Introduction - Understanding GPS: Principles and Applications - page 6

C/A code

P(Y) code P(Y) code

C/A code

L2C

P(Y) code

P(Y) code

L5

M code

M code

frequency

L5
(1,176.45 MHz)

L2
(1,227.6 MHz)

L1
(1,575.42 MHz)

Figure 1.1 GPS signal evolution.

Figure 1.2 Block IIR-M satellite. (Courtesy of Lockheed Martin Corp. Reprinted with permission.)

pleted, GALILEO will provide multiple levels of service to users throughout the
world. Five services are planned:

1. An open service that will be free of direct user charges;
2. A commercial service that will combine value-added data to a high-accuracy
positioning service;
3. Safety-of-life (SOL) service for safety critical users;
4. Public regulated service strictly for government-authorized users requiring a
higher level of protection (e.g., increased robustness against interference or
jamming);
5. Support for search and rescue .