The open services provided by Galileo are realized by using the signals at L1, E5a and E5b whether data or pilot. Morover several combinations are also possible, such as a dual frequency service based on using L1 and E5a (for best ionospheric error cancellation) to single frequency services (at L1, E5a, E5b or E5a and E5b together) on which case the ionopheric error is removed using a model, and even triple frequency services using all the signal together (L1, E5a and E5b) which can be exploited for very precise centimetric type of applications.