What redundancy systems are used in radio relay communications. Radio relay communication

1. General principles for constructing radio relay lines

1.1. Principles of radio relay communication

The radio frequency ranges used in RRL and TRL have a number of advantages. Each of these broadband bands can transmit a lot broadband signals. In these ranges, antennas with high gains are relatively small in size. The use of such antennas makes it possible to obtain stable communications at low transmitter power. The spectrum of external interference of atmospheric and industrial origin lies in a lower frequency region than UHF. Therefore, in the UHF and higher frequency bands there is practically no such interference. The most widespread on mainline RRLs are ARRS operating in the centimeter wavelength range.

A radio relay communication line is built in the form of a chain of transceiver radio stations. The RRL is equipped with transmitters with a power of 0.1...10 W, receivers with a noise figure of about 10 dB, antennas with a gain of about 40 dB (opening area about 10 m2).

On such an RRL there must be direct visibility between the antennas of neighboring RRLs. To do this, the antennas are installed on supports, most often at an altitude of 40...100 m. The distance between neighboring RRS of mainline RRL is usually about 50 km. On TRL, the average distance between neighboring stations is about 250 km. TRL uses transmitters with a power of 1...10 kW, receivers with low-noise amplifiers (LNA) having an effective noise temperature of 150...200 K, antennas with a gain of about 40 dB

Station types. The main types of RRS: terminal (ORS), hub (URS) and intermediate (PRS). Radio transmitters and radio receivers are installed on the ORS and URS (Fig. 1.1). The radio transmitter includes a modulator Md and a microwave signal transmitter P, and the radio receiver includes a microwave signal receiver Pr and a demodulator Dm (cf. Fig. B.1). In the microwave transmitter, the modulated intermediate frequency (IF) signal is converted into a microwave or UHF signal; in the microwave receiver, the received microwave signal is converted back into the IF signal. The microwave receiver and transmitter, the microwave together form a microwave transceiver installed on the PRS.

At the ORS located at the ends of the RRL, transmitted signals are input and isolated, for example MTS.

The radio signal is retransmitted at the RRS: reception, amplification, frequency shift and transmission in the direction of the next RRS. When transmitting broadcast television radio signals via RRL, each PRS has the ability to select a television program. A station where this feature is implemented is called a television-selected station (PRSV).

At the URS, radio signal retransmission and RRL branching take place. New RRL or cable communication lines often originate from the URS. At the URS, part of the TF signals is always separated from the MTS and new ones are introduced, so modulators and demodulators are always installed there. Structurally, they are often combined in a device called a modem. The average distance recommended for our country between neighboring URS is 250 km.

At the URS, as a rule, there is a branching of broadcast television radio signals, the so-called IF transit. Since modems introduce noise, eliminating them from the circuit improves the signal-to-noise ratio in the channel at the end of the RRL. At large URSs, where several RRLs converge, special switches are installed for IF signals of broadcast television, which allow one to quickly select one or another program. Modulators are installed only on those URSs where it is necessary to introduce a new TV program. The recommended distance between such URS in our country is 2500 km.

Radio relay span and radio relay section. The part of the radio relay communication line between neighboring RRS, including equipment and the radio signal propagation medium, is called a radio relay span. The part of a radio relay communication line limited by two nearby radio relay stations, which are terminal or hub, is called a radio relay section.

Frequency shift. The difference in signal levels at the output and input of the PRS transceiver exceeds 100 dB. To prevent self-excitation of this device, radio signals of one direction of communication on the PRS (URS) are received and transmitted at different frequencies f1 and f2. The frequency shift is the value fsdv = |fa -f1|. Usually on mainline RRL fsdv = 266 MHz.

Features of service. At the RRL, service personnel are constantly present only at the ORS and URS. To monitor and manage the condition of the equipment at the PRS, a teleservice system (TS) is used, during the organization of which the entire RRL is divided into operational sections containing up to 10 RRS. In the middle of such a section there is a URS, from which the operation of the PRS of the section located on both sides of the URS is controlled. Terminal RRSs serve nearby RRSs. To increase the reliability and stability of operation, RRL equipment is redundant. Two methods of automatic reservation are common: station-based and site-based. With station-by-station redundancy, in the event of a malfunction of the working set of equipment at a given station, it is automatically replaced with a backup one operating at the same frequencies.

With sectional redundancy, working and backup sets of microwave transceivers are installed at each station, and the operating frequencies of these sets do not coincide. If the equipment on any PRS is damaged, automatic switching modems at the ends of the radio relay section, after which signals are transmitted throughout the entire section using backup microwave transceivers. On RRS with sectional redundancy, redundancy equipment is installed at the ends of the section, with the help of which the state of the HF trunk equipment is monitored and modems are switched. The switching command from the end of the section to the beginning is transmitted via overhead communication channels. Service communication channels are also intended for transmission of maintenance signals and negotiations of maintenance personnel.

1.2. Multi-trunk radio relay lines

RRL trunks. At all stations of one RRL, as a rule, the same type of microwave receivers and transmitters are installed. In most radio relay systems, Pr and P on the PRS are connected via IF. A chain of such microwave transmitters and receivers in the radio relay section forms a high-frequency (HF) trunk. This trunk is universal, since it can be used to organize the transmission of various messages. Why are Md and Dm and the corresponding terminal devices connected to the HF trunk at OPC and URS? The latter are part of the modem. If MTS is transmitted via the HF trunk using the analog modulation, then such a trunk is called a telephone trunk (TF). In addition, using the analogue FM method, television (TV) trunks are organized through which TV programs are transmitted. A digital (DF) trunk is organized by supplying a digital signal to the PPC modulator.

The signal supplied to the modulator is called group signal trunk, and its spectrum is linear spectrum,In analog-to-digital (ADF) trunks, the HS is composed of an MTS and a digital signal.

Block diagram of a three-barrel RRL. To increase bandwidth at RRL, as a rule, they organize the simultaneous operation of several HF trunks at different frequencies on a common antenna-feeder path (AFT) and antenna. This kind of RRL is called multi-barreled. It has higher economic efficiency than a single-barrel one, since the cost of the antenna, antenna supports, as well as the technical building and power supply system common to all trunks, is significantly higher than the cost of the HF barrel equipment.

To connect several transceivers to one antenna (Fig. 1.2), combining devices (CD) and separating filters (RF) are used. Combining devices are needed to separate the receiving and transmitting waves. Polarization selectors or ferrite circulators are used as control systems. Reception separation filters (RF1) are used to separate signals from different reception channels at frequencies f1, f3, f5. Transmission separation filters (RF2) are used to combine transmission signals at frequencies f1", f3", f5".

In Fig. 1.2 shows the TF and TV trunks, as well as the reserve one - Res. Redundancy equipment is installed at the ends of the radio relay section: receiving - Res. pr and transmitting - Res. P. A signal about an accident may be received at point 3, which must be transmitted to the beginning of the section to the previous control unit, a similar signal from the subsequent control unit arrives at point 4. In the TV trunk, transit via the IF is organized. The selection of the branch program is carried out using a switch via IF-Km IF, to which the reverse direction TV trunk signal is also supplied (at point 5).

Barrel throughput. In modern trunk RRLs with FM, a frequency band of 28 MHz is allocated for the HF trunk. Therefore, FM signals transmitted along the trunk must have a spectrum no wider than 28 MHz. Recall that the spectral width of an FM signal is

(1.1)

where is the maximum frequency deviation, FB is the upper modulating frequency. Since the frequency deviation is specified on the RRL, the value of FB, and therefore the throughput of the barrel, is limited. Approximately F<9 МГц

1.3. Frequency plans

For RRL operation, frequency bands with a width of 400 MHz are allocated in the range 1 2 GHz (1.7...2.1 GHz), 500 MHz in the ranges 4 (3.4... 3.9), 6 (5.67 .. .6,17) and 8 (7.9... 8.4) GHz and a width of 1 GHz in the 11 and 13 GHz and higher frequency bands. These bands are distributed among the HF trunks of the radio relay system according to a specific plan, called a frequency allocation plan. Frequency plans are drawn up in such a way as to ensure minimal mutual interference between the trunks operating on a common antenna.

In the 400 MHz band, 6 duplex HF trunks can be organized in the 500 MHz band, and 8 in the 1 GHz band.

In terms of frequencies (Fig. 1.3), the average frequency f0 is usually indicated. The receiving frequencies of the trunks are located in one half of the allocated band, and the transmitting frequencies are in the other. With this division, a sufficiently large shift frequency is obtained, which ensures sufficient isolation between the reception and transmission signals, since RF reception (or RF transmission) will operate only in half of the entire frequency band of the system. In this case, you can use a common antenna to receive and transmit signals. If necessary, additional isolation is obtained between the receiving and transmitting waves in one antenna through the use of different polarizations. RRL uses waves with linear polarization: vertical or horizontal. Two variants of polarization distribution are used. In the first option, at each PRS and URS, the polarization changes so that waves of different polarizations are received and transmitted. In the second option, one wave polarization is used in the “there” direction, and another in the “back” direction.

Figure 1.3. Frequency distribution plan for the KURS radio relay system for an NV type station in bands 4 (f0=3.6536), 6(f0=5.92) and 8(f0=8.157)

A station at which the receiving frequencies are located in the lower (H) part of the allocated band, and the transmitting frequencies in the upper (B) is designated by the index “HB”. At the next station, the reception frequency will be higher than the transmission frequency and such a station is designated by the index “VN”.

For the reverse direction of communication of a given trunk, you can take either the same pair of frequencies as for the forward one, or a different one. Accordingly, they say that the frequency plan allows you to organize work using two-frequency (Fig. 1.4) or four-frequency (Fig. 1.5) systems. In these pictures, through f1н, f1в,…f5н, f5в the average frequencies of the trunks are indicated. The frequency indices correspond to the designations of the trunks in Fig. 1.3. With a two-frequency system, the same frequency must be taken on the PRS and the PC for reception from opposite directions. Antenna WA1 (Fig. 1.4a) will receive radio waves at the frequency f1н from two directions: main A and return B. A radio wave coming from direction B creates interference. The degree to which the antenna attenuates this interference depends on the protective properties of the antenna. If the antenna attenuates the return wave by at least 65 dB compared to the wave coming from the main direction, then such an antenna can be used in a dual-frequency system. A dual-frequency system has the advantage that it allows organizing 2 times more HF channels in a dedicated frequency band than a four-frequency system, but it requires more expensive antennas.

On mainline RRLs, as a rule, dual-frequency systems are used. The frequency plan does not provide for protective frequency intervals between adjacent reception (transmission) trunks. Therefore, signals from adjacent trunks are difficult to separate using RF. To avoid mutual interference between adjacent trunks, either even or odd trunks work on the same antenna. In terms of frequencies, the minimum frequency separation between the receiving and transmitting trunks connected to the same antenna is indicated (98 MHz in Fig. 1.3). As a rule, even trunks are used on main RRLs, and odd trunks are used on branches from them. In this case, the reception and transmission frequencies between the trunks of the main RRL are distributed according to Fig. 1.4, c, and between the trunks of the zone RRL with a four-frequency system - according to Fig. 1.5, c.

In practice, a frequency plan implemented on an RRL based on a two-frequency (four-frequency) system is called a two-frequency (four-frequency) plan.

On the RRL there is a repetition of transmission frequencies across the span (see Fig. 1.1). At the same time, in order to reduce mutual interference between RRS operating at the same frequencies, stations are located in a zigzag pattern relative to the direction between the end points (Fig. 1.6). Under normal propagation conditions, the signal from RRS1 at a distance of 150 km is greatly weakened and practically cannot be received at RRS4. However, in some cases, favorable conditions arise for era propagation. In order to reliably attenuate such interference, the directional properties of antennas are used. On the path between the direction of maximum radiation of the transmitting antenna RRS1, i.e. That is, the direction to RRS2, and the direction to RRS4 (direction AC in Fig. 1.6) provide a protective bending angle of the path a1 of several degrees, so that in the direction of AC the gain of the transmitting antenna at RRS1 is sufficiently small.

Questions for self-control

1. Name the energy parameters of radio relay equipment. Give their values ​​for RRL and TRL.
2. In what radio wave ranges and frequencies do RRL and TRL operate? What are the features of these ranges?
3. Name the types of stations on the RRL, the main functions of these stations.
4. What is an HF barrel? By what criteria are HF, TF and TV trunks distinguished?
5. Explain the purpose of the elements of the block diagram of the three-barreled RRL ORS.
6. Explain the principles of constructing an RRL frequency distribution plan. Compare plans organized by two- and four-frequency systems.

Separation (compaction) of channels.

Types of radio communication

Lecture 4. Radio relay and tropospheric communication lines.

Radio communication by wavelength is divided into radio communication c the use of repeaters :

Radio relay communication,

Satellite communications,

Cellular communications;

without the use of repeaters:

SDV connection,

DV communication,

NE communication,

HF communication by ground (surface) wave,

HF communication by ionospheric (spatial) wave,

VHF communication,

Tropospheric communication.

Communication channel May be:

simplex- that is, allowing data transmission only in one direction (radio broadcast, television);

half duplex - one by one;

duplex - that is, allowing data transfer in both directions simultaneously( telephone).

The creation of several channels on one communication line is ensured by separating them by frequency, time, codes, address, and wavelength.

- frequency division of channels(FDM, FDM) - separation of channels by frequency, each channel is allocated a certain frequency range;

- time division of channels (VRK, TDM) - time division of channels, each channel is allocated a time slice;

- code division of channels(KKK, CDMA) - separation of channels by codes, each channel has its own code, the overlay of which on the group signal allows you to highlight the information of a specific channel;

- spectral separation of channels(SRK, WDM) - separation of channels by wavelength.

It is possible to combine methods: PRK+VRK.

Radio relay communication- radio communication over a line (radio relay line, RRL) formed by a chain of transmitting and receiving (relay) radio stations. Terrestrial radio relay communication is usually carried out on deci - And centimeter waves (from hundreds of megahertz to tens of gigahertz).

RRLs have become an important part of telecommunication networks - departmental, corporate, regional, national and even international, since they have a number of advantages:

Possibility of quick installation of equipment with low capital costs;

Cost-effective, and sometimes the only, opportunity to organize multi-channel communication in areas with difficult terrain;

Possibility of use for emergency restoration of communications in the event of disasters and during rescue operations;

The efficiency of deploying extensive digital networks in large cities and industrial zones where laying new cables is too expensive or impossible;

High quality of information transmission via RRL, practically not inferior to fiber-optic lines and other cable lines.

RRL communications make it possible to transmit television programs and simultaneously hundreds and thousands of telephone messages. Such information flows require frequency bands of up to several tens and sometimes hundreds of megahertz and, accordingly, carrying at least several gigahertz. Radio signals at these frequencies are transmitted effectively only within line of sight . Therefore, to contact long distances in terrestrial conditions it is necessary to use rebroadcast radio signals. On radio relay lines of sight, they are mainly used active relay , during which the signals are amplified.

The length of spans R between neighboring stations depends on the terrain profile and antenna installation heights. Usually it is chosen close to the line-of-sight distance R0, km. For a smooth spherical surface of the Earth and without taking into account atmospheric refraction:

where h 1 and h 2 are the heights of the transmitting and receiving antennas (in meters). IN real conditions, in the case of slightly rough terrain, R 0 = 40...70 km, and h 1 and h 2 are 50...80 m.

Depending on the mechanism used radio wave propagation differentiate :

- radio relay line of sight RRL (due to terrestrial radio waves);

- TRL tropospheric radio relay line (due to tropospheric radio waves).

Terrestrial called a radio wave propagating near the earth's surface. Earth's radio waves are shorter 100 cm They spread well only within line of sight. Therefore, a radio relay communication line over long distances is built in the form of a chain of transmitting and receiving radio relay stations (RRS ), in which neighboring RRS are placed at a distance providing line-of-sight radio communication ( radio relay line of sight(RRL)).

Tropospheric radio wave spreads between points on the earth's surface along a trajectory that lies entirely in the troposphere. (Troposphere (Ancient Greek Τροπή - “turn”, “change” and σφαῖρα - “ball”) - the lower layer of the atmosphere, 8-10 km high in the polar regions, up to 10-12 km in temperate latitudes, at the equator - 16-18 km. More than 80% of the total mass of atmospheric air is concentrated in the troposphere, turbulence and convection are highly developed, the majority of water vapor is concentrated, clouds arise, atmospheric fronts form, cyclones and anticyclones develop, as well as other processes that determine weather and climate. When ascending every 100 m, the temperature in the troposphere decreases by an average of 0.65 ° and reaches 220 K (-53 ° C) in the upper part).

Tropospheric radio wave energy shorter than 100 cm scattered by inhomogeneities in the troposphere. In this case, part of the transmitted energy falls on the RRS receiving antenna, located beyond the line of sight at a distance 250...350 km . A chain of such RRSs forms tropospheric radio relay link (TRL).

By purpose Radio relay communication systems are divided into three categories:

- local lines communications from 0.39 GHz to 40.5 GHz,

- intrazone lines from 1.85 GHz to 15.35 GHz,

- trunk lines from 3.4 GHz to 11.7 GHz.

(According to the range of operating frequencies, RRLs are divided into lines of the decimeter range and centimeter ranges. In these ranges, by the decision of the SCRF of April 1996, bands 8 (7.9-8.4); 11 (10.7-11.7); 13 (12.75-13.25) were determined for new RRLs. ; 15 (14.4-15.35); 18 (17.7-19.7); 38 (36.0-40.50) GHz. However, previously built lines in the 3.4-3.9 range will be used for a long time; ; 5.6-6.4 GHz. New RRS are also used in the 2.3-2.5 GHz range. The possibility of using the 2.5-2.7 and 7.25-7.55 GHz ranges is being explored.

This division is associated with the influence of the propagation environment on ensuring the reliability of radio relay communications. Up to a frequency of 12 GHz, atmospheric phenomena have a weak effect on the quality of radio communications; at frequencies above 15 GHz this effect becomes noticeable, and above 40 GHz it is decisive (losses in oxygen atoms and water molecules).

Almost complete opacity of the atmosphere for radio waves observed at frequency 118.74 GHz (resonant absorption in oxygen atoms), and at frequencies above 60 GHz the linear attenuation exceeds 15 dB/km. Attenuation in atmospheric water vapor depends on its concentration and is very high in a humid, warm climate.

Negatively affects radio communications hydrometeors , which include raindrops, snow, hail, fog. The influence of hydrometeors is noticeable already at frequencies above 6 GHz, and in unfavorable environmental conditions (in the presence of metallized dust, smog, acids or alkalis in precipitation) and at much higher low frequencies.

The lower the range, the greater the communication range can be achieved with the same energy characteristics of the equipment, but the transition to high ranges allows you to increase the throughput of systems.

The antennas of neighboring stations are located within line of sight (except for tropospheric stations). To increase the length of the interval between stations, antennas are installed as high as possible - on masts (towers) height 10-100 m (visibility radius - 40-50 km ) and on tall buildings. Stations can be either stationary or mobile (on cars).

Depending from the method , adopted for signal generation, are distinguished:

Analog RRL(TRL);

Digital RRL(TRL).

Analog RRL communication depending on the carrier modulation method:

RRL with frequency division of channels (FDM) and frequency modulation (FM) of a harmonic carrier,

RRL with time division channels (TDK) and analog pulse modulation, which then modulates the carrier frequency.

Depending depending on the number of channels organized (N):

Small-channel - N =24;

With average throughput - N=60...300;

With high throughput - N=600...1920.

Digital radio relay lines (CRRL), pulses (message samples) are quantized by levels and encoded.

Digital RRL classified according to the carrier modulation method:

Depending from transmission speed binary characters B:

With low - B<10 Мбит/с,

Medium - B=10…100 Mbit/s,

High->100 Mbit/s throughput.

High-speed RRS are created almost exclusively on the basis of SDH technology and have a transmission speed in one trunk 155.52 Mbps (STM-1 ) And 622.08 Mbit/s in one trunk ( STM-4 ). They are used to build trunk and zone lines, as radio inserts in fiber-optic lines in areas with difficult terrain, to interface fiber-optic lines (STM-4 or STM-16) with accompanying local digital networks, as well as for redundancy of fiber-optic lines.

(Synchronous Digital Hierarchy (English) SDH - Synchronous Digital Hierarchy) is a technology of transport telecommunication networks. SDH standards define the characteristics of digital signals, including frame structure, multiplexing method, digital rate hierarchy, and interface code patterns.

Standardization of interfaces determines the possibility of connecting various equipment from different manufacturers. The SDH system provides standard levels of information structures, that is, a set of standard rates. Basic speed level - STM-1 155.52 Mbps. Digital rates of higher levels are determined by multiplying the STM-1 bit rate by, respectively, 4, 16, 64 etc.: 622 Mbit/s (STM-4), 2.5 Gbit/s (STM-16), 10 Gbit/s (STM-64) and 40 Gbit/s (STM-256)).

The fundamental difference radio relay station from other radio stations is duplex mode work, that is, reception and transmission occur simultaneously (at different carrier frequencies).

Length of terrestrial radio relay communication line - up to 10000 km, capacity - up to several thousand voice frequency channels in analog communication lines, and up to 622 megabits in digital communication lines. In general, distance and capacity (data transmission speed) are inversely proportional to each other: as a rule, the greater the distance, the lower the speed.

In the Russian Federation, transmission rates equal to 155 Mbit/s (STM-1 Synchronous Digital Hierarchy, SDH stream) or 140 Mbit/s (E4 stream of plesiochronous digital hierarchy, PDH, transmitted as part of the STM-1 signal).

In the USSR, the development of the radio relay industry began in the mid 50s . The reason is the low cost of radio relay communications compared to cable lines, especially in vast spaces with undeveloped infrastructure and complex geological structure of the area. The first backbone radio relay system R-600 established in 1958. In 1970, a complex of unified radio relay systems appeared "WELL" . All this made it possible in the 60-70s to develop the country’s communications network, provide high-quality telephony and establish the transmission of central television programs. By the mid-70s, a unique radio relay line was built in the country, the length of which was about 10 thousand km , with a capacity of each trunk equal to 14,400 voice frequency channels. The total length of the RRL in the USSR exceeded by the mid-70s 100 thousand km .

Radio relay communication This is one of the types of radio communications formed by a chain of transmitting and receiving (relay) radio stations. Terrestrial radio relay communications are usually carried out at deci- and centimeter waves (from hundreds of megahertz to tens of gigahertz).

Advantages of radio relay communication:

The ability to organize multi-channel communication and transmit any signals, both narrowband and broadband;

Possibility of providing two-way communication (duplex) communication between channel consumers (subscribers);

Possibility of creating 2-wire and 4-wire communication channel outputs;

Virtual absence of atmospheric and industrial interference;

Narrow directionality of radiation from antenna devices;

Reduced communication time compared to wired communication.

Disadvantages of radio relay communication:

The need to ensure direct geometric visibility between the antennas of neighboring stations;

The need to use high-elevation antennas;

The use of intermediate stations to organize communication over long distances, which causes a decrease in the reliability and quality of communication;

Cumbersome equipment;

Difficulty in building radio relay lines in hard-to-reach areas;/div>

According to their purpose, radio relay communication systems are divided into three categories, each of which is allocated its own frequency ranges on the territory of Russia:

local links from 0.39 GHz to 40.5 GHz intra-zone links from 1.85 GHz to 15.35 GHz trunk lines from 3.4 GHz to 11.7 GHz

RRL equipment is usually built on a modular basis. Functionally distinguish the module standard interfaces, usually including one or more PDH (E1, E3), SDH (STM-1), Fast Ethernet or Gigabit Ethernet interfaces or a combination of these interfaces, as well as RRL control and monitoring interfaces (RS-232, etc.) and interfaces synchronization The task of the standard interface module is to switch interfaces between itself and other RRL modules.

Structurally, a standard interface module can be a single block or consist of several blocks installed in a single chassis. In technical literature, the standard interface module is usually called an internal installation unit (IDU) because Typically, such a unit is installed in a hardware PPC or in a telecommunications container-hardware room). Data streams from several standard interfaces are combined into a single frame in the indoor mounting unit. Next, service channels necessary for RRL control and monitoring are added to the received frame. In total, all data streams form a radio frame. The radio frame from the internal mounting unit is usually transmitted at an intermediate frequency to another RRL functional block - the radio module (ODU). The radio module performs noise-resistant coding of the radio frame, modulates the radio frame according to the type of modulation used, and also converts the total data stream from the intermediate frequency to the RRL operating frequency. In addition, the radio module often performs the function automatic adjustment RRL transmitter power amplification.

Structurally, the radio module is one sealed unit with one interface connecting the radio module to the internal mounting unit. In the technical literature, the radio module is usually called an external mounting unit, because in most cases, the radio module is installed on a radio relay tower or mast in close proximity to the RRL antenna. The location of the radio module in close proximity to the RRL antenna is usually due to the desire to reduce the attenuation of the high-frequency signal in various transition waveguides (for frequencies above 6 - 7 GHz) or coaxial cables(for frequencies less than 6 GHz).

For particularly difficult conditions where maintenance of communications equipment is difficult, a lower location of radio modules is used. The operating frequency is transmitted to the antenna via a waveguide. This option The location of the blocks allows servicing the RRS (replacing radio modules) without personnel going to the antenna mast structures.

Redundancy configurations and methods

The state when a radio relay line cannot provide the required quality of channels for transmitting information is called unavailability, and the ratio of the time of unavailability to the total operating time of the line is called the unavailability coefficient.

In the most important directions, in order to reduce the unavailability of RRL intervals, they use various methods RRL equipment redundancy. Typically, configurations with redundant RRL equipment are denoted as the sum N+M, where N denotes the total number of RRL trunks, and M is the number of reserved RRL trunks (the set of equipment that provides communication in each direction over one radio frequency channel is called an RRL trunk). After the amount, add the abbreviation HSB, SD or FD, denoting the method of reserving RRL trunks.

Reducing the unavailability factor is achieved by duplicating RRL functional blocks or using a separate reserve RRL trunk.

Configuration 1+0

RRL equipment configuration with one barrel without redundancy.

N+0 configuration

Configuration of RRL equipment with N trunks without redundancy.

The N+0 configuration consists of several RRL frequency channels or channels with different polarization, operating through one antenna. In the case of using several frequency channels, the separation of the channels is carried out using a power divider and frequency bandpass filters. In the case of using RRL trunks with different polarizations, the separation of the trunks is carried out by using special antennas that support the reception and transmission of signals with different polarizations (for example, cross-polarization antennas that have the same gain for a signal with horizontal and vertical polarization).

N+0 configuration does not provide RRL reservations, Each trunk represents a separate physical data channel. This configuration is usually used to increase RRL throughput. In RRL equipment, individual physical data transmission channels can be combined into one logical channel.

N+1 HSB configuration (Hot Standby)

RRL equipment configuration with N trunks and one backup trunk located in hot standby. In fact, redundancy is achieved by duplicating all or part of the RRL functional blocks. If one of the RRL units fails, the units in hot standby replace the inoperative units.

N+M HSB configuration (Hot Standby)

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 diversify 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 communication of waves with different types of polarization; individual stations are located so that the route represents a 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 lower frequencies have less directional effect. 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 definition of radio relay communication is contrasted with direct radio communication. The subscriber's message is repeatedly transmitted by intermediate links in the chain, forming a radio relay line (RRL). The name was coined by the British: relay - change. The physical features of propagation forced engineers to use ultrashort waves (UHF): decimeter, centimeter, and less often, meter. Because long ones are capable of circumnavigating the globe on their own. The reason for using radio relay lines is explained by the need to store a large amount of information, which is impossible at low frequencies. The restrictions are explained by Kotelnikov's theorem.

Note. Tropospheric communication is considered a subtype of radio relay.

Advantages of the method

1. The first advantage is mentioned - the ability to store a larger amount of information. The number of channels is proportional to the bandwidth of the transmitting and receiving equipment. The value increases with increasing frequency. This fact is due to the formulas describing oscillatory circuit, other selective sections of the electrical circuit.
2. The linearity of VHF propagation determines high directional properties. Directivity increases with increasing antenna area relative to wavelength. Short ones are easier to cover with a plate. For example, long-distance communications are carried out over lengths reaching kilometers. Centimeter and decimeter waves are easily covered by relatively small paraboloids, significantly reducing the required power (except for the case of tropospheric information transmission) and the level of interference. Noise is actually limited by the internal imperfection of the receiver input stages.
3. Stability is explained by the fact of direct visibility of the transmitter-receiver tandem. The weather and time of day/year have little influence.

Already at the beginning of the second half of the 20th century, these advantages allowed economists to compare the economic efficiency of a chain with a cable. It was possible to transmit analog television channels. The equipment of towers is much more complex than regenerators. However, the cable has to replenish the signal every 6 km. The towers are usually separated by distances of 50-150 km, the distance (km) is limited to a value equal to square root from the height of the tower (m), multiplied by 7.2. Finally, permafrost greatly complicates the laying of cable lines; swamps, rocks, and rivers contribute.

Experts note the ease of deployment of the system and the savings in non-ferrous metals:

• Copper.
• Lead.
• Aluminum.

The low efficiency of autonomous towers is noted. Maintenance personnel are inevitably required. It is necessary to quarter people and assign a watch.

Operating principle

The line usually implements a duplex (bidirectional) mode of information transmission. Frequency division of channels was used more often. The first European agreements established spectrum areas:

• Decimeter waves:

1. 460-470 MHz.
2. 1300-1600 MHz.
3. 1700-2300 MHz.

• Centimeter:

1. 3500-4200 MHz.
2. 4400-5000 MHz.
3. 5925-8500 MHz.
4. 9800-10.000 MHz.

Meter waves are capable of bending around obstacles; use is allowed due to the lack of direct visibility. Frequencies above 10 GHz are disadvantageous because they are excellently absorbed by precipitation. Bell's post-war designs (11 GHz) proved uncompetitive. The spectrum section is often selected in accordance with obtaining the required number of channels.

Story

Digital dialing was offered before pulse dialing. However, the implementation of the idea was 60 years late. The fate of antibiotics is repeated by radio relay communications.

Inventing an idea

Historians unanimously give priority to the discovery to Johann Matthausch, who wrote a corresponding publication (1898) in the journal Electrical Engineering Notes (vol. 16, 35-36). Critics note the inconsistency of the theoretical part that proposed the creation of telegraph repeaters. However, a year later, Emil Guarini-Forestio built the first working copy. A native of the Italian community of Fasano (Apulia), while a student, on May 27, 1899, he patented a radio repeater in the Belgian division. The date is considered the official birthday of radio relay communications.

The device is represented by a combination of transceiver equipment. The design carried out demodulation of the received signal, subsequent formation, radiation by an omnidirectional antenna, forming a broadcast channel. The filter protected the receiving path from powerful radiation from the transmitter.

Feeling the shortcomings of the presented design, Guarini-Foresio (December 1899) patented (Switzerland, No. 21413) the design of a directional helical antenna (circular polarization), equipped with a metal reflector. The device prevented the towers from mutually intercepting other people's messages. Further improvements were made in close collaboration with Fernando Pontsele. Together, the inventors attempted to establish a connection between Brussels and Antwerp using Raspberries intermediate point, the location of the repeater.

The structure was equipped with cylindrical antennas with a diameter of 50 cm, equipping a high-rise building with equipment. Based on the results obtained in the hot June of 1901, preparations began for the Paris-Brussels line with a range of 275 km. The repeater installation step was 27 km. December brought success to the idea, providing a message delay time of 3..5 seconds.

Seeing bright prospects, Guarini had his head in the clouds, anticipating the commercial success (equivalent to the profits of the Bell Company) of radio relay communications, eliminating the problems of range. Reality has made adjustments. A wide range of solutions was required:

1. Power supply for transceiver equipment.
2. Designing more digestible antennas.
3. Reduced equipment costs.

It was only 30 years later that the invention of suitable high-frequency electronic tubes allowed the idea to surface. The inventor was awarded the Order of the Crown of Italy.

Lamp designs conquer the English Channel

In 1931, the Anglo-French consortium (Company international telephone and telegraph, England; Telephone Equipment Laboratory, France), headed by Andre Clavier, conquered the English Channel (Dover-Calais). The event was covered by Radio News magazine (August, 1931, p. 107). Let us recall the essence of the problem: laying a submarine cable is expensive, and a line break means the need to spend significant funds on repairs. The engineers of the two countries decided to overcome the water space (40 km) with seven-inch (18 cm) waves. The experimenters reported:

1. Telephone conversation.
2. Coded signal.
3. Images.

A 10-foot diameter parabolic antenna system (19-20 wavelengths) produced two parallel beams, a configuration that automatically blocked the interference phenomenon. The power consumption of the transmitter was 25 W, the efficiency was 50%. Positive results suggested the possibility of generating higher frequencies, including optical ones. Today, the inexpediency of such habits is obvious. Specifications vacuum tubes used were kept silent by the organizers, only mentioned general principle action, invented by Heinrich Barkhausen (University of Dresden), improved by the French experimenter Pierre. The entertainers expressed gratitude to their predecessor scientists:

1. Glagolieva-Arkadieva A.A. invented (1922) a microwave generator (5 cm..82 microns) from aluminum filings suspended in an oil vessel.
2. Professor Ernest Nichols and Dr. Teer conducted similar research in the USA, achieving the generation of waves comparable to the infrared range.
3. The developers were helped by countless experiments by Gustav Ferrier, who was involved in the miniaturization of vacuum devices in an attempt to reduce the wavelength.

The key was Barkhausen's idea to generate vibrations directly inside the lamp (the principle of operation of modern magnetrons). Observers immediately noted the possibility of laying multiple channels. UHF broadcasting was completely absent at that time. The range is four orders of magnitude wider than the waves then widely used by television. The sharp increase in the number of broadcast channels was becoming a real problem. The opportunities opened up by the decimeter spectrum clearly exceeded the needs.

Even then, the note suggested the use of atomic transitions to generate waves high frequency. X-rays were discussed. The journalists ended with a general call for engineers to explore the emerging prospects.

Take two

A few years later, experiments were resumed. A 56 km long line connected the shores of the strait:

1. Community of Saint Inglever (France).
2. Lympne Castle (Kent, UK).

The creators of the line expected to get serious by installing two steel towers decorated with parabolic antennas with a diameter of 9.75 feet. The generator hid behind the reflector, the thin tip of the waveguide pierced the plate, the feed was formed by a spherical mirror. A ground control station was built for the operator, equipped with the necessary panels, including a voltage regulator. The functional set involved the use of Morse code, fax, and television and radio broadcasting.

Superheterodyne receiver with quartz stabilization reduced input signal up to 300 kHz, decoding amplitude modulation. According to the organizers, the equipment is designed to replace marine telephone and telegraph cables. The American company Bell built a similar system, crossing Cape Cod Bay.

World War II radar technology

The outbreak of World War II spurred the development of microwave generators. The American (Stanford) inventors of the klystron (1937), Russell and Sigmund Varian, helped the endeavor. New lamps helped create amplifiers and microwave generators. Previously, Barkhausen-Kurz tubes and split-anode magnetrons, which produced too little power, were widely used. The prototype was successfully demonstrated on August 30, 1937. Western developers immediately began building aerial observation stations.

The brothers created an organization dedicated to commercializing the invention. The linear proton accelerator helped doctors treat some diseases (cancer). The operating principle uses the concept of speed modulation (1935) by Oskar Heil and his wife. Although experts assume that the Varians are completely unaware of the existence of this scientific work.

The work of the American physicist Hansen (1939) on particle acceleration could be used to slow down electrons transferring energy to the radio frequency output path. A Hansen resonator is sometimes called a rhumbatron. Klystrons were used primarily by the Nazis; Allied stations were filled with magnetrons. The US Army built mobile systems connections based on trucks that crossed the ocean to help the allies. The army liked the idea of ​​quickly establishing long-distance communications. After the war, AT&T used 4-watt klystrons to create a radio relay network covering North America. Thanks to 2K25, Western Union built its own infrastructure.

The main engine of rapid progress is considered to be the idea of ​​a sharp expansion of the volume of canals, acquired by the low cost of erecting towers. Relay networks (RRNs) enveloped the three lines of defense of North America during the Cold War. The TDX prototype was developed (1946) by Bell Laboratories. The system was quickly improved, updating the vacuum tubes:

• 416V.
• 416C.

Post-war attempts to organize communications were faced with the need to choose element base. Experts seriously discussed the designs of lamps and klystrons, and complained about the influence of rain. Typical problems unprotected analog communication. The first lines (including US defense air defense networks) were powered by diesel fuel. The tower certainly contained a lower floor for storage of fuels and lubricants, often toxic.

Fading technology

The transition to the centimeter range requires the abolition of metal-ceramic and beacon triodes. Instead, klystrons and traveling wave tubes are introduced. Antenna devices, on the contrary, come out smaller. The centimeter range greatly increases the losses of coaxial connections native to the UHF spectrum. Instead, they decided to install waveguides. The third generation TDX switched to solid-state electronics. Mobile options transmitted 24 channels with frequency division. Each contained 18 teletype lines. Similar systems were developed everywhere. It was only in the 1980s that the usefulness of the technology was questioned due to the introduction of satellite communications. The optical cable blocked the capabilities of radio links.

This is interesting! The Rhyolite satellite group was engaged in intercepting Soviet radio relay communications.

Current state

Nowadays the idea is widely used mobile networks ground-based. Scientists are increasingly considering the possibility of energy transfer. The source of the idea should be considered Nikola Tesla, who at the beginning of the 20th century planned to cover the territory of the United States with a network of transmitters. The inventor demonstrated complete safety high frequency discharges. Today experts mean moving the action into outer space.

Energy transfer

The discovery of electromagnetism left scientists scratching their heads, trying to figure out how to transfer energy. The first implemented method is the toroidal transformer of Mike Faraday (1831). Having considered Maxwell's equations, John Henry Poynting created a theorem (1884) describing the process of power transfer by an electromagnetic wave. Four years later, Heinrich Rudolf Hertz confirmed the theory with practice, observing the spark discharge of a receiving vibrator. The problem was addressed by William Henry Ward (1871) and Mahlon Loomis (1872), both of whom wanted to harness the potential of the Earth's atmosphere.

“Secret” books are full of Tesla’s projects to defeat fascist aviation with wireless emitters. The facts mention the posthumous total seizure of the inventor's papers by American intelligence services. Tesla coils jokingly made it possible to obtain high-frequency lightning discharges. Wardenclyffe Tower (1899) seriously frightened the area; copper producers were filled with horror at the idea of ​​wireless transmission. Tesla remotely ignited Giessler tubes (1891), incandescent light bulbs.

The Serbian inventor disseminated the technique of generating oscillations by resonant LC circuits. The brilliant Tesla's technique involved launching balloons to altitudes of 9.1 km. The reduced pressure facilitated the transmission of megavolt voltages. With the second idea, the inventor decided to force the electric potential Globe vibrate, supplying the stations of the planet with energy. The envisioned World Wireless System could also transmit information. It is not surprising that investors who lined their pockets with copper production were frightened.

The method of powering trains with a voltage of 3 kHz was patented by Maurice Hatin and Maurice Leblanc (1892). In 1964, William Brown created a model of a toy helicopter powered by electromagnetic wave energy. RFID technologies (for example, intercom key) were invented in the mid-70s:

1. Mario Cardullo (1973).
2. Koelle (1975).

Later, access cards appeared. Today the technology was tested mobile gadgets, recharged wirelessly. A similar technology is used by induction cooktops and melting furnaces. Engineers actively implement ideas computer games beginning of the second millennium, planning to create orbital solar power plants, defended by combat drones powered by the energy of electromagnetic waves. Most people are familiar with the laser scalpel, which uses the principle of transmitting power to the patient's skin.

This is interesting! The concept of wireless drones (1959) was put forward by Radeon, carrying out a project of the Ministry of Defense. The Canadian Communications Research Center (1987) created the first prototype, which performed its assigned functions for months.

Wireless Power Transmission Consortium

On December 17, 2008, an organization was formed to promote the Qi wireless device charging standard. Over 250 global companies supported the idea. Later the project was approved by Nokia, Huawei, Visteon. Plans to equip the technology became known in advance mobile devices. In October 2016, the intention to create charging hotspots was announced.

24 companies formed the “steel core” of the lobbying group. 2017 added to the list with marketing Apple managers. Regarding the safety of the technique, the opinions of scientists are divided. Experts agreed on one thing: soon the inductive charging technique will become generally accepted.

Communication with relay systems

Just as the first experimenters crossed the English Channel, early orbital solar power plants will power satellites, dramatically extending the life of the equipment. Then the energy transfer will become global, covering all human devices. The technology is most simply called relay technology. The energy will be received, amplified, and transmitted further.

This is interesting! Peter Glasser was the first (1968) to propose farming the solar energy with orbital factories, transmitting the beam to ground stations.

The laser beam transfers energy efficiently. 475 W power reached the target, traveling many miles free space. The system showed an efficiency of 54%. NASA laboratories transmitted 30 kW using the 2.38 GHz frequency (spectrum microwave oven) a plate with a diameter of 26 meters. The final efficiency reached 80%. Japan (1983) began research on energy transfer by a layer of the ionosphere full of free charge carriers.

The prototype was created by the team of Marin Solyasic (Massachusetts University of Technology). The resonant transmitter sent 60 W of energy at a frequency of 10 MHz, covering a distance of 2 meters, achieving an efficiency of 40%. A year later, the team of Greg Lay and Mike Kennan (Nevada), using a frequency of 60 kHz, conquered a range of 12 meters. We believe latest developments will quickly be classified.

The published story ends with NASA's creation of an aircraft (2003) powered by laser radiation. Announced on March 12, 2015, the JAXA project is intended to implement the ideas of Nikola Tesla.