How does GPS work? Principles of operation of a GPS navigator. GPS satellite navigation system - principle, diagram, application Coordinate systems in satellite navigation

Yatsenkov V.S. Sat Nav Basics
Information about the GPS NAVSTAR and GLONASS satellite navigation systems has been systematized. The history of the development and creation of systems is outlined, the basic principles of their operation are considered. The characteristics and structure of navigation signals, data on the technical capabilities and parameters of existing systems are given, definitions of basic concepts and terms are given, and the most educational Internet resources are listed.
For developers and users of navigation systems of various levels of training, from amateurs who use GPS receivers at home to specialists who use navigation aids in everyday work. May be useful for radio engineering students and graduate students.

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My distribution of literature on GEO sciences (Geodesy, Cartography, Land Management, GIS, Remote Sensing, etc.)
Geodesy and Satellite Positioning Systems

• The engineering geodesy: tutorial. In 2 parts. / E. S. Bogomolova, M. Ya. Bryn, V. A. Kougiya, etc.; edited by V. A. Kougiya. - St. Petersburg: St. Petersburg State Transport University, 2006-2008. - 179 p.


• Selikhanovich V.G., Kozlov V.P., Loginova G.P. Workshop on geodesy: Textbook / Ed. Selikhanovich V.G. 2nd ed., stereotypical. - M.: LLC Publishing House "Alliance", 2006. - 382 p.


• Genike A.A., Pobedinsky G.G. Global satellite positioning systems and their applications in geodesy. Ed. 2nd, revised and additional - M.: Kartgeotsentr, 2004. - 355 p.: ill.


• User's Guide for performing work in the 1995 coordinate system (SK-95). GKINP (GNTA)-06-278-04. - M: TsNIIGAiK, 2004. - 89 p.


• Instructions for leveling I, II, III and IV classes. GKINP (GNTA)-03-010-02. - M.: TsNIIGAiK, 2003. - 135 p.


• Khametov T.I. Geodetic support for the design, construction and operation of buildings and structures: Textbook. allowance. - M.: Publishing house ASV, 2002. - 200 p.


• Geodesy: textbook for technical schools / Glinsky S.P., Grechaninova G.I., Danilevich V.M., Gvozdeva V.A., Koshcheev A.I., Morozov B.N. - M.: Kartgeotsentr - Geodezizdat, 1995. - 483 p.: ill.


• Lukyanov V.F., Novak V.E. and etc. Laboratory workshop on engineering geodesy: Textbook for universities. - M.: "Nedra", 1990. - 336 p.


• Novak V.E., Lukyanov V.F. and etc. Engineering Geodesy Course: Textbook for universities, ed. prof. Novak V.E. - M.: "Nedra", 1989. - 432 p.


• Lukyanov V.F., Novak V.E., Ladonnikov V.G. and etc. A textbook on geodetic practice. - M.: “Nedra”, 1986 - 236 pp., ill.


• Sunsets P.S. Course of higher geodesy. - Ed. 4, revised and additional - M.: “Nedra”, 1976. - 511 p.


• Bolshakov V.D., Vasyutinsky I.Yu., Klyushin E.B. and etc. Methods and instruments for high-precision geodetic measurements in construction. / Ed. Bolshakova V.D. - M.: “Nedra”, 1976, - 335 p.


• Surveyor's Handbook (in two books)/ Bolshakov V.D., Levchuk G.P., Bagratuni G.V. and etc.; edited by Bolshakova V.D., Levchuka G.P. Ed. 2, revised and additional - M: "Nedra", 1975. - 1056 p.


• Golubeva Z.S., Kaloshina O.V., Sokolova I.I. Workshop on geodesy. Ed. 3rd, revised - M.: “Kolos”, 1969. - 240 p. from illus. (Textbooks and teaching aids for higher agricultural educational institutions).


• Krasovsky F.N. Selected Works: in 4 volumes. - M.: Geodesizdat, 1953-1956. - 2001 p.


• Krasovsky F.N. Guide to Higher Geodesy: Course of the Geodetic Faculty of the Moscow Land Survey Institute. Part I. - M.: Publication of the Geodetic Administration of V.S.N.H. THE USSR. and Moscow Land Survey Institute, 1926. - 479 p.

Photogrammetry, Topography and Cartography

• Serapinas B.B. Mathematical cartography: Textbook for universities / Balis Balio Serapinas. - M.: Publishing center "Academy", 2005. - 336 p.


• Vereshchaka T.V. Topographic maps: scientific basis of content. - M.: MAIK "Nauka/Interperiodika", 2002. - 319 p.


• Mathematical basis of maps. Chapter III from the book: Berlyant A.M. Cartography: Textbook for universities. - M.: Aspect Press, 2002. - 336 p.


• Instructions for photogrammetric work when creating digital topographic maps and plans. GKINP (GNTA)–02-036-02. - M.: TsNIIGAiK, 2002. - 49 p.


• Yuzhaninov V.S. Cartography with topography basics: Textbook for universities. - M.: Higher School, 2001. - 302 p.


• Tikunov V.S. Modeling in cartography: Textbook. - M.: Moscow State University Publishing House, 1997. - 405 p.


• Urmaev M.S. Space photogrammetry: Textbook for universities. - M.: Nedra, 1989. - 279 p.: ill.


• Compilation and use of soil maps(Edited by A.D. Kashansky, Candidate of Agricultural Sciences). - 2nd ed., revised. and additional - M.: Agropromizdat, 1987. - 273 p.: ill. - (Textbooks and teaching aids for students of higher educational institutions).


• Losyakov N.N., Skvortsov P.A., Kamenetsky A.V. and etc. Topographical drawing: Textbook for universities / Edited by Candidate of Technical Sciences Losyakov N.N. - M.: Nedra, 1986. - 325 p., ill.


• Bilic Yu. S., Vasmut A. S. Design and Mapping: Textbook for universities. - M.: Nedra, 1984. - 364 p.

Land management and Land Cadastre

• Varlamov A.A., Galchenko S.A. Land cadastre (in 6 volumes). Volume 6. Geographic and land information systems. - M.: KolosS, 2006. - 400 p. - (Textbooks and teaching aids for students of higher educational institutions).


• Unified system of technological documentation of the State Land Cadastre of the Russian Federation. System of classifiers for the purposes of maintaining the state land cadastre. State Committee of the Russian Federation on Land Policy. - M.: Goskomzem of Russia, 2000 - 182 p.


• Integrated quality management system for design and survey work. Enterprise standards for the design of graphic materials. - M.: Roszemproekt, 1983 - 86 p. (STP 71.x-82)


• Instructions for interpreting aerial photographs and photo plans at scales of 1:10000 and 1:25000 for the purposes of land management, state land registration and land cadastre. - M.: Ministry of Agriculture of the USSR, State University of Land Use and Land Management, VISKHAGI, 1978. - 143 p.

Geographic Information Systems (GIS)

• Popov I.V., Chikinev M.A. Using ArcObjects Effectively. Methodical manual. - Novosibirsk: Publishing House SB RAS, 2003 - 160 p.


• Geoinformatics / Ivannikov A.D., Kulagin V.P., Tikhonov A.N., Tsvetkov V.Ya. - M.: MAKS Press, 2001. - 349 p.


• Berlyant A.M., Koshkarev A.V. and others. Geoinformatics. Explanatory dictionary of basic terms. - M.: GIS-Association, 1999. - 204 p.


• DeMers Michael N. Geographic Information Systems. Fundamentals: Transl. from English - M: Data+, 1999. - 507 p.


• Zamai S.S., Yakubailik O.E. Software and technologies of geographic information systems: Educational. allowance. - Krasnoyarsk: Krasnoyar. state univ., 1998. - 110 p.


• Korolev Yu.K. General geoinformatics. Part I. Theoretical geoinformatics. Issue 1. - M.: SP LLC Data+, 1998. - 118 p.

Earth remote sensing (ERS)

• Medvedev E.M., Danilin I.M., Melnikov S.R. Laser location of land and forests: Tutorial. - 2nd ed., revised. and additional - M.: Geolidar, Geoscosmos; Krasnoyarsk: Forest Institute named after. V.N. Sukacheva SB RAS, 2007. - 230 p.


• Kashkin V.B., Sukhinin A.I. Remote sensing of the Earth from space. Digital image processing: Tutorial. - M.: Logos, 2001. - 264 p.: ill.


• Garbuk S.V., Gershenzon V.E. Space systems for remote sensing of the Earth. - M.: Publishing house A and B, 1997. - 296 p., ill.


• Vinogradov B.V. Aerospace ecosystem monitoring. - M.: Nauka, 1984. - 320 p.


• Davis S.M., Landgrebe D.A., Phillips T.L. and etc. Remote sensing: a quantitative approach/ Ed. F. Swaina and S. Davis. Per. from English - M.: Nedra, 1983. - 415 p.


• Vostokova E.A., Shevchenko L.A., Sushchenya V.A. and etc. Mapping from satellite images and environmental protection/ Ed. Vostokova E.A., Zlobina L.I. (responsible editor), Kellner Yu.G. - M.: "Nedra", 1982. - 251 p.


• Bogomolov L.A. Interpretation of aerial photographs. - M.: “Nedra”, 1976. - 145 p.


• Miller V., Miller K. Aerial photogeology/ Per. from English Voivode V.M. and Ilyina A.V., ed. Lungershausen G.F. - M.: MIR, 1964. - 292 p., ill.


• Bogomolov L.A. Topographic interpretation of the natural landscape on aerial photographs. - M.: Gosgeoltekhizdat, 1963. - 198 p.

Navigation, Orientation and Positioning

• Naiman V.S. GPS navigators for travelers, motorists, yachtsmen = The best GPS navigators/ Scientifically edited by V.V. Skrylev. - M.: NT Press, 2008. - 400 pp.: ill.


• Yatsenkov V.S. Sat Nav Basics. GPS systems NAVSTAR and GLONASS. - M: Hotline-Telecom, 2005. - 272 p.: ill.


• Gromakov Yu.A., Severin A.V., Shevtsov V.A. Location technologies in GSM and UMTS: Textbook. allowance. - M.: Eco-Trends, 2005. - 144 p.: ill.


• Soloviev Yu.A. Satellite navigation systems. - M.: Eco-Trends, 2000. - 270 p.


• Global satellite radio navigation system GLONASS/ Ed. Kharisova V.N., Perova A.I., Boldina V.A. - M.: IPRZHR, 1998. - 400 p. : ill.


• Shebshaevich V.S., Dmitriev P.P., Ivantsevich I.V. and etc. Networked satellite radio navigation systems/ Ed. Shebshaevich V.S. - 2nd ed., revised. and additional - M.: Radio and Communications, 1993. - 408 p.,: ill.


• Menchukov A.E. In the world of landmarks. Ed. 3, add. - M.: “Thought”, 1966. - 284 p.

- “Saying THANK YOU extends the life of the torrent” (Dark_Ambient )

The idea of ​​​​creating a satellite navigation system was born in the 50s of the last century. American scientists led by Richard Kershner observed the signal emanating from the Soviet satellite and discovered that, due to the Doppler effect, the frequency of the received signal increases as the satellite approaches and decreases as it moves away. Thus, knowing exactly your coordinates on Earth, you can measure the position and speed of the satellite, and vice versa, knowing the position of the satellite, you can determine your own speed and coordinates.

The first steps to create GPS were taken by the Americans in 1964 with the launch of satellites under the Timation program into low-Earth orbit. Initially, GPS was conceived as a military technology, but during the process they decided to use the system for civilian purposes. For this purpose, its accuracy was reduced by a special algorithm. Soviet scientists began work on the domestic GLONASS system in 1976. Initially, it also had only a military purpose.

The navigation system consists of three main segments: space, control and user. The space satellite is represented by 32 satellites for GPS and 28 for GLONASS, rotating in medium Earth orbit. The control segment consists of several monitoring stations and ground antennas that correct data on the location of objects. broadcast a signal from space, and all receivers use this signal to calculate their position in space using coordinates in real time. To do this, the receiver must receive a signal from at least three (and preferably four) satellites.

GPS satellites orbit the Earth in 6 circular orbital paths of 4 satellites each at an altitude of 20,180 km. During a sidereal day they make two complete orbits around the Earth. The orbit of GLONASS satellites, unlike GPS, is located at an altitude of 19,400 km for more accurate use in the northern and southern polar regions.

The satellites continuously send a signal to the entire accessible surface of the planet with information about their location and the time on their own clocks. They do not receive data from any receiving devices. The receiver receives the coordinates of the satellites and information about the time the signals were sent and calculates the distance to each satellite. The program does this by multiplying the speed of light by the difference between the time it receives and the time it sends the signal.

The task is complicated by the fact that the time on the receiving device's clock does not match what the satellites' clocks show. In addition, satellites are subject to the effects of relativistic and gravitational time distortion. At an altitude of 20,000 kilometers, gravity is quite weak, and satellites move at high speed. Because of these effects, the clock must be adjusted by 38 milliseconds per day. If this is not done, then the error in determining coordinates on Earth can be about 10 km!

Having calculated the distance to each of three or four satellites, the receiver analyzes the received data and determines its exact location.

The disadvantages of navigation systems are that under certain conditions the signal from the satellites may not reach the receiver: for example, in a basement or tunnel. Also, the reception level may deteriorate due to heavy clouds and magnetic storms.

GPS satellite navigation has long been a standard for creating positioning systems and is actively used in various trackers and navigators. In Arduino projects, GPS is integrated using various modules that do not require knowledge of theoretical fundamentals. But a real engineer should be interested in understanding the principle and operation of GPS in order to better understand the capabilities and limitations of this technology.

GPS operation scheme

GPS is a satellite navigation system developed by the US Department of Defense that determines precise coordinates and time. Works anywhere on Earth in any weather conditions. GPS consists of three parts - satellites, stations on Earth and signal receivers.

The idea of ​​​​creating a satellite navigation system originated in the 50s of the last century. An American group of scientists observing the launch of Soviet satellites noticed that as the satellite approaches, the frequency of the signal increases and decreases as it moves away. This made it possible to understand that it is possible to measure the position and speed of a satellite knowing its coordinates on Earth, and vice versa. The launch of satellites into low Earth orbit played a huge role in the development of the navigation system. And in 1973, the DNSS (NavStar) program was created, under this program satellites were launched into medium-Earth orbit. The program received its name GPS in the same 1973.

The GPS system is currently used not only in the military field, but also for civilian purposes. There are many areas of application for GPS:

• Mobile connection;
• Plate tectonics - tracking of plate fluctuations;
• Determination of seismic activity;
• Satellite tracking of transport – you can monitor the position, speed of transport and control their movement;
• Geodesy - determining the exact boundaries of land plots;
• Cartography;
• Navigation;
• Games, geotagging and other entertainment areas.

The most important disadvantage of the system can be considered the inability to receive a signal under certain conditions. GPS operating frequencies are in the decimeter wavelength range. This leads to the fact that the signal level may decrease due to high clouds and dense tree foliage. Radio sources, jammers, and in rare cases even magnetic storms can also interfere with normal signal transmission. The accuracy of data determination will deteriorate in the polar regions, since the satellites rise low above the Earth.

Navigation without GPS

The main competitor to GPS is the Russian GLONASS (Global Navigation Satellite System). The system began its full-fledged operation in 2010, and attempts to actively use it have been made since 1995. There are several differences between the two systems:

• Different encodings - Americans use CDMA, for the Russian system FDMA is used;
• Different dimensions of devices - GLONASS uses a more complex model, which increases power consumption and the size of devices;
• The placement and movement of satellites in orbit - the Russian system provides wider coverage of the territory and a more accurate determination of coordinates and time.
• Satellite lifespan – American satellites are made of higher quality, so they last longer.

In addition to GLONASS and GPS, there are other less popular navigation systems - the European Galileo and the Chinese Beidou.

Description of GPS

How GPS works

The GPS system works as follows: the signal receiver measures the delay in signal propagation from the satellite to the receiver. From the received signal, the receiver obtains data about the location of the satellite. To determine the distance from the satellite to the receiver, the signal delay is multiplied by the speed of light.

From a geometric point of view, the operation of the navigation system can be illustrated as follows: several spheres, in the middle of which there are satellites, intersect and the user is in them. The radius of each sphere is correspondingly equal to the distance to this visible satellite. Signals from three satellites provide information about latitude and longitude; the fourth satellite provides information about the height of an object above the surface. The obtained values ​​can be reduced to a system of equations from which the user’s coordinate can be found. Thus, to obtain an accurate location, it is necessary to carry out 4 measurements of distances to the satellite (if we exclude implausible results, three measurements are sufficient).

Amendments to the resulting equations are introduced by the discrepancy between the calculated and actual position of the satellite. The error that arises as a result of this is called ephemeris and ranges from 1 to 5 meters. Interference, atmospheric pressure, humidity, temperature, and the influence of the ionosphere and atmosphere also contribute. The totality of all errors can bring the error to 100 meters. Some errors can be eliminated mathematically.

To reduce all errors, use differential GPS mode. In it, the receiver receives all the necessary corrections to the coordinates from the base station via a radio channel. The final measurement accuracy reaches 1-5 meters. In differential mode, there are 2 methods for correcting the received data - this is the correction of the coordinates themselves and the correction of navigation parameters. The first method is inconvenient to use, since all users must work using the same satellites. In the second case, the complexity of the location determination equipment itself increases significantly.

There is a new class of systems that increases the measurement accuracy to 1 cm. The angle between the directions to the satellites has a huge impact on the accuracy. At a larger angle, the location will be determined with greater accuracy.

Measurement accuracy may be artificially reduced by the US Department of Defense. To do this, a special S/A mode is installed on navigation devices - limited access. The mode was developed for military purposes in order to not give the enemy an advantage in determining the exact coordinates. Since May 2000, the restricted access regime has been abolished.

All error sources can be divided into several groups:

• Error in orbit calculations;
• Receiver related errors;
• Errors associated with multiple reflections of the signal from obstacles;
• Ionosphere, tropospheric signal delays;
• The geometry of the satellites.

Main characteristics

The GPS system includes 24 artificial Earth satellites, a network of ground-based tracking stations and navigation receivers. Observation stations are required to determine and monitor orbital parameters, calculate ballistic characteristics, adjust deviations from motion trajectories, and monitor equipment onboard spacecraft.

Characteristics of GPS navigation systems:

• Number of satellites – 26, 21 main, 5 spare;
• Number of orbital planes – 6;
• Orbit altitude – 20,000 km;
• The service life of the satellites is 7.5 years;
• Operating frequencies – L1=1575.42 MHz; L2=12275.6 MHz, power 50 W and 8 W, respectively;
• Reliability of navigation determination is 95%.

There are several types of navigation receivers - portable, stationary and aircraft. Receivers are also characterized by a number of parameters:

• Number of channels – modern receivers use from 12 to 20 channels;
• Antenna type;
• Availability of cartographic support;
• Display type;
• Additional functions;
• Various technical characteristics - materials, strength, moisture protection, sensitivity, memory capacity and others.

The operating principle of the navigator itself is that first of all the device tries to communicate with the navigation satellite. As soon as the connection is established, the almanac is transmitted, that is, information about the orbits of satellites located within the same navigation system. Communication with one satellite alone is not enough to obtain an accurate position, so the remaining satellites transmit their ephemeris to the navigator, which is necessary to determine deviations, disturbance coefficients and other parameters.

Cold, warm and hot start of GPS navigator

When you turn on the navigator for the first time or after a long break, a long wait begins to receive data. The long waiting time is due to the fact that the almanac and ephemeris are missing or outdated in the navigator’s memory, so the device must perform a number of actions to obtain or update data. The waiting time, or the so-called cold start time, depends on various indicators - the quality of the receiver, the state of the atmosphere, noise, the number of satellites in the visibility zone.

To start working, the navigator must:

• Find a satellite and establish contact with it;
• Receive the almanac and save it in memory;
• Receive ephemeris from the satellite and save it;
• Find three more satellites and establish contact with them, receive ephemeris from them;
• Calculate coordinates using ephemeris and satellite locations.

Only after going through this entire cycle will the device begin to work. This kind of launch is called cold start.

A hot start is significantly different from a cold start. The navigator's memory already contains the currently relevant almanac and ephemeris. Almanac data is valid for 30 days, ephemeris data is valid for 30 minutes. It follows that the device was turned off for a short time. With a hot start, the algorithm will be simpler - the device establishes a connection with the satellite,, if necessary, updates the ephemeris and calculates the location.

There is a warm start - in this case the almanac is current, but the ephemeris needs to be updated. This takes a little more time than a hot start, but significantly less than a cold start.

Restrictions on the purchase and use of homemade GPS modules

Russian legislation requires manufacturers to reduce the accuracy of receiver detection. Working with uncoarsened precision can only be done if the user has a specialized license.

Special technical means intended for secretly obtaining information (STS NPI) are prohibited in the Russian Federation. These include GPS trackers, which are used for secret control over the movement of vehicles and other objects. The main feature of an illegal technical device is its secrecy. Therefore, before purchasing a device, you need to carefully study its characteristics, appearance, for the presence of hidden functions, and also review the necessary certificates of conformity.

It is also important in what form the device is sold. When disassembled, the device may not belong to the STS NPI. But when assembled, the finished device may already be classified as prohibited.

Paper maps of the area have been replaced by electronic maps, navigation on which is carried out using the GPS satellite system. From this article you will learn when satellite navigation appeared, what it is now and what awaits it in the near future.

During World War II, the US and British flotillas had a powerful trump card - the LORAN navigation system using radio beacons. At the end of hostilities, civilian ships of “pro-Western” countries received the technology at their disposal. A decade later, the USSR put into operation its answer - the Chaika navigation system, based on radio beacons, is still in use today.

But land navigation has significant drawbacks: uneven terrain becomes an obstacle, and the influence of the ionosphere negatively affects the signal transmission time. If the distance between the navigation radio beacon and the ship is too large, the error in determining the coordinates can be measured in kilometers, which is unacceptable.

Ground-based radio beacons were replaced by satellite navigation systems for military purposes, the first of which, the American Transit (another name for NAVSAT), was launched in 1964. Six low-orbit satellites ensured coordinate determination accuracy of up to two hundred meters.

In 1976, the USSR launched a similar military navigation system, Cyclone, and three years later, a civilian one called Cicada. The big drawback of early satellite navigation systems was that they could only be used for short periods of an hour. Low-orbit satellites, and even in small numbers, were not able to provide wide signal coverage.

GPS vs. GLONASS

In 1974, the US Army launched into orbit the first satellite of the then new NAVSTAR navigation system, which was later renamed GPS (Global Positioning System). In the mid-1980s, GPS technology was allowed to be used by civilian ships and aircraft, but for a long time they were able to provide much less accurate positioning than military ones. The twenty-fourth GPS satellite, the last required to completely cover the Earth's surface, was launched in 1993.

In 1982, the USSR presented its answer - it was GLONASS (Global Navigation Satellite System) technology. The final 24th GLONASS satellite entered orbit in 1995, but the short service life of the satellites (three to five years) and insufficient funding for the project put the system out of action for almost a decade. It was possible to restore worldwide GLONASS coverage only in 2010.

To avoid such failures, both GPS and GLONASS now use 31 satellites: 24 main and 7 reserve, as they say, just in case. Modern navigation satellites fly at an altitude of about 20 thousand km and manage to circle the Earth twice in a day.

How GPS works

Positioning in the GPS network is carried out by measuring the distance from the receiver to several satellites, the location of which is precisely known at the current moment in time. The distance to the satellite is measured by multiplying the signal delay by the speed of light.
Communication with the first satellite provides information only about the range of possible locations of the receiver. The intersection of two spheres will give a circle, three - two points, and four - the only correct point on the map. Our planet is most often used as one of the spheres, which allows positioning on only three instead of four satellites. In theory, GPS positioning accuracy can reach 2 meters (in practice, the error is much larger).

Each satellite sends a large set of information to the receiver: exact time and its correction, almanac, ephemeris data and ionospheric parameters. An accurate time signal is required to measure the delay between its sending and receiving.

Navigation satellites are equipped with high-precision cesium clocks, while receivers are equipped with much less accurate quartz clocks. Therefore, to check the time, contact is made with an additional (fourth) satellite.

But cesium clocks can also make mistakes, so they are checked against hydrogen clocks placed on the ground. For each satellite, the time correction is individually calculated in the navigation system control center, which is subsequently sent to the receiver along with the exact time.

Another important component of the satellite navigation system is the almanac, which is a table of satellite orbit parameters for the month ahead. The almanac, as well as the time correction, are calculated in the control center.

Satellites also transmit individual ephemeris data, on the basis of which orbital deviations are calculated. And given that the speed of light is not constant anywhere except in vacuum, the signal delay in the ionosphere must be taken into account.

Data transmission in the GPS network is carried out strictly at two frequencies: 1575.42 MHz and 1224.60 MHz. Different satellites broadcast on the same frequency, but use CDMA code division. That is, the satellite signal is just noise, which can only be decoded if you have the appropriate PRN code.

The above approach allows for high noise immunity and the use of a narrow frequency range. However, sometimes GPS receivers still have to search for satellites for a long time, which is caused by a number of reasons.

Firstly, the receiver initially does not know where the satellite is, whether it is moving away or approaching, and what the frequency offset of its signal is. Secondly, contact with a satellite is considered successful only when a complete set of information is received from it. The data transmission speed in the GPS network rarely exceeds 50 bps. And as soon as the signal is interrupted due to radio interference, the search begins again.

The future of satellite navigation

Now GPS and GLONASS are widely used for peaceful purposes and, in fact, are interchangeable. The latest navigation chips support both communication standards and connect to those satellites that are found first.

The American GPS and Russian GLONASS are far from the only satellite navigation systems in the world. For example, China, India and Japan have begun to deploy their own satellite systems called BeiDou, IRNSS and QZSS, respectively, which will operate only within their countries and therefore require a relatively small number of satellites.

But perhaps the greatest interest is in the Galileo project, which is being developed by the European Union and should be launched at full capacity before 2020. Initially, Galileo was conceived as a purely European network, but countries in the Middle East and South America have already expressed their desire to participate in its creation. So, a “third force” may soon appear in the global CLO market. If this system is compatible with existing ones, and most likely it will be, consumers will only benefit - the speed of searching for satellites and positioning accuracy should increase.

Many have heard words such as GPS, GLONASS, GALILEO. Most people know that these concepts mean navigation satellite systems (hereinafter referred to as NSS).

The abbreviation GPS refers to the American NSS NAVSTAR. This system was developed for military purposes, but has also been used to solve civilian problems - positioning for air, land, and sea users.

In the Soviet Union, the development of its own GLONASS NSS was hidden behind a veil of secrecy. After the collapse of the USSR, work in this direction was not carried out for a long time, so NAVSTAR became the only global system that was used to determine location anywhere on the planet. But only the United States has access to another purpose of this system - directing mass destruction at a target. And one more important factor - by decision of the US military department, the “civilian” signal from American navigation satellites and passenger aircraft may be turned off, the ships will lose orientation. This monopoly on the management of the satellite system by the United States does not suit many countries, including Russia. Therefore, many countries Russia, India, Japan, European countries, China, began to develop their own NSS positioning. All systems are dual-use systems - they can transmit two types of signals: for civilian objects and with increased accuracy for military consumers. The basic operating principle of the navigation system is complete autonomy: the system does not receive any signals from users (unsolicited) and has a high degree of noise immunity and reliability.

The creation and operation of any NSS is a very complex and expensive process, which, due to its military nature, should belong only to the state of the developing country, since it is a strategic type of weapon. In the event of an armed conflict, satellite navigation technology can be used not only for aiming weapons, but also for landing cargo, supporting the movement of military units, carrying out sabotage and reconnaissance operations, which will give a significant advantage to a country that has its own satellite positioning technology.

The Russian GLONASS system uses the same position determination principle as the American system. In October 1982, the first GLONASS satellite entered Earth orbit, but the system was put into operation only in 1993. The satellites of the Russian system continuously emit signals of standard accuracy (ST) - in the range of 1.6 GHz and high accuracy (HT) - in the range of 1.2 GHz. Reception of the CT signal is available to any user of the system and provides determination of horizontal and vertical coordinates, velocity vector, and time. For example, to accurately indicate coordinates and time, it is necessary to receive and process information from at least four satellites of the GLONASS system. The entire GLONASS system consists of twenty-four satellites located in circular orbits at an altitude of about 19,100 km. The revolution period of each of them is 11 hours and 15 minutes. All satellites are located in three orbital planes - each with 8 devices. The configuration of their placement provides global navigation field coverage not only of the earth's surface, but also of the near-Earth space. The GLONASS system includes a Control Center and a network of measurement and control stations, which are located throughout Russia. Each consumer receiving a navigation signal from GLOGASS satellites must have a navigation receiver and processing equipment that allows it to calculate its own coordinates, time and speed.

Currently, the GLONASS system does not provide 100% access to its services for users, but it assumes the presence of three satellites on the visible horizon of Russia, which, according to experts, makes it possible for users to calculate their location. Currently there are GLONASS-M satellites in Earth orbit, but after 2015 it is planned to replace them with a new generation of devices - GLONASS-K. The new satellite will have improved performance (the warranty period has been extended, a third frequency will appear for civilian consumers, etc.), the device will be two times lighter - 850 kg instead of 1415 kg. Also, to maintain the functionality of the entire system, only one group launch of GLONASS-K per year will be required, which will significantly reduce overall costs. To implement the GLONASS system and ensure its financing, the equipment of this navigation system is installed on all vehicles put into operation: aircraft, ships, ground transport, etc. Another main purpose of the GLONASS system is to ensure the country's national security. However, according to experts, the future of the Russian navigation system is not cloudless.

The Galileo system is being created with the goal of providing European consumers with an independent navigation system - independent, first of all, from the United States. The financial source of this program is about 10 billion euros per year and is financed one third from the budget and two thirds from private companies. The Galileo system includes 30 satellites and ground segments. Initially, China, along with other 28 states, joined the GALILEO program. Russia conducted negotiations on the interaction of the Russian navigation system with the European GALILEO. In addition to European countries, Argentina, Malaysia, Australia, Japan and Mexico have joined the GALILEO program. It is planned that GALILEO will transmit ten types of signals to provide the following types of services: determining location with an accuracy of 1 to 9 meters, providing information to rescue services of all types of transport, providing services to government services, ambulances, firefighters, police, military specialists and services, ensuring the livelihoods of the population. Another important detail is that the GALILEO program will create about 150 thousand jobs.

In 2006, India also decided to create its own navigation system, IRNSS. The program budget is about 15 billion rupees. It is planned to launch seven satellites into geosynchronous orbits. Work on the deployment of the Indian system is being carried out by the state company ISRO. All system hardware will be developed only by Indian companies.

China, wanting to take a leading position on the geopolitical map of the world, has developed its own Beidou satellite navigation system. In September 2012, two satellites included in this system were successfully launched from the Sichan Cosmodrome. They joined the list of 15 spacecraft launched by Chinese specialists into low-Earth orbit as part of the creation of a full-fledged satellite navigation system.

The implementation of the program began by Chinese developers back in 2000 with the launch of two satellites. Already in 2011, there were 11 satellites in orbit, and the system entered the experimental operation stage.

The deployment of its own navigation satellite system will allow China not to depend on the world's largest systems, the American (GPS) and Russian (GLONASS). This will increase the efficiency of Chinese industries, especially those related to telecommunications.

It is planned that by 2020, the Chinese NSS will use about 35 satellites, and then the Beidou system will be able to control the entire globe. The Chinese NSS provides the following types of services: location determination with an accuracy of up to 10 m, speed up to 0.2 m/s and time up to 50 ns. A special circle of users will have access to more accurate measurement parameters. China is ready to cooperate with other countries in the development and operation of satellite navigation. The Chinese Beidou system is fully compatible with the European Galileo, Russian GLONASS and American GPS.

Beidou is effectively used in weather forecasting, disaster prevention, land, air and sea transportation, as well as geological exploration.

China plans to continuously improve its satellite navigation system. An increase in the number of satellites will expand the service area of ​​the entire Asia-Pacific region.

Materials used:
http://www.odnako.org/blogs/show_20803/
http://www.masters.donntu.edu.ua/2004/ggeo/mikhedov/diss/libruary/mark.htm
http://overseer.com.ua/about_glonass.html
http://4pda.ru/2010/03/16/21851/
http://expert.com.ua/57706-galileo-%D0%BE%D0%B1%D0%BE%D0%B9%D0%B4%D1%91%D1%82%D1%81%D1%8F -%D0%B5%D0%B2%D1%80%D0%BE%D1%81%D0%BE%D1%8E%D0%B7%D1%83-%D0%BD%D0%B0%D0%BC %D0%BD%D0%BE%D0%B3%D0%BE-%D0%B4%D0%BE%D1%80%D0%BE%D0%B6%D0%B5.html