Air Transport

The signals broadcast by Navstar GPS and Galileo are not straightforward.

The GPS legacy signals, broadcast by its existing orbiting blocks, I, II, IIA and IIR are three signals on two frequencies, L1 and L2. On L1 is the civil signal and on L1 and L2 the old military signal, known as P for precision.

With the launch of the first GPS-IIR-M satellite there are, in addition to those signals, the new civil signal L2C, which is broadcast on frequency L2, and on L1 and L2 the new military signal, M.

Then the launch of GPS-IIF in 2008 will see a new civil signal, L1C, broadcast. Navstar GPS will be broadcasting seven signals on three frequencies in 2008. With GPS-IIIA there could be another new civil code, L1C, on the L1 frequency, bringing the total to eight from 2012.

Galileo will transmit 10 signals using the frequency allocations E5a, E5b, E6, E1 and E2 for its signals. E1 and E2 frequencies are close to L1 and so Galileo will effectively transmit at L1. E6 is close to L2. For any of these signals to be used globally, there need to be 24 satellites in orbit so any receiver anywhere on Earth can see four satellites to triangulate and check its position. As such the more recent and planned Navstar blocks' new signals will not be considered operational for years.