Chapter 17Anti-jamming for Satellite Navigation1




17.1. Satellite navigation principles

17.1.1. Triangulation

The GNSS (global navigation satellite systems) include any systems of radio navigation by satellite. The only GNSS operational is the US GPS (Global positioning system), and at a lower scale the Russian system (GLONASS, fewer operational satellites). Other GNSS systems are under construction like the European system GALILEO, but also the Chinese system (COMPASS/Beidou). These systems allow every user using a GNSS receiver to determine his navigation parameters (3D position, 3D speed and time) regardless of time or place.

Navigation by satellites is based on the triangulation principle. It consists of calculating the position of a receiver by estimating the distance between this receiver and 3 GNSS satellites (Figure 17.2), enabling us to resolve the 3 unknowns of the position: latitude, longitude and altitude.

The distance d between the receiver and every satellite is calculated by estimating the propagation delay of the signal from the satellite to the receiver. The emission time is known thanks to the very precise clocks installed on satellites, and transmitted in the signal via the message of navigation broadcasted by every satellite; the reception time is known thanks to the internal clock of the receiver. The distance d is thus proportional to the propagation delay (at the speed of light c):

Figure 17.1. Galileo constellation [MAG 06]

Figure 17.2. GNSS triangulation ...

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