Global navigation satellite systems. Navigation measurements in multichannel NAP. Determination of consumer coordinates

Alexey Mikhailov, head of the sector of the Federal State Institution Research Center "Protection"

Recently, there has been an increased use of global navigation systems to determine the coordinates of both stationary and moving objects of protection.

Stay away from use modern achievements technology and private security. The security departments have long been operating such navigation and monitoring systems as Almaz (LLC Kodos-B, Moscow), Argo-Guard (CJSC Navigation Systems, Omsk), Arkan CJSC "BaltAvtoPoisk", St. Petersburg, "Inflow of GPS" LLC ("Security Bureau Socrates", Irkutsk).

Also in this case, the satellites use two frequency bands, of which the second was originally intended only for high-precision military use. At this point, we can finally leave Earth's orbit and return to our smartphones to see what happens when we use an app that requires position knowledge.

However, if "high accuracy" is required, the device must necessarily resort to satellite positioning. This "last component" actually consists of speaker system, which can only resonate in a narrow frequency band.

Piezoelectric crystals inserted into these elements then convert electrical signal into sound waves, which, if they are in resonance, are amplified and returned to electricity. Of course, waves that are out of resonance are suppressed by the system.

These and many other navigation systems are based on a GPS receiver (the Arkan navigation system can also use the traditional direction-finding method for determining the location of an object), therefore, employees using these systems in their work need to have a general idea of the principles GPS operation and clearly know what can be required from such systems, and what should not be expected from them.

This requires a very robust oscillator to provide fast signal correction.

The speed of this process can be increased by using assisted positioning, which, using information sent over the cellular network, allows the receiving module to approximately know the list of satellites in the field of view and their position, which will significantly reduce the time of the first fix.

World satellite navigation, as you understand, moves very slowly and is subject to the presence of great constellations launched into orbit by the largest and richest states. This means, on the one hand, that no company can make important technological steps in the race to accuracy, and on the other hand, that the plans for the future of this component have long been known.

Understanding the principles of operation of navigation systems and their proper operation is the key to successful work.

Behind the mysterious abbreviation GPS is the Global Positioning System - a global positioning system. Initially, the project was created and used by the US military as a means to determine real-time coordinates anywhere in the world and was called Navstar (Navigation system with timing and ranging - navigation system for determining time and range), while the abbreviation GPS appeared later.

Integrity messages will be present to avoid position errors, and an increase in baud rate will allow global or local transmission of safety messages, weather, map updates, and traffic readings.

However, it is an important element that will further increase the redundancy and accuracy of satellite positioning systems.

How GPS works

The operation of any navigation system is based on the principle of triangulation, i.e. determining the location of an object by range up to three known points in space.

For simplicity, we will assume that we have three fixed satellites, and we know their coordinates with high accuracy, then, by analyzing the propagation time of the radio signal synchronously emitted from them, we will determine our coordinates in three-dimensional space. The range to the target, analyzing the time of arrival of the reflected radio signal from the object, was determined in radar at the beginning of the 20th century, and the same principle is used in satellite navigation systems.

The European team that patented it is in the final award of the European Patent Office. Currently, 4 billion instruments use information from the global navigation satellite system. This growth is due to the growing success of new applications that go beyond simple positioning and navigation.

The winners of the 12th edition of the award, established by the European Patent Office, will be announced during a ceremony in Venice on 15 June. Unlike its predecessors, the constellation of Galileo has no roots in the military world, and most of its services are aimed at civilian use.

Unfortunately, this is where the similarities between traditional and satellite systems for determining the location of objects end. In real life, satellites move with great speed in their orbits at an altitude of about 20 thousand km. Therefore, on Earth, we do not know the time of synchronous radiation from satellites and their coordinates.

To resolve these contradictions, the developers decided to install on board satellites atomic clock. They are extremely accurate and expensive. They cost about $100,000 and each satellite has 4 of them to ensure reliable performance. Thus, the problem of synchronization (the issue of simultaneous emission of a radio signal) from satellites was solved.

It will also offer a global search and rescue feature that will enable medical and rescue services to better locate people in need and provide them with faster assistance. Recent advances in automated technology and trends in the world of applications offering geo-localized services indicate the direction in which navigation technologies and satellite positioning.

Greater positioning accuracy is required to meet these growing demands. This, in turn, implies new ways of transmitting the used radio signal. The task of finding a solution was entrusted to a team that included Lestarquit and Avila Rodriguez, along with German teacher Günter Hein, French-Belgian engineer Lionel Rice, and a French space agency team led by Jean-Luc Iscler.

The issue of determining the location of a satellite in orbit is solved by transmitting data on their orbits from ground tracking stations to the control center, where the refined elements of the trajectories are calculated. These parameters are entered in the almanac and transmitted to the satellites, which, in turn, send this information to all operating receivers. To control the orbits and coordinates of the satellites, there are four ground tracking stations,

This signal is generated by composing two subsets, a narrow band, quite easy to use on modern systems reception and a wider bandwidth dedicated to the next generations of high-tech technologies. This concept gives a lot of flexibility, notes Avila Rodriguez, receiver manufacturers can decide whether to use only part of the signal or use it all to get very high position accuracy.

At the same time, Lestarquit posed the problem of improving accuracy by reducing the consumption of precious energy needed to transmit a signal from a satellite. He then developed a modulation method known as alternative binary shift carrier, which incorporates the four types of signals into a more complex signal.

communications systems and control center controlled by the US Department of Defense. Taking into account the fact that a flight at an altitude of 20 thousand km takes place in an airless space, it is described with high accuracy by mathematical dependencies. Taking into account all of the above, the problem of determining the location of the satellite in orbit was solved.

And older receivers can use one of the signals to locate a point with an accuracy of less than one meter. Global Navigation Satellite System global system positioning. It is a system that allows users to find the global coverage of satellites on Earth. Users of this service use small electronic radio receivers to calculate their position with an accuracy of tens to meters. Accuracy in specialty or scientific applications can range from a few centimeters to millimeters.

The name of the default measurement principle state of the satellite discharging the number of satellites polar track promotion oblique number of polar bands orbit height of the period of revolution scheduled in the transit Doppler service. The measured value is the signal transmission time from satellite dish To receiving antenna. The measured time is converted into a distance based on the speed of signal propagation. Time measurements use atomic clocks to determine the so-called atomic time from atomic frequencies, that is, completely independent of the rotation of the Earth.

It remains to solve the problem of determining the exact time in the terrestrial GPS receiver- signal. The fact is that our clock in the GPS signal receiver has a huge error in measuring time compared to the speed of propagation of the radio signal in space.

To solve this problem, the signal from the fourth satellite is used. Consider Fig. 1.

As a rule, there are two main ways of obtaining time: the movement of the Earth and the frequency of atoms. Positioning For 3D coordinates at least 4 satellites are required. Space segment - satellite system. Control segment: - control station, the control segment controls the space segment, controls satellites, maneuvers and maintains atomic clocks. User segment - a user with a device, the receiver consists of an antenna, a radio frequency unit, a microprocessor, a communication unit, memory and a voltage source.

If the distance A to one satellite is known, then the coordinates of the receiver cannot be determined (it can be located at any point of the sphere with radius A, described around the satellite). Let the distance B of the receiver from the second satellite be known. In this case, the determination of the coordinates is also not possible - the object is somewhere on a circle (shown in blue in Fig. 1), which is the intersection of two spheres. The distance C to the third satellite reduces the uncertainty in the coordinates to two points (indicated by two bold blue dots in Fig. 1). This is already enough to unambiguously determine the coordinates - the fact is that of the two possible locations of the receiver, only one is located on the surface of the Earth (or in close proximity to it), and the second, false, turns out to be either deep inside the Earth or very high above it. surface. Thus, theoretically, for three-dimensional navigation, it is enough to know the distances from the receiver to three satellites, however, it is necessary to correct the time in the GPS receiver, therefore, having received a signal from four (or more) satellites (circle data are not shown in the figure so as not to clutter the figure), the receiver looks for the intersection point of the corresponding spheres. If there is no such point, the receiver processor begins to correct its clock by successive approximations until it achieves the intersection of all spheres at one point.

Air, ship, cartography, time, measurement, space, navigation, travel, according to received signals: code, phase according to the number of received satellites: one or more channels according to accuracy. Road transport - vehicle position monitoring - monitoring of individual components of the rescue system in the context of crisis management - navigation driver intelligent transport systems transport network employment rail transport train position monitoring water transport - vessel navigation air transport - perspective.

Most important:

1. To determine the coordinates of an object, the GPS must “see” at least four satellites.

2. The more satellites the receiver “saw”, the more accurately it determines its coordinates.

Accuracy of determining coordinates in the GPS system

The indisputable advantage of GPS is the high accuracy of determining coordinates, regardless of the location of the monitoring object on the ground. The fact is that to ensure global action, 24 satellites are constantly in orbit, located in orbits with different declinations and theoretically ensuring their visibility anywhere in the world. To solve this problem, it is enough to have 18 satellites in orbit, but it was decided to use 24 - to improve the accuracy of determining the coordinates of the satellites themselves.

Coordinate distribution of fair action units. Archaeologists identify new discoveries, botanists bring valuable plant communities to phytogeographic maps, ethologists study animal migration routes. One of the main ideas of geocaching is to place caches in places that are interesting and not yet visited by tourists. The cache describes the site with its features and curiosities. Caches are also located in places of interest to the most visited.

Military space satellite system operated by the United States Department of Defense. During the Gulf War, a temporary man-made artificial import error was allowed to prevent the misuse of ballistic missiles.

The accuracy of determining coordinates in a GPS system depends on many parameters that depend both on physical parameters (in particular, on the signal-to-noise ratio in the received signal, see below) and on the position of the system owner (USA). In the GPS system, there is a mode of selective access (SA - selective availability) - an error artificially introduced into satellite signals for the inaccurate operation of civilian GPS receivers, which the United States carried out during Operation Desert Storm in Iraq. On fig. Figure 2 shows a graph for determining the error in the selective error mode and without it.

User segment software devices. These restrictions are based on the prevention of possible misuse as a space orientation system in weapons similar to ballistic missiles or flat earth missiles. The system should consist of 30 active satellites circling at an altitude of approximately 23,000 kilometers above the earth's surface, at an inclination of 56° to the Earth's equator in three planes shifted by 60° to each other. Each track will have 9 satellite positions and 1 position as backup so that the system can be quickly added completely when the satellite is down.

The accuracy of determining the coordinates also depends on:

From the state of the atmosphere and ionosphere, since the speed of propagation of the electromagnetic field is constant only in vacuum, and any propagation medium introduces a change in the speed of propagation of the radio signal;
From the "multipath" propagation of the radio signal;
From the relative position of the satellites in the sky, the so-called "GDOP" (Geometric Dilution of Accuracy Factor);
From mathematical processing on board the satellite and much more.

In view of the foregoing, the GPS receiver may completely stop determining its location near nearby high-rise buildings (the so-called city wells), in a dense spruce forest, and of course, inside a permanent structure or a metal garage or hangar.

The trajectories are shifted 120° to each other and there are eight 45° symmetrical satellites for the satellites, all of which are at full functionality - a state in which at least 24 satellites are fully functional, supporting new technologies.

It receives the signal from the satellites and calculates the adjustments to the settings they send. Chapter 2: Positioning page 8 Satellites transmit information about their position and transmission time. The receiver calculates its position as a fraction of the propagation speed of the radio waves and the time elapsed between transmitting data from the satellite and receiving the signal.

Some private security firms claim that it is possible to protect the life and health of citizens from attack using a GPS receiver. cell phone, however, these users need to remember that it is impossible to determine the location of a person using GPS inside a building, in an entrance, in transport (ie, where attacks most often occur).

The reference station focuses its position and provides information on rover errors. Most new receivers can work with the system. Both provide 95% of measurements with a horizontal error of less than 3 meters. Communication with cards. server via mobile data.

Prague, headquarters of the European Agency for the Global Navigation Satellite System. On Friday and Saturday, the European Agency for the Global Navigation Satellite System will be inaugurated in Holesovice. All fans of space and space technology are invited to the Open Day. As organized by the organizers of the event, children and adults will come into their own hands.

The real accuracy of determining coordinates in the GPS system in Russian conditions is 10-25 m. Naturally, this accuracy is not the maximum achievable for the GPS system, using differential methods of determining the accuracy can reach 10 cm or less, but we must talk about those systems which are actually used in security departments.

Most important:

GPS navigation systems are characterized by high accuracy of determining coordinates (about 10-25 m), regardless of the distance of the security object from the ARC and the time of movement of the object.
The accuracy of determining the coordinates can be reduced by the owner of the system (USA) up to the complete impossibility of determining the coordinates.
The GPS receiver can completely stop determining its location near nearby high-rise buildings (the so-called city wells), in a dense spruce forest, and of course inside a capital building, a metal garage or a hangar.

GPS system noise immunity

Interference immunity of the GPS-system, from the point of view of their use in security systems. The fact is that the satellite transmitter power is limited to 50 watts for the L1 radiation range and 8 watts for the L2 radiation range, and the satellite suspension height is about 20 thousand km.

Therefore, it is not difficult to understand how meager the flux density electromagnetic radiation comes to the GPS antenna. A simple geometric calculation shows that with a transmitter antenna pattern width of 2º and a satellite height above the Earth's surface of 20,000 km

the flow of electromagnetic radiation falls on a circle with a diameter of 700 km. This provision slightly saves the gigahertz range of radiation (with increasing operating frequency the noise level in the medium drops), but at the same time, a restriction is imposed on the electromagnetic wave around the obstacle. The propagation of an electromagnetic wave in this range occurs almost rectilinearly.

The next point that is often overlooked is that the GPS receiver determines its coordinates at its location, and information about the coordinates must be transmitted to the ARC. As a rule, networks are used for this cellular communication or VHF radio channel with all the ensuing consequences.

Cellular networks are easily suppressed, the user is completely dependent on the quality of services provided cellular company, which by and large is not responsible for the speed of delivery of the notice, the reliability of communication and the long-term nature of its obligations to the client. However, a large coverage area, low cost of equipment (but not the cost of regular transmission of object coordinates) is an attractive feature of such a solution.

The VHF radio channel is a more reliable communication channel compared to cellular networks, does not require an intermediary for transmitting coordinates between the object of protection and the CSS, but is characterized by a much smaller coverage area and the need to have its own frequency resource, which is not always easy to implement. In this case, there is no need to pay for the exchange traffic between the guarded object and the ARC.

Most important:

The user must clearly understand all the pitfalls associated with the use of GPS monitoring systems, and competently draw up contracts for services provided to the client, which must take into account force majeure circumstances.

GPS or Glonass

If GPS is global positional system manufactured in the USA, then GLONASS (GLOBAL NAVIGATION Sputnik System) produced by the USSR - Russia. In blessed times, the USSR had a full-fledged satellite navigation system, identical in characteristics to the US positioning system, which was used mainly for military purposes.

Then, during the years of perestroika, most of the satellites of the GLONASS system “hit” or failed, and in the worst years, instead of 24 satellites, only 7 satellites were in orbit. In 2006, there are 16 satellites in orbit, of which only 9 are working or will be working in the near future (since some of the satellites are at the stage of full exhaustion of their resource).

At the beginning of the development of satellite navigation for civil use in Russia, navigation receivers were introduced to the market that allow receiving both GPS and GLONASS signals, which is undoubtedly correct, since the number of satellites potentially available for reception is doubling. This, in turn, allows you to increase the probability of positioning and the accuracy of coordinates.

However, due to the actual death of the GLONASS system at the end of the 90s, only GPS receivers are present on the free market in Russia. But not everything is as bad as it seems.

Russian President Vladimir Putin identified as a priority national program for the revival of the GLONASS navigation system, and in 2007 it is planned to have 18 operating satellites in orbit, and by 2010 - 24 satellites, which will eliminate dependence in such important issue, as a global determination of coordinates (primarily for civil and departmental use *), from the will of the United States.

(*The reader may get the impression that the Russian military is currently unable to determine its coordinates. This is not entirely true, military navigation always uses redundant systems, for example, navigation systems based on the use of radio beacons, mechanical gyroscopes, ring laser gyroscopes, systems that register changes in the Earth's magnetic field, or other principles unknown to the author. However, all these systems are characterized by a high price, a much lower accuracy of position determination (perhaps, with the exception of systems based on ring laser gyroscopes), and a tendency for the accuracy of position determination to depend on the time of the object's movement (error accumulation effect).

Based on the foregoing, the level of navigation by these means is limited to the level aircraft(airplane, helicopter), and the use of a satellite navigation system allows you to track the location at a relatively small material cost of a huge number of objects, up to the position of an individual soldier for more than a battle, which is being implemented in the United States (the creation of the so-called "computer" divisions, the United States has already created two such divisions).

Most important:

At present, GPS receivers dominate the domestic market.
The developer of navigation systems, as well as the user, needs to think about the joint use of GPS and GLONASS systems in the near future.
As a complete orbital constellation it is necessary to switch to the GLONASS system (however, it will actually be possible to do this with the cost of the GLONASS receiver equal to or less than the GPS system, with approximately equal technical specifications receivers of both systems).

It is not a pity to spend the money of the stabilization fund of Russia on the creation of a truly competitive domestic global navigation system, although this is no longer the topic of this article.

Conclusions:

The global navigation system is one of the recent achievements of modern engineering thought and should be actively used in the practice of the work of the OBO.
The global navigation system is not a panacea for all ills.
An economically unjustified, technically unjustified application without taking into account the specifics of the navigation system can lead to a complete discredit of this direction in the eyes of the consumer.

The article was prepared jointly with the editors of the magazine "Protection"

Today, there are several navigation systems in the world that use artificial satellites Earth. But there are only two truly global positioning services in almost any place on our planet: the Russian GLONASS and the American GPS.

Global positioning system GPS

American GPS Positioning System functionality similar Russian system GLONASS. Its main purpose is a high-precision determination of the consumer's coordinates, the components of the velocity vector and binding to the system time scale.

Similar to the domestic GPS system developed for and under the control of the US Department of Defense. Like the GLONASS system, GPS consists of space segment, ground command and measuring complex and consumer segment.

Satellite navigation system Galileo

Within the next few years, the European Union (EU) and the European Space Agency (ESA) are planning to commission a new European global satellite navigation system, Galileo (“Galileo”). The existence of a second fully operational GNSS satellite system promises significant benefits for civilian users around the world. The successful launch of the Galileo project will more than double the number of working navigation satellites, available to users. Such an increase in the number of satellites will bring benefits not only when working in offline, but will also improve the quality of positioning and the ability of GPS equipment to resolve carrier-phase ambiguity for the tracked satellite signal.

Comparative characteristics

Indian Satellite Regional Navigation System

The Government of India approved on May 9, 2006, the deployment project of the Indian Satellite Regional System Navigation (IRNSS) with a budget of Rs 14.2 billion over the next 6-7 years. The IRNSS satellite constellation will consist of seven satellites in geosynchronous orbits. All seven satellites will have continuous radio visibility with Indian control stations.

The ground segment of the IRNSS will have a monitoring station, a redundancy station, a control and management station onboard systems. The state-owned company ISRO is responsible for the deployment of the IRNSS, which will be entirely under the control of the Indian government. Navigation receivers that will receive IRNSS signals will also be developed and produced by Indian companies.

Chinese Navigation Satellite System Compass

China being the fastest developing country in the world, also started building its own Compass satellite navigation system.

The space segment of the Compass satellite navigation system will be formed from 5 satellites in Geostationary Orbit (GSO) and 30 satellites in medium earth orbit.

Two types of services will be provided. For general use, a signal will be transmitted, the processing of which will achieve a positioning accuracy of 10 m, a speed of 0.2 m / s and determining the current time with an accuracy of 50 ns.

A limited circle of users will be able to measure with greater accuracy.

China is willing to work with other countries to develop satellite navigation to enable Compass to interoperate with other global navigation systems.

Japanese Quasi-Zenith Navigation System (QZSS)

The Japanese QZSS was originally conceived in 2002 as commercial system with a set of services for mobile communication, broadcasting and widespread use for navigation in Japan and neighboring areas of Southeast Asia. The first satellite launch for QZSS was planned for 2008. In March 2006, the Japanese government announced that the first satellite would not be intended for commercial use and would be launched entirely on budgetary funds to work out the decisions made in the interests of ensuring the solution of navigation problems. Only after the successful completion of the tests of the first satellite, the second stage will begin and the following satellites will fully provide the previously planned volume of services.