There are several global satellite navigation systems in the world that complement each other harmoniously: the American GPS, the Russian GLONASS, the European Galileo, and the Chinese Beidou. Global navigation systems are organized according to a similar principle. They combine complexes of ground and space equipment for positioning in space and time, based on which the determination of location, speed, direction, and other parameters of an object's movement is carried out.

1. Basic Principles of Operation

The principle of operation of navigation systems is based on measuring the distance from satellites in orbit, whose location is reliably known with high accuracy, to the antenna of the receiving device. Each satellite emits precise time signals using atomic clocks synchronized with system time. During the reception of the signal from orbital satellites, the delay between the time of signal emission and the time of its reception by the end device's antenna is calculated. Based on this information, the receiver calculates the coordinates of the antenna. The movement of the object is calculated based on the time spent moving between two or more points with coordinates determined by preliminary calculations.

Accurate positioning in space is ensured by receiving a signal from at least three satellites simultaneously.

For accurate positioning in space, the receiver's antenna must receive a signal from at least three satellites simultaneously, and preferably from four. A trio of satellites transmits data about their location relative to the Earth and each other, while the fourth fixes the time it takes for the signal to travel from the transmitter to the receiver. Since satellites are constantly in motion, their trajectory is tracked by ground stations. Current information is sent to gadgets in almanacs—libraries with the most accurate data on the location of all available satellites. Almanacs are updated via mobile networks or Wi-Fi, significantly reducing the duration of the navigation systems' "cold start."

Initially, satellite navigation systems were military developments. Many of them remain under the control of military departments to this day. The first publicly available navigation system was the American GPS. In fact, the words "navigation" and "GPS" were long perceived as synonyms.

2. GPS

The development of the NAVSTAR (Navigation Satellite Time and Ranging) project was undertaken by the US Department of Defense in the 1970s. The first satellite of the system was launched into orbit in 1974, and over the next 20 years, the necessary number of satellites for the system's correct operation (24 units) was launched into space. The GPS (The Global Positioning System) navigation system was opened for civilian use, but to prevent its military use by adversaries, the system's accuracy was forcibly reduced by special algorithms to about 100 meters. Most of the restrictions were lifted only at the beginning of the third millennium. The GPS navigation system consists of 32 satellites that orbit the Earth in circular orbits in six different planes. All satellites are located in a daily orbit—20,200 km above sea level. As a result, at any point on the planet, at least four satellites are always visible at any given time (usually from 4 to 12 satellites are visible simultaneously). Every 30 seconds, a satellite transmits radio signals at a frequency of 1575.42 MHz, containing information about the satellite's position in space, signal quality information, satellite clock error, and ionosphere model coefficients.

GPS system satellites orbit the planet in six different planes
in a daily orbit—20,200 km above sea level.

Ground stations are designed to improve the accuracy of coordinate determination by transmitting corrections for differential mode: WAAS in the US and Canada, EGNOS in European countries. Standard receivers fix the location with an accuracy of several meters, while the latest ones have an accuracy of up to several centimeters.

Early versions of GPS had a long "cold start" time. This was due to the need to transmit an almanac (astronomical calendar) and a whole bunch of accompanying corrections to the receiving device. The problem was solved by the auxiliary system aGPS (Assisted GPS). Devices with it can receive service information from the nearest base station of the cellular operator, freeing gadgets from the need to maintain direct communication with satellites and significantly reducing the navigation startup time (literally in a few seconds).

A visual principle of how aGPS technology is arranged.
Popular smartwatches with aGPS

3. Dual GPS

To increase the accuracy of location determination in modern navigation modules, Dual GPS technology is found. Receivers with its support operate not on one frequency, like traditional analogs, but on two (L1 + L5—1575 MHz + 1176 MHz). This format significantly increases positioning accuracy —in some cases up to 10–20 cm. Dual GPS allows for the correct processing of signals reflected from high-rise buildings in dense urban environments. Moreover, the L5 band has high bandwidth and transmission speed, so the amount of noise and interference is significantly reduced.

Dual GPS technology allows for a significant increase in location determination accuracy, especially in dense urban environments.

It should be noted that full support for L5 is available in the European Galileo system and the Japanese QZSS (more about them below). In GPS, only half of the satellites broadcast such signals, and in the GLONASS system, it is expected no earlier than 2030.

Popular phones with Dual GPS

4. GLONASS

The Russian radio navigation satellite system GLONASS began development back in the USSR in the 1970s. The system's flight tests started in 1982 with the launch of the first satellite into orbit. A full constellation of 24 satellites was deployed closer to 1995. However, due to funding problems and the short operational life of spacecraft, by 2001, the number of working satellites had decreased to six. The situation was turned around in the mid-2000s, and the completion of the GLONASS navigation system was announced at the end of 2015. Its foundation consists of 24 active satellites that orbit at an average altitude of 19,100 km above the Earth's surface in three orbital planes. Each orbit has 8 evenly distributed satellites. The GLONASS system also provides for reserve spacecraft.

The complete GLONASS satellite constellation is formed from 24 active spacecraft.

The system's satellites transmit two types of radio emissions: the L1 band navigation signal and the high-precision navigation signal in the L2 and L3 bands. Positioning errors are about 3-6 meters, and with corrections—up to 1 meter. An important feature of GLONASS is the ability to use the navigation system at high latitudes in the northern and southern polar regions, where the GPS signal is poorly received.

5. Galileo

Galileo is a European satellite navigation system created as an alternative to the American GPS and Russian GLONASS. Notably, it is under the control of civilian agencies. With a full fleet of 24 active satellites, the system provides accuracy up to 1 meter in public mode and up to 20 cm with the GHA service. In total, there are 30 Galileo system satellites in orbit (6 spacecraft are in hot reserve).

Orbits of the European Galileo navigation system satellites.

Galileo satellites orbit in three orbital planes at an altitude of 23,222 km above the planet's surface. Each orbit, when the system is fully deployed, contains 8 active and 2 reserve satellites. This constellation configuration ensures the simultaneous visibility of at least four spacecraft from any point on the globe. In the future, Galileo system satellites will be able to transmit user distress signals to regional rescue coordination centers. At the same time, feedback will be provided—confirmation of receipt of distress notifications.

Interesting fact. The function of satellite communication for sending emergency messages to rescue services in areas without traditional cellular coverage has been implemented in the entire line of Apple's 14th "iPhones" and subsequent models.

6. Beidou

In 2020, the creation of global coverage was completed for the Chinese Beidou navigation system. Its satellite fleet consists of 48 spacecraft, with 35 satellites in operation . Satellites are placed in three orbits: medium circular, geostationary, and geosynchronous inclined high.

A stand with a visualization of the principles of the Beidou global navigation satellite system's structure.

China's desire to create its own satellite navigation system is driven by the desire to gain independence from the US and its GPS system. Beidou's positioning accuracy for the civilian population is less than 10 meters, and the speed measurement accuracy reaches about 0.2 meters per second.

7. Other Regional Systems

Individual countries are developing their own navigation systems. They are only entering the global level, but as regional navigation systems, they are already actively operating IRNSS (Indian Regional Navigation Satellite System) in India, as well as QZSS (Quazi-Zenith Satellite System) in Japan and the Asia-Pacific region.

8. GNSS

GNSS is an abbreviation for Global Navigation Satellite System. Multi-GNSS receivers can receive signals transmitted by several navigation systems simultaneously: GPS, GLONASS, Galileo, Beidou, QZSS, IRNSS. This significantly increases positioning accuracy by receiving more signals from satellites.

In fact, the term GNSS refers to the combination of all global navigation positioning systems . Although each of them uses its own encodings for signal transmission, GNSS receivers correctly interpret the received information within a single device.

9. Satellite Communication in Apple Smartphones

It is worth mentioning satellite communication in Apple smartphones separately. It serves for emergency message sending to rescue services outside the mobile network coverage area. It is not used as a navigation system. "iPhones" (from the 14th model and newer) can send distress signals to the local emergency service. However, it is not possible to write messages independently—templates of ready-made appeals are initially embedded in the smartphone. The device catches the satellite signal in open areas. It will prompt which direction to point the smartphone for better signal reception. After establishing a connection, the phone sends the rescue service the geolocation, some personal data (from the medical card in the "Health" app), and the iPhone's battery level.

When launching the emergency satellite communication system, the iPhone itself suggests
where to turn in space for confident signal reception.

Initially, satellite communication support was implemented only in the US and Canada. However, it is now available almost worldwide. The option does not work only on devices purchased in Armenia, Belarus, Hong Kong, Kazakhstan, China, Kyrgyzstan, Macau, and Russia. To operate the emergency communication system, Apple deployed a fleet of 17 low-orbit spacecraft launched by the satellite operator GlobalStar. At the end of 2024, Apple implemented full support for message exchange via satellite communication (an iPhone with iOS 18 will be required for this) and invested over $1 billion in launching new satellites. With the increase in the fleet's size, the appearance of other functions, such as calls or internet access from anywhere on the globe, is quite possible. It is too early to predict, but such services will likely be expensive.

Popular smartphones with satellite communication

10. Conclusion

Working together in a single synergy, different navigation systems provide more accurate location measurement, especially in densely populated areas and large metropolises, where the signal is repeatedly reflected from tall structures. Modern gadgets often support working with all known satellite systems , making navigation more accurate literally day by day.