Some options for organizing operational radio communications for security and safety services.

Some options for organizing operational radio communications for security and protection services..

Vorobyov Sergey Viktorovich
Ovchinnikov Andrey Mikhailovich

SOME OPTIONS FOR ORGANIZING OPERATIONAL RADIO COMMUNICATION
OF SECURITY AND PROTECTION SERVICES

The article examines the issues of building operational radio communication networks for commercial security and protection services. Recommendations are given for choosing network building options.

Almost all security and guard services use radio communications in their activities to organize interaction and control of employees. A radio station is currently an integral attribute of a security officer, like cold and firearms or personal protective equipment. At the same time, unlike them, a radio station can ensure the performance of its functions (information exchange) only when interacting with other similar radio stations, that is, when working in a network. Thus, along with the parameters and functional capabilities of radio stations, the correct organization of their interaction is important, i.e. unification into networks and communication systems.

Let's consider the features of building communication networks for security services. Such networks are designed to serve subscribers united in groups of 20-30 people. The group may include mobile (in cars, on foot) and stationary subscribers. As a rule, each subscriber within the group must hear all its members. In some cases, communication with subscribers of telephone networks is necessary. Rapid changes in the operational situation require minimal connection establishment time with maximum ease of radio station control. Additional requirements are imposed on the equipment of such communication networks to protect transmitted information from eavesdropping and for weight and size characteristics.

Recently, many radio operators provide services based on trunking systems of the type  SmarTrunk II, MPT 1327and others. In many cases, the volume and quality of services meet the requirements of security services and leasing the resources of these systems is the only possible solution, especially where the subscriber density is high enough and the radio frequency resource is almost exhausted. First of all, this concerns large cities. At the same time, in many cases it is preferable to have your own independent (corporate) radio network. For example, in the absence of a trunking operator (which is most likely in small cities), or the insufficiency of the volume of services provided by it, for example, in the absence of the possibility of exchanging confidential information.

This article discusses some options for building small autonomous radio communication networks taking into account the specifics of security and protection services. The appendix explains individual terms used in the article.

In technical terms, corporate operational communication systems are built mainly on the basis of a radial structure using a fixed distribution of communication channels. Depending on the tasks being solved, the options for organizing radio communication in the network may be different. Let's consider typical options.

Option 1.The mobile group of subscribers operates autonomously, moving around the territory. Communication is carried out in a local area of ​​subscriber concentration with a radius of 0.5-1 km. Most often, this type of communication organization is used when protecting VIPs.

The structural diagram of communication is shown in Fig. 1, where A is a car radio station; H is a portable radio station. Depending on the task being performed, openly carried radio stations or radio stations for hidden wearing can be used as portable radio stations.

One radio frequency channel is sufficient to organize communication, i.e. all subscribers in the group work on one channel and hear each other. Radio equipment operates in simplex mode. In general, the number of subscribers in a group is determined by organizational and tactical requirements.

Since the average intensity of a subscriber's work in the network is low (usually no more than 1-2 communications per minute with an average message duration of 5-7 sec), then independent operation of several groups on a common frequency channel with separate message delivery is possible. In this case, the total number of subscribers on one radio frequency channel should not exceed 20-50 people. Separation of groups is carried out using the so-called selective call (CTCSS codec-decoder).To reduce interference in radio stations, it is advisable to program a ban on transmission on a busy channel.

It can be noted that in this task, the use of a single-zone trunking network communication may be worse than the proposed option, since the movement of the guarded object and the group is not territorially limited. That is, they can leave the service area of ​​the trunking network,which will lead to instability or loss of communication. In the proposed version, the operating area of ​​the mobile group is practically unlimited, and due to the compactness of the group, communication reliability is quite high.

Within the framework of the considered communication network structure, interaction of several groups is possible. This version is shown in Fig. 2.

Fig. 2

Group 1 (Gr.1) operates on channel K 1, group 2 (Gr.2) — on channel K 2. When transmitting a message from Gr.1 to Gr.2, the subscriber of Gr. 1 switches the radio station to channel K2. And, vice versa, when Gr. 2 initiates the transmission of a message, the exchange of information is carried out on channel K 1. A virtual channel can be used as a communication channel.

Option 2.Several independent mobile groups of subscribers in a limited area with a radius of 1-2 km under the control of a common dispatcher each perform their own task. This option describes well the radio communication network of the security of a large industrial facility, when the independent groups are the fire safety, security, alarm control departments, etc.

Fig. 3

The structural diagram of the radio communication network is shown in Fig. 3, where H, St. are portable and stationary radio stations. Group 1 (Gr.1) operates on channel K1, group 2 (Gr.2) on channel K2. With a larger number of groups, the number of channels should increase proportionally.

The operation of a stationary radio station can be organized in two ways.

The first is that a separate communication channel KZ is allocated for communication with the dispatcher, to which portable radio stations are switched when communicating with him. The dispatcher communicates with the corresponding group of subscribers on the channel of this group. With this organization, the dispatcher does not hear conversations within the groups, but can connect to the negotiations at any time by switching the radio station to the corresponding communication channel.

The second method of organizing communication with the dispatcher involves the use of a stationary radio station in the scanning mode on channels K1 and K2. In this case, the dispatcher constantly monitors conversations within the groups.

Obviously, as in the previous example, with appropriate programming of portable radio stations, interaction between groups is possible. When transmitting a message from Group 1 to Group 2, the subscriber of Group 1 switches the radio station to channel K2, and vice versa, when initiating the transmission of a message from Group 2, the exchange of information is carried out on channel K1. To separate into channels, it is sufficient to use the CTCSS coder signals, and to reduce interference, prohibition of transmission on a busy channel.Radio stations in the network operate in simplex mode, so to deploy the network it is enough to have one radio channel.

A special feature of this communication organization scheme is the ability to increase the communication range. For this purpose, a stationary radio station, switched on in duplex mode, is used as a repeater, its antenna is placed at a dominant height, and in the radio equipment of mobile subscribers, the two-frequency simplex mode is switched on.In this case, all communication sessions between mobile subscribers are carried out by retransmitting signals through a stationary radio station. However, this mode also has a drawback — at the boundary of the service area of ​​​​the stationary station, there may be no communication, even if the mobile subscribers are in close proximity to each other. Therefore, as a rule, a backup channel is provided in which the radio stations operate in simplex mode, as discussed in option 1. In addition, the implementation of the retransmission mode requires the allocation of a duplex pair of radio frequencies.

Option 3. Several mobile groups work in a small city with a radius of 5-10 km, off-site activities in suburban areas are possible. Communication with a stationary subscriber and access to telephone lines are required. This option may describe the work of a private detective or security agency.

Fig. 4 shows a structural diagram of one of the options for constructing such a communication network. Its new elements are: a repeater (RT) and a telephone controller (TC) connected to a base station (BS). A subscriber line of the telephone network (SL) is connected to the telephone controller.

Fig. 4

The operation of groups in the city is no different from the case considered in option 2. Subscribers of the group work on the channel of the K1 group. Communication with the dispatcher is carried out on the K3 channel. As before, subscriber radio stations work on one radio frequency channel in simplex mode.

During off-site events, communication is maintained through a repeater (RT), placed in the direction of the off-site events, for example, near suburban summer cottages. This allows for communication between the BS and the car at distances of up to 100 km. The repeater operates in duplex mode,therefore, a duplex pair of radio frequencies must be allocated for its operation. Let us assume that the repeater's reception frequency corresponds to the fp value, and the transmission frequency coincides with the frequency of the city's communication network. Channels K1 and K3 are separated using CTCSS encoder signals. Thus, one duplex pair of radio frequencies is sufficient for the operation of a small communication network.

The communication between the mobile group and the dispatcher is as follows. In the repeater operation zone, the mobile group (Group 2) switches the radio station to the repeater operation channel, while the radio station must operate in the two-frequency simplex modewith a transmission frequency of fp, and a reception frequency on the KZ channel. The dispatcher, using a stationary radio station operating on the KZ channel, receives messages from subscribers in the city or from a repeater. When responding, the dispatcher switches the radio station to the communication channel with the corresponding group. Obviously, on the channel operating through a repeater, the stationary radio station must operate in two-frequency simplex mode.

The use of a duplex pair of radio frequencies in this version allows for the implementation of communication between mobile subscribers and subscribers of the telephone network.

In this case, a telephone interface is connected to the stationary radio station, for example, CS-900 from CSI, and the subscribers are equipped with a keypad for dialing a number and a DTMF board.A separate channel for access to the telephone network is allocated to subscriber radio stations. On this channel, the radio station must operate in the dual-frequency simplex mode with a transmission frequency corresponding to the KZ channel and a reception frequency fp. The CTCSS encoder signals for this channel must be selected separately. Thus, a common duplex pair of radio frequencies with the repeater is used to communicate with subscribers of the telephone network. Interaction between subscribers of the telephone and radio networks occurs in the usual way (see, for example, V.M. Tamarkin, V.B. Gromov, S.I. Sergeev “Systems and standards of trunking communication”).

The number of subscribers served by this communication network is determined as in option 1.

The options given do not exhaust the diversity of building small corporate radio communication networks. It is obvious that individual elements of the considered options can be combined with each other to implement new capabilities.

For building the described communication networks, there is a wide range of imported VHF radio stationsand domestic production, implementing the necessary set of functional capabilities. However, it is advisable to build corporate communication networks on the basis of professional radio station sets, such as TK-250, TK-260, TK-768 by KENWOOD, GP300, GM300 by MOTOROLA, etc. Distinctive features of professional radio stations are simplicity and ease of control, reliability at operation in adverse conditions, protection against unskilled reprogramming.

The table provides generalized estimated technical and economic parameters of the considered communication networks. This table should not be considered as comparative, since each of the options has its own niche of application. At the same time, it allows you to estimate the resources required to deploy the system.

Table

* Here, stationary radio stations are understood to mean car radio stations equipped for use in stationary conditions.

When selecting and ordering equipment for deploying communication networks, it is necessary to remember about purchasing auxiliary equipment and accessories, without which reliable operation of the communication network is unthinkable. Such attributes include batteries, chargers, antenna-feeder devices, control and test equipment, technical documentation, etc.

THESAURUS

CTCSS codec — a personal and group call unit. Subscribers are separated (call addressing) by continuous radiation (on the transmitting side) and detection (on the receiving side) of a predetermined subtone harmonic signal of a certain frequency for the duration of the communication.

DTMF — two-tone a signaling system used for personal and group calling, and for dialing a telephone number.

MRI 1327 is an open standard for trunked analog radio communication developed by order of the British Post Office and Telecommunications Ministry. Communication systems of this standard can have a multi-zone configuration and serve subscribers over a large area. The standard provides for a wide range of user services, including the organization of independent local groups with communication support when placing subscribers of the group in different zones.

SmarTrunk П is a corporate standard for trunking analog radio communications from SmarTrunk Systems, Inc. This standard is intended primarily to create small, inexpensive multi-user communication networks with a standard set of services dispatch application.

Duplex mode — a radio station operating mode in which it is possible to simultaneously receive and transmit messages.

Ban on transmission on a busy channel— a radio station operating mode in which the transmission of information is prohibited if there is another signal on the radio frequency.

Intensity — the number of radio communications per unit of time.

Communication reliability the ratio of the number of messages received to the number of messages transmitted under certain communication conditions.

Dual-frequency simplex mode simplex mode of radio station operation, in which the radio frequencies of reception and transmission differ by the value of the duplex spacing.

Selective calling — a call or exchange of information with a specific subscriber (group of subscribers). Technically, it is carried out using additional signals of a certain type, for example, CTCSS or DTMF.

Simplex mode is a radio station operating mode in which the reception and transmission of information are carried out alternately under the control of the subscriber.

Scanning is a sequential search for an information signal on several communication channels. Usually, the search is carried out according to certain signal characteristics, for example, by the presence of a certain CTCSS tone in the signal.

Trunking distribution of communication channels is a method of distributing communication channels in which, upon request, a subscriber is provided with an arbitrary free radio frequency channel from among those allocated to the communication system. This principle allows to significantly increase the efficiency of using radio frequency resources.

Trunking systems a type of communication system using trunking distribution of communication channels.