GPS isn’t the only navigation system around. The European Space Agency (ESA) is developing the Galileo Navigation System for the European Union. Unlike GPS, it will be under civilian control. But the two systems aren’t all that different. SiGe Semiconductor’s highly integrated SE4120L receiver uses software-defined radio (SDR) techniques to comply with both navigation standards.

The Galileo system uses 30 satellites in three orbits 23,222 km high with a 56° inclination to the equator for full world coverage. The satellites transmit on the same frequencies as GPS, but the signals use a different modulation scheme. The CDMA signals are easily sorted out and distinguished from one another because of their unique codes.

GPS uses binary phase-shift keying (BPSK) modulation while Galileo uses a new form of modulation called binary offset carrier (BOC) 1.1. This difference lets the United States or the ESA block each other’s signals whenever necessary. The Galileo system is more accurate than the GPS system. It provides a 1-m margin of error, whereas GPS has a 3-m margin.

Thanks to an agreement between the U.S. and the ESA, GPS and Galileo are complementary, so their coverage of the Earth is far more complete than each system alone. All the major gaps across the globe are filled in, making reception more reliable from almost anywhere—if you have a receiver that covers both systems. That’s where the SiGe SE4120L comes in.
[via elecdesign]