The principle of construction and features of trunking communication. Trunking: A smart replacement for cellular

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Federal Agency for Communications State Educational Institution of Higher Professional Education “Siberian State University of Telecommunications and Informatics” (branch)

Khabarovsk Institute of Infocommunication Faculty of Correspondence Education

course project

by discipline: Radio communication systems with mobile objects

on the topic: Designing a trunking communication network

Completed by: 4th year student of FZO

specialties MTS (usk.)

Malysheva V.V.

Khabarovsk 2010

Introduction

3.4 Determining the number of RFK in the presence of several radio coverage areas with access to the PBX through one base station

Literature

trunked radio network

The building type of the service area is set. Determine the operating frequency range based on the type of building.

1. Determine the average value of the size of the service areas based on the type of development of the area, the power of the radio transmitter, the height of the antenna suspension and the operating frequency range.

2. Perform network frequency planning.

3.1 Develop a plan for the placement of base stations, taking into account the topology of the area.

3.2 Definition of channels for each BS.

3.3 Calculation of the service area and interference zone for each BS.

4. Calculation of the radio communication range.

5. Draw up a diagram of the organization of communication.

6. Draw up a block diagram of the network based on the number of BS.

7. Draw up a block diagram of the BS, determining the type of basic equipment.

8. Draw up a block diagram of a single-zone or multi-zone trunking system.

9. Draw up a block diagram of management in a trunking system.

Initial data for the implementation of the course project (option No. 6):

Building type: mid-rise building

Type of object: mobile objects

Transmitter power: Rper = 30 W

Receiver sensitivity: Ec = 0.5 μV

Antenna suspension height: h = 25m

Number of users: 325

Height difference: Hmax = 250m, Hmin = 50m

Antenna Gain: G=7dB

Gravity coefficient: G = 0.35

Attenuation in AFU: 10 dB

Average number of calls: C = 4.4

Average call duration: tav = 28 sec

Transport density: V = 7 vehicles/km2

BS transmitter feeder length: lperBS = 17 m

AC transmitter feeder length: lperAC = 1.1 m

Feeder loss: DRf = 2.5 dB

Losses in the combiner: DRc = 4 dB

Also, the initial data are given in Table 1.

Table 1

Options	base station no.

Introduction

Currently, there are a number of land mobile radio systems:

Personal radio call systems (paging);

Dispatch (operational) radio communication systems;

Trunking radio communication systems;

Cellular telephone radio communication systems.

Trunked radio communication systems have become the most successful implementation of the development of operational mobile communication systems, which are highly efficient with intensive exchange of operational information for a large number of subscribers who can be combined into groups according to operational and functional characteristics. The set of services provided by trunking systems is very wide and practically includes all their diversity: from data transmission to radiotelephony and from simple notification to automatic location of moving objects.

Trunking radio communication systems are multi-channel systems in which the subscriber is automatically provided with a radio channel and other system resources at his request according to a given algorithm, which ensures high efficiency in the use of the frequency resource.

According to the principle of organizing a radio channel, all trunking systems can be divided into three conditional groups:

Analog - radio communication systems with selective call (DTMF, Select 5, etc.);

Analog-digital - systems in which the transfer of service information when establishing a connection is carried out in digital, and the transfer in analog mode (SmarTrunk II, MPT 1327, LTR, EDACS);

Digital - EDACS ProtoCall, TETRA, Astro.

By the presence of a control channel in the system:

Systems that have a control channel at the time of connection establishment - SmarTrank II, Selekt 5, etc.;

Systems with a permanent control channel formed in various ways - TETRA, MPT 1327, LTR, etc.

By way of providing a communication channel:

Permanent for the entire communication session - SmarTrank II, MPT 1327, etc.;

Provided only for message transmission and changes during a communication session - EDACS, TETRA.

According to the principle of organizing the management of basic equipment: decentralized - SmarTrank II, etc.; centralized - MRT 1327, EDACS, TETRA, etc. In addition, all protocols of trunking systems can be divided into 2 classes:

1. Open protocols (MPT 1327, TETRA);

2. "Proprietary" protocols (LTR, SmartNet, SmartZone, EDACS, ESAS, etc.).

Open protocols are available to any manufacturer. These protocols are recommended for use in many countries. Systems with such protocols are manufactured by many companies, equipment due to mass production and high competition, as a rule, is cheaper than in specialized systems.

In Russia, the following protocols of trunking systems are the most famous: SmarTrank II, MPT 1327, LTR, EDACS and SmartZone. Therefore, in the course project, when choosing typical equipment, the MRI protocol 1327 was adopted as the basis.

The MRT 1327 protocol is designed to create large operational radio communication networks with an almost unlimited number of subscribers. The most important advantages of the MRI 1327 protocol are:

The ability to build multi-zone systems on a national scale with a large number of base stations, which allows you to "cover" large areas with communications;

A wide range of subscriber and basic equipment MRT 1327: it is produced by many companies - Motorola, Tait Electronics, Fylde Microsystems, Bosch, Philips, Nokia, Rohde & Schwarz, etc.;

The protocol is not tied to certain frequencies, which allows you to select them depending on the availability of a frequency plan and the corresponding permission of the SCRF;

Standardization of system components makes it possible to simplify and reduce the cost of operation, maintenance, development and integration of networks into larger systems;

EFFECT: possibility of economical transmission of short messages;

The protocols make it possible to build effective networks for collecting information from state and accident sensors;

Guaranteed modernization and maintenance;

Implementation of a smooth transition to a new generation of signaling protocols (from analog systems to digital systems of the TETRA standard).

Opportunities provided to subscribers of MRT 1327 protocol trunking systems:

Individual call of a mobile radio station;

Broadcast call, in which the called subscribers can only listen to the information;

Calling a group of subscribers;

Priority and emergency calls;

Nested call, which allows you to include other subscribers in an existing conversation;

Connection with subscribers of city and departmental telephone networks;

Forwarding by the user of the radio station of incoming calls to another subscriber;

Queuing calls;

Protection against unauthorized access.

Trunking systems of MRT 1327 standard support data exchange mode, which provides transmission of: status messages; short up to 25 characters; extended to 88 characters; messages of unlimited length.

1. Determination of the operating frequency range

In this course project, the type of building is set to medium-rise, therefore, it can be assumed that the type of area is urban. For urban areas, the 300, 450 and 900 MHz bands are optimal. Let's take the range equal to 300 MHz.

2. Determination of the average value of the sizes of service areas

The average size of the service areas depends on the power of the radio transmitter, the height of the antennas, the type of building, the service area, the type of subscriber station and the operating frequency range.

For mid-rise buildings, the value of the resources of the service areas of mobile objects is 15-30 km.

3. Frequency network planning

Frequency planning of the network is based on the calculation of the zone of reliable communication for a given reception quality. In this case, it is necessary to use the principle of uneven distribution of the radio frequency resource over the territory proportional to the concentration of subscribers: to use low-channel equipment in local networks of trunking radio communication that provides services from 100-200 to 1500-2000 subscribers.

3.1 Development of a plan for the placement of base stations

When developing a BS placement plan, they are guided by the following: the approximate radius of the BS service area for 300 MHz is 10-15 km. Proceeding from this, preliminary placement of the BS is carried out, taking into account the full or partial coverage of the service area and the use of single or multi-zone systems. The number of repeaters for the BS is determined based on the distribution of the subscriber load within the service area at the rate of 80-100 subscribers per channel.

3.2 Determination of the number of radio frequency channels in one service area without access to the PBX

When calculating the number of RCHs, it is assumed that all traffic on the network is created only by radio subscribers and is completely distributed between them, i.e. inclination of radio subscribers to ATS subscribers. To determine the capacity of the RFC beam, you need to know:

N is the number of radio subscribers;

Cnn - the average number of calls in the CNN, created by one radio subscriber;

Tav - the average duration of the conversation.

where is the load coming from one subscriber to the CNN, equal to:

Knowing that the average number of calls in a busy hour created by one radio subscriber is 4.4, and the average call duration is:

tav = 28 sec = 0.007778 hours,

determine the load coming from one subscriber to the CNN:

When permanently blocking a call:

for given N = 325,

according to the schedule (Figure 1), we determine that the required number of radio frequency channels:

V = 13 channels.

And the specific load coming from 250 subscribers is equal to:

3.3 Determination of the number of RFK in one service area with access to the PBX

In some cases, radio subscribers of a trunking network may have access to the PBX. In this case, part of the incoming load is the load between the system and the exchange of the telephone network. Figure 2 shows the scheme of servicing a base station of one zone with a PBX.

According to the task, the gravity coefficient is set:

network subscribers to the PBX. Let's determine the total load created by all subscribers, taking into account the gravity coefficient using the following formula:

According to the graph (Figure 3) for the calculated value:

Ae = 4 Earl,

we find the capacity of the channel bundle V1 for servicing the load between the system and the exchange.

Channel bundle capacity V1 = 11 channels.

3.4 Determination of the number of RFK in the presence of several radio coverage areas with access to the PBX through one base station

Figure 4 shows a diagram in the presence of several radio coverage areas with access to one base station. Values, N and G (load coming from one subscriber to the CNN, number of radio subscribers and gravity coefficient) for BS-1, BS-2, BS-3 and BS-4 are shown in Table 1.

If there are several base stations (BS), one of them will be the main one, which has access to the PBX via cable communication lines. The rest of the BS are connected with the main one via radio relay channels. Each BSi has Ni - the number of radio subscribers, and each of them creates a load i. For each BSi, the coefficient of attraction to the ATS is given - Gi. The traffic of each BSi goes to the PBX through the main BS. It is necessary to calculate the number of radio channels:

In each VBS zone;

Between the main BS and PBX - V1;

The radio relay system connecting the BSi with the main one - Vpp.

Calculate the required values according to the following algorithm:

1. Determine the total incoming load for each BSi using the formula:

2. According to the graph (Figure 1), we determine the number of RFK according to the given values of i and Ni:

3. Calculate the incoming load Ae between each BSi and ATS, taking into account the gravity coefficient:

4. Determine the total incoming load from the BS to the PBX:

5. According to the graph (Figure 3), we determine the capacity of the bundle of channels V1 between the main BS and the PBX according to the found value of Ae total: V1 = 9 channels.

6. Based on the calculated loads Aei for each BSi, we determine the number of radio channels of the radio relay system Vpp, connecting each BS with the main one. The determination of Vpp is carried out according to the graphical dependence shown in Figure 5.

4. Calculation of the coverage area of the base station

To determine the BS service area, we will perform the following calculations:

1. Determine the effectively radiated power of the BS transmitter:

where RBS is the power of the BS transmitter, equal in this course project:

DRf - losses in the feeder, equal to 2.5 dB;

DRk - losses in the combiner, equal to 4 dB;

Go BS - BS antenna gain equal to 7 dB.

Substituting the values, we get:

2. Let's define the parameter Дh, which characterizes the irregularities of the terrain. Approximately Dh can be determined by the difference between DH of the maximum and minimum elevation marks of the terrain:

Knowing that Hmax = 250m and Hmin = 50m, we calculate:

3. Determine the effective height of the BS transmitting antenna:

where hBS is the height of the BS antenna suspension relative to sea level (hBS = 25m);

the average level of the terrain relative to sea level in terms of heights hi at a distance of 1000 + 250i meters from the BS, equal to 1.5 m.

4. Determine the median value of the minimum signal field strength for the subscriber station from the BS:

where is the field strength corresponding to the sensitivity of the AU receiver, dBµV/m;

Usign - receiver sensitivity, μV.

The effective length of the receiving antenna, m.

GAC - antenna gain AC;

Rin - input impedance of the receiver, let's take Rin = 50 Ohm;

Ko - reliability coefficient of the logarithmic distribution depending on the required reliability of communication in time and place (Ko = 1.64);

where and are the standard deviations of the signal over time and place:

DE and Dh - correction for uneven terrain:

Substituting the obtained values, we get:

5. Calculation of interference at the location of the base station

The calculation of the average effective value of the interference field strength at the point of the BS receiving antenna is carried out at a frequency f MHz for a given transport density in the reception area V.

Figure 6 shows the radio interference characteristics observed in BS antennas. When assessing the interference, the zone of interference perception by the BS receiving antenna with a size of 1 km 2 was determined, the interference was divided into three groups depending on the traffic density within the zone for each moment of time:

Transport density in the zone of high noise levels (Н) VН = 100 vehicles/km 2 ;

In the zone of medium (M) transport density VM = 10 cars / km 2;

In the area of low interference levels (L), the traffic density is VL = 1 vehicle/km 2 .

In this course project, the interference, depending on the density of transport, is in the zone of medium levels, because VM = 7 vehicles/km2

We accept the average frequency of repetition of interference pulses:

Fu = 3650 imp/p,

which weakly depends on the operating frequency; the standard deviation of the peak noise values is taken equal to:

According to Figure 6, for a given value of V and f, we find:

Eu (Ei = 22 dB).

Then, using the following formula, we find the average effective value of the interference intensity:

where Piz is the effective bandwidth of a typical interference meter, we accept:

Ppr - effective bandwidth of the receiver, we accept.

Taking into account the intrinsic noise of the equipment, the average effective value of the field strength of the total interference:

where GN is the nominal sensitivity of the receiver, μV;

Attenuation in the antenna path of the receiver;

Feeder length;

(S / N) pr.in - nominal signal-to-noise ratio, taken equal to 10-12;

hd.pr - effective antenna height:

6. Calculation of radio communication range

Let us determine the field strength actually created by the transmitting BS at the receiving point for a given communication quality according to the formula:

where Ec is the signal field strength required to obtain the specified quality indicators:

where EP.EF is the average effective value of the field strength of the total interference, equal to 9.43 dB

R0 = 5-10 dB - protection ratio to obtain a given reception quality

C = 8 dB - the value of the protection factor required to provide the required protection ratio

Wr.n. - correction taking into account the difference between the nominal power of the transmitter and the power of 1 kW:

where Rn is the rated power of the transmitter, equal to 30 W. That's why:

Vf - attenuation in resonators, bridge filters and antenna separators is taken equal to 3 dB;

Вh2 - correction taking into account the height of the AC receiving antenna, dB:

For h2 = 3m: ;

Vrel - an amendment that takes into account the terrain, which differs from Dh = 50 m, dB.

Dh is determined by the formula:

where Hmax and Hmin are the maximum and minimum height marks of the terrain on the propagation path in the selected direction, equal to 200 m and 50 m.

Consequently,

According to the graph (Figure 7), we determine Vrel (Vrel = 9 dB)

Du - gain of the receiving and transmitting antenna, equal to 7 dB;

Substituting the obtained values, we determine the field strength actually created by the transmitting BS at the receiving point for a given communication quality:

Having determined the field strength, according to the schedule (Figure 8), we determine the expected communication range - 40 km.

7. Structural diagram of the base station

Figure 9 shows the general principle of building a base station.

7.1 Structural diagram of a single-zone trunking system

The structure of a single-zone trunking system is shown in Figure 10.

The radio signal combiner is used to combine and split the signals coming from the transmitter and receiver of the repeater. A repeater is a set of transceivers serving one pair of carrier frequencies. One repeater can provide two or four traffic channels. Four channels to serve 50-100 radio channels; 8 channels - 200-500AC; 16 channels - up to 2000 radio subscribers. BS coverage area at a frequency of 160 MHz - 40 km; at a frequency of 300 MHz - 25-30 km; at a frequency of 300 MHz - 20 km.

The switch handles all system traffic. The control device ensures the interaction of all BS nodes. It handles calls, performs caller authentication, call queuing, and entry into payroll databases.

The maintenance and operation terminal is designed to monitor the state of the system, diagnose faults, make changes to the subscriber database.

The central station of the service area includes several transceivers, the number of which depends on the number of channels and the number of subscribers served.

The transceiver of each channel is controlled by the controller. The maximum number of channels at the central station is up to 24. One channel can serve up to 30-50 subscribers. For the interaction of all controllers of the central station, an interface unit is used, which is connected to all controllers via a common control bus, thus providing control, accounting and billing of connections.

In Russia, the following protocols of trunking systems are the most famous: SmarTrunk II, MPT 1327, LTR and SmartZone. The MPT 1327 protocol is designed to create large operational radio networks with an almost unlimited number of subscribers.

Typical equipment specification in the 450 MHz band for mobile objects:

Basic equipment: Quantity:

Regional control processor Т1530 1;

Operator console consisting of: computer and printer;

Operator console software Т1504 1;

Switching unit Т1560 1;

Channel interface board Т1560-02 3;

Interface board T1560-03 for one 2-wire line 1;

Repeater Т850 (50W, 100% working mode) 4;

Trunking channel controller Т1510 4;

System interface T1520 1;

Modem Т902-15 2;

Cabinet 3 8RU 2.

Antenna-feeder equipment: Quantity:

Combiner M101-450-TRM 1;

Duplex filter TMND-4516 1;

Receiving distribution panel TWR8/16-450 1;

Stationary antenna ANT 450 D6 - 9 (us. 6-9 dB) 2;

Coaxial cable RK 50-7-58 70m;

Connector for RK 50-7-58 2;

Lightning arrester 1;

Adapter cables 8.

Trunking radio stations from TAIT ELECTRONICS LTD:

Wearable T3035;

Mobile T2050.

It is most expedient to build small multi-zone systems with centralized control and connection to the PBX based on the TAITNET system from TAIT Electronics.

The TAITNET system consists of a regional control center, a system control terminal, base stations and user equipment. A typical functional diagram of a four-zone trunking communication system TAITNET is shown in the block diagram (Figure 11).

7.2 Structural diagram of a multi-zone trunking system

The system consists of a regional control center, a system control terminal, base stations, user equipment. The regional control center includes: regional controller, switch and interface boards.

Regional controller (regional control processor T1530), which combines all T1510 base station controllers into a single multi-channel multi-zone system. This controller can manage a system consisting of 10 zones with 24 channels in each zone. It collects information from all connected BSs and transmits it to the system management terminal.

The system control terminal is an IBM-compatible personal computer and operates using special T1504 software from TAIT Electronics.

The T1560 switch consists of a switching matrix and interface boards. It provides switching of audio channels for interzone connections and audio channels with telephone lines.

Interface boards Т1560-03 provide interface with two-wire telephone subscriber lines. The T1560-02 boards provide connection of the T1560 switch with BS traffic channels via dedicated four wire lines.

If the operator of the TAITNET system has subscriber capacity at the PBX, then it is possible to organize a single numbering of telephone network subscribers and subscribers of the trunking system. General numbering is organized by the trunk controller.

The base station equipment consists of antenna-feeder equipment, T850 transceivers, T1510 channel controllers and T1520 system interface.

The BS controllers support the communication session and interact with the system interface. The system interface checks and records connections, provides information about the system status and exchanges data with the BS controllers. Communication with the regional control processor is provided via dedicated two wired lines via a modem. 4-wire audio lines are used to connect BS subscribers with a regional node. The control and management of base stations is performed by the regional controller.

Each BZ also has a system controller. Communication between system controllers of base stations is carried out using modems. Interface boards in the regional control center provide access to the public telephone network.

Literature

1. Guidelines and task for the course project on the subject "Communication systems with mobile objects"

2. Lecture notes on the subject "Communication systems with mobile objects"

3. Catalog "Systems and means of radio communication", 1998

4. Radioma equipment catalog, 1999

5. Summary table of characteristics of trunking radio stations MRT-1327

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System Services

Mobile dispatch radio communication based on iDEN technology provides all types of services provided by modern digital trunking systems:

group call (group call) for mobile subscribers and dispatchers in half-duplex communication mode. One button press is enough to make a call; the connection establishment time does not exceed 0.5 s. In this case, only one voice communication channel is used - regardless of the number of subscribers in the group. The number of possible groups in iDEN is large enough (65,535) to eliminate the need for dynamic group reconfiguration. All configurations can be created in advance: if necessary, subscribers simply go to the appropriate groups. Group members can be located at a distance of tens and hundreds of kilometers from each other (of course, within the coverage area of the system);
a personal call (private call) in half-duplex mode, when only two subscribers participate in a conversation and complete confidentiality of negotiations is ensured. Note that in the group and individual call mode, the caller's name or digital identifier appears on the display of the subscriber terminal of the called subscriber;
call signaling (call alert) - the transmission of a special signal to the subscriber (or group), indicating the need to establish radio communication. If at this moment the subscriber is outside the system zone or the subscriber terminal is disconnected, the call is stored in the system. At the moment when the subscriber becomes available, he receives a sound signal, and the caller ID appears on the terminal screen. Only then does the caller receive an acknowledgment of receiving the call.

In addition to the services typical of conventional trunked communication, the iDEN system provides a number of features of modern mobile telephone systems:

mobile telephone communication between subscribers, including through the PSTN (both incoming and outgoing in duplex mode). The iDEN system provides the functions of local telephony (mini-ATS, UPATS), voice mail (voice mail), long-distance and international communication;
sending text messages. Subscribers can receive alphanumeric messages displayed on the screen of the subscriber terminal, which is capable of storing up to 16 messages of 140 characters. At the same time, both group and individual mailing of messages is provided. Receiving text messages is possible simultaneously with a mobile phone session;
data transfer. iDEN portable (wearable) terminals have built-in modems and can be connected to a PC via an RS-232C adapter. In the circuit switching mode, the data transfer rate is up to 9600 bps, and in the packet mode - up to 64 kbps. To improve the reliability of data transmission, the system uses a forward error correction scheme. The data transfer function allows mobile subscribers to receive and send faxes and e-mails, exchange data with office computers and provide access to the Internet. In burst mode, the standard TCP/IP network protocol is supported.

Note that adding a data transfer function to an existing iDEN system does not require the installation of additional equipment at base stations (BS). It is only necessary to install additional blocks of the central system management infrastructure and install the appropriate software on the base stations and the central system.

Subscriber terminals

Although the iDEN system provides several types of communication, this does not mean that the subscriber needs to "subscribe" to all types of services and, accordingly, purchase a fully functional subscriber terminal from the operator. The user can always choose a model that matches the package of services he is interested in. The cost of iDEN portable subscriber terminals and digital cellular phones is approximately the same.

The i370/r370 portable terminals are capable of operating as both trunked radios and mobile phones. They are equipped with a multi-line LCD display, which displays lists of available groups (subscribers) and alphanumeric messages. The advanced i600 multifunctional terminal is smaller and lighter and has longer battery life.

The latest model of the i1000 handheld terminal has even smaller weight and size: its weight without batteries is 120 g, dimensions are 120x60x30 mm.

The i470/r470 models have a built-in modem, making them suitable for data and fax communications. In addition, these terminals support additional functions of the iDEN system, such as simultaneous operation in several groups, communication in isolated BS mode (in case of communication failure with the central infrastructure of the system), Emergency Call, etc.

Models r370 and 470, which meet the requirements of US military standards, have a shock-resistant case and are not afraid of moisture. The signal output power of portable terminals of all types is 600 mW.

The family of mobile user terminals iDEN consists of three models - m100, m370 and m470. The first one works only in dispatch radio mode, the other two are equipped with a handset and support mobile telephony. In addition, the m470 has a built-in modem and provides the same special features as the i470/r470 terminals. All types of mobile terminals have an output power of 3W.

The iDEN system also provides desktop dispatch stations based on m100/m370/m470 mobile terminals. They have an external antenna, a tabletop microphone, and an AC power supply.

Air interface and voice coding

The iDEN technology is based on the TDMA (Time Division Multiple Access) standard, according to which 6 digitized speech signals are simultaneously transmitted over each 25 kHz wide frequency channel. iDEN technology does not require all frequency channels to be contiguous.

The time interval of 90 ms is divided into 6 time slots of 15 ms each, in each of which one voice signal is transmitted (Fig. 2). The use of radio signal modulation using the M16-QAM (Quadrature Amplitude Modulation) method provides a total data transfer rate over one frequency channel of 64 kbps (the transmission rate in the voice channel is 7.2 kbps). Adequate reproduction of the human voice and other sounds at such a low transmission rate is achieved through the use of an improved coding scheme using the VSELP algorithm.

Figure 2.
iDEN frequency channel capacity

Frequency range

The system based on iDEN technology operates in the standard for America and Asia trunking band 806-825/851-870 MHz. Note that recently in Russia a part of this range, namely 815-820/860-865 MHz, is also reserved for trunked radio communication systems (Fig. 3).

Figure 3
The frequency range allocated for the iDEN system in Russia: mobile terminals (MT) 806-821 MHz; base stations (BS) 851-866 MHz

When developing iDEN technology, Motorola wanted to achieve the most efficient use of the frequency resource, at least not inferior to existing implementations of the CDMA standard. Since iDEN provides for the simultaneous transmission of six voice signals on each 25 kHz wide frequency channel, 240 such channels can be placed in 1 MHz of spectrum. For comparison, with a bandwidth of 1 MHz, analog and digital trunking communication systems can support no more than 80, analog cellular communication systems - from 30 to 40, and systems in the GSM standard - 40 voice channels (Fig. 4).

Figure 4
Comparison of spectrum utilization efficiency. In 1 MHz spectrum it is possible to place voice channels (GC): analog trunking systems - 40/80; analog cellular systems - 33-40; GSM - 40; TETRA - 160; IDEN-240

Structure of the iDEN system

The system based on iDEN technology consists of two main components: BS and central infrastructure. (Fig. 5). The iDEN infrastructure is organized to maximize the functionality of the BS, so the most important functional element is the EBTS Enhanced Base Transceiver System base station. The EBTS includes an integrated node controller (iSC), up to 20 base radio stations (BR) of the omni type or 24 sector BRs, an amplifier and radio signal transmitters, a synchronizing receiver, and BS antennas.

Figure 5
The structure of the system based on iDEN technology: * provide telephone communication; ** provide radio communication; *** provided by the system operator; DACS (Digital Access Crossconnect Switch) - digital access switch; IWF (Interworking Function) - data transfer interface with PSTN; VMS (Voice Mail System) - voice mail

EBTS provides interaction between the system and subscriber devices, supports the transmission of voice traffic on several frequency channels, and also performs a number of control functions, such as separation of radio and telephone traffic, synchronization of the BS and subscriber terminals, radio signal level control, etc. Multifunctionality of EBTS allows you to significantly reduce the load on the components of the central infrastructure, primarily on the MSC (Mobile Switching Center). The EBTS transmitter supports a maximum of 144 voice channels per system node.

The main function of the BSC (Base Site Controller) is communication management when user terminals move from one coverage area to another (handover). Each BSC is capable of supporting up to 30 zones, performing the full range of actions for concentrating traffic from node stations and distributing it to the appropriate zones.

The XCDR transcoder converts VSELP audio to and from PCM digital format.

The MPS (Metro Packet Switch) packet switch consists of a switch and a packet duplicator. It transmits voice packets arriving in dispatch radio mode and control information from EBTS to DAP and vice versa.

Dispatch Application Processor (DAP) manages group and personal calls, call signaling and other functions. With a large number of system subscribers, it is possible to create clusters of four DAPs.

The HLR/VLR (Home Location Register/Visited Location Register) subscriber location registration units serve mobile telephony. The HLR stores complete information about all subscriber terminals registered in various geographical segments of the system. VLR contains information about the movement of subscriber devices and provides the system with the information necessary to perform roaming. Note that in the iDEN system there is no roaming in the sense in which it is understood in cellular systems, since not PSTN, but dedicated E1 channels are used to connect geographically distant segments of the system.

The MSC (Mobile Switching Center) provides an interface between the PSTN and iDEN mobile phones, performing the typical functions of such a switch, and also manages the transfer when subscribers move from an area controlled by one BSC to an area controlled by another. If the iDEN network covers a large area, several MSCs can be installed in it. The functions of the MSC of the iDEN system are completely identical to the functions of the GSM cellular network switch.

The main control module of the system is OMC (Operation Maitenance Center), which provides system configuration, emergency management, collection of statistical data on system operation and a number of other management functions.

The Short Message Service (SMS) supports all text messaging functions, including text notifications of the presence of messages for a given subscriber (voice mail).

iDEN MicroLite

Motorola is currently finalizing the iDEN MicroLite system, which is a "small" iDEN-based system designed to serve hundreds to thousands of subscribers. While maintaining all iDEN technological solutions, using the same subscriber equipment and base stations, this system differs, first of all, in the maximum number of frequency channels (there are 40 of them).

The main technological difference between iDEN MicroLite and iDEN is the organization of the central infrastructure of the system. In the iDEN MicroLite system, it is implemented on a single Compact PCI standard computer platform (a variant of the PCI platform for industrial computers) running under the Neutrino real-time OS from QNX Labs.

The first version of iDEN MicroLite will provide two types of communication - group (individual) radio communication and mobile telephone communication. Future releases will add short message and dial-up/packet data services to the system. The maximum number of base stations that the central infrastructure of the first version of the system can support is 5, in the future it will be increased to 8-10.

If it is necessary to migrate from iDEN MicroLite to a complete iDEN system, a new installation of the central infrastructure of the system is required, however, by modifying the appropriate software, subscriber terminals and existing BS equipment can be used.

Deliveries of the iDEN MicroLite system will begin in the II quarter of 1999. The technical study of the projects of the iDEN MicroLite systems is expected from the III quarter of 1998.

Applications for iDEN

iDEN technology is focused on the creation of systems such as SMR (Shared Mobile Radio), i.e. commercial networks that provide integrated services to organizations and individuals. In order to provide communication between individual departments and groups of employees, a so-called "fleet" is created for each corporate user of the system - a virtual private network within the organization's network. Different groups can be created within the fleet, corresponding to the company's divisions (the maximum number of groups in one fleet is 255). The possibility of accidental or deliberate intrusion of subscribers into foreign fleets is absolutely excluded. Fleet members can be located in different geographical regions, move from one city to another.

Thus, an organization can build its own mobile telecommunications system, which is completely equivalent to the network of this organization. At the same time, she does not need to purchase equipment and build antennas, as well as spend several months installing and debugging the system. All you need to do is to become a corporate user of the already existing iDEN system.

Where and when

The first commercial system based on iDEN technology, deployed in the US by NEXTEL in mid-1994, is now nationwide. It has about 4500 BS and about 2 million subscribers. In the southwestern US, there is another network based on iDEN technology, operated by the energy company Southern Co. In addition, in the southwestern provinces of Canada, Clearnet also provides communication services in the iDEN network, which consists of 320 BS.

In Latin America, iDEN networks already exist in Bogota (Colombia) and Buenos Aires (Argentina). They are being built in Sao Paulo and Rio de Janeiro (Brazil), as well as in Mexico City (Mexico). Rollouts of iDEN-based systems are planned for the near future in Peru, Venezuela and Chile, as well as system expansions in Colombia and Argentina.

In Asia, iDEN systems are operated in several countries: such systems have been operating in Tokyo and Osaka (Japan) for more than two years, and in Singapore for about a year. There are systems in China, South Korea and the Philippines. Construction is underway in Indonesia. In the Middle East, a nationwide iDEN network has been deployed in Israel, and the construction of such systems has begun in Morocco and Jordan.

Each of these systems is designed to serve tens of thousands of subscribers.

The modular principle of the system organization provides its various implementations. For example, iDEN could initially be deployed as a purely trunked system and then added mobile telephony, text messaging and data capabilities as needed. According to the developers of the system, today iDEN is one of the few technologies tested in commercial operation that provide the entire range of mobile communication services.

Andrey Aleksandrovich Denisov is Motorola's manager for the iDEN system in the region of Eastern Europe and the former USSR. He can be contacted at: [email protected] and fax 785-0160

Section 4 Mobile trunking systems

Lecture #23

What is a "trunk"? Let's try to figure out what is hidden behind this "fashionable" word? Here is the translation given by the English-Russian Dictionary of Radio Electronics, 1987 edition:

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

Trunking (trunking) - group formation

The electronic dictionary "PROMT" of 1999 is more "educated":

Trunking - provision of free channels

Trunked radio system - radio system with automatic redistribution of channels

As can be seen from the translation, there is nothing special behind the word "trunk". It's just "auto channel provisioning".

Trunking principles have been used for over 70 years in telephony. Any automatic telephone exchange, mini PBX, cellular communication uses trunking as the basis of its work. We all use trunking almost daily. Although not many of us realize that when we pick up the phone and dial a number... we are using trunking. After all, it would be an unaffordable luxury to allocate a separate line to each telephone subscriber, especially long-distance. All of us are allocated a line for the conversation only for the duration of the communication session. The rest of the time (free from our conversations) other users are served on it.

Imagine a situation where residents of, say, one of the districts of Tashkent would simultaneously decide to call their friends. What would happen in this case? But nothing. They simply could not do this, since the number of telephone lines (between automatic telephone exchanges) is limited and a quite certain number of subscribers can conduct communication sessions at the same time (how many specifically is a topic for a separate conversation).

Now imagine that all telephone sets have been replaced with radio stations, and wire lines with radio frequency channels. As you probably already guessed, we received a trunk - a radio communication system with automatic provision of a free channel.

SOME EXPLANATIONS

Trunk systems DO NOT regulate:

access to the telephone network;

the use of duplex (“I speak and listen” at the same time, as in telephony);

huge range;

the highest service;

free access;

and much more...

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

More scientifically, the essence of trunk communication is that the subscriber is not assigned to a specific channel, but has equal access to all channels in the system. And which one to use for a communication session is decided by special control equipment. At the request of the subscriber, the system automatically provides the subscriber with a free channel.

ABOUT TERMINOLOGY

In Russian publications, the words “trunking” and “trunking systems” have become established. Let's leave these turns on the conscience of translators and linguists. In our opinion, the words "trunk" and "trunk systems" are more harmonious in pronunciation and easier to write. As a rule, their use does not cause ambiguous understanding. Therefore, in what follows, we will mainly use “our” formulations.

MYTHS AND REALITY

Ten considerations to cool the ardor of optimists and lift the spirits of pessimists regarding the "miracles" of trunking:

Trunk is not a miracle, but a process of development of radio communications.

A trunk does not replace a cell phone, it does not replace a pager ... a trunk does not replace anything at all, but complements.

Trunked means: convenient, flexible, expandable, versatile, reliable, complex, expensive...

Trunk systems are used to communicate between radios and once again radios, and not between radios and telephone lines.

Trunk systems can do a lot, but not all.

There are many trunk systems, and which one to choose depends on the tasks.

If the trunk system does not solve the task, then this is the wrong task.

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

There are many suppliers, but little money - do not pay twice.

Don't flatter yourself! Entrust the choice to specialists.

But seriously, what are the advantages of trunk systems in comparison with traditional, so-called "ordinary" communication networks, with cellular telephony, with personal radio call systems (paging)?

It is rather difficult to answer this question unambiguously. As with any system, there are both advantages and disadvantages.

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

BENEFITS OF TRUNK NETWORKS

Compared to cellular systems:

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

high speed of establishing a connection (0.2–1 sec);

queuing to system resources when busy and automatic connection after the possibility of access;

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

lower costs for deployment and operation of systems.

Compared to "conventional" radio systems:

saving frequency resources;

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

the possibility of digital data transmission;

communication coverage of large areas due to multi-zone configuration.

Compared to paging networks:

two-way communication;

the ability to transmit short messages (similar to paging) over trunk channels using existing equipment.

This is not a complete list of available benefits. Still, the trunk is not a panacea for all ills. Along with trunk systems, there are a number of users who, for various reasons, need a cell phone, someone needs a pager, and a number of users get by (and will get by) with “normal” communication systems.

It must be clearly understood that the trunk is not a universal solution to the entire set of radio communication tasks. In any, even the most “trunk” state, there are still a number of problems that are solved by other communication systems that have nothing to do with trunk ones.

The disadvantages of trunk systems include:

low profitability with a small number of subscribers;

relatively high cost of equipment (compared to "conventional" radio communication systems);

the need for inter-zone communication lines (wire, radio frequency, radio relay, fiber optic) and, as a result, the complexity and cost of deployment *;

the need for professional service.

* It is worth noting that in order to cover large areas, most radio communication systems require multi-zone implementation and, of course, inter-zone communication lines.

CLASSIFICATION OF TRUNK SYSTEMS

Trunked systems can be classified according to many criteria, for example, by the format of the transmitted data (analogue, digital), by the types of protocols (LTR, MPT 1327, SmarTrunk II), by the number of serviced zones (single or multi-zone), by the methods of presenting the radio channel (" transmission trunking” or “message trunking”), by methods of controlling base stations (centralized or distributed), by types 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 methodology 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 trunked systems

Trunking systems are called radial-zone systems of terrestrial mobile radio communication, which automatically distribute communication channels of repeaters between subscribers. This is a fairly general definition, but it contains a set of features that unite all trunking systems, from the simplest SmarTrunk to modern TETRA. The term "trunking" comes from the English Trunking, which can be translated as "bundling".

Single zone systems

Figure 67 Structural diagram of a single-zone trunking system

The main architectural principles of trunking systems are easily seen in the generalized block diagram of a single-zone trunking system, shown in fig. 67. The infrastructure of the trunking system is represented by a base station (BS), which, in addition to radio frequency equipment (repeaters, radio signal combiner, antennas), also includes a switch, a 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 vast majority of TSSs, one pair of carriers meant one traffic channel (CT). Currently, with the advent of the TETRA standard and the EDACS ProtoCALL system, which provide for temporary consolidation, one RT can provide two or four CTs.

Antennas. The most important principle in building trunked systems is to create radio coverage areas as large as possible. Therefore, base station antennas are usually placed on high masts or structures and have a circular radiation pattern. Of course, when the base station is located at the edge of the zone, directional antennas are used. The base station can have both a single transceiver antenna and separate antennas for receiving and transmitting. In some cases, multiple receive antennas may be placed on a single mast to combat multipath fading.

The radio signal combining device allows the use of the same antenna equipment for the simultaneous operation of receivers and transmitters on several frequency channels. Transponders of trunking systems operate only in duplex mode, and the frequency spacing between receiving and transmitting (duplex spacing), depending on the operating range, ranges from 3 MHz to 45 MHz.

The switch in a single-zone trunked system handles all of its traffic, including the connection of mobile subscribers to the public switched telephone network (PSTN) and all data calls.

The control device ensures the interaction of all nodes of the base station. It also handles calls, performs caller authentication (friend or foe verification), call queuing, and time billing database entries. In some systems, the control device regulates the maximum allowed duration of a connection to the telephone network. As a rule, two throttling options are used: reducing the duration of connections during predefined peak hours, or adaptively changing the duration of a connection depending on the current load.

The PSTN interface is implemented in trunked systems in various ways. In low-cost systems (such as SmarTrunk), the connection can be made over two-wire switched lines. More modern TSNs have DID (Direct Inward Dialing) direct dialing equipment as part of the interface to the PSTN, which provides access to trunked network subscribers using standard PBX numbering. A number of systems use a digital PCM connection to PBX equipment.

One of the main problems in registering and using trunking systems in Russia is the problem of their interface with the PSTN. When outgoing calls from trunked subscribers to the telephone network, the difficulty lies in the fact that some trunking systems cannot dial a number in ten-day mode over subscriber lines in electromechanical exchanges. Thus, it is necessary to use an additional tone-to-decade converter.

Incoming communication from PSTN subscribers to radio subscribers is also problematic, but for a number of reasons. Most trunked networks interface with the telephone network via two-wire subscriber lines or E&M type lines. In this case, after dialing the PSTN number, additional dialing of the radio subscriber's number is required. However, after the subscriber line is fully dialed and the loop is closed by the trunking system control device, the telephone connection is considered established, and further dialing in the pulse mode is difficult, and in some cases impossible. The “click” detector used in the SmarTrunk II system does not guarantee the correctness of the pulse dialing, since the quality of the “click pulses” coming from the subscriber line depends on its electrical characteristics, length, etc.

To get out of this situation, in the laboratory of IVP, together with specialists from ELTA-R, a telephone interface (TI) ELTA 200 was developed for interfacing trunking communication systems of various types with the PSTN. Such an interface allows pairing trunking communication systems and PSTN via digital channels (2.048 Mbit s), three-wire connecting lines with ten-day dialing, as well as via four-wire PM channels with signaling systems of various types when interfaced with private telephone networks.

Connection with the PSTN is traditional for TSN, but recently the number of applications involving PD has been increasing, and therefore the presence of an interface to the SCP also becomes mandatory.

The maintenance and operation terminal (TOE terminal) is located, as a rule, at the base station of a single-zone network. The terminal is designed to monitor the state of the system, diagnose faults, record billing information, and make changes to the subscriber database. The vast majority of manufactured and developed trunking systems have the ability to remotely connect the TOE terminal via the PSTN or SCP.

Dispatching console. Optional, but very characteristic elements of the infrastructure of a trunking system are dispatch consoles. The fact is that trunking systems are used primarily by those consumers whose work is not complete without a dispatcher. These are law enforcement services, emergency medical services, fire protection, transport companies, municipal services.

Dispatch consoles can be included in the system via subscriber radio channels, or connected via dedicated lines directly to the base station switch. It should be noted that several independent communication networks can be organized within one trunking system, each of which can have its own dispatcher console. Users of each of these networks will not notice the work of their neighbors, and, no less important, will not be able to interfere with the work of other networks.

The subscriber equipment of trunking systems includes a wide range of devices. As a rule, half-duplex radio stations are the most numerous, because. they are the most suitable for working in closed groups. For the most part, these are radios with a limited number of functions that do not have a numeric keypad. Their users, as a rule, have the ability to communicate only with subscribers within their workgroup, as well as send emergency calls to the dispatcher. However, this is quite enough for most consumers of communication services of trunking systems. There are also half-duplex radio stations with a wide range of functions and a numeric keypad, but they, being somewhat more expensive, are intended for a narrower privileged circle of subscribers.

Trunked systems, especially those designed for commercial use, also use duplex radios, which are more like cell phones, but have much more functionality than the latter. Duplex radios of trunked systems provide users with a full connection to the PSTN. As for group work in the radio network, it is performed in half-duplex mode. In corporate trunking networks, duplex radios are used primarily for senior management personnel.

Both half-duplex and full-duplex trunked radios are available not only in portable, but also in automotive versions. As a rule, the output power of car radio transmitters is 3-5 times higher than that of portable radios.

A relatively new class of devices for trunking systems are data terminals. In analog trunking systems, data terminals are specialized radio modems that support the appropriate radio interface protocol. For digital systems, it is more typical to embed a data interface in subscriber radio stations of various classes. The composition of the automobile data transmission terminal sometimes includes a satellite navigation receiver of the GPS (Global Positioning System), designed to determine the current coordinates and then transfer them to the dispatcher on the console.

Trunking systems also use fixed radio stations, mainly for connecting dispatcher consoles. The output power of fixed radio transmitters is approximately the same as that of car radios.

Multizone systems

Early standards for trunked systems did not provide for any mechanisms for the interaction of different service areas. Meanwhile, customer requirements have increased significantly, and although equipment for single-zone systems is still being manufactured and successfully sold, all newly developed trunked systems and standards are multi-zone.

The architecture of multi-zone trunking systems can be based on two different principles. In the event that the determining factor is the cost of equipment, distributed inter-zone 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 the PSTN. This is already quite enough to organize a multi-zone system - if necessary, a call from one zone to another is made through the PSTN interface, including the dialing procedure. In addition, base stations can be directly connected using physical leased communication lines (most often, small-channel radio-relay lines are used).

Each BS in such a system has its own connection to the PSTN. If it is necessary to call from one area to another, it is made through the PSTN interface, including the dialing procedure. In addition, BSs can be directly connected using physical leased lines.

The use of distributed inter-zone switching is reasonable only for systems with a small number of zones and with low requirements for the efficiency of inter-zone calls (especially in the case of connection via switched PSTN channels). High QoS systems use a CC architecture. The structure of a multizone TSS with a CC is shown in Fig. . 68.

The main element of this scheme is the interzonal switch. It handles all kinds of inter-zone calls, ie. all interzonal traffic passes through one switch connected to the BS via leased lines. This provides fast call processing, the ability to connect centralized DPs. Information about the location of the subscribers of the system with the Central Committee is stored in a single place, so it is easier to protect it. In addition, the interzone switch also performs the functions of a centralized interface to the PSTN and SCP, which allows, if necessary, to fully control both the voice traffic of the TS and the traffic of all PD applications associated with external SCPs, such as the Internet. Thus, the system with the CC has a higher controllability.

Figure 68 Structural diagram of a trunking network with distributed inter-area switching

Figure 69 Structural diagram of a trunking network with centralized inter-zone switching

So, we can single out several important architectural features inherent in trunking systems.

First, it is a limited (and therefore inexpensive) infrastructure. In multi-zone trunking systems, it is more developed, but still cannot be compared with the power of cellular network infrastructure.

Secondly, this is a large spatial coverage of base station service areas, which is explained by the need to maintain group work over vast territories and the requirements to minimize the cost of the system. In cellular networks, where investments in infrastructure quickly pay off and traffic is constantly growing, base stations are placed more and more densely, and the radius of coverage areas (cells) decreases. When deploying trunked systems, things are a little different - the amount of funding is usually limited, and to achieve a high return on investment, it is necessary to serve as large an area as possible with one set of base station equipment.

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

Fourthly, trunking systems allow organizing independent dedicated communication networks (or, as they say in recent times, private virtual networks) on the basis of their channels. This means that multiple organizations can work together to deploy a single system instead of installing separate systems. At the same time, a tangible saving of the radio frequency resource is achieved, as well as a reduction in the cost of infrastructure.

All of the above indicates the strength of the position of trunking systems in the corporate sector of the market of systems and mobile communications.

Classification of trunking systems

The following features can be used to classify trunking communication systems.

Voice information transmission method

According to the method of voice information transmission, trunking 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 grid step is usually 12.5 kHz or 25 kHz.

To transmit speech in digital systems, various types of vocoders are used that convert an analog speech signal into a digital stream at a rate of no more than 4.8 Kbps.

Number of zones

Depending on the number of base stations and the overall architecture, single-zone and multi-zone systems are distinguished. The former have only one base station, the latter - several base stations with the possibility of roaming.

Method of combining base stations in multi-zone systems

Base stations in trunked systems can be combined using a single switch (centralized switching systems), as well as connected to each other directly or through public networks (distributed switching systems).

Multiple access type

The vast majority of trunked systems, including digital systems, use frequency division multiple access (FDMA). For FDMA systems, the relationship "one carrier - one channel" is valid.

Single-zone TETRA systems use Time Division Multiple Access (TDMA). At the same time, TETRA multizone systems use a combination of FDMA and TDMA.

Channel search and assignment method

According to the method of searching and assigning a channel, systems with decentralized and centralized control are distinguished.

In systems with decentralized control, the procedure for searching for a free channel is performed by subscriber radio stations. In these systems, the base station repeaters are usually not connected to each other and operate independently. A feature of systems with decentralized control is a relatively long time for establishing a connection between subscribers, which grows with an increase in the number of repeaters. This dependence is caused by the fact that subscriber radio stations are forced to continuously sequentially scan channels in search of a ringing signal (the latter can come from any repeater) or a free channel (if the subscriber himself sends a call). The most characteristic representatives of this class are the SmarTrunk protocol systems.

In systems with centralized control, the search and assignment of a free channel is performed at the base station. To ensure the normal functioning of such systems, two types of channels are organized: working (Traffic Channels) and a control channel (Control Channel). All communication requests are sent over the control channel. On the same channel, the base station notifies the subscriber devices about the assignment of the working channel, the rejection of the request, or the queuing of the request.

Control channel type

In all trunked systems, the control channels are digital. There are systems with a dedicated frequency control channel and systems with a distributed control channel. In systems of the first type, data transmission in the control channel is carried out at a speed of up to 9.6 Kbps, and protocols such as ALOHA are used to resolve conflicts.

All MPT1327 protocol trunking systems, Motorola systems (Startsite, Smartnet, Smartzone), Ericsson EDACS and some others have a dedicated control channel.

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

Channel hold method

Trunking systems allow subscribers to hold the communication channel throughout the conversation, or only for the duration of the transfer. The first method, also called message trunking (Message Trunking), is the most traditional for communication systems, and is necessarily used in all cases of duplex communication or connection with the PSTN.

The second method, which involves holding the channel only for the duration of the transmission, is called transmission trunking. It can only be implemented using half-duplex radios. In the latter, the transmitter is turned on only for the time the subscriber pronounces the phrases of the conversation. In the pauses between the end of the phrases of one subscriber and the beginning of the response phrases of the other, the transmitters of both radio stations are turned off. Some trunking systems make effective use of such pauses, releasing the working channel immediately after the end of the user's radio station transmitter. The working channel will be re-assigned for the response cue, and replicas of the same conversation will most likely be transmitted on different channels.

The trade-off for some improvement in overall system efficiency with transmission trunking is a reduction in the comfort of conversations, especially during busy hours. The working channels for continuing the started conversation during such periods will be provided with a delay of up to several seconds, which will lead to fragmentation and fragmentation of the conversation.

Trunked radio communication systems, which are radial-zone mobile VHF radio communication systems that automatically distribute communication channels of repeaters between subscribers, are a class of mobile communication systems oriented primarily to the creation of various departmental and corporate communication networks, which provide for the active use of the mode connections of subscribers in the group. They are widely used by power and law enforcement agencies, public security services of various countries to ensure communication between mobile subscribers, with fixed subscribers and subscribers of the telephone network.

There are a large number of different standards of trunked systems for public mobile radio communications (PSR-OP), which differ from each other in the method of transmitting voice information (analog and digital), the type of multiple access (FDMA - with frequency division channels, TDMA - with time division channels or CDMA - with code division of channels), the method of searching and assigning a channel (with decentralized and centralized control), the type of control channel (dedicated and distributed) and other characteristics.

At present, both in the world and in Russia, the previously appeared analog trunking radio communication systems, such as SmarTrunk, MPT1327 protocol systems (ACCESSNET, ACTIONET, etc.), Motorola systems (Startsite, Smartnet, Smartzone), systems with distributed control channel (LTR and Multi-Net from E.F. Johnson Co and ESAS from Uniden). The MPT1327 systems are the most widespread, which is explained by the significant advantages of this standard compared to other analog systems.

It should be said that in Russia the majority of large trunking networks are built on the basis of equipment of the MPT1327 standard. The heads of companies involved in the supply of equipment and system integration in the field of professional radio communications note that most of the tasks of operational voice communication facing their customers are quite effectively solved using analog systems of the MPT1327 standard.

Digital standards for trunked radio communications have not yet become so widespread in Russia, but even 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. In Russia, large customers of professional radio systems are also emerging, whose requirements are driving the transition to digital technologies. First of all, these are large departments and corporations, such as RAO UES, the Ministry of Transport, the Ministry of Railways, Sibneft and others, as well as law enforcement agencies and law enforcement agencies.

The need for the transition is explained by a number of advantages of digital trunking over analog systems, such as greater spectral efficiency due to the use of complex types of signal modulation and low-speed speech conversion algorithms, increased capacity of communication systems, equalization of the quality of voice exchange throughout the coverage area of the base station due to the use of digital signals in combination with error-free coding. The development of the global market for trunked radio communication systems today is characterized by the widespread introduction of digital technologies. The world's leading manufacturers of equipment for trunking systems announce the transition to digital radio communication standards, while providing for either the release of fundamentally new equipment, or the adaptation of analog systems to digital communications.

Compared to analog trunking systems, digital trunking systems have a number of advantages due to the implementation of requirements for increased communication efficiency and security, providing ample opportunities for data transfer, a wider range of communication services (including specific communication services to meet the special requirements of public security services), and opportunities for organizing interaction subscribers of various networks.

1. High communication efficiency. First of all, this requirement means the minimum possible time to establish a communication channel (access time) for various types of connections (individual, group, with telephone network subscribers, etc.). In conventional communication systems, when transmitting digital information that requires time synchronization of the transmitter and receiver, it takes more time to establish a communication channel than an analog system. However, for trunked radio communication systems, where information exchange is mainly carried out through base stations, the digital mode is comparable in access time to the analog one (in both analog and digital radio communication systems, as a rule, the control channel is implemented based on digital signals).

In addition, in digital trunked radio communication systems, various communication modes are more easily implemented that increase its efficiency, such as direct mode between mobile subscribers (without using a base station), open channel mode(allocation and assignment of network frequency resources to a certain group of subscribers for their further negotiations without performing any installation procedure, including without delay), emergency and priority call modes, etc.

Digital trunked radio systems are better adapted to various data transmission modes, which provides, for example, law enforcement and public security officers with ample opportunities to quickly obtain information from centralized databases, transmit the necessary information, including images, from incident sites, and organize centralized dispatch systems for positioning mobile objects based on satellite radio navigation systems. These systems allow consumers of the oil and gas complex to use them as a transport not only for the transmission of voice communications, but also for the transmission of telemetry and telecontrol.

2. Data transfer. Digital trunked radio communication systems are better adapted to various data transmission modes, which provides subscribers of digital networks with ample opportunities for promptly obtaining information from centralized databases, transmitting the necessary information, including images, and organizing centralized dispatch systems for locating mobile objects based on satellite radio navigation systems. The data transfer rate in digital systems is much higher than in analog systems.

In most radio communication systems based on digital standards, services are implemented for the transmission of short and status messages, personal radio call, facsimile, access to fixed communication networks (including those operating on the basis of TCP / IP protocols).

3. Communication security. It includes requirements for ensuring the secrecy of negotiations (exclusion of the possibility of extracting information from communication channels to anyone other than an authorized recipient) and protection against unauthorized access to the system (exclusion of the possibility of seizing control of the system and attempts to disable it, protection from "twins" and etc.). As a rule, the main mechanisms for ensuring communication security are encryption and authentication of subscribers.

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

Digital trunked radio systems allow the use of a variety of subscriber authentication mechanisms: various identification keys and SIM cards, complex authentication algorithms using encryption, etc.

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

Along with the standard network service functions at the request of law enforcement agencies, digital trunked radio communication standards often include requirements for the availability of specific communication services: a call mode that comes only with the authorization of the system manager; the mode of dynamic modification of user groups; the mode of remote activation of radio stations for acoustic listening to the situation, etc.

5. Possibility of interaction. Digital radio communication systems, which have a flexible subscriber addressing structure, provide ample opportunities both for creating various virtual networks within one system and for organizing, if necessary, the interaction of subscribers of various communication networks. For public security services, the requirement to ensure the possibility of interaction between departments of various departments to coordinate joint actions in emergency situations: natural disasters, terrorist attacks, etc. is especially relevant.

The most popular, internationally recognized standards for digital trunked radio communication, on the basis of which communication systems are deployed in many countries, include:

EDACS, developed by Ericsson;
TETRA, developed by the European Telecommunications Standards Institute;
APCO 25, developed by the Association of Communication Officials of Public Security Agencies;
Tetrapol, developed by Matra Communication (France);
IDEN, developed by Motorola (USA).

All these standards meet modern requirements for trunked radio communication systems. They allow you to create various configurations of communication networks: from the simplest local single-zone systems to complex multi-zone systems at the regional or national level. Systems based on these standards provide various modes of voice transmission (individual communication, group communication, broadcast call, etc.) and data (switched packets, circuit-switched data transmission, short messages, etc.) and the possibility of organizing communication with various systems via standard interfaces (with a digital network with integrated services, with a public telephone network, with private exchanges, etc.). In the radio communication systems of these standards, modern methods of speech conversion are used, combined with effective methods of noise-immune coding of information. Radio manufacturers ensure that they meet MIL STD 810 standards for various environmental and mechanical conditions.

2. General information about digital trunked radio standards

2.1. SystemEDACS

One of the first digital trunking radio communication standards was the EDACS (Enhanced Digital Access Communication System) standard developed by Ericsson (Sweden). Initially, it provided only analog voice transmission, but later a special digital modification of the EDACS Aegis system was developed.

The EDACS system operates in accordance with a closed proprietary protocol that meets the security requirements for the use of trunked radio communication systems, which were developed by a number of mobile equipment manufacturers in cooperation with law enforcement agencies (Document APS 16).

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

EDACS systems use frequency division of communication channels using a high-speed (9600 bps) dedicated control channel, which is intended for the exchange of digital information between radio stations and system control devices. This ensures high efficiency of communication in the system (the time of establishing a communication channel in a single-zone system does not exceed 0.25 s). The information transfer rate in the working channel also corresponds to 9600 bps.

Speech coding in the system is performed by compressing a pulse-code sequence at a rate of 64 Kbps, obtained using analog-to-digital signal conversion with a clock frequency of 8 kHz and a bit depth of 8 bits. The compression algorithm, which implements the method of adaptive multilevel coding (developed by Ericsson), provides dynamic adaptation to the individual characteristics of the subscriber's speech and forms a low-speed digital sequence, which is subjected to error-correcting coding, bringing the bit rate up to 9.2 Kbps. Next, the generated sequence is divided into packets, each of which includes synchronization and control signals. The resulting sequence is transmitted to the communication channel at a rate of 9600 bps.

The main functions of the EDACS standard, which provide the specifics of public safety services, are various call modes (group, individual, emergency, status), dynamic call priority control (up to 8 priority levels can be used in the system), dynamic modification of subscriber groups (regrouping), remote shutdown radio stations (in case of loss or theft of radio equipment).

EDACS systems provide the ability to operate radios in both digital and analog modes, which allows users to use the old fleet of radio equipment at some stage.

One of the main objectives of the system development was to achieve high reliability and fault tolerance of communication networks based on this standard. This goal has been achieved, as evidenced by the reliable and stable operation of communication systems in various regions of the world. High fault tolerance is ensured by the implementation of a distributed architecture in the EDACS system hardware and the underlying principle of distributed data processing. The base station of the communication network remains operational even in the event of failure of all repeaters, except for one. In this case, the last operational repeater in the initial state works as a control channel repeater, when calls arrive, it processes them, assigning its own frequency channel, after which it switches to the working channel repeater mode. When the base station controller fails, the system goes into emergency mode, in which some network functions are lost, however, partial operability remains (repeaters work autonomously).

End-to-end encryption of information is possible in the EDACS system, however, due to the closed protocol, it is necessary to use either the standard security algorithm offered by Ericsson, or to coordinate with it the possibility of using its own software and hardware modules that implement original algorithms that must be compatible with the EDACS system protocol.

To date, a large number of EDACS networks have been deployed in the world, including multi-zone communication networks used by public security services in various countries. About ten networks of this standard operate in Russia, the largest is the communication network of the Federal Security Service of Russia in Moscow, which includes 9 base stations. At the same time, Ericsson is currently not working on improving the EDACS system, has stopped deliveries of equipment for the deployment of new networks of this standard, and only supports the operation of existing networks.

2.2 TETRA system

TETRA is a digital trunked radio standard consisting of a set of specifications developed by the European Telecommunications Standards Institute (ETSI). The TETRA standard was created as a single pan-European digital standard. Therefore, until April 1997, the abbreviation TETRA meant Trans-European Trunked Radio (Trans-European Trunked Radio). However, due to the great interest in the standard in other regions, its scope is not limited to Europe. Currently, TETRA stands for Terrestrial Trunked Radio (TERrestrial Trunked Radio).

TETRA is an open standard, meaning that equipment from different manufacturers is expected to be compatible. Access to the TETRA specifications is free for all interested parties who have joined the Association "Memorandum of Understanding and Promoting the TETRA Standard" (MoU TETRA). The Association, which at the end of 2001 included more than 80 members, brings together developers, manufacturers, testing laboratories and users from different countries.

The TETRA standard consists of two parts: TETRA V + D (TETRA Voice + Data) - a standard for an integrated voice and data transmission system, and TETRA PDO (TETRA Packet Data Optimized) - a standard describing a special version of a trunking system focused only on data transmission .

The TETRA standard includes specifications for the wireless interface, interfaces between the TETRA network and the integrated services digital network (ISDN), public telephone network, data network, private branch exchanges, etc. The standard includes a description of all basic and additional services provided by networks TETRA. Interfaces for local and external centralized network management are also specified.

The TETRA standard radio interface assumes operation in a standard frequency grid with a step of 25 kHz. The required minimum duplex spacing of radio channels is 10 MHz. For TETRA systems, some frequency sub-bands may be used. In European countries, the 380-385 / 390-395 MHz bands are assigned to security services, and the 410-430 / 450-470 MHz bands are provided for commercial organizations. In Asia, 806-870 MHz is used for TETRA systems.

TETRA V+D systems use the time division multiple access (TDMA) method of communication channels. Up to 4 independent information channels can be organized on one physical frequency.

Messages are transmitted in multiframes with a duration of 1.02 s. A multiframe contains 18 frames, one of which is a control frame. The frame has a duration of 56.67 ms and contains 4 time slots. In each of the time intervals, information of its time channel is transmitted. The time interval has a length of 510 bits, of which 432 are informational (2 blocks of 216 bits each).

TETRA systems use p/4-DQPSK (Differential Quadrum Phase Shift Keying) relative phase modulation. Modulation rate - 36 Kbps.

For speech conversion, the standard uses a codec with a conversion algorithm like CELP (Code Excited Linear Prediction). The bit rate at the output of the codec 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 capacity of one information channel is 7.2 Kbps, and the speed of the digital information data flow is 28.8 Kbps. (In this case, the total symbol rate in the radio channel due to the additional service information and the control frame in the multiframe corresponds to the modulation rate and is equal to 36 Kbps.)

TETRA standard systems can operate in the following modes:

trunking communication;
with an open channel;
direct connection.

In mode trunking communication the service area is covered by the coverage areas of the base transceiver stations. The TETRA standard allows both using only a distributed control channel in systems, and organizing its combination with a dedicated frequency control channel. When operating a network with a distributed control channel, service information is transmitted either only in the control frame of a multiframe (one of 18), or in a specially dedicated time channel (one of 4 channels organized at the same frequency). In addition to the distributed network, the communication network can use a dedicated frequency control channel specially designed for the exchange of service information (maximum communication services are realized in this case).

In mode with open channel a user group has the ability to set up a one-point-multiple-point connection without any setup procedure. Any subscriber who joins the group can use this channel at any time. In the open channel mode, the radio stations operate in a two-frequency simplex.

In mode direct (direct) connection point-to-point and multipoint connections are established between the terminals over radio channels not associated with the network control channel, without signal transmission through base transceiver stations.

In TETRA standard systems, mobile stations can operate in the so-called. “Dual Watch” mode, which ensures the reception of messages from subscribers operating both in the trunking and direct communication modes.

To increase service areas, the TETRA standard provides for the possibility of using subscriber radio stations as repeaters.

TETRA provides users with a number of services that are included in the standard at the request of the European Police Association (Schengen Group), cooperating with the ETSI technical committee:

dispatcher authorized call(mode in which calls are received only with the approval of the dispatcher);
priority access(in case of network congestion, available resources are assigned according to the priority scheme);
priority call(assignment of calls in accordance with the priority scheme);
preemption call service(interruption of service calls with low priority, if the system resources are exhausted);
selective listening(interception of an incoming call without affecting the work of other subscribers);
remote listening(remote activation of a subscriber radio station for transmission to listen to the situation at the subscriber);
dynamic rearrangement(dynamic creation, modification and deletion of user groups);
caller identification.

The TETRA standard provides two levels of security for transmitted information:

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

The TETRA air interface security features include mechanisms for subscriber and infrastructure authentication, traffic confidentiality through pseudo-name flow, and specified information encryption. A certain additional protection of information is provided by the possibility of switching information channels and control channels in the process of conducting a communication session.

A higher level of information security is a unique requirement for special user groups. End-to-end encryption ensures the protection of voice and data at any point in the communication line between fixed and mobile subscribers. The TETRA standard specifies only an interface for end-to-end encryption, thus providing the ability to use original information protection algorithms.

It should also be noted that in the TETRA standard, in connection with the use of the time division channel method (TDMA) of communication in all subscriber terminals, it is possible to organize communication in full duplex mode.

TETRA networks are deployed in Europe, North and South America, China, Southeast Asia, Australia, Africa.

Currently, the development of the second stage of the standard (TETRA Release 2 (R2)) is being completed, aimed at integration with 3rd generation mobile networks, a radical increase in data transfer speed, the transition from specialized SIM cards to universal ones, further increasing the efficiency of communication networks and expanding possible service areas.

In Russia, TETRA equipment is offered by a number of system integrator companies. Several pilot projects of TETRA networks have been implemented. Under the auspices of the Ministry of Communications, the development of the system project "The Federal Network of Mobile Radio Communications TETRA", called "Tetrarus", is being carried out. In 2001, the Russian TETRA Forum was established, whose tasks include promoting TETRA technology in Russia, organizing the exchange of information, promoting the development of national production, participating in the harmonization of the radio frequency spectrum, etc. d. the use of the TETRA standard is recognized as promising "... in order to provide communications for government at all levels, defense, security, law enforcement, the needs of departments and large corporations."

2.3. APCO 25 system

The APCO 25 standard was developed by the Association of Public Safety Communications Officials-international, which brings together users of communications systems working in the public safety services.

Work on the creation of the standard began at the end of 1989, and the last documents to establish the standard were approved and signed in August 1995 at the APCO International Conference and Exhibition in Detroit. Currently, the standard includes all the main documents that define the principles for constructing the radio interface and other system interfaces, encryption protocols, speech coding methods, etc.

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

The fundamental principles for the development of the APCO 25 standard, formulated by its developers, were the requirements:

to ensure a smooth transition to digital radio communications (i.e., the possibility of joint work at the initial stage of standard base stations with subscriber analog radio stations currently in use);
to create an open system architecture to stimulate competition among equipment manufacturers;
to ensure the possibility of interaction between various departments of public security services during joint activities.

The system architecture of the standard supports both trunking and conventional (conventional) radio communication systems, in which subscribers interact with each other either in direct communication mode or through a repeater. The main functional block of the APCO 25 standard system is the radio subsystem, defined as a communication network, which is built on the basis of one or more base stations. In addition, each base station must support the Common Radio Interface (CAI - Common Radio Interface) and other standardized interfaces (intersystem, PSTN, data port, data network and network management).

The APCO 25 standard provides for the ability to operate in any of the standard frequency bands used by mobile radio systems: 138-174, 406-512 or 746-869 MHz. The main method of access to communication channels is frequency (FDMA), however, at the request of Ericsson, Phase II includes the possibility of using time division multiple access (TDMA) in APCO 25 standard systems.

In Phase I, the standard frequency grid spacing is 12.5 kHz, in Phase II it is 6.25 kHz. At the same time, with a bandwidth of 12.5 kHz, four-position frequency modulation is carried out using the C4FM method at a rate of 4800 symbols per second, and with a bandwidth of 6.25 kHz, four-position phase modulation with phase smoothing is performed using the CQPSK method. The combination of these modulation methods makes it possible to use the same receivers in different phases, supplemented by different power amplifiers (for Phase I - simple amplifiers with high efficiency, for Phase II - amplifiers with high linearity and a limited width of the emitted spectrum). In this case, the demodulator can process signals using any of the methods.

Voice information in the radio channel is transmitted in frames of 180 ms, grouped in 2 frames. For speech coding, the standard uses the IMBE (Improved MultiBand Excitation) codec, which is also used in the Inmarsat satellite communication system. Encoding speed - 4400 bps. After error-correcting coding of speech information, the information flow rate increases to 7200 bps, and after the formation of speech frames by adding service information - up to 9600 bps.

The subscriber identification system incorporated in the APCO 25 standard allows addressing at least 2 million radio stations and up to 65 thousand groups in one network. In this case, the delay in 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 direct communication mode - 250 ms, in communication through a repeater - 350 ms).

APCO 25 systems, in accordance with functional and technical requirements, must provide 4 levels of cryptographic protection. A streaming method of information encryption is used with the use of non-linear algorithms for the formation of an encryption sequence. When using the special OTAR (Over-the-air-re-keying) mode, encryption keys can be transmitted over the air.

Due to the fact that the main method of access to communication channels in APCO is MDIR, at the moment there are no terminals that would ensure the subscriber's work in full duplex mode.

Despite the fact that APCO is an international organization with offices in Canada, Australia, and the Caribbean, American firms supported by the US government play a major role in promoting this standard. Members of the public sector of the Association include the FBI, the US Department of Defense, the Federal Communications Committee, the police of several US states, the Secret Service and many other government organizations. Leading companies such as Motorola (the main developer of the standard), E.F. Johnson, Transcrypt, Stanlite Electronics and others have already declared themselves as manufacturers of APCO 25 equipment. Motorola has already introduced its first system based on the APCO 25 standard, called ASTRO.

Specialists of the Ministry of Internal Affairs of Russia show the greatest interest in this standard. A pilot network (so far not trunking, but conventional radio communication) based on two base stations was deployed by the Ministry of Internal Affairs of Russia in Moscow in 2001. In 2003, in St. power structures.

2.4. Tetrapol system

Work on the creation of the Tetrapol digital trunked radio standard began in 1987, when Matra Communications entered into a contract with the French gendarmerie to develop and commission the Rubis digital radio network. The communication network was put into operation in 1994. According to Matra, today the network of the 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 own Tetrapol forum, under the auspices of which the Tetrapol PAS (Publicly Available Specifications) specifications were developed, which define the standard for digital trunked radio communication.

The Tetrapol standard describes a digital trunked radio communication system with a dedicated control channel and a frequency separation method for communication channels. The standard allows you to create both single-zone and multi-zone communication networks of various configurations, also providing the possibility of direct communication between mobile subscribers without using the network infrastructure and relaying signals on fixed channels.

Communication systems of the Tetrapol standard have the ability to operate in the frequency range from 70 to 520 MHz, which, in accordance with the standard, is defined as a combination of two sub-bands: below 150 MHz (VHF) and above 150 MHz (UHF). Most of the radio interfaces for systems in these subbands are common, the difference lies in the use of different methods of error-correcting coding and code interleaving. In the UHF subband, the recommended duplex separation of the receive and transmit channels is 10 MHz.

The frequency separation between adjacent communication channels can be 12.5 or 10 kHz. In the future, a transition to a spacing between channels of 6.25 kHz is expected. Tetrapol systems support bandwidths up to 5 MHz, allowing 400 (at 12.5 kHz spacing) or 500 (at 10 kHz spacing) radio channels to be used in the network. At the same time, from 1 to 24 channels can be used in each zone.

The information transfer rate in the communication channel is 8000 bps. The transmission of information is organized by frames 160 bits long and 20 ms long. Frames are combined into superframes with a duration of 4 s (200 frames). The information undergoes complex processing, including convolutional coding, interleaving, scrambling, differential coding, and final frame formatting.

Tetrapol systems use GMSK modulation with BT=0.25.

For speech conversion, the standard uses a codec with a speech conversion algorithm that uses the RPCELP (Regular Pulse Code Excited Linear Prediction) analysis-by-synthesis method. The conversion speed is 6000 bps.

The standard defines three main communication modes: trunked, direct mode and relay mode.

AT network mode(or trunking mode), the interaction of subscribers is carried out using base stations (BS), which distribute communication channels between subscribers. In this case, control signals are transmitted on a separate frequency channel specially allocated for each BS. In the direct mode, the exchange of information between mobile subscribers is carried out directly without the participation of the base station. AT relay mode communication between subscribers is carried out through a repeater, which has fixed channels for transmitting and receiving information.

Tetrapol standard systems support 2 main types of information exchange: voice transmission and data transmission.

Voice Services allow you to make the following types of calls: broadcast call, open channel setup call, group call, individual call, multiple call using the list of subscribers, emergency call.

Data services provide a number of application-level services supported by the functions inherent in the radio terminals, such as interpersonal messaging in accordance with the X.400 protocol, access to centralized databases, access to fixed networks in accordance with the TCP / IP protocol, facsimile transmission, file transfer, transmission of paging signals, transmission of short messages, transmission of status calls, support for the transmission mode of object location data received using GPS receivers, transmission of video images.

The Tetrapol standard provides for standard network procedures that provide a modern level of subscriber service: dynamic regrouping, subscriber authentication, roaming, priority call, subscriber transmitter control, subscriber “profile” management (remote change of subscriber radio terminal parameters programmed into it), etc.

Tetrapol standard systems provide users with a number of additional services, which, along with the provision of services, allow the effective implementation of specific communication networks of public security and law enforcement agencies. These services include priority access (providing preferential access to the system when radio links are congested); priority call (assignment of calls in accordance with the priority scheme); priority scanning (providing a user belonging to several groups with the opportunity to receive calls from a subscriber of any of the groups); call authorized by the dispatcher (a mode in which calls are received only with the authorization of the communication network dispatcher); call forwarding (unconditional call forwarding to another subscriber or forwarding if the called subscriber is busy); connecting to a call (activating a mode in which one user interacting with another can make a third subscriber a participant in the connection); selective listening (interception of an incoming call without affecting the work of other subscribers); remote listening (remote activation of a subscriber radio station for transmission to listen to the situation at the subscriber); caller identification (definition and display on the terminal of the called subscriber of the identifier of the calling party); “double surveillance” (the ability of a subscriber radio terminal operating in network mode to also receive messages in direct communication mode) and many others.

Due to the fact that from the very beginning the Tetrapol standard was focused on meeting the requirements of law enforcement agencies, it provides various mechanisms for ensuring communication security aimed at preventing threats such as unauthorized access to the system, wiretapping of ongoing conversations, creation of intentional interference, traffic analysis specific subscribers, etc. These mechanisms include:

automatic network reconfiguration(periodic redistribution of communication network resources (configuration change) due to the installation and cancellation of open channels, dynamic regrouping, reassignment of communication channels by the network manager, etc.);
system access control(control of access to communication network equipment by means of smart cards and password system);
end-to-end encryption of information(ensuring the possibility of protecting transmitted information at any point of the communication line between subscribers);
subscriber authentication(automatic or conducted at the request of the network manager authentication of subscribers);
use of temporary subscriber identifiers(replacement of unique identification numbers of subscribers with pseudonyms that are changed with each new communication session);
imitation of activity of radio subscribers(the mode of maintaining constant traffic during a break in negotiations by sending signals to the BS over communication channels that are difficult to distinguish from information ones);
remote shutdown of the radio terminal(possibility of switching off the subscriber radio terminal by the network manager);
distribution of keys over the air(possibility of transmission by the network manager of secret keys to subscribers via radio channel).

Tetrapol standard systems are widely used in France. Apparently, not without the support of the government of the domestic manufacturer, in addition to the Rubis communication network of the national gendarmerie, the Tetrapol systems are operated by the French police (Acropole system) and the railway service (Iris system).

The Tetrapol standard is also popular in some other European countries. On the basis of this standard, the communication networks of the police of Madrid and Catalonia, the security units of the Czech Republic, and the airport service in Frankfurt are deployed. The special communication network Matracom 9600 is deployed in the interests of the Berlin transport company. Communication network radio stations will be installed on more than 2,000 buses of the enterprise. In addition to radio communications, the network uses the function of determining the location of vehicles.

In 1997, Matra Communications won a tender to build a digital radio communications system for the Royal Thai Police. The contract is part of an order to modernize the police radio network, which will bring together 70 police stations. It is supposed to use the most advanced system capabilities, including access to a centralized database, e-mail, end-to-end encryption of information, location. There are also reports of the deployment of several systems in two other countries in Southeast Asia, as well as in the interests of the Mexico City police.

In our country, Tetrapol standard systems are not yet used. At present, FAPSI assumes the deployment in Russia of an experimental area for trunking radio communications of this standard.

2.5. SystemIDEN

iDEN (integrated Digital Enhanced Network) technology was developed by Motorola in the early 90s. The first commercial system based on this technology was deployed in the USA by NEXTEL in 1994.

In terms of standard status, iDEN can be described as an enterprise standard with an open architecture. This means that Motorola, while retaining all rights to modify the system protocol, licenses the production of system components to various manufacturers.

This standard was developed for the implementation of integrated systems that provide all types of mobile radio communications: dispatch communications, mobile telephone communications, text messaging and data packets. iDEN technology is focused on the creation of corporate networks of large organizations or commercial systems that provide services to both organizations and individuals.

In the implementation of mobile radio dispatcher networks, iDEN provides group and individual call capabilities, as well as a call signaling mode, in which, if the subscriber is unavailable, the call is stored in the system, and then transferred to the subscriber when it becomes available. The number of possible groups in iDEN is 65535. The set up time for a group call in half duplex mode is less than 0.5 s.

iDEN systems provide the possibility of organizing telephone communication in any direction: mobile subscriber - mobile subscriber, mobile subscriber - PSTN subscriber. Telephone communication is full duplex. The system provides the possibility of voice mail.

Subscribers of iDEN systems have the ability to send 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 mode up to 32 Kbps), which makes it possible to organize facsimile and electronic communications. mail, as well as interaction with fixed networks, in particular with the Internet. Packet data transfer mode supports TCP/IP protocol.

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

For speech coding, a codec is used that works according to an algorithm such as VSELP. The information transfer rate in one channel is 7.2 Kbps, and the total rate of the digital stream in the radio channel (due to the use of error-correcting coding and the addition of control information) reaches 64 Kbps. Such a high data rate in the 25 kHz band can be achieved through the use of 16-position quadrature modulation M16-QAM.

The standard uses the standard for America and Asia frequency range 805-821 / 855-866 MHz. IDEN has the highest spectral efficiency among the considered digital trunking communication standards, it allows placing up to 240 information channels in 1 MHz. At the same time, the coverage areas of base stations (cells) in iDEN systems are smaller 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 stations).

The iDEN system architecture has features that are common to both trunked and cellular systems, which emphasizes iDEN's focus on serving a large number of subscribers and heavy traffic. When creating commercial systems to serve various organizations or enterprises, up to 10,000 virtual networks can be created in the system, each of which can have up to 65,500 subscribers, combined if necessary into 255 groups. In this case, 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 now nationwide with about 5,500 sites and 2.7 million subscribers. There is another network in the US operated by 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 network projects of this standard.

3. Brief comparative analysis of digital radio standards

3.1. Specifications and functionality

Generalized information about the systems of the EDACS, TETRA, APCO 25, Tetrapol, iDEN standards and their technical characteristics are presented in Table 1.

Table 1.

Character- ristika standard (systems) connections				Tetrapol
Standard Developer	Ericsson (Sweden)			Matra Communications (France)
Status standard	corporate- active	open	open	corporate- active	corporate- tive with open archiving texture
Main radio manufacturers		Nokia, Motorola, OTE, Rohde&Schwarz	Motorola, E.F. Johnson Inc., Transcrypt, ADI Limited	Matra, Nortel, CS Telecom
Possible range operating 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
spacing between frequency channels, kHz	12,5 (data transfer)
Effective bandwidth for one speech channel, kHz
Type of modulation			C4FM (12.5 kHz) CQPSK (6.25 kHz)	GMSK (BT=0.25)
Speech coding method and speech conversion rate calling	adaptive multi- level coding (transformation title 64Kbps and compression up to 9.2 Kbps)	CELP (4.8 kbps)	IMBE (4.4 kbps)	RPCELP (6 Kbps)	(7.2 Kbps)
The rate of information transfer in the channel, bps		7200 (28800 - when transmitting 4 information channels on one physical frequency)			9600 (up to 32K in burst mode)
Settling time communication channel, with	0,25 (in single zone system)	0.2 s - with indiv. call(min); 0.17 s - for group call (min)	0.25 - in direct mode; 0.35 - in relay mode; 0.5 - in radio subsystem	no more than 0.5	no more than 0.5
Separation method communication channels		MDVR (using frequency division in multizone systems)
Channel type management	dedicated	dedicated or distributed (depending on configuration) network guidance)	dedicated	dedicated	Dedicated or distributed divided (depending on the configuration network guidance)
Capabilities encryption information	standard branded algorithm through encryption	1) standard algorithms; 2) through encryption	4 levels of information protection	1) standard algorithms; 2) end-to-end encryption	no information

The functionality provided by the digital trunked radio standards systems is shown in Table 2.

Table 2.

	Functionality of the communication system
	Support for basic call types (individual, group, broadcast)
	Access to the PSTN
	Full duplex subscriber terminals
	Data transfer and access to centralized databases
	Direct mode
	Automatic registration of mobile subscribers
	Personal call
	Access to fixed IP networks
	Sending Status Messages
	Sending short messages
	Support for transmitting position data from the GPS system
	Fax
	Possibility to set an open channel
	Multiple access using the subscriber list
	Availability of a standard signal relay mode
	The presence of the "dual observation" mode

Note:(n/s - no information)

Considering the technical characteristics and functionality of the presented trunking communication standards, it can be noted that all standards have high (relative to this class of mobile radio communication systems) technical indicators. They allow you to build various configurations of communication networks, provide a variety of voice and data transmission modes, communication with the PSTN and fixed networks. In the means of radio communication of these standards, effective methods of speech conversion and noise-immune coding of information are used. All standards provide high communication efficiency.

It can be noted that compared to other standards, EDACS has a slightly lower spectral efficiency. In addition, some experts note that the EDACS standard does not use digital modulation methods, which allows us to speak of it as a standard in which digitized speech information is transmitted over an analog communication channel.

In terms of functionality, the EDACS standard is also, to a certain extent, inferior to the other three standards, since it was developed somewhat earlier. The TETRA, APCO 25, Tetrapol and iDEN standards specify a wide range of standard communication services provided, comparable in level. (As a rule, the list of services provided is determined during the design of a particular system or radio communication network.)

3.2. Fulfillment of special requirements for radio communication systems of public safety services

Information about the availability of some specific communication services targeted at use by members of the public safety services is presented in Table 3. The iDEN standard is not considered here, since this standard was developed without taking into account the special requirements of the public safety services. Currently, there are only a few reports of ongoing attempts to adapt the systems of this standard to special requirements.

Table 3

	Special communication services				Tetrapol
	Access Priority
	Priority Call System
	Dynamic rearrangement
	Selective Listening
	Remote listening
	Caller ID
	Call authorized by dispatcher
	Key transfer over the air (OTAR)
	Simulation of subscriber activity
	Remote disconnection of the subscriber
	Subscriber authentication

Since the standards presented in the table were developed in the interests of public security services, they all ensure that most of the requirements for special communication systems are met, which can be seen in Table 2. The presented digital standards provide high communication efficiency (access time for all systems is no more than 0 , 5 c) and provide for the possibility of increasing the resiliency of radio networks through a flexible architecture. All standards make it possible to implement information protection: for TETRA and Tetrapol systems, the 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 proprietary algorithm or specifically coordinate with the company the possibility of using their own protection system; According to the functional and technical requirements for APCO 25 systems, 4 levels of information security must be provided (of which only one can be intended for export applications).

When considering the list of special communication services provided by each standard, it can be noted that the TETRA, APCO 25, Tetrapol standards provide a comparable level of special services, and EDACS - somewhat less. The iDEN standard is not designed to fulfill special requirements.

3.3. RF Spectrum Resources

The availability of radio frequency spectrum (RFS) resources for the deployment of a radio communication system is the most important criterion for choosing a particular system. In this case, the most promising standards are those that provide the ability to build communication networks in the widest range.

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

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

APCO 25 systems, in accordance with 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 their systems to 520 MHz.

iDEN standard systems operate only in the 800 MHz band, which limits their use to build a certain range of systems.

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

3.4. Standard status (open/closed)

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

Corporate standards (EDACS and Tetrapol) are the property of their developers. Equipment can only be purchased from a limited number of manufacturers.

Open standards, which include TETRA and APCO 25, provide a competitive environment, attracting a large number of manufacturers of basic equipment, subscriber radio stations, test equipment for the production of compatible radio equipment, which helps to reduce their cost. Access to standards specifications is provided to any organizations and firms that have joined the relevant association. Users choosing an open radio standard are not dependent on a single manufacturer and can change equipment vendors. Open standards are supported by government and law enforcement agencies, large companies in many countries of the world, and are also supported by the world's leading manufacturers of element and node base.

Conclusion

A brief comparative analysis of these standards for digital trunking radio communications according to the main criteria considered allows us to draw 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 lower spectral efficiency and less extensive functionality. Ericsson does not plan to expand the capabilities of the standard and has practically curtailed the production of equipment.

The iDEN standard does not provide many special requirements, and, despite the high spectral efficiency, is limited by the need to use the 800 MHz band. It is likely that systems in this standard have some potential and will continue to be deployed and operated, especially in the Americas. In other regions, the prospects for deploying systems of this standard look doubtful.

The Tetrapol standard has good technical performance and sufficient functionality, however, like the EDACS and iDEN standards, it does not have the status of an open standard, which can significantly hinder its development in technical terms, as well as in terms of the cost of subscriber and stationary equipment.

The TETRA and APCO 25 standards have high technical characteristics and wide functionality, including meeting the special requirements of law enforcement agencies, and have sufficient spectral efficiency. The most important argument in favor of these systems is the status of open standards.

At the same time, most experts are inclined to believe that the market for digital trunked radio communications will be conquered by the TETRA standard. This standard is widely supported by most of the world's major equipment manufacturers and communications administrations in various countries. Recent events in the domestic market of professional radio communications allow us to conclude that in Russia this standard will be most widely used.