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. Physical Features distribution forced engineers to use ultrashort waves (VHF): 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 formulas describing the oscillatory circuit and 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 produced demodulation 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) a directional design 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 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. Phone 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 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 high-frequency waves. 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.

A crystal-stabilized superheterodyne receiver reduced the input signal 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-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 (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 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 of 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 benefits of the technology were questioned due to the introduction 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 thought 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 his second idea, the inventor planned to make the electrical potential of the Earth vibrate, supplying the planet’s stations with energy. Conceived 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 mobile devices with the technology became known in advance. 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 a frequency of 2.38 GHz (microwave spectrum) with a dish 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 concludes 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 communication lines (RRLS)

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

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

Radio relay span structure

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

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

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

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

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

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

Application of radio relay communication lines

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

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

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

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

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

Construction principle, equipment used, application

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

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

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

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

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

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

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

Rice. 8.1 Radio relay link

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

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

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

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

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

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

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

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

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

Radio relay communication (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 play an important role in cellular communications because they allow the transmission of very large volumes of traffic at minimal cost. In the future, this technology can cover the needs mobile operators V bandwidth 100%, 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. This is of great importance in light of the commercial launch of fifth generation (5G) networks planned for 2020.

For modernization existing networks The 5G rollout will use a combination of radio relay and fiber optic technologies. 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 everything possible ways construction and modernization of 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 a transmission medium (the exceptions 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.

Frequency ranges used

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 last years There is a growing number of deployments in the E-band range, 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 this 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-bands and technologies such as XPIC, MIMO, and ultra-high performance antennas such as ETSI class 4, more effective use available 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 Technical University Chalmers recently demonstrated a chipset capable of delivering data at 40 Gbps over 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 short time and allow you to quickly start earning income from providing Internet access services. RRL is increasingly used for broadcasting terrestrial television, this technology has become especially important in connection with the transition from analog 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 RRL continue to be used mainly in the northern regions, but their role is gradually being reduced 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, best indicator TCO. 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 reuse equipment that provides savings 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 a complete replacement of all equipment, as well as an upgrade of base stations and cables. Sharing switches, fans, power supplies and processors has 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 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.