newly developed truncording systems and standards are multi-zone.

The architecture of multi-zone trunking systems can be built over two different principles. In the event that the defining factor is the cost of the equipment, a distributed interband switching is used. The structure of such a system is shown in Fig. 2. Each base station in such a system has its own connection to TFP. This is already enough to organize a multi-zone system - if necessary, calling from one zone to another, it is performed through the PSTN interface, including a telephone number set procedure. In addition, base stations can be directly connected using physical dedicated communication lines (small-channel radio relay lines are most often used).

Each BS in such a system has its own connection to TFP. If it is necessary to call from one zone to another, it is performed through the PSTN interface, including a telephone number set procedure. In addition, the BS can be directly connected using physical allocated communication lines.

The use of distributed interband switching is advisable only for systems with a small amount of zones and with low requirements for the efficiency of interzal calls (especially in the case of a connection through the switched channels of TFPT). In systems with high quality maintenance uses architecture from the Central Committee. The structure of the multizone TCC with the Central Committee is depicted in Fig. 68.

The main element of this scheme is an interband switch. It processes all types of inter-call calls, i.e. All interband traffic passes through one switch connected to the BS on the dedicated lines. This ensures fast call processing, the ability to connect centralized DP. Information about the location of the subscribers of the system from the Central Committee is kept in a single place, so it is easier to protect it. In addition, the interband switch also performs the functions of a centralized interface to TFP and UCB, which allows you to fully monitor both speech traffic TC and traffic of all PD applications associated with external SCPs, such as the Internet. Thus, the system with the Central Committee has a higher handling.

Figure 68 Structural diagram of a trotting network with distributed interband switching

Figure 69 Structural diagram of a trotting network with centralized interband switching

So, you can distinguish several of the most important architectural features inherent in trunking systems.

First, it is limited (and therefore inexpensive) infrastructure. In multi-zone trunking systems, it is more developed, but still does not matter any comparison with the power of the infrastructure of cellular networks.

Secondly, it is a large spatial coverage of base stations service areas, which is due to the need to maintain group work in extensive territories and minimizing system costs. In cellular networks, where investments in infrastructure quickly pay off, and traffic is constantly growing, the base stations are placed more and more tight, and the radius of the coating zones (cells) decreases. With the deployment of trunking systems, everything is somewhat different - the amount of funding is usually limited, and to achieve high investment efficiency, it is necessary to serve a more extensive territory with a single set of equipment for the basic station.

Thirdly, a wide range of subscriber equipment allows trotking systems to cover almost the entire spectrum of corporate consumer needs in mobile communications. The possibility of servicing dissimilar to functional devices in a single system is another way to minimize costs.

Fourthly, trunking systems allow on the basis of their channels to organize independent allocated communication networks (or, as they say recently, private virtual networks). This means that several organizations can jointly deploy a unified system instead of installing individual systems. At the same time, the tangible savings of the radio frequency resource are achieved, as well as a decrease in the cost of infrastructure.

All of the above testifies to the strength of the positions of truncording systems in the corporate sector of the market of systems and means of mobile communication.

Classification of trunking systems

For classifying trinting communication systems, you can use the following features.

Speech information transfer method

According to the method of transmitting speech information, trotting systems are divided into analog and digital. Speech transmission in the radio channel of analog systems is carried out using frequency modulation, and the frequency mesh step is usually 12.5 kHz or 25 kHz.

To transmit speech in digital systems, various types of vocoders are used, converting an analog speech signal into a digital stream at a speed of not more than 4.8 kbps.

Number of zones

Depending on the number of base stations and the overall architecture, one-room and multi-zone systems distinguish. The first people have only one base station, the second - a few BS with the possibility of roaming.

Method for combining basic stations in multizone systems

Basic stations in trunking systems can be combined with a single switch (centralized switching system), as well as connect to each other directly or via common networks (distributed switching systems).

Type of multiple access

In the overwhelming majority of trunking systems, including digital systems, multiplexing access with frequency separation (MDCH) is used. For MDCH systems, the "One Channel One Channel" ratio is valid.

In the mononono-bed systems, TETRA standard uses multi-section access with temporary seal (MDW). At the same time, the TETRA multiple systems use a combination of MDCH and MDW.

Channel search and appointment method

By the method of searching and destination, the channel distinguish systems with decentralized and centralized management.

In systems with decentralized management, the procedure for finding a free channel is performed by subscriber radio stations. In these systems, the base station repeaters are usually not associated with each other and work independently. A feature of systems with decentralized control is a relatively long time to establish a connection between subscribers growing with an increase in the number of repeaters. This dependence is caused by the fact that subscriber radio stations are forced to continuously repeat the channels in search of the call signal (the latter can come from any repeater) or free channel (if the subscriber itself sends a call). The most characteristic representatives of this class are the SMARTRUNK protocol systems.

In centralized control systems, the search and destination of the free channel is made at the base station. To ensure the normal functioning of such systems, channels of two types are organized: workers (Traffic Channels) and control channel (Control Channel). All communication requests are sent over the control channel. By the same channel, the base station informs subscriber devices to assign the working channel, deviating the request, or on the queue in the queue.

Channel type control

In all trunking systems, control channels are digital. There are systems with a dedicated frequency control channel and systems with a distributed control channel. In the system of the first type, the data transmission in the control channel is performed at a speed of up to 9.6 kbps, and AloHA protocols are used to resolve conflicts.

The dedicated control channel has all the MRI1327 transit protocol systems, Motorola system (Startsite, Smartnet, SmartZone), EDACSON EDACSON system and some others.

In systems with a distributed control channel, information about the status of the system and incoming calls is distributed between low-speed data subcarlands, combined with all operating channels. Thus, in each frequency channel of the system, not only speech is transmitted, but also the data of the control channel. To organize such a partial channel in analog systems, the subtonal frequency range of 0 - 300 Hz is usually used. The most characteristic representatives of this class are the LTR protocol systems.

Channel hold method

Transking systems allow subscribers to hold the communication channel throughout the entire conversation, or only for transmission. The first method, also called Message Trunking, is most traditional for communication systems, and is necessarily used in all cases of duplex communication or a compound with TFP.

The second method providing for the holding of the channel only for the transmission time is called transmission trunking. It can only be implemented when using half-duplex radio stations. In the last transmitter turns on only at the time of pronouncing the subscriber's conversation. In the pauses between the end of the phrases of one subscriber and the beginning of the response phrases of other transmitters of both radio stations are turned off. Some trunking systems effectively use such pauses, freeing the working channel immediately after the end of the transmitter of the subscriber radio station. For a response replica, the assignment of the working channel will be reinstalled, while the replicas of the same conversation will most likely be transmitted along different channels.

A payment for some increase in the efficiency of using the system as a whole when the transmission is used to reduce the comfort of negotiations, especially during high loads. Working channels to continue the started conversation in such periods will be provided with a delay reaching a few seconds, which will lead to fragmentation and fragmentation of the conversation.

In almost every salon of cellular communication, showcases of which are broken from mobile phones, is a security guard with a mandatory bulky warrant. There is unwittingly wondering: "Why does this person use a simple mobile phone for service?"

Today, along with the usual cellular bond there are so-called professional Mobile Radio Systems (PMR) (Professional Mobile Radio.- PMR), or transkding Mobile Radio Communication. They occupy their mobile equipment market sector for corporate users, various departments and social services, performing the functions necessary for these users.

Transcribing mobile radio (from eng. trunking. - provision of free channels, Trunk - The main line) is a system of double-sided mobile radio, which uses a range of ultra-screw waves. In practice, the PMR system is arranged similar to Cellular: Custom Terminals and Base Stations (BS), Equipment for increasing the range - repeaters and controller, which manages the station's operation, processes the channels of repeaters (commutes) and provides access to the city telephone network. Tranking networks may be one-room (contain one BS) or multi-zone (several BS). There are analog and digital trunking communication systems.

Better than cellular?

What is different from the cell phone, if, not counting the difference between the user terminal (by the radio / telephone), everything is designed equally?

Cellular communication is positioned as "telephone in pocket", and the trunking is designed to solve a narrow circle of professional tasks. Cellular communication, for example, provides a variety of multimedia services, but the oilman, on duty on the drilling platform in the Baltic Sea, or the rescue center of the Ministry of Emergency Situations is unlikely to be able to download the new Madonna album. Trans-trigge links choose organizations such as MES, security agencies, taxi companies, etc. For the ordinary office workers, the option "Cell phone + corporate tariff plan" is quite suitable.

The communication system that professionals enjoy must support such functions as:

Interventional communication (0.2-0.5 sec) inside a group of subscribers, which can be specified in advance;

The possibility of redistributing participants in groups during a communication session;

Call priorities system (mobile operator does not make differences between subscribers);

Conservation of communication even when the base station fails;

Transmission of the broadcast signal to network subscribers;

The ability to quickly reconfigure the network.

These requirements are not fully represented in cellular communication systems, but fully supported by trunking systems. It is worth noting that the participants of the mobile market are still not sitting and offer a service. Push-to-Talk With the ability to establish a group call and rapidly establishing a connection. However, innovation in any case does not meet the requirements of professionals. Read more about Push-to-Talk here.

We offer a comparative table using the example of two versions of Tetra - the popular standard of digital trintaging radio communications, and GSM networks.

Modes and Functional Features, Tetra Communication Standards Tetra Tetra (R2) GSM Group Call + + +/- Broadcasting + + - Alarm Call + + +/- Priority Call + +/- Priority Access + + - Duplex Communication + + + Calling + + - delayed entry in connection + + - direct communication mode (without base station) + + - mode - "only reception" - + - the ability to expand the zone of communication - + - selection of zone + + - status messages + + - Transfer of short text messages + + + Challenge of the + + dispatcher - Providing on request of the subscriber of a wide band + + - the capabilities of signal encryption and radio interface + + +/- Simultaneous voice and data transmission + + + high-speed data transmission - + + selective listening to the subscribers by the dispatcher + + - Remote listening to the acoustic setting + + - dynamic rearrangement + + - from the steampunk to cyber

Professional analogue communication existed almost from the beginning of the 20th century and during this time he had time to change a lot, coming to digital technologies with an impressive luggage.

Each one knows that radio communication began in 1895, when A. Popov (and only a year later, the city of Marconi) created the first receiver. From 1897 to 1915 Markoni organizes the first connected companies and unfolds the production of equipment; Relociation regulations appear, including the frequency distribution between different services. Professional radio communication in the Perid from 1915 to the 1950s originated.

In the first half of the 20th century, the possibilities of communication on different wavelengths were investigated. Until 1920, communication was carried out using waves from hundreds of hundredth meters to tens of kilometers. In 1922, the property of short waves was known to spread at any distances, refracted in the upper layers of the atmosphere and reflecting them, is the ideal means for further communication. The 1930s became the time of meter waves; And the 1940s of the decimamers and centimeters propagating straight-line 40-50 km within the limits of direct visibility. Popularization of radio communications directly depended on the achievements of technology. Before the emergence of miniature semiconductors, the receivers remained cumbersome and at best fit in the suitcase, which imposed certain limitations.

The history of professional telecommunication networks is usually divided into steps. First stage We are considered networks of conventional type (from English. conventional - Normal, traditional). Their not like capabilities are the following: simplex mode of operation (pressed the button - asked a question - released the button - received the answer - I clicked on the button - ...), making individual and group calls (up to several dozen subscribers) in conventional communication channel systems (frequency) It is rigidly fixed for a specific group of subscribers. At the same time, high efficiency is guaranteed (you only need to configure the frequency), but it causes the small bandwidth of the network (little frequencies).

Second phase - Transking networks. Such networks made it possible to maintain up to several hundred subscribers and allowed to more effectively use the radio frequency resource. Such communication systems have become systems with shared subscribers access to the frequency range, in contrast to the conventional systems. This provides increased bandwidth and a large coverage area.

Multi-zone trunking networks third stage. The service area in them increased even more due to several base stations. The number of served subscribers has become practically unlimited, a call priority system appeared, the ability to duplex call mode (the guide button is not required, the connection is similar to the phone with amendment on a much greater call speed), access to public telephone networks, data transmission.

Simplex, half duplex and duplex

No, it is not the name of the sequels to the comedy "duplex", in which the Hollywood stars were starred Ben Stiller and Drew Berrymore. The title caused the names of three basic modes of wireless radio communications.

1. Simplex communication uses one frequency - for receiving and transmission. Only the exchange of replicas is possible. Due to the restrictions that physician imposes, to use this, the most economical type of wireless radio communications, will be at a distance of no more than 5 km. For a stable signal, an open area is extremely desirable. Communication is carried out through user terminals.

2. The half-duplex link also uses two frequencies, but they will have to communicate, as in the simplex mode. The base station (BS) at one frequency constantly accepts subscriber signals, and then on another frequency broadcasts what has accepted. The radio uses the frequency for reception on which the BS broadcasts, and must contain a radio frequency switch. The principle of half-cups underlies low-cost networks that associate dozens of subscribers at different points of the city and the open area.

3. A duplex connection involves two frequencies - one on the reception, the other - on the transfer and is intended to lead the usual dialogue. Naturally, basic stations are involved to relay signals. Analog duplex systems require two channels (4 radio frequencies) to connect subscribers. The terminal is equipped with an overall duplex filter, whose role to give a receiver and transmitter simultaneous access to the antenna. Digital duplex is implemented differently and does not require a cumbersome filter - at each moment of time the subscriber receives or transmits. For example, in the Tetra standard, switching occurs 18 times per second.

Modern digital trunking networks (Ts.) are the top of the evolutionary chain of professional communications. In addition to the capabilities available to users of analog systems, reliable protection against unauthorized access (moreover, listening to negotiations with analog device becomes impossible) and packet data transmission (Internet access). The subscriber's device is recognized using various identification mechanisms or SIM cards. In essence, digital trunking systems are universal communication networks that ensure the confidentiality of subscriber contacts, and are capable of simultaneously transmitting large data streams over communication channels, whether telemetry data or video information (in the last editions of standards, such capabilities are provided for).

There are a large number of different standards of transit-winning systems of mobile radio communications, differing in many assessments. In our country, as well as around the world, analog systems of various versions and standards are still distributed. However, by virtue of their moral obsolence, they are not so interesting for consideration as their digital fellow. The top five most popular and recognized in many countries of the world should be considered more detailed.

EDACS (Enhanced Digital Access Communication System)

Firm Ericsson. (Sweden) before others (until she bought it Sony In the 1980s), the problem of obsolescence of analog technology and the insufficient degree of negotiations in such systems and was engaged in the development of the EDACS corporate closed standards (Enhanced Digital Access Communication System). Initially, the standard provided for the transmission of speech on analog protocols, later the standard was modified and a digital version of the system called EDACS AEGIS.. EDACS systems operate at 138-174 MHz frequencies, 403-423 MHz, 450-470 MHz and 806-870 MHz; The network can be drawn to more than 16,000 subscribers. In Russia, this standard is not too popular due to its closedness and fast obsolescence (in fact, this is a digital standard for transmitting analog signals). All rights belong to the developer, and just to release the equipment will not allow you. In addition, Ericsson stopped the supply of equipment for the deployment of new networks of this standard and is engaged only by supporting existing ones.

IDEN technology ( iNTEGRATED DIGITAL ENHANCED NETWORK) - a closed corporate standard, the development of which was started by the company Motorola.in the early 1990s. In 1994, in the US company Nextel On the basis of this technology, the first network of commercial use is deployed. Today, similar networks are deployed in many countries of the North and North of South America, Asia. Today IDEN subscribers are more than 3,000,000 people (90% of them fall into the United States). Such popularity of IDen has gained due to the fact that it is a certain compromise between trotanking and cellular systems (provides the ability to send messages, fax communication, data transmission using TCP / IP protocol at a speed of up to 36 kbps, low cost). Each organization that uses the IDEN standard can be created up to 10,000 virtual networks, each of which can be up to 65,500 subscribers. IDEN uses the frequency range of 805-821 / 855-866 MHz. In Russia, IDEN systems are not likely due to the inconvenience of using a similar frequency range when solving the tasks for which the professional communications systems are calculated. It is noteworthy that the company Motorola. Various IDEN devices are available with the functions of modern mobile phones. For example, Motorola IC502 - CDMA / IDEN-phone with GPS and Motorola I290 with MP3 player.

Tetrapol PAS (Tetrapol)

Developed by a French company Matra Communication. The creation of this closed standard was launched in 1987 by Matra Communications by order of French gendarmerie. TETRAPOL standard communication network operates on half of the territory of France since 1994 and serves more than 15,000 subscribers. TETRAPOL standard communication systems work starting at a frequency of 70 MHz and have a 520 MHz functioning ceiling, which does not contribute to popularization in other countries, where other frequency ranges can traditionally be given to such systems. In Russia, experienced areas of operation of the TetraPol network have been created.

TETRA (Terrestrial Trunked Radio)

Tetra. - Open Standard of Professional Radiocommunication, Developed since 1994 Etsi. (European Telecommunications Standards Institute - European Institute of Telecommunication Standards). Tetra means TERRESTRIAL TRUNKED RADIO - "Ground Transit Radio". Initially, until the standard has gained popularity outside Europe, Tetra has deciphered as TRANS-EUROPEAN Trunked Radio - "Trans-European Transking Radio". In Europe, the TETRA PMR standard works in frequency bands 380-385 / 390-395 MHz, 410-430 / 450-470 MHz. In Asia - 806-870 MHz.

In the Tetra specifications, as an open standard, which means everyone who wishes to produce equipment for communication may not think about compatibility issues with the equipment of other companies and about the delegation of copyright. To produce products supporting this standard, you must join the organization Mou Tetra. - Memorandum of promoting the Tetra standard. Nokia., Motorola., RohDeschwarz. And other large companies engaged in the production of equipment for communication support this standard. Tetra networks are deployed almost across Europe, in Asia, Africa and South America. Tetra Release 2. - A new version of the standard that allows you to carry out tight integration with third-generation mobile networks and significantly increase the data transfer rate. The project to deploy networks of this standard in Russia is called "Tetrarus". Muchly says at least the fact that "within the framework of the Federal Target Program" Development of the G. Sochi as a Mountain Limitational Resort until 2014 " In the fields of sports competitions and throughout the Krasnodar Territory will function the radio communication of the TETRA standard.

APCO PROJECT 25 (APCO 25)

Open Standard APCO 25 created by the Organization Associationof.PublicS.afety.Communications.Officials-iNTERNATIONAL.- Association of representatives of public security bodies. The standard was created and improved (building a radio interface, encryption protocols, speech coding methods) in the period from 1989 to 1995. One of the main advantages of APCO 25 is that it allows you to work in any of the frequency ranges available for mobile radio systems: 138-174, 406-512 or 746-869 MHz. To one network, up to two million people and up to 65 thousand groups can be combined. Since 2003, a similar network is operating in St. Petersburg for several hundred subscribers for the purposes of the Ministry of Internal Affairs of Russia.

Transcribing can use not only for communication:

The newest trunking system JRC Trunked Radio System With the function of automatically determining the location of the car based on GPS and MPT standards 1327/1343. In addition, in fact, providing communications between subscribers, the standard provides automatic transmission of data on the location and the status of each machine to the terminal in the control center.

Example of two ways to organize a trunking network:

More complete standards features are reflected in the table:

Functionality, digital trunking standards APCO 25 EDACS IDEN TETRA TETRAPOL individual, group, broadcast calls + + + + + output to TFP + + + + + full-duplex subscriber terminals - + + + - data transmission and access to databases + + + + + + Direct connection mode + +? + + Automatic registration of mobile subscribers + + + + + personal call + - + + + access to IP networks + + + + + transmission status messages + + + + + transmission of short messages + - + + + transmission of the location data from the subscriber from GPS receiver? +? + + Fax + - + + + + possibility of installing an open channel? - - + + Multiple access using the list of subscribers + - + + + signal relay mode +? ? + + Double Observation Mode? -? + + Access priority / Call + + - + + Dynamic rearrangement + + - + + selective listening + + - + + remote listening? - - + + identification of the caller + + - + + call authorized by the + + - + - + + - + - - - - + and imitation of subscribers' activity - - - - + remote disconnection of the subscriber +? - + + Subscribers' authentication +? - + +.

In Russia, simultaneously with the introduction, successful use and development of digital networks of various trunking standards, analog systems based on the old one are widespread. MRT1327. And this is not bad. Digital trunking is convenient where not only operational communication is needed, but also data transfer and telephony. Often customers are quite enough simplex voice communications and sending messages. The use of analog systems saves time and money.

In general, the situation with professional mobile radio reminds the transition from the use of second-generation cellular networks of the standard GSM. To standards 3G.. Cellular networks, despite the rates of their growth, in the near future will not be able to fully replace networks of professional radio communications due to the fact that other functions perform.