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Radio relay communication. General principles for constructing line-of-sight radio relay communication lines

Radio relay communication lines are one of the largest and most advanced networks for transmitting, receiving and processing data throughout the world. The very principle of message transmission is based on the propagation of radio waves in the atmosphere. In order for the signal to travel long distances, it is necessary to use special radio relay communication equipment - a chain of repeaters, thanks to which radio waves of a certain frequency will propagate.

Operating principle of a radio relay communication line

To understand the nature of radio wave propagation, it is necessary to study the physics, mechanics and dynamics of these phenomena, which are directly related to atmospheric properties and the electromagnetic field. Based on many factors, radio relay communication lines are calculated. Without going into details, the operating principle of the entire system is as follows:

  • first, high-frequency oscillations are generated in a special transmitting device and a so-called carrier signal is released;
  • the information that needs to be transmitted (voice, video, text) is encoded and converted into frequency vibrations, and then modulated along with the carrier signal;
  • using special antennas, the prepared signal is transmitted into space, reaching receiving devices that are located within a certain radius from the transmitter;
  • in case of insufficient signal power, the complexity of its propagation or a large distance between the transmitter and receiver, radio relay communication lines are used, the equipment of which allows solving the problems that have arisen. As a rule, this is a network of ground repeaters that not only receive the signal, but also amplify it, eliminate interference and transmit it along the chain to the next object through highly directional antennas;
  • the signal reaches the receiver, where it is separated from the carrier frequency and converted to its original form, followed by display on the communication terminal. This could be just a voice message or a full-fledged video broadcast. Terrestrial radio and television broadcasting are precisely built on this principle of signal transmission.

Communication Line Types

Radio relay and satellite communication lines are a set of equipment that combines ground-based and orbital repeaters, which make it possible to broadcast a signal to almost any point on the surface of the planet.

There are two types of basic radio signal transmission methods:

  • line-of-sight transmission;
  • radio relay tropospheric communication.

In the first case, the signal is transmitted according to a standard algorithm - from the source (transmitter) through a system of terrestrial relay networks directly to the receiver. One of the features is that the repeaters are located virtually in the immediate visibility zone, on natural elevations (mountains, hills). If there is no direct signal passage between the antennas, interference and distortion occur due to diffraction fading, which can lead to significant signal attenuation and loss of communication. The use of this type of communications is limited in places without the necessary infrastructure and is inappropriate in sparsely populated areas of our country, mainly in the northern part.

The solution to the above problems was a new technology - a tropospheric radio relay communication line. The principle of signal propagation has remained the same, but its method has changed, which basically contains the physical processes of reflection of radio waves of various ranges from the lower layers of the atmosphere. Numerous tests have shown that the greatest effect is achieved by using VHF waves. Thanks to correct calculations, it was possible to broadcast a radio signal over a distance of 300 km.

Advantages of radio relay communication line

The advantages of the new technology are obvious:
  • there is no need to build repeaters in the line of sight zone;
  • a significant increase in the radius of the signal transmission range;
  • the ability to ensure a maximum range of information transmission over a distance of up to 450 kilometers due to the location of repeater antennas on hills and other elevations.

One of the main problems that scientists have encountered is the strong damping effect of oscillations when broadcasting radio waves. The issue was resolved thanks to the use of active repeater equipment, which allows not only to receive and transmit radio waves, but also to stabilize the signal level, amplify it and filter out interference. Modern radio relay military communications operate on the basis of signal propagation technology in the troposphere, which is complemented by other innovative solutions.

home Radio relay communication RADIO RELAY COMMUNICATION

1.1. PRINCIPLES OF RADIO RELAY COMMUNICATION. CLASSIFICATION OF RADIO RELAY SYSTEMS

In its most general form, a radio relay link (RRL) can be defined as a chain of transceiver radio stations. The receiver of each station receives the signal sent by the transmitter of the previous station and amplifies it. The amplified signal arrives at the transmitter of a given station and is then radiated in the direction of the next station. The chain of stations constructed in this way ensures high-quality and reliable transmission of various messages over long distances.

Depending on the type of radio propagation used, RRL can be divided into two classes: line-of-sight radio relay lines, in which there is direct visibility between the antennas of neighboring stations, and tropospheric radio relay lines, in which there is no direct visibility between the antennas of neighboring stations.

The most common are line-of-sight RRLs, which operate in the decimeter and centimeter wavelength ranges. In these ranges it is possible to build broadband receivers and transmitters. Therefore, RRLs ensure the transmission of broadband signals and, first of all, multi-channel telephony and television signals. In the decimeter and especially centimeter wavelength ranges, it is possible to use sharply directed antennas, since due to the short length of the wavelength it is possible to construct such antennas of acceptable overall dimensions. The use of highly directional antennas with a high gain (1000-10,000 or more in power) makes it possible to use low transmitter powers (from fractions of a watt to 10-20 W) and, therefore, have compact and economical equipment. For lines of this class, corresponding frequency bands are allocated in the ranges of 2, 4, 6, 8, 11 and 13 GHz and in higher frequency ranges.

The need for direct visibility between the antennas of neighboring stations requires raising the antennas above ground level and, therefore, constructing appropriate antenna supports - towers or masts. The height of the antheia's suspension is determined by the distance between neighboring stations, as well as the nature of the terrain between them. Depending on these factors, the height of the ors can reach up to 100 m, and sometimes more. In some cases, with favorable terrain, antennas can be located at a low height, for example, on the roof of the building in which the equipment is installed.

The distance between neighboring stations is usually within 40-70 km. In some cases, these intervals are reduced to 20-30 km due to the need to connect the line to a specific point, as well as in the case of particularly unfavorable terrain.

Based on capacity, line-of-sight radio relay systems are divided into three main types:

High-capacity radio relay systems. The capacity of the radio channel of such systems is 600-2700, sometimes more, PM channels or a channel for transmitting television image signals with one or more channels for transmitting audio signals of television and sound broadcasting. These systems are used to organize long-distance backbone radio relay lines.

Construction of a radio relay line. Reservation system

Medium capacity radio relay systems. The capacity of the radio channel of these systems is 60-600 HF channels or a channel for transmitting television image signals with one or more channels for transmitting audio signals of television and sound broadcasting. In some cases, systems of this class are not designed to transmit television image signals. Such systems are used to organize intrazonal connecting lines.

Small-channel radio relay systems with the number of PM channels in the radio channel from 6 to 60. These systems are not designed for transmitting television signals; they are used to organize local connecting lines.

The above classification of radio relay systems is conditional: it mainly reflects the situation that occurs on fixed radio relay lines of the USSR Ministry of Communications and the Ministries of Communications of the Union Republics. Radio relay systems for technological communications (in railway transport, gas pipelines, power lines, etc.) have their own specifics and do not always fit into the above classification. The same applies to radio relay television systems for reporting purposes.

When transmitting multichannel telephony signals in large and medium-capacity radio relay systems, as a rule, equipment of cable transmission systems with frequency division of channels is used.

In small-channel radio relay systems, both equipment with frequency and time division of channels is used.

This Handbook discusses radio relay systems that use frequency division cable transmission system equipment and frequency modulation of the radio signal.

1.2. BUILDING A RADIO RELAY LINE. RESERVATION SYSTEM

The cost of towers or masts, feeder structures, technical buildings and power supply systems significantly exceeds the cost of transceivers. Therefore, to increase economic efficiency and throughput, radio relay systems, as a rule, are made multi-barreled.

"p. 1.1. Block diagram of stations of a multi-channel radio relay line

MI, in which at each station several transceivers operate at different frequencies on a common antenna-funder system, using the same antenna support, technical building and power supply system.

A simplified block diagram of a multi-barrel radio relay line is shown in Fig. 1.1. The operation of several PM-PD transceivers on a common antenna system is carried out using microwave compaction systems (separation filters and devices for combining reception and transmission signals).

To ensure high reliability of operation at the RRL, equipment redundancy is used. There are two main reservation systems: station-based and site-based.

The stationary redundancy system (Fig. 1.2) provides for each working transceiver the presence of a backup one, which has the same operating frequencies. If a working transceiver fails, it is automatically replaced by a backup one. The automatic reservation management system (ARS) operates independently at each station.

Disadvantages of the systems: large volume of transceiver equipment (100 percent reserve); lack of any protection against signal fading; the complexity of microwave switching devices and long switching times when using mechanical switches. In modern radio relay systems, station redundancy is not used.

With a sectional reservation system, each direction between two hub (or hub and terminal) stations is combined into a single

system (Fig. 1.3). For purposes of re-

A separate reserve trunk is allocated, operating at its own frequencies. The backup barrel equipment is constantly switched on. In the absence of an accident in the working shafts, the reserve shaft is not loaded with gear. To monitor the quality of operation of the trunks, special pilot signals are continuously transmitted through them.

The plot signal is introduced into the barrel through the modulator of the first station of the reservation section, and the allocated

Rice. 1.2. The block diagram of the post-application solution is solved with a special demodulation

zsrvirovaipya rum FROM the last station of this

plot. The selected pilot signal is compared with the amount of noise in a special measuring channel. If the noise to pilot signal ratio exceeds a preset value or the pilot signal level falls below normal, then the process of switching to the backup trunk begins. To do this, at the station located at the end of the section, a reverse emergency signal generator (ROAS) is turned on. For each working shaft there is a separate GOAS operating at its own frequency. The reverse alarm signal is sent through a special channel in the intercom system to the first station of the backup section, where it affects the switching device, which connects the backup trunk parallel to the damaged one. As a result, the message and pilot signal also begin to be transmitted along the reserve trunk. The pilot signal allocated at the output of the reserve trunk (at the last station of the reservation section) is converted into a command signal, which further switches the transmission path from the output of the damaged working trunk to the output of the reserve trunk. The time of communication interruption during sectional redundancy is determined by the parameters of the redundancy equipment and the nature of the accident.

In case of a so-called “instantaneous” accident (for example, a contact failure or a short circuit in the transceiver path of any station in the reservation section), the communication interruption time is composed of the return travel time

Build a radio link. Reservation system

emergency signal from the receiving end to the transmitting end of the section, travel times of a useful message along the reserve trunk from the transmitting end of the section to the receiving end, travel times of control signals in the equipment

Pilosh-sigial

Rabochiy stSh

pilot-G*1 signal. Analysis.

Psht-sigial

Radot cmSon

Reserve barrel

sl1/shonSh~ with Vyazi

Rice. 1.3. Structural diagram of sectional reservation

redundancy and response time of switching devices. The communication interruption time during an “instant” failure is usually in the range of 10-40 ms.

In case of a so-called “slow” accident (for example, deep signal fading), when the parameter by which the accident state is determined (the ratio of the noise level to the pilot signal) changes at a speed not exceeding 100 dB/s, the communication interruption time is determined only by the time , necessary for operation of the switching device at the other end of the reserved section. With the current level of technology, this time can be reduced to units of microseconds.

The advantage of a sectional redundancy system is that the volume of transceiver equipment is smaller than with a stationary redundancy system (one reserve shaft for several working shafts); short switching time to reserve; definitions of protection against deep signal fading of an interference nature due to the weak correlation of deep signal fading in trunks operating at different frequencies. This protection is more effective the greater the difference between the frequencies at which the working and reserve barrels operate. But this difference can sometimes be insufficient, since specific frequency bands are allocated for the operation of the radio relay system, beyond which it is unacceptable.

It should also be borne in mind that the site-by-section redundancy system provides some protection against signal fading only at a time when the reserve trunk is not used to back up the failed equipment of the working trunk.

The system of sectional redundancy of radio relay systems is usually abbreviated as the sum of two numbers, of which the first indicates the number of working trunks, and the second the number of reserve trunks. Thus, the 3-1-1 system means a radio relay system that has three working trunks and one reserve trunk.

1.3. FREQUENCY ALLOCATION PLANS

IN DIRECT RADIO RELAY COMMUNICATION SYSTEMS

VISIBILITY

The dual-frequency system (Fig. 1.4) is economical from the point of view of using the frequency band allocated for radio relay communication in this range, but requires high protective properties of the antennas from receiving signals from the opposite direction. With a two-frequency system, horn-parabolic, high-quality axisymmetric antennas and other types of antennas are used that have a protective effect of -60-70 dB.

The four-frequency system (Fig. 1.5) allows the use of simpler and cheaper antenna systems. However, the number of duplex radio channels that can be formed in a given frequency band with a four-frequency system is 2 times less than with a two-frequency system. As a rule, modern radio relay equipment uses a dual-frequency system. The quad-frequency system was typically used on RRLs with periscope antennas in the 2 GHz band.

The reception and transmission frequencies in one RRL radio channel alternate from station to station. Stations that receive on a lower frequency and transmit on a higher frequency are indicated by the symbol “HB>”, and

Broadcast

Broadcast

Broadcast

Rice. 1.4. Dual frequency system

Rice. 1.5. Four frequency system

Frequency distribution plans for multi-channel RRLs are designed in such a way as to minimize interference interference that occurs when several receivers and transmitters operate simultaneously on a common antenna-feeder path.

Frequency Allocation Plans

All modern radio relay systems use radio frequency plans that place receive frequencies in one half of the allocated frequency band and transmit frequencies in the other half.

Station N-

Station N°3

Rice. 1.6. Scheme of the t;)assy RRL site

Puc. 1.7. System with separated reception and transmission frequencies

The block diagram of a radio relay station using this principle is shown in Fig. 1.7. One common antenna is used to receive and transmit signals. The crossover filter system is designed to operate only in half the frequency band allocated for the radio relay system. The receiving and transmitting paths are combined into a common path using a polarizing filter or ferrite circulator (FC) (see Fig. 17)

The frequency distribution plan for the KURS-2M radio relay system in the Ic range is shown in Fig. 1.8. It complies with Recommendation 382-2 IKKR and ensures the organization of six duplex trunks using a two-frequency ZL system and duplex trunks using a four-frequency system). The nominal values ​​using the formula for the lower half of the range are determined

/» = /, -208 + 29 p,

and in the upper half of the range f„ - no formula /„“/, + 5+29 p

In line-of-sight RRSP, to increase the distance between radio relay line stations, repeater antennas are suspended on high structures (masts, supports, high-rise buildings, etc.). In flat terrain, antenna heights of 60...100 meters allow for reliable communication at distances of 40...60 kilometers.

The radio relay line chain consists of three types of radio relay stations: terminal radio relay stations (ORS), intermediate radio relay stations (IRS), and node radio relay stations (URS). A conventional radio relay communication line is shown schematically in Figure 8.1.

Rice. 8.1 Radio relay link

The transmission path begins and ends at the terminal radio relay station. OPC equipment converts signals coming from different sources of information (telephone signals from a long-distance telephone exchange, television signals from a long-distance television equipment room, etc.) into signals transmitted via a radio relay line, as well as reverse conversion of signals arriving via RRL into broadcasting or telephony signals. OPC radio signals are emitted using a transmitting device and antenna in the direction of the next, usually intermediate, radio relay station.

Intermediate radio relay stations are designed to receive signals from the previous radio relay line station, amplify these signals and radiate in the direction of the subsequent RRL station.

At each intermediate radio relay station, two antennas are installed, oriented towards neighboring RRSPs. Each of the antennas is a transceiver, that is, it is used for both receiving and transmitting signals. One of the advantages of operating a radio relay communication line in the ultra-high frequency (microwave) range is the possibility of using highly directional antennas with small dimensions. The small size of the antennas simplifies their installation on tall structures. The good directional properties of microwave range antennas make it possible to ease the requirements for the characteristics of the transceiver path.

To eliminate such phenomena, radio relay communication line repeaters are placed not in a straight line, but in a zigzag, so that the main directions of adjacent sections of the route that use the same frequencies do not coincide. In this case, the directional properties of antennas are used. Radio relay stations are spaced from the general direction of the radio relay communication line in such a way that the direction to the station, located three spans apart, corresponds to the minimum levels of the antenna radiation pattern. Figure 8.4 shows three spans of the RRL route section. The same frequencies are used on the outer spans. On such a path, even with strong refraction of radio waves, signals from stations with numbers PRS i and PRS i+2 practically do not affect each other. It is noticeable in the figure that the antennas practically do not perceive radio waves coming from the direction lying on the straight line connecting these stations. Rice. 8.4 Layout of repeaters on the radio relay communication line route

Tropospheric radio relay transmission systems use local volumetric inhomogeneities of the atmosphere caused by various physical processes occurring in near-Earth space. These inhomogeneities are capable of reflecting and scattering electromagnetic waves as they propagate in the atmosphere. Since inhomogeneities are located at a considerable height, the radio waves scattered by them can propagate over long distances, significantly exceeding the line of sight distance.

Due to the irregular structure of tropospheric inhomogeneities, signals from tropospheric lines are subject to deep fading.

Satellite communication systems can be considered as a special type of radio relay communication lines if the repeater antenna is suspended on a support whose height is equal to the height of the satellite’s orbit. In such a communication system, the line-of-sight zone of the Earth's surface viewed from the satellite and, accordingly, the size of the earth's territory from which the satellite is visible at the same moment in time significantly increases.

The radio equipment of a satellite communication system located on a satellite is called a space radio station, and the radio equipment located on Earth is called a ground radio station. The channel for transmitting a radio signal from a ground station to a satellite is called upstream, and the channel for transmitting signals in the opposite direction is called downstream. In addition to relay equipment, satellites also contain power sources (solar batteries). In addition, the satellites have equipment that ensures stabilization of the position of the satellites in orbit and orientation in space (repeater antennas are directed towards the Earth, solar panels - towards the Sun).

The characteristics of satellite communication systems largely depend on the parameters of the satellite's orbit. A satellite's orbit is the trajectory of the satellite's movement in space.

Radio relay communication lines (RRLS)

Cellular communication systems are by their nature distributed telecommunications facilities. The elements of the base station system (/), namely the base stations themselves (,), received the greatest geographical dispersion in their specificity. This is due to the fact that the task of base stations is to provide coverage over as wide an area as possible. One of the limiting factors for the rapid deployment of a cellular network is the need to organize transport flows between base stations and the base station controller. The construction of cable structures (electrical or optical) may require a long time: from several months to several years. If we are talking about mountainous, swampy or other difficult terrain, then the construction of a cable communication line may turn out to be almost impossible. In addition, the construction of a wired communication line requires large financial costs, which may not be economically viable if it is necessary to organize an interface of only one or two base stations. A convenient solution in such a situation is offered by radio relay communication lines. Construction of an RRL span takes no more than a few days, taking into account the time required for setup and launch. Also, the deployment of a radio relay span requires much lower financial costs, and the maximum length can reach 50 km or more.

Let's consider the principle of organizing communication using radio relay transmission systems. At each of the two ends, a communication equipment kit must be installed, which usually includes an indoor unit, an outdoor module and a radiating parabolic antenna. The internal module is installed in the equipment room, in close proximity to telecommunications equipment, or in a special thermally insulated container. It performs the tasks of switching and multiplexing several signals into one, modulating the signal to an intermediate frequency, controlling an external module, and is also responsible for switching to reserve, if provided for by the radar design. The internal module can serve from one to several sets of external equipment (external module + antenna). The external module is a converter that transfers the signal from the intermediate frequency received from the internal module to the main frequency, which lies in the range of 6-38 GHz. This is its main function. The internal and external modules are usually connected by a coaxial cable. After the signal is remodulated in the external module, the signal is radiated through a parabolic antenna. A similar set of equipment should be installed on the opposite side. Typically, all modern RRLs are duplex, that is, they can both transmit and receive a signal through the same set of equipment.

Radio relay span structure

When setting up the radar, direct visibility between both antennas must be ensured. The adjustment process itself is called “adjustment”. In this case, by changing the direction of radiation of the main lobe for both antennas, the maximum possible level of signal reception on each side is achieved. The higher the level of the received signal, the more stable the radio relay flight will be to external weather conditions. In addition, the signal level can affect the system capacity, because equipment from some manufacturers provides for a reduction in the radar capacity when a certain minimum level is reached.

The maximum range of modern RRLs is usually limited to 50 km. Thanks to the digital transmission method, they can withstand adverse weather conditions. However, usually for long spans some restrictions are introduced: the span must be as “clean” as possible, i.e. There should be no obstacles between the antennas. In addition, the minimum frequency and maximum diameter of the parabolic antenna must be used. Also usually these radars have a reduced capacity. In practice, shorter spans (up to 30 km in length) are more often used.

Currently, the telecommunications equipment market offers many options from different manufacturers, both in terms of capacity and cost. There are RRLs that allow transmission of up to 500 Mbit/s and support 2xSTM-1, Fast and Gigabit transport streams

Radio relay communications provide high-quality duplex communication channels that are practically little dependent on the time of year and day, weather conditions and atmospheric interference.

When organizing radio relay communications, it is necessary to take into account its dependence on the terrain, which necessitates careful selection of the communication line route, the impossibility of operation or a significant reduction in the range of radio relay stations in motion, the possibility of interception of transmissions and the creation of radio interference by the enemy.

Radio relay communication can be organized by direction, by network and by axis. The use of one method or another in each individual case depends on the specific conditions of the situation, the characteristics of the management organization, the terrain, the importance of this connection, the need for exchange, the availability of funds and other factors.

Direction of radio relay communication - this is a way of organizing communication between two control points (commanders, headquarters) (Fig. 19).

Figure 19. Organization of radio relay communications by directions

This method provides the greatest reliability of the communication direction and its greater throughput, but compared to other methods it usually requires an increased consumption of frequencies and radio relay stations at the headquarters organizing communications. In addition, when organizing communications in directions, difficulties arise in placing a large number of radio relay stations without mutual interference at the communications center of the senior headquarters and the possibility of maneuvering channels between directions is excluded.

Radio relay network - this is a method of organizing communications in which communication between a senior control point (commander, headquarters) and several subordinate control points (commanders, headquarters) is carried out using one radio relay semi-set (Fig. 20).

Figure 20. Organization of a radio relay communication network

When working over a network, the transmitters of the radio relay stations of the subordinate correspondents are constantly tuned to the frequency of the receiver of the main station. It should be borne in mind that in the absence of exchange, all network stations must be in simplex mode, that is, in standby reception mode. The calling right is granted primarily to the main station. After the main station calls one of the correspondents, the conversation between them can continue in duplex mode. At the end of the conversation, the stations switch back to simplex mode. The number of radio relay stations in the network should not exceed three or four.

Network communication is possible mainly when the main station operates on an omnidirectional (whip) antenna. Depending on the situation, slave correspondents can use either whip or directional antennas. If subordinate correspondents are located relative to the main station in any one direction or within the directional radiation sector of the main station antenna, then communication between the senior commander and subordinates can be ensured via the network and when working on a directional antenna having a relatively large directional angle (60 - 70° ).

Radio relay axis - this is a method of organizing radio relay communication in which communication between a senior control point (commander, headquarters) and several subordinate control points (commanders, headquarters) is carried out via one radio relay line deployed in the direction of movement of its control point or one of the control points of 1 subordinate headquarters (Fig. .23).


Figure 21. Organization of the radio relay communication axis

Communication between the senior headquarters control center and control points is carried out through support (auxiliary) communication nodes, where telephone and telegraph channels are distributed between control points.

Compared to directional communication, the organization of radio relay communication along an axis reduces the number of radio relay stations at the communications center of the senior headquarters control point and thereby simplifies the assignment of frequencies to these stations without mutual interference, makes it possible to maneuver channels, ensures their more efficient use, and reduces the time for selection and calculation of routes, facilitates the management of radio relay communications and requires fewer personnel required for the protection and defense of intermediate stations. The disadvantages of this method are the dependence of all radio relay communications on the operation of the center line and the need for additional channel switching at reference (auxiliary) communication nodes. The capacity of the axis is determined by the capacity of the center line, therefore, the organization of radio relay communication along the axis is advisable only if multi-channel stations are used on the center line, and few-channel stations are used on the reference lines. The use of few-channel stations for the axis does not give the desired effect, since it requires a significant number of these stations and frequencies.

Radio relay communication is carried out directly or through intermediate (relay) radio relay stations. These stations are deployed in cases where communication directly between the end stations is not provided due to their distance from each other or due to terrain conditions, as well as when it is necessary to allocate channels at an intermediate point.