Radio relay and wire communications. Radio relay communication

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 on 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 communication is carried out over distances 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. The possibility of transmitting analogue television channels was allowed. The equipment of towers is much more complex than regenerators. However, the cable has to replenish the signal every 6 km. Towers are usually separated by distances of 50-150 km, the distance (km) being limited to the square root of the tower height (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 communication between Brussels and Antwerp, using Maliny as an intermediate point and 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 Bell's profits) 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, an Anglo-French consortium (International Telephone and Telegraph Company, England; Telephone Equipment Laboratory, France), led 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. The technical characteristics of the vacuum tubes used were kept silent by the organizers; only the general principle of operation, invented by Heinrich Barkhausen (University of Dresden), improved by the French experimenter Pierre, was mentioned. 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 Bell Company 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-Kurtz 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 truck-based mobile communications systems that sailed across 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 (RRLS) 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 encountered the need to select an 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 versions 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 by land-based mobile networks. 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 the complete safety of 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 are actively implementing the ideas of computer games from the 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 Apple marketing managers to the list. 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. The 475 W power reached the target, covering many miles of 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 into 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.

Radio relay stations are relay (receive-transmit) radio stations. From chains of such stations, radio relay lines (RRL) are formed, through which radio relay communication is carried out. Radio relay stations have fundamental difference from any other radio stations. This difference is working in duplex mode, which means that the radio relay station simultaneously receives and transmits, but they are conducted on different carrier frequencies.

Ground radio relay stations usually operate at centimeter and decimeter waves with frequencies ranging from one hundred megahertz to several tens of gigahertz. Frequency ranges for radio relay communications have three categories depending on the purpose of communication lines, which are local, intrazonal and trunk. In Russia, a frequency range from 0.39 GHz to 40.5 GHz is allocated for local communication lines, from 1.85 GHz to 15.35 GHz for intrazonal lines, and from 3.4 GHz to 11.7 GHz for trunk communication lines.

This distribution of frequency ranges is due to the influence of the external environment on wave propagation. Atmospheric phenomena have little effect on the quality of communication at frequencies up to 10 GHz, but already at frequencies from 15 GHz this influence is already very noticeable, and at frequencies from 30 GHz it becomes decisive.

Therefore, for trunk communication lines, as the busiest lines that transmit large amounts of information over considerable distances, the most favorable frequency range is selected from the point of view of the influence of the environment on electromagnetic waves.

In some megacities and their surrounding areas, there is a rather tense electromagnetic environment, which can be observed especially often in the most developed frequency ranges. Therefore, before purchasing radio relay stations, it is worth familiarizing yourself with the local situation in the field of frequency allocation at the nearest branch of Rossvyaznadzor.

Antennas of neighboring radio relay stations (except for tropospheric stations) are located in the line of sight zone. To increase the length of intervals between radio relay stations, antennas are installed as high as possible, on high-rise buildings, towers or masts up to one hundred meters high. Thanks to this, you can get a visibility radius of 40- 50 km. Radio relay stations can be not only stationary, but also mobile; such stations are transported by car.

The operating temperature range for radio relay stations installed outdoors is ±50 °C. Both for long-term changes and for frequent fluctuations in ambient temperature, within these limits the stability of the frequency and energy characteristics of radio relay stations is achievable.

The transmission speed provided by radio relay stations consists of the main and additional traffic. The main traffic signals for modern radio relay stations can be information flows with speeds from 2.048 to 622.080 Mbit/s, and additional traffic - 2.048 Mbit/s, 9.6 kbit/s, etc. High speeds data transmissions are only achievable using multi-position modulation. Today, quadrature amplitude modulation (QAM) is most often used.

The type of modulation determines both the width of the spectrum of radio signals and the noise immunity when receiving them. More recently, two-level relative phase modulation (RPM-2) and frequency modulation were most often used in radio relay stations, but recently, in order to increase the efficiency of spectrum use, it is increasingly necessary to use multi-position modulation.

" times="" new="" roman=""> AR-SA">However, multi-position modulation requires a significant increase in energy parameters. For example, with KAM-128, compared to OFM-2, the required signal-to-noise ratio at the receiver input increases by 14 dB. This is not easy to achieve only by increasing energy parameters, so multi-position modulation is usually used in combination with noise-resistant coding. In addition, to increase the stability of communication, modern radio relay stations use other technologies - for example, leveling the frequency response using equalizers or using diversity reception.

When using materials, a link to the site is required.

DNEPROPETROVSK STATE UNIVERSITY

Abstract

“Situation and prospects for the development of radio relay and tropospheric communications”

student XXXXXX

Checked:

teacher: XXXXXX

Dnepropetrovsk

Introduction to the section

The development of modern technology has led to the need to quickly and accurately solve control and coordination problems, taking into account events occurring at large distances from control centers. At the same time, the role of communication has sharply increased not only in the “person-to-person” circuit, but also for data transmission in a circuit connecting two electronic machines.

The nature in this case determines special requirements for the path: firstly, an increase in the throughput of communication systems, and, secondly, an increase in the requirements for reliability and quality of transmission.

A peculiarity of the use of radio relay and tropospheric communications is the use of the VHF range in which they operate.

The first advantage is that in the VHF range it is possible to use antennas with high directivity with small dimensions. This reduces mutual interference between stations and makes it possible to use low power transmitters.

The second advantage is that a wide range of frequencies can be transmitted in the VHF band. This makes it possible to transmit signals from a large number of channels on one carrier frequency. Modern lines are built with the expectation of transmitting from one or two to a thousand tons of telephone messages.

The third advantage of the VHF range is the fact that in this range the influence of various types of interference is very small. At the higher frequency part of the range, lines are less susceptible to interference, because on the one hand, the probability of interference in this range is less, and on the other hand, the directivity of the antennas is higher and, therefore, the probability of interference penetrating into the receiver is less. At lower frequencies in the meter wave region, the likelihood of interference from the ignition system of internal combustion engines or industrial and atmospheric interference is high, and the directivity of the antennas is low. Therefore, the quality of the channels of such lines is usually lower.

1. Radio relay communication. Basic concepts.

Under radio relay communication understand radio communications based on the retransmission of radio signals of decimeter and shorter waves by stations located on the surface of the Earth. Totality technical means and the radio wave propagation environment to ensure radio relay communication forms radio relay communication line.

Terrestrial called a radio wave propagating near the earth's surface. Earth radio waves shorter than 100 cm propagate well only within the 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, and it is called radio relay line line of sight(RRL).

Figure 1.1 – To explain the principle of constructing RRL

Classification of radio relay communication lines.

• Depending on the primary EASC network, there are:
• Trunk RRL
• Intrazone RRL
• Local RRL.
• Depending on the method of formation HS There are analogue and digital RRLs. Analog RRLs, depending on the method of combining (separation) of electrical signals and the method of carrier modulation, are distinguished:
• RRL with ChRC
• CHMRRL with FIM-AM
• Depending on the number N organized TV channels:
• Small channel - N£24
• With average throughput - N = 60 ... 300
• With a big bandwidth-N = 600 ... 1920.

• Digital RRLs are classified according to the carrier modulation method:
• PCM-FM
• PCM-FM
• and others
• Depending on the bit rate IN :
• with low capacity - B<10 Мбит/с
• with average throughput - B=10...100 Mbit/s
• with high throughput - >100 Mbit/s

1.1. Some types of stations used and their parameters

Radio relay station R-415

RRS R-415 is designed to create temporary, quickly deployable, small-channel radio relay communication lines. The radio station allows counter operation in a radio line with a radio relay station of type R-405M. Depending on the operating conditions, the station can be installed in cars, airplanes, and helicopters. The RRS is manufactured in six versions, differing in the number and type of transceivers (H, V, NV) and supply voltage (27 V, 220 V 50 Hz/27 V).

Figure 1.1.1 – Appearance station R-415

R-415 provides the following operating modes:

• internal compaction mode, which ensures simultaneous operation of two telephone and two telegraph channels;
• external compaction mode using “Azur” type equipment via three operational and one service telephone channels;
• external compression mode with data transmission equipment at a speed of 12-4 8 kBit/s;
• remote control mode for HF or VHF radio stations;
• simplex mode, which ensures operation via one of the telephone channels with increased frequency deviation;
• automated control mode, providing identification of a faulty unit.

Technical data

Radio relay station R-419S

RCP-419 C is designed for organizing independent radio relay and cable communication lines, as well as for branching channels from multi-channel radio relay, tropospheric and wire communication lines at fixed communication facilities. The station has seven versions, differing in configuration (number of transceivers, presence of an interface unit, types of antenna devices),

Figure 1.1.2 – Appearance of the R-419S station

TECHNICAL DATA

Radio relay station R-419A

Features of the use of radio relay stations for solving subscriber access problems
Among the technical means used in the construction of telecommunication networks, radio relay stations (RRS) occupy a special place. Quite often, their use remains the only means of ensuring traffic transmission where laying cable is impossible or impractical for economic reasons. The main typical tasks solved with the help of this type of equipment are the organization of inter-site connections, subscriber extensions, connection to transport highways, and the construction of long-distance technological communication lines. Recently, there has been a demand for the implementation of “last mile” tasks, providing subscribers with voice telephone services, Internet, and cable television. In suburban and rural areas with insufficient penetration of modern telecommunications infrastructure, the use of radio relay stations solves this problem due to such characteristics of this equipment as speed of deployment, relatively quick payback, high throughput, integration into PDH networks, broadcast of the necessary subscriber interfaces as part of a group digital stream. Depending on the specific situation, RRS can be used to solve “last mile” problems:

• as a separate self-sufficient link in the presence of functionally complete subscriber terminations in the RRS equipment;
• in combination with terminal multiplexer equipment or PBX equipment;
• in combination with other means of subscriber radio access.

The main parameters that determine the choice of RRS for a specific situation are most often:

• frequency range, since the length of the radio relay line interval depends on it;
• route topology (“line”, “star”, “ring” or variations);
• information capacity of the station;
• a set of additional services (implementation of additional Ethernet interfaces, low-speed digital channels in addition to the main digital streams, the possibility of telecontrol and telesignaling, software control and configuration, etc.);
• station cost.

Technical review of solutions from domestic and foreign manufacturers of radio relay equipment PDH - hierarchy in the frequency range 1.4...38 GHz

This article briefly examines the capabilities of medium-speed radio relay stations from domestic and foreign manufacturers that implement interfaces from E1 to E3.

NPF "MIKRAN"
In combination with terminal multiplexers of subscriber interfaces, medium-speed radio relay stations MIK-RL, produced by NPF MIKRAN, allow solving a wide range of problems in providing users with analog and digital channels. MIK-RL are designed for communication in 14 frequency ranges with transmission speeds E1, E2, E3. The family includes radio relay stations with medium and low transmission rates of the PDH hierarchy (7...40 GHz), as well as small-channel radio stations operating in the low-frequency ranges (150 / 400 MHz). Transceiver devices (remote equipment) for all frequency ranges are made according to a unified block diagram with digital modulation QPSK, 16/64/128QAM. In the range of 23...40 GHz, the transceiver device is integrated with the antenna, which facilitates installation operations. Barrels can work with different polarizations. Access modules (internal equipment) provide control and switching functions of main and additional digital channels, control of MIK-RL operating parameters, and service communications. The first level equipment has the most complete set of functionality, a TU-TS system with software support for 128 stations. The second level equipment has a local TU-TS system. MIK-RL provides for the organization of additional digital channels n*64 kbit/s. Some of the additional channels are used for intra-system purposes (service communications, conference calls with selective and group calls, monitoring and control), the remaining channels with RS-232/422/485, V.35 interfaces, E&M telephone terminations are provided to users. Low-speed alarm channels provide connection to external fire and security alarm devices, etc. The RPC may also include a separate module of additional channels nx64 kbit/s produced by the enterprise, access modules with interfaces Ethernet +n*E1 (n=0...4), Ethernet + n*4E1 (n=0...4), multiplexers of secondary MDCs -12-xx (E2) and tertiary MCP-13-xx (E3) digital streams with the functions of transmitting Ethernet interfaces + n*E1 (n-0...4). Multiplexers and power supplies are included in a single control system via the CAN interface.

NETWORK+SERVICE
RRS FLOX is an example of domestic equipment that has gained popularity in the creation of corporate technological communication systems and public communication systems, both in Russia and in the CIS countries. The basic model of RRS FLOX in the frequency range 1.427 .. 2.690 MHz was developed in 1995 as part of the conversion and fully uses all modern achievements of microwave technologies: digital methods of data transmission, efficient use of frequency resources, compact design. Partially (about 30%) imported components are used. Serial production is organized at the Ground and Space Communications Equipment (ANICS) plant with strict quality control.
In 2003-2004, developments were completed that significantly expanded the use of the frequency range: FLOX-4 (3,600 .. 4,200 MHz), FLOX-7 (7,250 .. 7,550 MHz), FLOX-23 (21,200 .. 23,600 MHz). The entire RRS FLOX model range retains the main advantages that have gained popularity: reliable operation in any region of Russia and the CIS, operation at the maximum possible intervals for the range, unpretentious maintenance, and a relatively low price. Flexible design allows for convenient and natural placement of equipment at the communication center. Supported redundancy levels: 1+0, 1+1, 2+0, n+1.
2 types of FLOX equipment are produced: low- and medium-speed PDH levels support digital channels with a capacity of 2-, 8- and 34-Mbit/s and are designed for organizing digital telephone communication channels at the local and zonal level, and high-speed SDH levels support digital channels with a capacity of 51-Mbit/s. and 155-Mbit/s (STM-0 and STM-1) and are intended for organizing both telephony and data transmission systems in backbone multiservice communication networks. For use in rural communication systems, an economical integrated model FLOX-light with a capacity of 2 Mbit/s has been developed and is being produced. Currently, R&D is underway to create RRS with COFDM modulation, which effectively uses the reflected signal and allows the construction of radio relay communication lines in port waters, on the shelf and on reflected signals in conditions where there is no direct radio visibility: in urban areas, in rocky river gorges, in wooded hills and mountains.
All FLOX RRL models are provided with a unified operational control system that supports any communication network topology and redundancy scheme.
RRS FLOX are operated in almost all regions of Russia, in the republics of Kazakhstan, Tajikistan, and Uzbekistan. They really work stably, for example, in the low temperatures of Yakutia (down to -60? C), high temperatures Stavropol region (up to +50? C), the sharply continental climate of Buryatia and Kazakhstan (daily temperature drop up to 20? C), the subtropical climate of Abkhazia and the marine climate of Arkhangelsk, Vladivostok and Petropavlovsk-Kamchatsky. RRS FLOX has been implemented in the communication systems of the Ministry of Emergency Situations, the Ministry of Internal Affairs and the Ministry of Defense of Russia, regional branches of OJSC Rostelecom (Chitatelecom, Telesvyaz of the Republic of Buryatia, Telesvyaz of the Republic of Karelia), communication enterprises as part of the Fisheries Committee (Arkhangelsk, Vladivostok, Krasnoyarsk, Murmansk, Petropavlovsk-Kamchatsky), Ministry of Transport (Makhachkala, Karelia and Arkhangelsk region), a number of operators cellular communication: Saratov-GSM, Chuvashia-Mobile, Astrakhan-GSM, StavTeleSot, in the CIS countries (KRIS-Service/Kazakhstan; SOMONKOM/Tajikistan, Ministry of Defense of the Republic of Uzbekistan). All users highly appreciate the performance of the equipment.

RADIAN
JSC "Radian" produces radio relay stations in the 4...23 GHz range. Digital streams E1, E2 and E3 and analog television/radio programs, analog telephony, data from 9.6 kbit/s to 10 Mbit/s are transmitted. Modem equipment provides modern modulation methods OQPSK and 64/128QAM with digital filtering and adaptive equalizer.
Depending on the type of terminal equipment, input/output of user signals is provided: streams E1, E2, E3 (equipment MD-8, MD-34, AST-155), signals analogue television(KTVM-200 and DTVM-200) to transmit them through a digital system with one or two stereo audio channels. The TV signal is transmitted in the MPEG-2 standard in 3 or 4 E1 streams. The quality of the TV signal supports the Russian color TV standard SECAM, as well as PAL and corresponds to television centers of the 2nd quality group. The equipment provides two channels of service communication, including conference calls with address calls and additional user data channels with speeds from 9.6 to 115 kbit/s.
If a radio relay station is equipped with a flexible multiplexer MF-20 developed by Radian CJSC, 2-wire analogue telephone connection both in “subscriber extender” mode and in direct telephone mode, 4- and 6-wire interstation trunk lines, serial synchronous and asynchronous data transmission channels according to V.35/V.36/RS-422/RS- standards 232/RS-485 with speeds from 9.6 kbit/s to 10 Mbit/s, audio broadcasting signals top quality with MUSICAM compression both on analogue interfaces and on the AES/EBU digital interface.
It is possible to connect fire, security and other alarm systems from external sensors by installing an additional interface device connected to the PPC equipment via the RS-485 interface. The equipment has a developed automated control system (ACS), which provides control of station parameters.

PKP "BIST"
PKP "BIST" has been producing radio relay equipment of various modifications with a throughput from 2 to 34 Mbit/s for more than ten years. The company strives to actively introduce its products to other market segments, including as a means of solving the problems of the “extended last mile”.
Based on current trends in the development of subregional digital infrastructure, the basic requirements for equipment capable of creating an optimal transport environment for small local access networks, including rural and technological communication networks, have been identified. For operators of such networks, the problem of minimizing both implementation costs and operating costs becomes vitally important. It is solved by using inexpensive equipment, increasing the fault tolerance of the transport environment, and covering the network with an effective monitoring system.
The RRS concept for subregional networks with domestic specifics received support from NIIR, and in 2002-2003. The Federal State Institution “Russian Fund for Technological Development” provided funding for R&D “Development of a low-speed radio relay station for networks with a low-speed subscriber density, including rural ones.” As part of R&D, low-cost RRS with a throughput of up to 2 Mbit/s, and RRS 8 and 34 Mbit/s were developed based on a unified approach.
Network multiplexers from the new generation BIST family of RPCs allow the equipment to operate effectively in networks of various topologies, including ring ones, using route reservation technology. The equipment has a built-in monitoring system, which is not inferior in efficiency to automated control systems of basic modifications. Implemented projects for the use of RRL of the "BIST" family in the "extended last mile" sections, as a rule, are 3-4 hop RRL, combining geographically dispersed capacities of local PBXs, DECT base stations, or allowing access of remote direct subscribers (DS) to information fields of node PBXs. Typical examples are the Kulebaki-Lomovka-Teplovo-Gremyachevo lines (Volga Telecom OJSC, Nizhny Novgorod) and the transport network built in the Republic of Uzbekistan by order of K.D.M. Enteprises, L.L.S."
In both cases, RPCs were used as a transport medium for connecting distributed subscriber capacities (in the first case, wired PAs were connected to the PBX, in the second case, a BS standard MPT 1327 was connected to the Actionet switching center). Additionally, as a companion, with the help of flexible multiplexing equipment, the problem of providing leased data exchange channels within a LAN to third parties was solved. To solve such problems, in particular, network multiplexers from the BIST family of RRS can be provided with up to 2 Ethernet 10 BaseT ports and V.24 ports for connecting geographically dispersed subscribers and LAN sections.
Complete with appropriate digital codecs, radio relay equipment produced by PKP "BIST" is used to distribute television and audio signals to subscribers in the cities. Saratov, Samara, Kazan, Primorsky Krai, including together with digital telephony signals.

ALCATEL
Alcatel 9400AWY is a family of digital radio relay systems designed for communication in the 7...38 GHz range with a 1+0 or 1+1 configuration and a throughput of 4...34 Mbit/s. The Alcatel 9400AWY RRL belongs to the class of separate installation systems, which provides flexibility in choosing the required bandwidth and frequency range. Many parameters are configured by software and do not require replacement of equipment: frequency adjustment, modulation adjustment, bandwidth adjustment. The radio relay station has the function automatic control output power of the transceiver in all ranges. One external unit can be used to operate at any frequency within a quarter of the frequency range. At the same time, the range of spare parts and accessories is reduced to 4 types of ODU for the entire frequency range. The 9400AWY external unit, if necessary, can be quickly reconfigured to operate at a different frequency. The indoor unit is equipped replaceable modules interfaces. Thanks to this, the 9400AWY RRL finds its application not only in voice networks (up to 16 E1 ports or 1 E3 port per 1 IDU), but also in data networks and multiservice networks, for which a combined 2x10BaseT+8xE1 module is provided. In the latter case, the system user has the ability to redistribute bandwidth for packet and voice traffic. The availability of replaceable interface modules implements the “pay as you grow” concept, where the appropriate interface can be added to the system as needed. Another example of the implementation of the same concept in Alcatel 9400AWY equipment is the presence of software keys. The information on the software key determines the set of functions available to the user. To add new interfaces or increase the available bandwidth, just install a new software key or add the corresponding module.
The Alcatel 9400AWY RRL uses advanced monitoring and control functions optimized for operation and maintenance. This allows you to create scalable solutions for both local control of a single channel (for networks of sizes from 128 radio equipment elements), and global solutions for complex transport networks (based on the Alcatel 1353NM centralized network management system), providing fault detection, performance measurement, configuration and protection management.

ERICSSON
Ericsson's mid-capacity point-to-point microwave systems, MINI-LINK E, are suitable for any type of network. MINI-LINK E can be configured to meet the requirements of any network in terms of range and data transfer speed. This equipment operates in the frequency ranges of 7...38 GHz and has a data transfer rate from 2 to 2x17 Mbit/s. MINI-LINK E terminals can be used in networks of any configuration - in the form of a star, tree, or ring. To increase reliability, redundant 1+1 type systems or networks with a ring structure can be used. MINI-LINK E products are divided into two product lines to better meet the cost-effective requirements of high-density networks: the stand-alone, all-outdoor MINI-LINK E for minimal site costs, and the flexible MINI-LINK E split system for optimal multi-terminal site layouts. Configurations are available that support up to four radio modules. Software control of traffic speed makes it easier to expand the network without replacing equipment. Software management of site configuration and interconnections allows you to minimize the number of cable connections, ensure high reliability and reduce installation time. The all-outdoor MINI-LINK E Micro contains all necessary transmission components, eliminating the need for a centralized indoor infrastructure. This is especially important when quick commissioning and minimal cost of the site are especially important.
The Ethernet Interface Unit (ETU) provides wireless communication between LAN networks across MINI-LINK E spans. ETU has one interface for LAN connection. It can be flexibly configured for any throughput that meets G.703, 2, 8 or 34 Mbps.
MINI-LINK cross-connect units (MXU) support redundant ring switching, 64 kbps data compression, and embedded management. They are fully compatible with the extensive Ericsson DXX family of equipment.
For centralized management and operation of all MINI-LINK equipment, the MINI-LINK Netman system is used. It can be used as a standalone system or integrated into a higher order Network Management System (NMS) using a standardized SNMP interface.

NEC
NEC Corporation supplies the Russian market with radio relay stations of the Pasolink family for the frequency range from 4 to 38 GHz. Communication systems built on this equipment are distinguished by high reliability (mean time between failures - up to 400,000 hours), ease and simplicity of deployment and maintenance. The equipment structurally consists of a compact external radio frequency unit (ODU, weight about 3 kg) and a channel-forming internal modulator-demodulator unit (IDU, size 1U), connected by one coaxial cable. The modular design allows for a simple transition from a 1+0 to 1+1 or 2+0 redundancy scheme and allows for cost-effective capacity expansion. The use of automatic transmit power control reduces interference, reduces residual error rates and, in combination with a transversal adaptive equalizer, makes it easier to solve fading problems. The use of orthogonal polarization mode allows doubling the system throughput on one RRL interval, and modern Reed-Solomon coding improves the BER characteristics (probability of errors per bit of information). Programmable modulation scheme: PSK/QPSK/16-QAM in PHD systems and 16-QAM/128-QAM in SHD systems, allows you to achieve high efficiency in the use of frequency spectrum or system gain. A flexible combination of Ethernet and E1 interfaces is provided. All equipment of the Pasolink+ family works with a single centralized management system PNMS (PASOLINK Network Management System), in the Windows’NT or Unix operating environment, supports up to 100 PPC stations in one network and uses the SNMP network management protocol. Pasolink equipment is certified in Russia. A full cycle of tests is carried out at ±50°С, including “ cold start». Model range The PDH level includes Pasolink PPC with an Ethernet interface for communication or data transmission systems with low and medium throughput (up to 16xE1 or 2x10/100Base-TX) and Pasolink Mx PPC with increased throughput from 5xE1 to 40xE1. The programmable QPSK/16-QAM modulation scheme gives an increase in capacity from 16xE1 to 40xE1 in the same band (28 MHz). Designed for use on mobile operator networks, corporate IP networks, and Internet service provider networks.
The most well-known implementation in Russia is as part of the Trans-Siberian main RRL “Moscow-Khabarovsk” with a length of 8300 km. Pasolink equipment has been used to build core communication networks of leading domestic cellular companies: VimpelCom, MEGAFON and MTS.

NERA
The CompactLink family is a cost-effective, high-performance digital point-to-point radio relay system designed for short-haul communications systems. The frequency range is from 7 to 23 GHz with both ANSI and ETSI bandwidths of 4-16 DS1/E1. The total transmission speed is 9.2 Mbit/s for 4xE1, 18.4 Mbit/s for 8xE1, 36.9 Mbit/s for 16xE1, 39 Mbit/s for E3+E1. CompactLink provides redundancy of 1+0 or 1+1 barrels with hardware redundancy (Hot-Standby). The system provides automatic adjustment transmitter power with a range of 20 dB. The user interface and digital electronics are housed in a 1U high internal module in a 19" rack. It performs all digital processing and control functions of the system and does not require adjustment or configuration during or after installation. A personal computer is used as the interface for monitoring and control, interfaces SNMP-Ethernet, SNMP-PPP, CIT Hot standby systems require two cables. The hot standby (1+1) configuration has two external modules connected to the frame-mounted component input/output ports. - These are standard 120 ohm balanced ports for ETSI and 100 ohm for ANSI. CompactLink has an optional line interface panel that provides individual connection of 4-16 E1 channels with an unbalanced 75 ohm interface and a BNC connector. The interface blocks are mounted on a 19" wide and tall panel. 2U. 2 service channels up to 9.6 kbit/s (RS-422, RS-485) are implemented.

NOKIA
FlexiHopper production Nokia covers the 7...38 GHz range, supports up to 3 transmission directions with one internal unit (one of the “flights” can be reserved).
The FIU19(E) indoor unit provides standard telecommunications interfaces using three plug-in modules. Available interfaces: 12 E1; to provide a capacity of 16 E1, an additional expansion unit EXU is used; 2 Ethernet 10/100Base-T interfaces; 2 additional Flexbus interfaces for communication with external units and internal units with each other; additional (AUX) interfaces EIA-232 or V.11 at speeds of 4.8 or 9.6 kbit/s; V.11 interface with speeds from 9.6...64 kbit/s or G.703 kbit/s interface). The speed of additional digital channels depends on the traffic load on E1 channels. So, for example, with 2 E1 channels used, it is possible to transmit the “slow” V.11 interface at a speed of 4.8 kbit/s + the “fast” G.703 interface at a speed of 64 kbit/s, and when loading all possible 16 E1 - EIA-232 at 9,600 bps + V.11 at 64 kbps. To connect external devices, 4 programmable TTL I/O channels and/or 4 relay controllers are used. The entire radio part is concentrated in the external radio module (21 x 23 x (12 - 21) cm3 / 4.0 - 6 kg).
The radio relay station is equipped with an integrated low-profile parabolic or square antenna with a diameter of 20, 30, 60, 90, 120, or 180 cm, as well as 240 and 300 cm. Hot standby, frequency, spatial and polarization diversity are used. Polarization can be changed by rotating the feeds, which are integrated into the antenna unit. Dual polarization antennas can be used.
To improve signal quality, Nokia FlexiHopper microwave equipment uses forward error correction (FEC, Reed-Salomon coding) and two- or four-depth interleaving. The ALCQ automatic transmit power control method allows the transmit power to be increased or decreased automatically in accordance with the response received from the other end of the microwave link section. The equipment features automatic fading limit measurement and transmission quality is monitored using built-in bit error rate (BER) measurement (ITU-T G.826).
Examples of the effective operation of FlexiHopper equipment are the communication schemes implemented by the Moscow company RK-Telecom for GSM base stations for JSC MSS-Povolzhye, JSC Penza-GSM and other telecom operators. Currently, work is underway to organize the transmission of Ethernet traffic in the interests of corporate customers.

Features of RRS technical solutions for operation in the frequency range 150/400 MHz
To solve problems of subscriber access in sparsely populated, remote and hard-to-reach areas, small-channel radio relay stations in the meter and decimeter ranges are used. They are designed for organizing local communications over long distances, including on semi-closed routes. Although the speed of the digital signal in the radio channels formed by such RRS is low (up to 2.048 Mbit/s), in areas with low population density, bandwidth does not play a key role. Much more important is the length of the radio relay line interval, and due to the physical properties of radio waves in this part of the spectrum, it can reach 70 km.

NPF "MIKRAN"
Radio relay stations for these applications, produced by the NPF MIKRAN enterprise, are made in the frequency ranges of 150 MHz (MIK-RL 150M) and 400 MHz (MIK-RL 400M). This platform implements the principle: connecting a radio communication line at any level - from the digital backbone to the rural subscriber. In MIK-RL 150M equipment, the functions of a subscriber access terminal and a radio relay station modem are implemented in the MD1-2-B256 access module. The module provides subscribers with 4- or 2-wire telephone terminations, as well as data channels with RS-232, RS-422, RS-485, V.35 interfaces. The multicast stream is transmitted at a speed of 256 kbit/s. The MIK-RL 400M equipment uses the MD1-1-B2 access module. Channel slots are allocated from the 2.048 Mbit/s multicast stream using primary multiplexers. In addition to the main digital streams, low-speed digital channels are implemented, allowing you to enable telemetry systems and others peripherals. The MIK-RL 150M/400M equipment has the ability to control station parameters using the TU-TS system. It is possible to build geographically distributed integrated access networks with a total number of stations up to 64. Network configuration and management is provided by software.

NPF SELSOFT
In the frequency range 150/400 MHz, NPF Selsoft produces radio relay stations R-150 (f = 150 MHz, 512 kbit/s) and P6 (f = 400 MHz, 512...2048 Mbit/s). They consist of a radio unit in a 19” housing and a “wave channel” antenna. The buttons located on the front panel allow you to set the required (or the maximum possible under radio visibility conditions) group transmission rate in the radio channel in increments of 64 kbit/s. The number of transmitted channels (time slots) from the E1 stream is selected programmatically. The low-power version of the P6-mini is designed to organize a radio channel on short distances- up to 20 km (P= 1W). To combine analog and digital subscriber terminals into the E1 stream entering the radio unit, multiplexers produced by NPF Selsoft are used. For example, using MC-115T terminal equipment, insertion/selection occurs at the access point and provides users with Ethernet up to 2.048 Mbit/s, up to 27 subscriber telephone channels, as well as data transmission (RS-232), which provides access to the PSTN, as well as collective or subscriber access to Internet resources. The length of the radio path with a three-span RRL construction option reaches 150 km.

Conclusion
Today, the radio relay equipment market is developing dynamically, as evidenced by the increasing demand for radio relay equipment. This is facilitated by such factors as the need to provide communications to the fields of the booming oil and gas industry, the increased need of the population to obtain integrated access to voice communications and the Internet, and the provision of universal communication services in new residential areas. The ability to transmit voice, data, video, build networks of various topologies, speed of line deployment, and reasonable cost make digital radio relay stations attractive for bringing digital services to subscribers in various regions of the Russian Federation and neighboring countries.

The author expresses gratitude for providing information on the products: "MIK-RL" - S. Volk (NPF "MIKRAN"), "Phlox" - L. Brusilovsky (Network + Service), "Radian" - M. Makhk (Radian), " BIST" - T. Gogoberidze (PKP BIST), "R-150" and "R6" - S. Strigin (NPF Selsoft), "Alcatel 9400AWY" - G. Muratov (Alcatel), "Ericsson MiniLink" - A. Izyumov ( Lanit), "NEC Pasolink" - A. Ovsyannikov (Network + Service), "NERA CompactLink" - D. Mermelshtein (NERA), "Nokia FlexiHopper" - A. Kuznetsov (RK-Telecom).

Radio relay communication (RRL) is a type of radio communication resulting from the operation of a chain of receiving and transmitting radio stations. Terrestrial radio relay communications operate on millimeter, centimeter and decimeter waves. RRL networks are playing important role in cellular communications, since they allow the transmission of very large volumes of traffic with minimum costs. In the future, this technology will be able to cover 100% of the bandwidth needs of cellular operators, which means ensuring high-quality operation of many different services and applications, connecting devices and things to the Internet.

RRL capabilities

The main advantage of RRL is associated with the ability to increase the throughput of both backhaul and fronthaul networks. RRL allows you to use several frequency ranges at once and thus increase network capacity at minimal costs. For example, using frequencies in the E-band range (70/80 GHz), you can increase throughput by seven times and at the same time relieve the congestion of traditional cellular frequencies. It has great value in light of the commercial launch of fifth generation networks (5G), planned for 2020.

For modernization existing networks 5G deployment will use a combination of radio relay and fiber optic communications. When choosing between RRL and optical fiber as a transport network development technology, operators make a decision based on the availability of optical fiber in a particular area and the cost of network ownership (TCO indicator). “In Russia, it is not possible or advisable to lay fiber-optic lines everywhere, so we do not plan to abandon the use of RRL. In each specific case, we study all possible ways to build and modernize the network and choose the one that is optimal,” explains MegaFon representative Yulia Dorokhina. Tele2 follows a similar strategy. “We use radio relay equipment where it is economically feasible,” says Tele2 representative Konstantin Prokshin.

Due to the reliability of the connections provided, optical fiber is increasingly used for public services and fixed-line communications, for example, when deploying FTTH solutions in the access domain. RRL, in turn, is the main technology for connecting base stations; its advantages are speed, low cost of deployment and a significant increase in throughput. “Radio relay communication is the main way to connect base stations on our network, along with fiber optic lines. We use this connection method now and plan to use it in the future. At the same time, we are building fiber-optic lines to positions in cities and at key positions, which ensures an effective target architecture of the transport network,” -

Sergey Knyshev, Director for Network Development of VimpelCom PJSC, comments.

According to Ericsson forecasts, by 2020, about 65% of all types of base stations in the world will use RRL as the transmission medium (the exception will be China, Japan, South Korea and Taiwan, where optical fiber penetration is high). At the same time, the E-band frequency range will be most actively developed, which in 2020 will account for about 20% of newly deployed RRL systems. By this time, the share of traditional frequency ranges 6-42 GHz will be 70% for newly deployed RRS. However, the popularity of RRL will vary greatly from region to region. For example, in North America by 2020 the number of base stations connected via RRL will reach 20%, and in India this figure will be 70%. Such a significant difference has developed historically and is mainly related to the degree of maturity of telecommunications markets and the availability of fixed-line services.

Used frequency ranges

Currently, a band of about 40 GHz is used for radio relay communications, but it is not entirely available in all countries of the world. The RRL has 5 ranges, each of which has its own characteristics:

6–13 GHz These are low frequency ranges, they are less sensitive to rain, and for this reason they are used in rainy regions over long transit sections.

Bandwidth in this range is limited, but the problem is solved by aggregation of several channels. The most commonly used band is 7 GHz, with 6 GHz and 8 GHz less popular. In the higher portions of this spectrum, most of the world uses 13 GHz, while North America uses 11 GHz. The 10 GHz band is used mainly in the Middle East.

15–23 GHz These frequencies are now used in many countries around the world and will continue to play an important role in the coming years. Wider channels have recently been used in these bands, and this, when combined with technologies that improve spectrum efficiency, will allow for increased network capacity in the future.

26–42 GHz In these ranges there are both widely used frequencies and not used at all. In Europe, operators are actively working in the 38 GHz band, and the situation will not change in the future. The 26 GHz band is also occupied by operators, and there is growing interest in frequencies in the 28 GHz and 32 GHz bands. Great prospects frequency channels with a width of 56 MHz and 112 MHz, since they are capable of providing gigabit data rates.

60 GHz The V-band (58.25-63.25 GHz) is ideal for small cell applications as it provides high throughput due to large channel widths and low interference due to high attenuation. Until now, the 60 GHz band has not been actively used because street networks of small cells have not been deployed on a large scale. In a number of countries, operators have already begun to build RRL networks in this range, but in many parts of the world its status remains unclear. Now it is important to decide on the regulation of the sharing of this range, so that operators and different services do not interfere with each other’s work.

70/80 GHz In recent years, there has been a growing number of E-band deployments, the main advantage of which is the ability to provide very high throughput. These frequencies are used to transmit data over a relatively short distance of 2-5 km, but this is sufficient for urban conditions. Many countries have a simplified licensing regime for this range, which stimulates interest in it from operators.

“During new construction, a fairly popular solution in urban conditions is the use of equipment in unlicensed frequency ranges of 60, 70/80 GHz (V-band, E-band) due to a number of factors: the relative simplicity of the equipment itself, efficiency, versatility, notification nature of use,” - explains Rostelecom representative Andrey Polyakov.

"We use the most modern types IP-based RRL equipment and new technologies: broadband RRL and RRL in high-frequency bands - Eband, Vband, which provide high speeds when using unlicensed bands,” says Sergey Knyshev, director of network development at VimpelCom PJSC.

On at the moment in the E-band range, RRL equipment is capable of providing data transmission at speeds of up to 5 Gbit/s. In particular, since February of this year, such speeds have been available on the network of the Egyptian operator Mobinil, part of the Orange Group. The operator uses Ericsson MINI-LINK 6352 systems. “The E-band range provides high network capacity,” explains Rafiah Ibrahim, head of Ericsson in the Middle East and Africa region. “The use of MINI-LINK 6352 systems has improved LTE coverage and significantly increased data transfer speeds in the Mobinil network.”

In general, each of the five radio relay communication bands has great potential, the full use of which requires amendments to the legislation. By using V- and E-band technologies and XPIC, MIMO, and ultra-high performance antennas such as ETSI class 4, more efficient use of existing frequency spectrum and increase network capacity. “In traditional bands, we began to use adaptive modulation, XPIC, and other technologies that increase network capacity and reliability,” says Sergey Knyshev.

In addition, there are currently discussions about the use of the W-band (92-114.5 GHz) and D-band (141-174.8 GHz). In particular, Ericsson and Chalmers University of Technology recently demonstrated a chipset that provides data transfer speeds of 40 Gbps in the 140 GHz band.

Prospects for RRL

Ease of use, speed of deployment and high network capacity are in demand across all industries. RRL is used in the housing and communal services sector to transmit SCA DA traffic, for which high throughput is important. Thanks to its reliability and flexibility, RRL is used in the work of public services, in particular the police. RRL is also used in corporate networks as a technology that complements optical fiber. Internet providers use radio relay communications to provide services to households, since such networks are built in a short time and allow you to quickly begin to earn income from the provision of Internet access services. RRL is increasingly used for broadcasting terrestrial television, this technology has become especially important in connection with the transition from analogue to digital broadcasting. In addition, RRL is used in the creation of multiservice networks in which it is necessary to ensure transmission stability and data protection.

“The scope of application of RRL is being transformed, increasingly shifting to the segment of regional and city communication lines, as well as to the segment of access lines. Traditional backbone RRLs continue to be used mainly in northern regions, but their role is gradually decreasing in favor of optical technologies where such a replacement is possible and economically feasible,” says Andrey Polyakov, a representative of Rostelecom. - RRLs, in my opinion, may have development prospects in northern regions with low population density and, accordingly, insignificant projected growth in traffic, and also, due to the natural features of the territories (mountains, permafrost, unstable soils), which make laying fiber optic lines more expensive compared to with the central zone of the Russian Federation. Also, RRLs may be in demand in places where laying fiber optic lines is practically impossible - various environmental areas and reserves.”

Options for deploying RRL networks

There are many options for deploying microwave networks. At the same time, the selected deployment scenario affects all aspects of operation, from base stations and network maintenance costs to performance and upgrade opportunities. One way is to deploy incrementally (hop-by-hop), similar to pizza boxes with a fixed configuration that is created gradually based on current needs. In this case, network nodes are modules, which makes it easy to expand them, increasing their throughput. The value of this approach is the guarantee of the minimum cost of each step and, as a result, the best TCO indicator. The disadvantage of this model is that you can end up with a network consisting entirely of equipment from different vendors.

To fully appreciate the benefits of the network node concept, Ericsson studied a typical network cluster of nodes consisting of 109 transit segments built on the basis of microwave equipment from six different vendors. When designing the network, a star topology was used, in which a central node aggregates all traffic from all RRL nodes. At the same time, a modernization plan was provided for the cluster, designed for five years and taking into account support for growing 3G and 4G traffic.

Three models have been developed:

Step-by-step (hop-by-hop) model,

Model using network nodes,

A model combining both options.

The network development plan consisted of the following stages:

Increase in data transfer speed over the 3G network: 30 Mbit/s in the first year with further growth by 10% per year;

4G network expansion: 10 MHz in the first year, 10+10 MHz in the second and third years, 10+20 MHz in the fourth and fifth years.

As a result of the research, it turned out that the use of network nodes is the most effective and least expensive way to increase throughput, in which new functionality is introduced step by step. After five years of using a network of nodes, costs were reduced by 40%. This was achieved through the reuse of equipment, saving on costs associated with the purchase of new equipment and components. At the same time, as the network developed, the step-by-step model required complete replacement of all equipment, as well as upgrade of base stations and cables. Sharing switches, fans, power supplies and processors have reduced power consumption and therefore reduced hardware costs when expanding existing sites.

The model based on network nodes ensured a threefold reduction in the number of equipment. This has led to simplification of operations and network support processes, which ultimately translates into reduced labor and costs. It also achieved cost savings by reducing the time required to resolve performance issues and equipment failures. In addition, the upgrade of existing equipment was actively used, which also reduced possible costs. In addition, reducing the number of pieces of equipment has improved monitoring processes and minimized the time required to recover from network failures and the time required to take action to improve user performance.

In addition to all of the above, during testing, Ericsson specialists found that when using a model with network nodes, three times less area is required than when using a step-by-step model. Reducing the number of racks with a node model allows you to save on the purchase of cabinets. The fact is that at many sites, the costs of cabinets and related infrastructure can exceed the costs of transport equipment, and by building a network based on a hub-and-spoke approach, these costs can be avoided. This model also results in a significant reduction in OPEX over a five-year period because less equipment requires less space, resulting in lower rental costs and lower energy consumption.