How the GPS system works: from satellites to the navigator in your car

Today it is difficult to imagine a trip without a navigator - be it a built-in system in a car or a smartphone with Google Maps. But how exactly does this technology work? Why does GPS sometimes “lie”, showing your location with an error of tens of meters, and in tunnels or between high-rise buildings the connection disappears completely? The answers lie in the design of the global positioning system, which is based on physics, mathematics and space technology.

Many people mistakenly think that GPS is an exclusively American development for the military, which was later adapted for civilians. In fact, today there are several independent systems: the American GPS, Russian GLONASS, European Galileo and Chinese BeiDou. Your car navigator most likely uses data from several of them at once to improve accuracy. But how exactly do satellites in orbit determine your coordinates to within a meter? Let's look at it step by step - from starting the signal to displaying the route on the screen.

In this article we will not delve into complex formulas or military standards. Instead you will receive practical knowledgethat will help you understand:

• 🛰️ How satellites transmit data to Earth and why there must be at least 4 of them for accurate positioning
• 📡 What are “almanac” and “ephemerides” - and why your navigator can “think” for up to 10 minutes when you first turn it on
• 🚗 Why does GPS work worse in the city than in open areas, and how to fix it
• ⚡ What errors are introduced by the atmosphere, multipath and delays in equipment - and how to compensate for them

1. Space segment: how GPS satellites work

The basis of the system is 31 active satellites, rotating in medium Earth orbit (about 20,200 km). They are distributed over 6 orbital planes with an inclination of 55° and an orbital period of ~12 hours. This configuration guarantees that at any point on the planet a minimum of 4 satellites — minimum quantity for three-dimensional positioning (latitude, longitude, height).

Each satellite weighs about 900 kg and is equipped with:

• 🔋 Solar batteries (power ~1 kW) and backup batteries
• 📡 Atomic clocks based on rubidium or cesium standards (accuracy ~1 nanosecond per day)
• 📶 L-band transmitters (frequency L1=1575.42 MHz for civil signals)
• 🛡️ Protected military channels (frequency L2 and new L5)

Satellites continuously broadcast two types of data:

1. Almanac — simplified orbital parameters of all satellites in the system (updated every few days). Allows the receiver to “know” where to look for signals.
2. Ephemerides — accurate orbital data of a specific satellite (updated every 2 hours). Used for high-precision calculations.

⚠️ Attention: If your navigator has not been used for more than 6 months, the first satellite search may take up to 15 minutes. This is due to the obsolescence of the almanac - the receiver has to download the latest data “from scratch”.

2. The principle of trilateration: how coordinates are calculated

The GPS receiver in your car doesn't "determine" your location - it calculates it based on the propagation time of signals from satellites. Here's how it works:

1. Latency measurement. The receiver records the time of arrival of the signal from each satellite and compares it with the internal clock. The difference is multiplied by the speed of light (~300,000 km/s), which gives the distance to the satellite.
2. Scope of possible positions. Each satellite defines a sphere with radius = distance to it. The intersection of two spheres gives a circle, three - two points (one of them is outside the Earth, it is discarded).
3. The fourth satellite. Needed to correct time (the receiver clock is less accurate than the atomic clock on satellites) and determine altitude.

The formula for calculating coordinates is based on a system of equations:

(x - x₁)² + (y - y₁)² + (z - z₁)² = (c × Δt₁)²
(x - x₂)² + (y - y₂)² + (z - z₂)² = (c × Δt₂)²
...

where (x₁, y₁, z₁) — satellite coordinates, Δt — signal delay, c - speed of light.

3. Ground segment: control and correction stations

Satellites are only part of the system. Their work is monitored 5 ground monitoring stations (mainly based at the US Air Force base in Colorado) and a network of 16 loading antennas, distributed along the equator. These stations perform three key functions:

• 🔄 Orbit correction. Satellites are subject to gravitational disturbances from the Moon and Sun. Stations calculate corrections and load them on board 1–2 times a day.
• ⏱️ Time synchronization. Atomic clocks on satellites drift by ~10 nanoseconds per day. Without correction, this would give an error of ~3 meters.
• 📡 Ephemeris update. Orbital data is transmitted to satellites every 2 hours to minimize errors.

For civilian users, differential correction systems provide additional accuracy:

• WAAS (USA), EGNOS (Europe), SDCM (Russia) - transmit corrections via geostationary satellites.
• RTK (Real-Time Kinematic) - used in geodesy and drones (accuracy up to 1 cm!).

⚠️ Attention: In 2026, the United States began testing a new signal L1Ccompatible with Galileo and BeiDou. If your navigator supports multi-system (for example, Garmin DriveSmart 66 or Pioneer AVIC-Z920DAB), after updating the firmware, accuracy can improve by 20–30%.

4. Receiver in a car: how the GPS module works

Car navigators and smartphones are equipped GPS chipsets, which consist of:

• 📶 Antennas (passive or active with amplifier). The built-in antennas in smartphones are weaker than external antennas in cars.
• 🔌 RF-frontal — signal amplifier and filter (cuts off interference).
• 🧠 CPU for decoding signals and calculating coordinates (for example, Broadcom BCM47755 in iPhone 13).

Key characteristics of receivers:

Modern chipsets (for example, Qualcomm Snapdragon Auto or MediaTek Dimensity Auto) support hybrid positioning:

• 📱 A-GPS — acceleration of searching for satellites via the mobile Internet (downloads the current almanac).
• 📡 Cell-ID — approximate location based on cell towers (accuracy ~500 m).
• 🌐 Wi-Fi positioning — in cities, accuracy is up to 20 m due to the base of access points.

Install an external antenna on the roof (eg Garmin GA 38>)

Update your navigator firmware to the latest version

Disable power saving mode (it may turn off the GPS module)

Use a smartphone holder on the windshield (maximum view of the sky)

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5. Sources of errors: why GPS lies

Even under ideal conditions, GPS has an error of ~3–5 meters. In reality, errors accumulate due to:

1. Atmospheric delays. The ionosphere and troposphere slow down the signal. Corrections are transmitted in ephemeris, but are not ideal.
   How does the atmosphere affect GPS?

   The signal passes through the ionosphere (100–1000 km), where electrons slow down radio waves by 5–30 m, and the troposphere (up to 10 km), where humidity and temperature add another 0.5–2 m of error.

2. Multipath. The signal is reflected from buildings, mountains or water and arrives at the receiver with a delay. In cities, this is the main reason for “jumping” coordinates.
3. Doppler effect. The satellite's movement (speed ~3.9 km/s) shifts the signal frequency. Modern chipsets compensate for this, but budget ones can be off by 1–2 m.
4. Receiver clock errors. Crystal oscillators in smartphones lose ~1 ms/day, which gives an error of ~300 km without correction!

Car navigators use several methods to reduce errors:

• 🔄 Kalman filtering — a mathematical algorithm that smoothes out “jumps” of coordinates.
• 📊 Comparison with a map - if the GPS shows that you are driving along a lake, the navigator “pulls” the point to the road (map matching).
• 🚗 Vehicle sensors — data from the odometer and gyroscope help when the signal is lost (for example, in a tunnel).

• 🚨 ERA-GLONASS (mandatory in Russia since 2017) - transmits coordinates in case of an accident.
• 🅿️ Automatic parking — uses GPS + cameras to build a 3D map.
• 🤖 Autopilot (Tesla Autopilot, Nissan ProPilot) - combines GPS with lidar and radar for ±10 cm accuracy.

GPS/GLONASS antenna (roof)
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Chipset Broadcom BCM47765 (28 nm, 10 channels)
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Central computer NVIDIA Drive PX 2
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Merging data from cameras (8×1.2 MP) and radars