RRL reservation. Radio relay communication lines

The current state of society is characterized by a continuously increasing need for the use of information transmission systems. Despite the enormous progress in the field of telecommunications - both in the development of new technologies in the field of communication and in the volume of communication systems, objective obstacles to further development. The tightness both in private bands and in space has led to an increase in mutual interference between functioning radio systems. To solve the problem electromagnetic compatibility International and domestic regulation of radio communications is carried out. The solution goes, among other things, along the path of narrowing the radiation patterns antenna systems, radiated power limitations. This allows for spatial diversity of radio systems and limiting their use to local areas. However, this resource is not unlimited.

Regulation of the time operating modes of radio systems allows their use in a limited area in one frequency interval. But this places a limitation on information capabilities radiosystem.

As the number of users grows, the required frequency band increases, reaching tens of megahertz. Even in the HF range, its total bandwidth is 27 MHz. Availability sound broadcasting in these ranges makes the development of radio communications using these frequencies unrealistic. Using these bands to exchange television programs, each of which requires a 6.5 MHz band (and this does not take into account the guard interval), is also unrealistic. Consequently, the transition to UHF, microwave and EHF ranges is caused by objective needs for information exchange.

However, as noted in subsection. 6.1.1, electromagnetic vibrations These frequencies propagate only in a straight line and, therefore, the receiving and transmitting antennas must be within the limits of geometric visibility, without taking into account diffraction, which increases the radio horizon by 14% compared to the visible one. The natural solution is to increase the range of information transmission by sequential retransmission of transmitted signals - this method of communication is called “radio relay communication” (Fig. 11.12).

Rice. 6.12.

Terminal (OS) and intermediate (IS) radio stations are within line of sight. The line usually uses duplex (two-way) radio communication. It can be seen that limiting the propagation range of radio waves, starting from the UHF range and above, by direct visibility, on the one hand, is a disadvantage - it is necessary to use additional relay equipment, and, on the other hand, an advantage - taking into account directed radiation, it is possible to use the same frequencies in a limited area .

Radio relay lines are used where it is economically justified, for example, to organize communications for a limited time or in difficult conditions - terrain, swampy areas, etc.

A simplified functional diagram of a radio relay line is shown in Fig. 6.13.

Rice. 6.13.

Radio terminals include transmitting and receiving parts. Information sources (IS) are united by an information compression circuit (ICC), which generates a group signal arriving at the input of the transmitter (ID). Intermediate radio stations receive and transmit further a radio signal, which is restored in order to maintain the required quality of communication. There may be several such intermediate radio stations, depending on the terrain and the length of the radio relay line. At the intermediate station, the selection and addition of information can be provided, thereby converting the line into seg and the location of the intermediate station is tied to the sources and recipients of information. At the terminal radio station, in addition to reception, separation is carried out group signal into components by an information separation scheme (ISS) and transfer to the corresponding information recipients (PI).

The figurative channel looks absolutely similar. The formation of the group signal mentioned here and its subsequent separation will be discussed further in a separate section. This method is general and is used for the purpose of more rational use of transmitting, receiving and antenna devices, as well as structures - towers, buildings included in the system.

A separate issue is the reduction of the level of intra-system interference. To solve this problem, a number of measures are being taken (Fig. 6.14).

Rice. 6.14.

Reception and transmission work is carried out at different frequencies and polarizations. This makes it possible to exclude, within the OS and PS, the emitted signal from reaching the receiver input. In addition, carrier frequencies are changed along the line. Additionally, it is provided that the stations are not located in a straight line in order to prevent the signal of a transmitter located across one station from entering the receiver input simultaneously with the signal of an adjacent station. Information flows are grouped into radio frequency channels and form radio relay line (RRL) trunks and there can be several of them, therefore those shown in Fig. 6.13 and 6.14 diagrams are simplified, explaining only the principle of constructing the RRL.

The distance between stations is determined by line of sight. For simplicity, we will assume that the terrain is flat, without hills or depressions.

In Fig. 6. 15 designated:- radius of the Earth(R y = 6370km);/;,Andh 2 -antenna lifting height L, andA 2above the Earth. Line of sight equal to L, +d2, almost touches the surface of the Earth. Let's take into account the smallness of /?, andh 2compared to /? 3 and determine the distance between the antennas D equald) + d 2

Rice. 6.15.

Because f2R= 3500 m, we accept, taking into account some bending of the Earth’s surface by radio waves:

(D measured in kilometers, A, and /g - in meters). If we count /g, " /g, "25, then D= 40 km. As a rule, the amount of antenna lifting in order to reduce the cost of masts is not made more than 40 m and D= 40 - 60 km. When designing, the terrain is taken into account and, if possible, antenna masts are installed on elevated surfaces.

PPJI uses frequencies in the 4 and 6 GHz region. This allows you to obtain a fairly wide frequency band and, therefore, provide high throughput. At the same time, the influence of precipitation on the radio does not significantly affect the absorption of electromagnetic waves in the atmosphere.

In practice, in the 6 GHz range, a frequency band of 500 MHz is allocated, in which 16 channels are formed - 8 in each direction, i.e. 8 trunks. The use of vertical and horizontal polarizations allows one antenna to receive and transmit radio signals. But this is possible with a small number of trunks.

The domestic radio relay industry is more than 50 years old. During its development, the industry has reached the expected positions. Today, radio relay channels (RRL) have proven themselves in providing remote areas with low infrastructure, covering large spaces and areas with a complex geological structure. Among the noticeable differences from wired technology a lower equipment budget was added.

Radio relay communication refers to wireless communication channels, but they should not be confused with the well-known WI-FI. The differences are as follows:

• In RRL, backup channels are created and aggregation is applied. Theoretically, the concept of communication range does not apply to radio relay stations, since the relay distance depends on the number of towers;
• High throughput;
• Work in full channel duplex;
• Use of own (local) ranges and highly efficient modulations.

Application of radio relay communication lines

Radio relay communication lines are widely used in various industries. In general, wireless channels replace wired networks multichannel telephone communication. Kyrgyzstan remains the leader in the length of radio relay communication lines. The use of RRL is due to the predominance of mountainous terrain throughout the Republic. The second direction of equipping with modern transmission lines is television. Considering that the average broadcast radius is 100 kilometers, federal channels They are increasingly mastering the construction of so-called program-free television centers.

Wireless RRL communication is actively used by Internet providers, mobile operators. It is known to use radio relay channels for organizing corporate communications. Due to the larger budget than WI-FI and the need to obtain a license, RLL remains inaccessible to small and medium-sized businesses and individuals. The service life of the equipment reaches 30 years, taking into account the fact that the complexes can operate even in harsh climate conditions.

Traditional trunk-type RRLs are gradually moving into the urban lines segment, giving way to fiber optic lines. However, such steps require approval of the project budget. The use of RRL remains unconditional in northern, sparsely populated areas where there is no need for traffic forecasting.

In RRL deployment practice today, two types of technology are used. The first is PDH - plesiochronous digital hierarchy. With this organization of signal transmission, speed is ensured in 32 channel or multiplexing modes at speeds from 2 to 139 Mbit per second. Considered outdated technology radio relay communication. The previous generation was replaced by the SDH standard. The digital timing hierarchy provides more resilient communication channels through STM transport modules. Stream speeds in this range range from 155 Mbps to 160 Gbps. According to the developers of the standard, the data transfer speed of PDH-compatible technology may be higher.

In the practice of using RRL networks, several deployment options are used. The most popular station placement scenario is step-by-step placement of towers along the equipment route. The use of hop-by-hop technology provides the ability to quickly make changes to existing configurations or upgrade outdated equipment.

Construction principle, equipment used, application

The main components that provide signal transmission to long distances, are line-of-sight radio relay lines. Their tasks include ensuring stable communication when transmitting messages to the consumer in digital format, television and sound broadcasts. The wave spectrum includes the ranges of centimeter and decimeter waves.

In the used line-of-sight ranges, interference of atmospheric and man-made origin is not observed. The distance between the nearest stations operating in the 30 GHz spectrum width is calculated and depends on the height of the towers and the topography in the location.

A complex of equipment is used to transmit information at one frequency or duplex. These are a radio channel (a channel with wide bandwidth), a telephone channel and a TV channel, designed for transmitting signals of the corresponding type. The topology of constructing the equipment complex is represented by a three-level system:

Radio relay communications have found wide application in areas of the national economy. The relay principle is actively used to organize and build local networks large corporations. The reliability and reliability of transmitted signals is used for command and control of troops and the organization of commercial communications.

The advantages of RRL technology are successfully implemented in the infrastructure of production facilities with a large number of remote facilities. These are airports, railway and maritime transport ministries. The only drawback that remains noticeable when constructing data transmission systems is the need to ensure direct visibility between repeaters. This requirement poses a number of conditions for technical equipment services and increases the project budget due to the need to increase the number of intermediate stations.

Radio relay lines (RRL) are a chain of transceiver radio stations (terminal, intermediate, hub), which carry out sequential multiple retransmission (reception, conversion, amplification and transmission) of transmitted signals.

Depending on the type of radio wave propagation used, RRLs can be divided into two groups: line-of-sight and tropospheric.

Line-of-sight RRLs are one of the main ground-based means of transmitting telephone signals, audio and TV broadcasting programs, digital data and other messages over long distances. The frequency bandwidth of multichannel telephony and TV signals is several tens of megahertz, so for their transmission only decimeter and centimeter wave bands can practically be used, the total spectrum width of which is 30 GHz.

In addition, these ranges are almost completely free of atmospheric and industrial interference. Distance between adjacent stations (flight length) R depends on the terrain and the height of the antennas. It is usually chosen close to or equal to the line of sight distance R o . For the spherical surface of the Earth taking into account atmospheric refraction

where h 1 and h 2 are the heights of the suspension of the transmitting and receiving antennas, respectively (in meters). IN real conditions, in the case of slightly rough terrain, 40 - 70 km with a height of antenna masts of 60-100 m.

Rice. 11.1. Conventional image of RRL.

The complex of RRL transceiver equipment for transmitting information on one carrier frequency (or on two carrier frequencies when organizing duplex communications) forms a broadband channel called a trunk (radio trunk). Equipment designed for transmitting telephone messages and including, in addition to the radio trunk, modems and equipment for combining and disconnecting channels, is called a telephone trunk.

The corresponding set of equipment for transmitting complete TV signals (together with audio signals, and often audio broadcasting) is called a TV trunk. Most modern RRLs are multi-barreled. In this case, in addition to working trunks, there may be one or two reserve trunks, and sometimes a separate trunk for service communications. As the number of trunks increases, the volume of equipment (the number of transmitters and receivers) at RRL stations increases accordingly.

Part of the RRL (one of possible options) is conventionally shown in Fig. 11.1, where radio relay stations of three types are directly marked: terminal (ORS), intermediate (PRS) and node (URS).

The OPC converts messages arriving via trunk lines from long-distance telephone exchanges (MTS), long-distance TV control rooms (ITA) and long-distance broadcast control rooms (IBA) into signals transmitted via RRL, as well as the reverse conversion. The linear signal transmission path begins and ends at the OPC.

With the help of the URS, information flows transmitted over different RRLs are branched and combined, at the intersection of which the URS is located. The URS also includes RRL stations at which telephone, TV and other signals are input and output, through which a populated area located near the URS is connected with other points on the same line.

Rice. 11.2.Block diagram single-barreled RRL repeater.

1 , 10 - antennas; 2,6 - feeder paths; 3,7 - transceivers; 4,9 - receivers;
5,8 - transmitters.

At the ORS or URS there are always technical personnel who service not only these stations, but also monitor and manage the nearest ORS using a special teleservice system. The RRL section (300-500 km) between neighboring served stations is divided approximately in half so that one part of the RRL is included in the teleservice area of ​​one URS (ORS), and the other part of the RRL is served by another URS (ORS).

PRSs perform the functions of active repeaters without isolating transmitted telecommunication signals and introducing new ones and, as a rule, operate without permanent maintenance personnel. The block diagram of the PRS repeater is shown in Fig. 11.2. When actively relaying signals to the PRS, two antennas are used, located on the same mast. Under these conditions, it is difficult to prevent some of the power from entering amplified signal, radiated by the transmitting antenna, to the input of the receiving antenna. If special measures are not taken, the specified connection between the output and input of the repeater amplifier can lead to its self-excitation, in which it ceases to perform its functions.

Rice. 11.3. Frequency distribution schemes in RRL.

An effective way to eliminate the danger of self-excitation is to separate the frequency of signals at the input and output of the repeater. In this case, the repeater has to install receivers and transmitters operating at different frequencies. If the RRL provides for simultaneous communication in the forward and reverse directions, then the number of receivers and transmitters doubles, and such a trunk is called duplex (see Fig. 11.2). In this case, each antenna at the stations is used to both transmit and receive high-frequency signals in each direction of communication.

The simultaneous operation of several radio equipment at stations and at the RRL as a whole is possible only if mutual influence between them is eliminated. For this purpose, frequency plans are created, i.e. plans for the distribution of transmission, reception and local oscillator frequencies on the RRL.

Research has shown that in the extreme case, only two operating frequencies ƒ 1 and ƒ 2 can be used for two-way communication via RRL (duplex mode). An example of an RRL with such a dual-frequency plan is conventionally depicted in Fig. 11.3, A. The fewer operating frequencies are used on a line, the more difficult it is to eliminate the interference of signals that match in frequency but are intended for different receivers. To avoid such situations, RRLs try to use antennas with a narrow radiation pattern, with the lowest possible level of side and back lobes; used for different directions of wave communication with different types polarization; individual stations are located so that the route represents some kind of broken line.

The application of these measures does not cause difficulties if communication is carried out in the centimeter wave range. Real antenna devices operating at less than high frequencies, have less directional action. Therefore, on the UHF RRL it is necessary to separate the reception frequencies at each station. In this case, for the forward and reverse communication directions, different pairs of frequencies ƒ 1, ƒ 2 and ƒ 3, ƒ 4 (four-frequency plan) are selected (see Fig. 11.3, b), and the frequency band required for the communication system will double. The four-frequency plan does not require the above protection measures, but it is not economical in terms of frequency use. The number of radio channels that can be formed in the allocated frequency range is half as much with a four-frequency plan as with a two-frequency plan.

For radio relay communications, centimeter waves are mainly used, so the dual-frequency plan is most widespread.

The development of antennas, like the entire development of radio engineering, has come a long and complex path from the first antenna of A. S. Popov in the form of a long wire suspended above the ground, to complex structures such as modern radar and radio relay antennas. Entire teams of scientists and engineers are currently working on their design and research.

Creation broadband systems in radio engineering”, be it antennas, amplifiers, etc., is always associated with significant difficulties. Anyone who has a TV at home knows that for high-quality reception, for example, third-party television channel another antenna with different dimensions is required compared to the antenna for the first channel. And it's very difficult to create TV antennas, equally effective for everyone television programs. At centimeter and decimeter waves, however, these difficulties were overcome. Radio relay lines use very broadband antennas that work equally well in the frequency band occupied by several high-frequency channels. On the other hand, these antennas have high directivity.

Let's see how you can get a highly directional antenna and what difficulties you have to overcome to achieve this.

First of all, we note one of the basic principles of antenna technology, which is that the properties of the antenna when emitting radio waves, i.e., directivity, broadband and others, remain unchanged when using the same antenna to receive radio waves. Based on this principle, in the future we will only talk about transmitting antennas, considering that the receiving antennas are identical in design and therefore work just as efficiently. In practice, in radio relay lines, the transmitting and receiving antennas are always the same.

A typical radio or television station antenna emits radio waves evenly in all directions. This means that the power of the transmitter is distributed equally in all directions and only a small part of the radiated energy is distributed in any one direction.

Let us assume that on the receiving side we receive signals from the transmitting station. If a transmitter emits radio waves through an omnidirectional antenna, then at the receiving end we will receive a signal of a certain magnitude. Let us now change the transmitter antenna to a directional one and “aim” the direction of maximum radiation at the receiving antenna. On the receiving side there will be a sharp increase in the received signal, although the transmitter power remains unchanged. It turns out that the antenna, as it were, amplifies the signal.

On radio relay lines, pointed antennas are used that have a gain (in power) of the order of a thousand and even tens of thousands and a radio beam width of about 1-2 degrees. The latter means that the antenna emits almost nothing in all directions that differ from the main one by more than 0.5-1 degree.

Thus, by "amplifying" the antennas, the power of the transmitters can be reduced by several thousand times compared to the power that would be required if the antennas were omnidirectional. On the other hand, due to the directionality of the antennas, the interference of one radio relay line is sharply reduced

To another, even if they are located close to each other and operate at the same frequencies.

The “gain” of a directional antenna is explained by the fact that it does not distribute the energy emitted by the transmitter equally in all directions, but directs it in one direction, i.e., as if it collects the energy of the transmitter from all directions into one. The word “amplification” is put in quotation marks because in the antenna there is no conversion of the energy of an external source into the energy of a radio signal, as is the case in the transmitter and receiver, ^ where the energy of power sources is converted in radio tubes into high-frequency energy and where only due to energy power sources, the useful signal is amplified.

The most common antennas used on radio relay lines are parabolic and lens antennas.

Rice. 17 explains the operating principle of a parabolic antenna. Appearance it is given in Fig. 14.

It has an irradiator either of a special design, or in the form of an open end of a waveguide, which directs the energy emitted by it to a metal reflector of a parabolic shape (most often in the form of a paraboloid of rotation). The irradiator emitting a diverging beam of radio waves (rays AB and AB" in Fig. 17) d is located at the focus of the paraboloid, i.e. at a certain point A on its axis of rotation. If the irradiator were very small or, as they say, point-like, then the rays reflected from the paraboloid would be parallel and directed towards the receiving antenna (in Fig. 17, beam BV is parallel to beam B"B"), i.e. almost
all the radio wave energy emitted by the transmitter would propagate in the direction we need.

But since the irradiator has finite dimensions and is not strictly in focus, the rays reflected from the paraboloid are not completely parallel: they diverge somewhat.

Numerous studies of highly directional antennas, and in particular parabolic ones, have shown that the larger the diameter of the parabolic surface compared to the wavelength, the narrower the beam of radio waves it emits, the higher its directivity.

Paraboloids of radio relay stations on centimeter waves have a diameter of 3-4 meters and have a power gain of from one thousand to ten thousand. At meter waves, the directivity of the antennas is less, and the gain is only 50-*-500, since we cannot increase the size of the antennas in proportion to the increase in wavelength when moving from centimeter waves to meter ones. Otherwise we would have to have parabolic mirrors tens of meters in size. Installing them would require very bulky and expensive antenna supports.

The design of lens antennas is based on the principle of refraction of radio waves at the boundary of two media, i.e., a change in the direction of the beam when passing from one medium to another.

If the lens for light waves, i.e., an optical lens, is a glass or some other body transparent to light of a certain convex or concave shape (glasses, camera lens, etc.), then the lens for radio waves usually has a completely different view. For example, it can be a set of metal plates of a special shape parallel to each other (Fig. 18), separated by air gaps. The shape of the plates is chosen so that the diverging beam of radio waves incident on the lens from the waveguide, having passed the lens, becomes parallel. And here than larger sizes the exit hole of the lens compared to the wavelength, the higher the directivity of the antenna.

The horn in front of the lens serves to ensure that all the high-frequency energy coming out of the waveguide hits the lens.

Sometimes purely horn antennas are used on radio relay lines. Structurally, they are simpler and much lighter than horn-lens ones, however, with the same hole sizes, the former have slightly less gain. In addition, the length of the horn here has to be taken at 1.5-

2 times more than when using lenses.

In addition to directionality, radio relay line antennas are required to have no mutual influences between receiving and transmitting antennas located at the same intermediate station.

It turns out that the antennas described above do not radiate all the energy in the main direction. Insignificant part

A/justylenses

In Fig. Figure 20 shows the design of another relay station antenna system used on “local” radio links. Thanks to the ingenious use of flat reflectors, the construction of this station is much cheaper than the stations shown in Fig. 12 and fig. 16.

The principle of operation of such an antenna system is as follows: antennas with high gain are installed very close to the transceiver on the roof of a one-story relay station building than

A short length of waveguides or cables is achieved, and, consequently, a small amount of losses in them. The radiation from the transmitting antenna is directed vertically upward. On light steel masts, perforated (i.e., with holes to reduce wind load) metal sheets are fixed at the required height, inclined at an angle of 45 degrees to the horizontal. A vertically directed radio beam, like light from a mirror, is reflected from the sheets towards the next relay station. The receiving antenna is designed in a similar way.

Note also that quite often at intermediate stations of radio relay lines, instead of four antennas, only two are used. Transmission and reception of one direction is carried out on one antenna. This
is possible only on relatively few-channel lines, where the number of high-frequency trunks does not exceed three. To ensure that the emitted signal does not affect the received signal, their frequency bands are spaced approximately

At 100 megahertz (remember the channel multiplexing system at frequency). In this case, using filters, the transmitted and received frequency bands can be separated quite well.

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 or another method 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 placement large quantity 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 for 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 point and control points is carried out through support (auxiliary) communication nodes, where telephone and telephone lines are distributed. telegraph channels 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. Bandwidth 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 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.