How does a GPS work in a phone? What is A-GPS and what is its use?

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Navigation today is a simple, necessary and incredibly popular service. Not only are navigators almost the most popular product on mobile market(only the ubiquitous phones are ahead of them), and over the past couple of years, many smartphones have acquired their own GPS and A-GPS chips - and users are so accustomed to this that a “smartphone without navigation” now causes them, at least, surprise. All this, of course, is very pleasing (progress! civilization!), but there is only one problem: manufacturers are trying so hard to sell their goods that they often wishful thinking, luring buyers not with the specifications of their goods, but with big words on the boxes. We will tell you what these words mean and what navigation actually is like in this article.

Technology: how does it work?

Today, there are essentially only two technologies that allow users mobile technology Don't get lost in the concrete jungle: satellite and cellular navigation. The first is GPS itself, a global satellite positioning system invented by American scientists for the American military, and then presented to the rest of the world for Thanksgiving. The second is AGPS (not to be confused with A-GPS), technology cellular communications, allowing you to determine your approximate location (with an accuracy of 500 meters) if you are in the coverage area cellular network.

GPS is good, first of all, because it is accurate (it determines your position to within five meters) and absolutely free (good Americans allow everyone to use their satellites). Of course, you will have to pay for specific navigation programs and maps - but this payment will be a one-time fee, and no subscription to GPS services exists in nature. It's too bad GPS themes that it only works outdoors, and mainly in clear weather - if the sky is cloudy, it is quite difficult to find the number of satellites required for operation. In order to deal with clouds, a special A-GPS (Assisted GPS) technology was invented: with this technology, instead of sending signals to the skies, the navigator simply connected to a certain server, where it downloaded information about the location of satellites, and, using these coordinates, found them much faster. Today A-GPS is an indispensable companion to any GPS receiver in a car navigator. The most popular maps that work with the GPS service: iGo, Avtosputnik, Navitel, Be-On-Road.

The cellular system AGPS (Alternative Global Position System) gives, of course, a much less accurate determination of the position of an object on the map, but it does not depend at all on the weather and the depth of the building. The main thing is that your smartphone can catch the network, your number is connected GPRS service, and there was still money left in your account. The principle of operation of AGPS is similar to the principle of operation of a satellite navigation system: the smartphone receives signals from several (at least three) base stations and, based on the signal strength of each of them and taking into account their location, calculates your coordinates. Cheap and cheerful: you, of course, won’t be able to get anywhere with AGPS, but you definitely won’t get lost on the map. The most popular cards that work with the AGPS service: Google Maps, "Yandex maps".

Devices: what happens?

The simplest GPS navigation device that exists in nature is an external GPS receiver. By itself, it only communicates with satellites, and, in fact, does not provide any navigation. But you can connect it to almost any device - laptop, PDA, phone or smartphone - and then, if you have the right software, you will be able to navigate in space and get directions to your destination. Receivers are especially useful for tourists who prefer narrow mountain or forest paths to well-trodden roads: receivers, unlike most other devices, are not tied to a map, and if you really want to, they can even guide you along scanned graph paper with a navigation grid superimposed on it. If, of course, you find one for the region you need.

The most popular navigation device today is car GPS navigator. It's essentially a small computer with touch screen, running on a closed operating system. The navigator already has a navigation program installed by the manufacturer, which usually cannot be changed without violating licenses. In addition to navigation itself, car navigators can often do many other things: play music, show movies, work with e-books and images, and even connect to the Internet.

IN Lately appeared on the market new class devices – smartphones with a built-in GPS receiver. On the one hand, these devices are extremely convenient: they can make calls, tell you the way, and do a lot of other things. On the other hand, the software component of such devices is still very weak: mainly in quality navigation programs“online solutions” like Nokia Maps or Google Maps are used, to work with which you need permanent connection to the Internet (although some smartphones can also have real navigation software). And such smartphones are more suitable for pedestrians than for car navigation– their screen is small, the map is hard to see, and with the maps of our vast homeland, everything is bad, to put it mildly. You can only travel around the city.

The latest type of navigation devices are smartphones with cellular navigation (AGPS). They do not have a built-in GPS chip. They are suitable only for those who do not want to carry a paper map with them - they do not provide route guidance or even an accurate determination of your location. But they do a great job of helping you orient yourself in space during long trip or find some particularly inconspicuous alley that none of the passers-by you interviewed had heard of.

Unfortunately, there is no ideal map in nature (if only because everyone has their own idea of the ideal), so first you have to understand why you need a navigator in principle and what you will do with it: one type is suitable for hiking trips devices and maps, for car navigation – another, for pedestrian navigation – a third. In addition, you need to pay attention to the cartographic database itself: the nicest-looking program may suddenly not have a map of your city, and the most “urban” of the maps will show you blank spots just beyond the ring road. In general, no matter how you look at it, you still have to devote some time to the selection process. You can read about how to choose a map for your navigator in the article “What types of navigation maps are there?”

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GPS technology is used not only by car enthusiasts and taxi drivers. It is also popular among outdoor enthusiasts, fishermen and just people driving active image life and constantly walking/driving back and forth. If someone needs to know where he is, where the location he needs is located, how fast he is moving and how soon he will reach his goal, GPS will come to the rescue.

The reason for the widespread popularity of this technology lies in the following:

coverage area covers the entire Earth;
the technology is used not only in expensive secure GPS trackers, but also in relatively cheap GPS navigators for cars and even in smartphones;
There is no need to pay for using GPS.

About the history of GPS and navigation satellites

The Americans came up with the idea of creating a satellite navigation system back in the 1950s, when the first artificial satellite Earth. In 1973, the DNSS program was launched, which was later renamed Navstar-GPS, and then simply GPS. The first satellite (test) was launched into orbit in 1974.

After the first Soviet navigation satellite GLONASS (Global Navigation Satellite System) was launched into orbit in 1982, the US Congress allocated funds to the US military to speed up the work. The first working GPS satellite was launched in February 1978, and the system began to operate at full capacity at the end of 1993, when all 24 satellites took their places in Earth orbit.

Each navigation satellite weighs about 900-1000 kg, and reaches 5 meters in length with deployed solar panels. Average term satellite service life - 10 years. After this period, a new satellite is launched to replace the exhausted satellite.

About GPS receivers

The speed of calculating coordinates when the receiver is turned on, its sensitivity and positioning accuracy are determined by the chipset with which it is equipped. Chipsets for GPS devices are made by several manufacturers, but the most common is SiRFstarIII from SiRf Technology.

Receivers with the SiRfstarIII chipset have a short cold start time (a few seconds) and can simultaneously receive signals from 20 satellites. They are very sensitive and allow you to determine coordinates with high accuracy.

What is the difference between GPS and A-GPS

The list of characteristics of some smartphones indicates the presence of a GPS module, others - A-GPS. How are these modules different?

During a cold start (when the navigation system has not been used for a long time), a device with a conventional GPS receiver can search for satellites for a long time - the waiting time sometimes reaches 10 minutes or more. This is because the GPS receiver searches for satellites without knowing their location.

At using A-GPS the device immediately receives the part necessary information using a GPRS/3G network (traffic no more than 10 KB). Thus, A-GPS is a software add-on over the GPS receiver, which significantly reduces the time it takes to search for satellites during a cold start. In addition, this add-on allows you to increase the accuracy of location in areas with weak signal from satellites.

However, A-GPS has one small disadvantage. Unlike GPS, which is completely free to use, A-GPS must be paid according to the tariff set by your provider, since it consumes Internet traffic (however small).

As often happens with high-tech projects, the military initiated the development and implementation of the GPS (Global Positioning System) system. The project of a satellite network for determining coordinates in real time anywhere in the world was called Navstar (Navigation system with timing and ranging - navigation system determination of time and range), while the abbreviation GPS appeared later, when the system began to be used not only for defense, but also for civilian purposes.

The first steps to deploy a navigation network were taken in the mid-seventies, and commercial operation of the system in its current form began in 1995. IN currently There are 28 satellites in operation, evenly distributed in orbits with an altitude of 20,350 km (24 satellites are sufficient for full functionality).

Looking ahead a little, I will say that a truly key moment in the history of GPS was the decision of the US President to abolish the so-called selective access (SA - selective availability) regime on May 1, 2000 - an error artificially introduced into satellite signals for inaccurate operation of civilian GPS receivers . From now on, the amateur terminal can determine coordinates with an accuracy of several meters (previously the error was tens of meters)! Fig. 1 shows errors in navigation before and after disabling the selective access mode (data). Fig. 1.

Let’s try to understand in general terms how the global positioning system works, and then we’ll touch on a number of user aspects. Let's begin our consideration with the principle of determining range, which underlies the operation of the space navigation system.

Algorithm for measuring the distance from the observation point to the satellite.

Ranging is based on calculating the distance from the time delay of radio signal propagation from the satellite to the receiver. If you know the propagation time of a radio signal, then the path it travels can be easily calculated by simply multiplying the time by the speed of light.

Each GPS satellite continuously generates radio waves of two frequencies - L1=1575.42 MHz and L2=1227.60 MHz. The transmitter power is 50 and 8 Watts, respectively. The navigation signal is a phase-shifted pseudo-random code PRN (Pseudo Random Number code). There are two types of PRN: the first, C/A code (Coarse Acquisition code) is used in civilian receivers, the second P code (Precision code) is used for military purposes, and also, sometimes, for solving problems geodesy and cartography. The L1 frequency is modulated by both C/A and P-code, the L2 frequency exists only for transmitting the P-code. In addition to those described, there is also a Y-code, which is an encrypted P-code (in wartime, the encryption system may change).

The code repetition period is quite long (for example, for a P-code it is 267 days). Each GPS receiver has its own generator, operating at the same frequency and modulating the signal according to the same law as the satellite generator. Thus, from the delay time between identical sections of the code received from the satellite and generated independently, it is possible to calculate the signal propagation time, and, consequently, the distance to the satellite.

One of the main technical difficulties of the method described above is the synchronization of the clocks on the satellite and in the receiver. Even a tiny error by ordinary standards can lead to a huge error in determining the distance. Each satellite carries high-precision atomic clock. It is clear that it is impossible to install such a thing in every receiver. Therefore, to correct errors in determining coordinates due to errors in the clock built into the receiver, some redundancy in the data necessary for unambiguous georeferencing is used (more on this a little later).

In addition to the navigation signals themselves, the satellite continuously transmits various types of service information. The receiver receives, for example, ephemeris (precise data about the satellite’s orbit), a forecast of the delay in the propagation of a radio signal in the ionosphere (since the speed of light changes as it passes through different layers of the atmosphere), as well as information about the performance of the satellite (the so-called “almanac”, which is updated every 12.5 minutes information about the status and orbits of all satellites). This data is transmitted at 50 bps on L1 or L2 frequencies.

General principles of determining coordinates using GPS.

The basis of the idea of determining the coordinates of a GPS receiver is to calculate the distance from it to several satellites, the location of which is considered known (this data is contained in the almanac received from the satellite). In geodesy, a method of calculating the position of an object by measuring its distance from points with given coordinates called trilateration. Fig2.

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 on a sphere of radius A described around the satellite). Let the distance B of the receiver from the second satellite be known. In this case, determining the coordinates is also not possible - the object is located somewhere on a circle (shown in blue in Fig. 2), which is the intersection of two spheres. Distance C to the third satellite reduces the uncertainty in coordinates to two points (indicated by two thick blue dots in Fig. 2). This is already enough to unambiguously determine the coordinates - the fact is that of the two possible points location of the receiver, only one is located on the surface of the Earth (or in the immediate vicinity of it), and the second, false, turns out to be either deep inside the Earth or very high above its surface. Thus, theoretically, for three-dimensional navigation it is enough to know the distances from the receiver to three satellites.

However, in life everything is not so simple. The above considerations were made for the case when the distances from the observation point to the satellites are known with absolute accuracy. Of course, no matter how sophisticated the engineers are, some error always occurs (at least in terms of the inaccurate synchronization of the receiver and satellite clocks indicated in the previous section, the dependence of the speed of light on the state of the atmosphere, etc.). Therefore, to determine the three-dimensional coordinates of the receiver, not three, but at least four satellites are involved.

Having received a signal from four (or more) satellites, the receiver looks for the intersection point of the corresponding spheres. If there is no such point, the receiver processor starts using the method successive approximations adjust your clock until you achieve the intersection of all the spheres at one point.

It should be noted that the accuracy of determining coordinates is associated not only with the precision calculation of the distance from the receiver to the satellites, but also with the magnitude of the error in specifying the location of the satellites themselves. To monitor the orbits and coordinates of satellites, there are four ground tracking stations, communications systems and a control center controlled by the US Department of Defense. Tracking stations constantly monitor all satellites in the system and transmit data about their orbits to the control center, where updated trajectory elements and satellite clock corrections are calculated. Specified parameters are entered into the almanac and transmitted to satellites, and they, in turn, send this information to all operating receivers.

In addition to those listed, there are a lot of special systems that increase the accuracy of navigation - for example, special signal processing circuits reduce errors from interference (the interaction of a direct satellite signal with a signal reflected, for example, from buildings). We will not delve into the specifics of the functioning of these devices, so as not to unnecessarily complicate the text.

After canceling the selective access mode described above, civilian receivers are “locked to the terrain” with an error of 3-5 meters (the height is determined with an accuracy of about 10 meters). The given figures correspond to the simultaneous reception of a signal from 6-8 satellites (most modern devices have a 12-channel receiver that allows you to simultaneously process information from 12 satellites).

The so-called differential correction mode (DGPS - Differential GPS) allows you to qualitatively reduce the error (up to several centimeters) in coordinate measurement. The differential mode consists of using two receivers - one is stationary at a point with known coordinates and is called “base”, and the second, as before, is mobile. The data received by the base receiver is used to correct the information collected by the mobile device. Correction can be carried out both in real time and during “offline” data processing, for example, on a computer.

Typically, a professional receiver belonging to a company specializing in the provision of navigation services or engaged in geodesy is used as a base one. For example, in February 1998, near St. Petersburg, the NavGeoCom company installed the first ground station in Russia differential GPS. The station's transmitter power is 100 Watts (frequency 298.5 kHz), which allows you to use DGPS at a distance of up to 300 km from the station by sea and up to 150 km by land. In addition to ground-based base receivers, the OmniStar satellite differential service system can be used for differential correction of GPS data. Data for correction is transmitted from several geostationary satellites of the company.

It should be noted that the main customers of differential correction are geodetic and topographic services - for a private user, DGPS is not of interest due to the high cost (the OmniStar service package in Europe costs more than $1,500 per year) and the bulkiness of the equipment. Yes, and it’s unlikely Everyday life Situations arise when you need to know your absolute geographic coordinates with an error of 10-30 cm.

In conclusion of the part telling about the “theoretical” aspects of the functioning of GPS, I will say that Russia, in the case of space navigation, has gone its own way and is developing its own GLONASS system (GLOBAL NAVIGATION Satellite System). But due to lack of proper investment, there are currently only seven satellites in orbit out of the twenty-four needed for the normal functioning of the system...

Brief subjective notes from a GPS user.

It just so happened that I learned about the possibility of determining my location using a wearable device the size of a cell phone in the year 1997 from some magazine. However, the wonderful prospects drawn by the authors of the article were mercilessly crushed by the price of the navigation device stated in the text - almost 400 dollars!

A year and a half later (in August 1998), fate brought me to a small sports store in the American city of Boston. Imagine my surprise and joy when, on one of the windows, I accidentally noticed several different navigators, the most expensive of which cost $250 (simple models were offered for $99). Of course, I could no longer leave the store without the device, so I began to torture the sellers about the characteristics, advantages and disadvantages of each model. I didn’t hear anything intelligible from them (and not at all because I don’t know English well), so I had to figure it out myself. And as a result, as often happens, the most advanced and expensive model was purchased - Garmin GPS II+, as well as a special case for it and a power cord from the car’s cigarette lighter socket. The store had two more accessories for my now device - a device for mounting the navigator on a bicycle handlebar and a cord for connecting to a PC. I played with the latter for a long time, but in the end I decided not to buy it because of the high price (a little over $30). As it turned out later, I didn’t buy the cord completely correctly, because the entire interaction of the device with the computer comes down to “fading” the route traveled into the computer (as well as, I think, coordinates in real time, but there are certain doubts about this), and even then subject to the purchase of software from Garmin. Unfortunately, there is no option to load maps into the device.

Giving detailed description I will not have my own device, if only because it has already been discontinued (those who wish to familiarize themselves with the detailed technical specifications can do so). I will only note that the weight of the navigator is 255 grams, dimensions are 59x127x41 mm. Thanks to its triangular cross-section, the device is extremely stable on a table or car dashboard (Velcro is included for a more secure fit). Power is supplied from four AA batteries AA (they are only enough for 24 hours of continuous operation) or external source. I’ll try to talk about the main capabilities of my device, which, I think, have the vast majority of navigators on the market.

At first glance, GPS II+ can be mistaken for a mobile phone released a couple of years ago. As soon as you look closely, you notice an unusually thick antenna, a huge display (56x38 mm!) and a small number of keys, by telephone standards.

When you turn on the device, the process of collecting information from satellites begins, and a simple animation (a rotating globe) appears on the screen. After the initial initialization (which takes a couple of minutes in an open place), a primitive sky map with numbers appears on the display visible satellites, and next to it is a histogram indicating the signal level from each satellite. In addition, the navigation error is indicated (in meters) - the more satellites the device sees, the more accurate the coordinates will be, of course.

The GPS II+ interface is built on the principle of “turning” pages (there is even a special PAGE button for this). The “satellite page” was described above, and besides it, there is a “navigation page”, “map”, “return page”, “menu page” and a number of others. It should be noted that the described device is not Russified, but even with poor knowledge of English you can understand its operation.

The navigation page displays: absolute geographic coordinates, distance traveled, instantaneous and average speed, altitude, travel time and, at the top of the screen, an electronic compass. It must be said that the altitude is determined with a much greater error than two horizontal coordinates (there is even a special note about this in the user manual), which does not allow the use of GPS, for example, to determine altitude by paragliders. But the instantaneous speed is calculated extremely accurately (especially for fast-moving objects), which makes it possible to use the device to determine the speed of snowmobiles (the speedometers of which tend to lie significantly). I can give you “bad advice” - when you rent a car, turn off its speedometer (so that it counts fewer kilometers - after all, the payment is often proportional to the mileage), and determine the speed and distance traveled using GPS (fortunately, it can measure both in miles and in kilometers ).

The average speed of movement is determined by a somewhat strange algorithm - idle time (when the instantaneous speed is zero) is not taken into account in the calculations (more logical, in my opinion, it would be to simply divide the distance traveled by the total travel time, but the creators of GPS II+ were guided by some other considerations).

The distance traveled is displayed on the “map” (the device’s memory lasts for 800 kilometers - with more mileage, the oldest marks are automatically erased), so if you wish, you can see the pattern of your wanderings. The scale of the map varies from tens of meters to hundreds of kilometers, which is undoubtedly extremely convenient. The most remarkable thing is that the device’s memory contains the coordinates of the main settlements all over the world! The USA, of course, is presented in more detail (for example, all areas of Boston are present on the map with names) than Russia (the location of only such cities as Moscow, Tver, Podolsk, etc. is indicated here). Imagine, for example, that you are heading from Moscow to Brest. Find "Brest" in the navigator's memory, press special button“GO TO”, and the local direction of your movement appears on the screen; global direction to Brest; the number of kilometers (in a straight line, of course) remaining to the destination; average speed and estimated time of arrival. And so anywhere in the world - even in the Czech Republic, even in Australia, even in Thailand...

No less useful is the so-called return function. The device's memory allows you to record up to 500 key points (waypoints). The user can name each point at his own discretion (for example, DOM, DACHA, etc.), and various icons are also provided for displaying information on the display. By turning on the function of returning to a point (any of the pre-recorded ones), the owner of the navigator receives the same capabilities as in the case with Brest described above (i.e. distance to the point, estimated time of arrival and everything else). For example, I had such a case. Having arrived in Prague by car and settled into a hotel, my friend and I went to the city center. We left the car in the parking lot and went for a wander. After an aimless three-hour walk and dinner at a restaurant, we realized that we had absolutely no memory of where we left the car. It’s night outside, we are on one of the small streets of an unfamiliar city... Fortunately, before leaving the car, I wrote down its location in the navigator. Now, having pressed a couple of buttons on the device, I found out that the car was parked 500 meters away from us and after 15 minutes we were already listening to quiet music while heading to the hotel by car.

In addition to moving to a recorded mark in a straight line, which is not always convenient in city conditions, Garmin offers the TrackBack function - returning along your own path. Roughly speaking, the motion curve is approximated by a number of straight sections, and marks are placed at the break points. On each straight section, the navigator leads the user to the nearest mark, and upon reaching it, it automatically switches to the next mark. Exclusively convenient function when driving a car in an unfamiliar area (the signal from satellites, of course, does not pass through buildings, so in order to obtain data about your coordinates in densely built-up conditions, you have to look for a more or less open place).

I will not go further into the description of the device’s capabilities - believe me, in addition to those described, it also has a lot of pleasant and necessary gadgets. Just changing the display orientation is worth it - you can use the device in both horizontal (car) and vertical (pedestrian) positions (see Fig. 3).

I consider one of the main advantages of GPS for the user to be the absence of any fees for using the system. I bought the device once and enjoy it!

Conclusion.

I think there is no need to list the areas of application of the considered global positioning system. GPS receivers are built into cars, cell phones, and even wrist watch! Recently I came across a message about the development of a chip that combines a miniature GPS receiver and GSM module- it is proposed to equip dog collars with devices based on it, so that the owner can easily locate a lost dog via a cellular network.

But in every barrel of honey there is a fly in the ointment. IN in this case Russian laws play the role of the latter. I will not discuss in detail the legal aspects of the use of GPS navigators in Russia (something about this can be found), I will only note that theoretically high-precision navigation devices (which, without a doubt, are even amateur GPS receivers) are prohibited in our country, and their owners will face confiscation of the device and a considerable fine.

Fortunately for users, in Russia the severity of the laws is compensated by the optionality of their implementation - for example, he travels around Moscow great amount limousines with a washer-antenna for GPS receivers on the trunk lid. Everything is more or less serious sea vessels equipped with GPS (and a whole generation of yachtsmen has already grown up, having difficulty finding their way around using a compass and other traditional means of navigation). I hope that the authorities will not put a spoke in the wheels of technological progress and will soon legalize the use of GPS receivers in our country (they have canceled permits for Cell Phones), and will also give the go-ahead for declassification and replication detailed maps areas needed for full use car navigation systems.

Let's start, perhaps, with an explanation of what it is A-GPS and how is it different from GPS. In most cases, cell phones do not have enough good receiver, which could ensure reliable signal reception in a room or between high-rise buildings. This is where the so-called A-GPS, which in most others mobile phones called simply GPS.

A-GPS(eng. Assisted GPS) system that speeds up coordinate determination GPS receiver

Most big problem For GPS the receiver is the so-called " cold start" It is at this moment that the search for satellites occurs. Depending on the external factors The start-up process may be delayed, which not only causes discomfort, but also leads to increased energy consumption. Technology A-GPS helps to cope not only with this problem, but to make life a little easier GPS receiver.

In case of iPhone it means that current position will be determined using GPS, Wi-Fi and stations mobile operators(craftsmen from Apple For all this, we managed to use only 2 antennas, which are located in unexpected places - a ring around the camera, an audio jack, a metal rim around the screen, etc. All this data will be processed by the auxiliary server. This is precisely the advantage A-GPS before GPS: the first one works much faster, but the second one “slows down” during a “cold start” when searching for satellites. With regular GPS With a positioning receiver, you need several strong signals and a certain amount of time to obtain coordinates. At A-GPS The secondary server itself tells your phone where the nearest satellites are, thereby reducing search time. In addition, this approach also saves battery.

Unlike many other phones, A-GPS V iPhone will work without connection to the network, which will allow you to use it outdoors, and indeed anywhere in the world where a satellite signal is received (however, do not forget that you will need Google Maps, you will have to download it in advance).

It is currently not known how quickly A-GPS will drain the battery: iPhone will automatically turn the positioning system on and off as needed, which will save charge. It is expected that during active operation (constant position tracking, etc.) it will still consume quite a lot.

Realizing how good he really is GPS will be in iPhone, we move on to the most interesting part - navigation. Here it is Apple as always in my repertoire. Current version SDK prohibits its use for navigation in real time (“Real-Time Route Guidance”). But it's not all bad, giant GPS industry TomTom stated that they are already working on a navigator for the iPhone. Apparently, large companies have to somehow obtain permission to use SDK on an individual basis. Thus, additional expenses await us in order to turn iPhone acceptable for use navigator. But we are apparently no strangers :-).

The Global Positioning System appeared in the 50s thanks to the launch of the satellite. When the first Soviet satellite went into orbit, the Americans noticed: as it moved away, it evenly changed the frequency of the signal. Scientists analyzed the data and realized that satellite signal allows you to accurately determine the coordinates of objects on the ground, as well as the speed of their movement. First GPS system The military adopted it: the Ministry of Defense launched satellite navigation for its own purposes, but after a few years it became available to civilians.

There are currently 24 satellites in low-Earth orbit that transmit binding signals. The number of satellites changes periodically, but always remains sufficient to maintain the smooth operation of the Global Positioning System. In case of force majeure, spare satellites are provided, and every decade new, modernized spacecraft go into orbit, because nothing should disrupt the operation of GPS.

The satellites orbit in six orbits, forming an interconnected network. It is operated by dedicated GPS stations that are located in the tropics but linked to a focal point in the United States. Thanks to this network, you can find out the exact coordinates of a person, car or aircraft at the speed of signal transmission from satellites, that is, almost instantly, and the accuracy of the readings does not depend on weather conditions and time of day. At the same time, the use of the Global Positioning System itself is free, and the only thing you need to use this navigation system is a navigator or other device that supports the GPS function.

How GPS works

The technology is based on simplicity navigation principle marker objects, which was used long before the advent of GPS. A marker object is a landmark whose coordinates are precisely known. To determine the coordinates of an object, you also need to know the distance from it to the marker object, then you can draw lines on the map towards the markers from possible location: the point of intersection of these lines will be the coordinates.

Satellites in low-Earth orbit play the role of marker objects in GPS. They rotate quickly, but their location is constantly monitored, and each navigator has a receiver tuned to the desired frequency. Satellites send signals that encode a large amount of information, including exact time. Precise time data is one of the most important for determining geographic coordinates: based on the difference between the output and reception of the radio signal, satellites calculate the distance between themselves and the navigator.

How GPS works in smartphones

Navigators are one of the most popular products on the gadget market; they are surpassed in popularity only by smartphones. But manufacturers also integrate GPS chips into smartphones so that the device can perform the functions of a navigator. However, a trap may lie in wait for the user here, because in the pursuit of profit, manufacturers allow intentional or accidental inaccuracies in the description of their product, allowing buyers to confuse GPS technology and AGPS.

Jeepies is a free high-precision navigation system. There is no subscription to it and cannot be, because the Americans allow the use of their satellites for navigation free of charge. Smartphone owners, if they pay, pay only for applications or cards. GPS receivers have small disadvantages: they only work outdoors, and due to bad weather there may be problems with receiving a signal from the satellite, but these disadvantages were solved with the help of A-GPS technology(not to be confused with AGPS). The bottom line is that the signal from the receiver is redirected to a server that contains all the information about the position of the satellites, so there are no difficulties in receiving the signal. A-GPS is used by all modern car navigators.

But there is also AGPS cellular navigation - it works only in the coverage area of the cellular network and determines the location with an accuracy of up to 500 m. It is less accurate compared to GPS, it gives a general idea of the place where you are, but it offers satellite map surroundings. It is important that the service is activated mobile internet, and there was money left in the account. Google Maps works with the AGPS service. Cellular navigation capabilities are often sufficient, but they should not be confused with an accurate and free GPS system.

Types of GPS devices

The simplest navigation device - external receiver. It communicates with satellites and receives signals from them, but in order for you to use the information, the receiver needs to be connected to another device - for example, a smartphone or laptop; fortunately, it is compatible with all popular gadgets and programs. As a last resort, you will need a card. GPS receivers are used by hiking tourists: the device is inexpensive, and to decipher the information it receives, you can even use a regular tourist map of the area. You just need to have a navigation mesh overlaid on it.

But the most popular GPS device today is car navigator. It is much more complex and functional than the receiver: the navigator is more like a smaller version of a computer. All necessary software already installed by the manufacturer, the operating system is closed. Many additional functions are added to navigation, including Internet access.

A separate class of devices are smartphones with built-in GPS receivers. Do not confuse them with models that use cellular navigation! The system does not work as smoothly on smartphones as on standalone devices. Not all models allow you to install full-fledged navigation software, and if you use online solutions, the function will become unavailable when the Internet is turned off, and then one of the advantages of the technology will disappear: constant access. However, smartphones with satellite navigation are suitable for pedestrians - it’s easy to navigate and the data is accurate, so you won’t get lost even in the most impassable thicket.

How does a GPS work in a phone? What is A-GPS and what is its use?

Read more about what GPS is

About the history of GPS and navigation satellites

About GPS receivers

What is the difference between GPS and A-GPS

Algorithm for measuring the distance from the observation point to the satellite.

General principles of determining coordinates using GPS.

Brief subjective notes from a GPS user.

Conclusion.

How GPS works

How GPS works in smartphones

Types of GPS devices

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