Galileo provides global positioning, navigation and timing under civilian control. A receiver can combine its measurements with GPS, but Galileo has its own satellites, navigation messages and system time. Sharing a carrier frequency does not make the transmitted signals identical.
Related: GPS constellation and GPS receiver principles. Reviewed October 30, 2026. Baseline designs below are not live satellite inventories.
Executive Summary
Item | Meaning |
|---|---|
System scope | Global; European Union |
Design baseline | 24 nominal MEO satellites in three orbital planes |
Nominal orbit | 23,222 km altitude; 56 degrees inclination |
Role | Global navigation; complementary measurements to GPS |
Constellation and Coverage
Orbit design
Galileo uses three orbital planes. Each plane contains eight nominal satellites in the 24/3/1 Walker baseline. The planes give receivers changing viewing directions as Earth and the satellites move. Spares and deployment history mean that a total spacecraft count need not equal this baseline. [1]
Figure 1 groups the main design elements. Read the rows as categories, not as a map of the sky. Satellites within one orbital plane travel around Earth; they do not remain above fixed user locations unless the orbit is geostationary.
Figure 1. The design groups explain the constellation architecture; operational inventory can differ.
What does the geometry mean ?
The nominal altitude is 23,222 km and inclination is 56 degrees. Inclination describes the orbital plane relative to the equator; it is not a boundary beyond which users cannot receive signals. A satellite can illuminate locations outside the latitude range of its ground track. [2]
Signals and Receiver Operation
Spectrum / RF details
Galileo separates satellites by ranging codes on shared carriers. E5 includes E5a and E5b components; the combined E5 signal is centred at 1191.795 MHz. A receiver may process individual components or the wider signal, depending on its bandwidth and implementation. [3]
Signal / parameter | Carrier centre (MHz unless stated) | Receiver implication |
|---|---|---|
E1 | 1575.420 | Open Service components; shared carrier centre with GPS L1 |
E5a | 1176.450 | Shared carrier centre with GPS L5 |
E5b | 1207.140 | Additional open navigation component |
E6 | 1278.750 | Separate signal family; receiver/service support must be checked |
Carrier centres do not describe occupied bandwidth. Two services at the same centre can use different codes, modulation and navigation data. The RF front end must pass the required bandwidth, and the baseband must implement the particular signal.
What does another constellation add ?
Consider a street where buildings hide several GPS satellites. Galileo can add measurements from different directions, improving the available geometry. But two signals from the same direction do not remove the obstruction. A receiver still needs to reject reflected signals and model measurement errors. Dual-frequency measurements also allow the receiver to estimate the dominant ionospheric delay instead of relying only on a broadcast model.
Combining constellations
A multi-GNSS receiver combines pseudoranges after accounting for each system's timing and measurement conventions. More satellites can help geometry and availability, but they do not automatically eliminate interference, multipath or clock biases. If an extra system-time offset is unknown, the estimator needs an additional bias parameter or external timing information. Four arbitrary satellites from mixed systems are therefore not always sufficient for an unconstrained solution.