What is jeepies on your phone? A-GPS technology: what is it and how does it work? How GPS navigation works

While looking through various types of GPS equipment, you have probably come across the abbreviation A-GPS (most often found on smartphones). What is A-GPS and why would it be good to have this feature?
It should be noted that since 2012, all GPS trackers Intel companies have this function.

A-GPS stands for Assisted GPS(accompanied by GPS), the function helps the GPS module to establish a satellite signal. The so-called “cold start time” is the time required to determine coordinates from the moment the GPS is turned on with the device completely turned off. There is a so-called TTFF parameter (time to determine coordinates), this period increases significantly in difficult conditions when there is no direct visibility of all satellites. Most often this happens in dense urban areas, when satellite signals reflected from all nearby buildings.

It must be said that the AGPS function only works when connected to the mobile Internet. This can be GPRS data transmission or WCDMA (3g mobile internet). By transmitting and receiving location-related data from the Internet, the technology allows you to speed up the process of determining your coordinates. What data is transmitted via the Internet will be discussed below.

The first start of a GPS device is called a cold start or factory start. At this time, three types of data are loaded into the device: satellite signals, almanac data and ephemeris data) to determine its location. A cold start occurs after a prolonged shutdown, moving over long distances, or when resetting the cache data (saved data about the last location of the module.

For standalone GPS receivers, a cold start can take up to 10 minutes. However, if the signal is uncertain and is interrupted during the start of coordinate determination, (due to low level signal weather conditions, buildings, etc.), a cold start may take longer.

A-GPS helps speed up coordinate determination by connecting via the Internet to a web server (called an Assisted Server), which already contains up-to-date information about all satellites. This information is transmitted via GPRS to the phone.

In addition, it has been shown that even a warm start is faster using A-GPS, by an average of a minute.

What A-GPS technology doesn't do

Despite the fact that the described function remarkably improves the performance of the satellite module, there are certain limitations. The satellite signal will not be detected inside large and reinforced concrete buildings (far from windows). Also, the GPS signal will not work underwater or even underground. By the way, in the absence mobile communications(Internet), this function doesn't work either.

Also, don't be confused A-GPS function with Wi-Fi positioning or the “triangulation” method for cell phones, when determining coordinates by GPS is impossible.

Some devices combine these positioning methods. These methods of determining location are called: hybrid systems positioning.

Where is Intelli LLC heading with its developments? First of all, these are integrated positioning systems.

Under ideal conditions, GPS or Glonass is the fastest and most accurate way to determine the location of an object. At the same time, there are certain positioning restrictions: inside buildings, underground (underground parking, for example), under water, etc. The positioning technology we have come to is to provide our clients with a comprehensive solution.

At the 2010 FIG Congress, the main trend was ubiquitous positioning using all available technologies: GPS/Glonass, Wi-Fi positioning and triangulation method for cell phones.

Combining the advantages of these technologies will improve not only the accuracy and stability of systems GPS monitoring, but will also be used everywhere in all popular mobile devices Oh.

• Back

As often happens with high-tech projects, the initiators of development and implementation GPS systems(Global Positioning System - system global positioning) became military. Project of a satellite network for determining coordinates in real time at any point globe was named 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 truly key point in the history of GPS was the decision of the US President to abolish the so-called selective access (SA - selective availability) regime from 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 figure it out general outline, how the global positioning system works, and then we will 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. The specified parameters are entered into the almanac and transmitted to the satellites, and they, in turn, send this information to all operating receivers.

In addition to those listed, there are many more special systems, increasing the accuracy of navigation - for example, special signal processing circuits reduce errors from interference (interaction of a direct satellite signal with a reflected signal, 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. And it’s unlikely that situations arise in everyday life 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, only seven satellites out of the twenty-four needed are currently in orbit. normal functioning systems...

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 device, if only because it has already been discontinued (those who wish to familiarize themselves with the detailed technical characteristics can do this). 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 an 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 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 enabling 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, automatic switching 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 won't go into detail about legal aspects 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.

Increasingly, smartphones are used by their owners as navigators, since it is very convenient to always have a compact device on hand that allows you to determine your location or build a route to the desired object.

It communicates with satellites in orbit, receiving signals from them, and shows its coordinates on the map. Sometimes, due to various circumstances, detecting available satellites can be difficult and take a long time. This occurs in buildings, tunnels, and also near sources electromagnetic radiation. Even outdoors in large cities with dense buildings may experience interruptions in the satellite signal.

To correct this situation, the A-GPS function is used, which is found in most modern smartphones.

A-GPS technology

A-GPS is a technology that provides the GPS module Additional information about the most accessible satellites and their signal strength. When you turn on navigation, the smartphone almost instantly determines its location on the map, and searching for satellites is possible even in enclosed spaces, and interfloor ceilings are not a hindrance.

The successful launch of A-GPS occurred in the USA in the fall of 2001 as part of communication networks national rescue service (911).

How does A-GPS work?

For up-to-date information this technology uses alternative communication channels. In the case of our smartphones, this is the Internet provided by a cellular operator or via Wi-Fi.

A-GPS communicates with its servers, transmitting location information, which is determined by the operator’s base stations (towers). In response, these servers receive fresh messages about active satellites in the area. Using them, the smartphone’s geolocation module quickly establishes a connection with necessary companions, without wasting time searching for everyone. The more base stations there are around the smartphone, or the closer the user is to cell tower, the more accurately the location of the smartphone is recorded, which means the more accurate the information about available satellites.

Pros and cons of A-GPS

As we can see, the benefits of having A-GPS are undeniable. This and quick installation communication with satellites, and battery saving, since during a “cold” start and searching for signals GPS module consumes battery power intensively. At the same time, communication with servers consumes very little Internet traffic - up to 10 kilobytes per session. It is important that A-GPS does not require user participation, and data is updated automatically as needed.

But this function also has disadvantages, albeit minor ones. She won't provide fast connection with satellites in areas with a shortage of towers mobile operators or their absence. Therefore, far from civilization, A-GPS is useless.

Despite modest internet consumption, regular frequent updates and A-GPS synchronization will result in increased traffic. And when you are in roaming, especially international, communication costs can increase significantly.

How to enable or disable A-GPS?

When activating the “Geodata” function (GPS navigation, geolocation), the smartphone prompts you to select a determination method. The user can prioritize battery conservation or geolocation accuracy. Typically, the following methods are available (menu item names may vary depending on Android versions and phone manufacturer):

• According to all sources (high accuracy). Location is determined using GPS, Wi-Fi and Internet traffic mobile networks. A-GPS technology active
• By network coordinates (conserving battery charge). The location is detected when Wi-Fi assistance and and mobile networks. GPS protocol is disabled, A-GPS is active.
• By GPS satellites (device only). Determining location solely by satellites without using additional channels communications. A-GPS technology is disabled.

A-GPS technology is necessary for normal navigation using a smartphone - it can be used regularly.

2 years ago

GPS technology is used not only by car enthusiasts and taxi drivers. It is also popular among outdoor enthusiasts, fishermen and just people who lead an active lifestyle and are 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 globe;
• 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.

Read more about what GPS is

GPS is an abbreviation for the English concept Global Positioning System, which is translated into Russian as “global positioning system”. This project was conceived and implemented by the US military exclusively for military purposes, but later became widely used for civilian needs.

The basis of the GPS system is 24 NAVSTAR navigation satellites, which form a single network and are located in Earth's orbit in such a way that at least 4 satellites can be accessed from anywhere on the globe.

Performance global system positioning is monitored from the ground by observation stations located in the Hawaiian Islands, in the city of Colorado Springs (Colorado), in Kwajalein Atoll and on the islands of Ascension and Diego Garcia. All information collected by these stations is recorded and then transmitted to the command post, which is located at Shriver Air Force Base (Colorado). Here the navigation information and satellite orbits are adjusted.

The GPS tracker coordinates are calculated according to the following principle. A radio signal passes from each navigation satellite to a receiver located in their access area. The delay of this signal is measured, and from these measurements the distance to each satellite is calculated. The location of the receiver is calculated based on measuring the distance from it to all available satellites (in geodesy this method is called triangulation), the coordinates of which are known and contained in the signals they transmit.

The GPS receiver is capable of not only determining its location, but also calculating the speed of movement, the time it takes to reach the designated place, and showing the direction. But this already applies not so much to the capabilities of the GPS system itself, but software navigator.

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. First worker GPS satellite was launched in February 1978, and the system began to function 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 in length with open solar panels reaches 5 meters. 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.

When using A-GPS, the device immediately receives 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).