Global satellite systems: GPS, Galileo, BeiDou and GLONASS

Space Clocks and Light Signals

These systems are built on a single principle: satellites transmit radio signals, and receivers on Earth — in smartphones, trackers, or platforms like Waliot — calculate the location. Each satellite is equipped with an atomic clock that measures time with an accuracy of nanoseconds. The signal carries a time stamp of sending and the satellite’s coordinates, flying at the speed of light — 300 thousand km/s. The delay between sending and receiving reveals the distance to the satellite. For example, if the signal takes 0.067 seconds to travel, the distance is about 20,000 km, the altitude of a typical orbit.

But one satellite is not enough. At least four are needed to determine three-dimensional coordinates — latitude, longitude, altitude — and calibrate the receiver’s time. The process resembles the intersection of spheres: the first satellite gives a sphere of possible positions, the second narrows it down to a circle, the third to two points, and the fourth indicates the exact location. This is called trilateration, and the equation behind it is: distance is equal to the speed of light multiplied by the time difference.

From chaos to precision: how signals become coordinates

Satellite signals are not just radio waves. They operate on different frequencies: GPS uses L1 (1575.42 MHz) and L2 (1227.60 MHz), Galileo adds E5, BeiDou uses B1 and B3, and GLONASS shifts its frequencies slightly for uniqueness. Each satellite transmits its own “ephemeris” – precise data about the orbit – and an “almanac” with the approximate positions of all satellites in the system. The receiver assembles these puzzle pieces and solves the problem: where do all the signals intersect?

The atmosphere complicates matters. The ionosphere and troposphere distort the waves, adding delays. To cope, systems use dual-frequency measurements: by comparing signals on L1 and L2, interference can be calculated and removed. And additions such as SBAS (WAAS in the US, EGNOS in Europe) bring the accuracy to 1–2 meters.

Four systems, four characters

Although the principle is the same, each system is unique – a reflection of the technology and ambitions of its creators.

• GPS: Launched in 1978, with 31 satellites in orbit 20,200 km. Accuracy: 5 meters for civilian use, up to centimeters for military use. It is a pioneer, whose L5 signals have made it even more accurate since the 2010s.
• Galileo: Launched in 1999, in service since 2016. 24 satellites covering 23,222 km, hydrogen clocks and commercial accuracy up to 1 cm. Europe has focused on innovation and openness.
• BeiDou: From a regional system in the 2000s, it has grown into a global one by 2020. 35 satellites, including geostationary satellites covering 36,000 km. Unique in its SMS services and focus on Asia.
• GLONASS: Launched in 1982, revived in the 2000s. 24 satellites at 19,100 km, strong in northern latitudes where others lose signal. Accuracy is 5-10 meters.

Fighting Interference

Satellite signals are fragile. Mountains, buildings, and forests block them, and the atmosphere adds noise. Dual-frequency technologies and ground correction stations solve the problem. BeiDou adds geostationary satellites for stability, and GLONASS works better in the Arctic. It’s a battle between engineering and nature, and so far the score is in favor of technology.

Why all this?

These systems are not just dots on a map. GPS saves climbers in the mountains, Galileo guides tractors in the fields, BeiDou coordinates logistics in China, and GLONASS tracks ships in icy waters. Platforms like Waliot use them to cut fleet costs by millions. This is not abstract science, it is the engine of the modern world.