GPS, an active program for over 30 years and characterized by consistent, predictable, and dependable performance as a global utility, continues to evolve as a modernized component of the GNSS. The 2004 U.S. Space-Based Positioning, Navigation, and Timing (PNT) policy responds to changing international conditions and the worldwide growth of GPS applications. The 2004 PNT Policy ensures continued continuity in the U.S. national management of GPS as a dual-use civil and military system, a partnership that maintains GPS as a modernized global utility and providing a solid foundation for international use by the civil community. The paper provides an overview on: current GPS constellation status and performance, improvements in GPS (L2C and L5) that are or will soon become available to the civil worldwide users, goals for the next generation system of satellites (GPS-III), pending design for the new L1C signal, current GPS modernization schedule, international coordination activities, and U.S. national policy update and the National Space-Based PNT Coordination Office - http://pnt.gov.

The surveying and mapping industry has been revolutionised by the use of Global Navigation Satellite Systems (GNSS) involving satellites, ground reference station infrastructure and user equipment to determine positions around the world. The Global Positioning System (GPS) from the USA is the best-known, currently fully operational system. Russia also runs its own GNSS called GLONASS. Fuelling growth in the coming decade will be next generation GNSS that are currently being developed. The USA is modernizing GPS, Russia is revitalising GLONASS and Europe is moving ahead with its own Galileo system. This paper looks at some of the implications of these improvements for the service providers of continuously operating reference stations (CORS), as well as for survey users. For example, the EU's Galileo system is much more open to civilian and commercial involvement and allows for regional and local augmentation to the core system. How will current CORS infrastructure be able to cope providing differential positioning services to users tracking a combination of GPS, Galileo and perhaps GLONASS signals? How will users benefit from next generation GNSS?

Intended to mitigate the Galileo project risks, the European Space Agency launched in 2003 the Galileo System Test Bed Version 2 (GSTB-V2) with the development of two satellites GIOVE-A and B (Galileo In-Orbit Validation Element) as the first step in the in-orbit validation of the Galileo system. The objectives of these two satellites are:

Galileo is the European Global Navigation Satellite System, under civilian control, and consists on a constellation of medium Earth orbit satellites and its associated ground infrastructure. Galileo will provide to their users highly accurate global positioning services and their associated integrity information. The elements in charge of the computation of Galileo navigation and integrity information are the OSPF (Orbit Synchronization Processing Facility) and IPF (Integrity Processing Facility), within the Galileo Ground Mission Segment.

Navigation algorithms play a key role in the provision of the Galileo Mission, since they are responsible for computing the essential information the users need to calculate their position: the satellite ephemeris and clock offsets. Such information is generated in the Galileo Ground Mission Segment (GMS) and broadcast by the satellites within the navigation signal, together with the expected a-priori accuracy (SISA: Signal-In-Space Accuracy), which is the parameter that in fault-free conditions makes the overbounding the predicted ephemeris and clock model errors for the Worst User Location.

In parallel, the integrity algorithms of the GMS are responsible of providing a real-time monitoring of the satellite status with timely alarm messages in case of failures. The accuracy of the integrity monitoring system is characterized by the SISMA (Signal In Space Monitoring Accuracy), which is also broadcast to the users through the integrity message.

Galileo is currently in its detailed design and development phase. The design and development phase for the OSPF started on February 2005 and for the IPF in May 2005. In both cases, the Preliminary Design Reviews (PDR) have been successfully held and the algorithms are now entering in the final prototyping activities, which are expected to be finished by the middle of 2006. Innovative changes have been proposed with respect to the initial baseline coming from the previous Galileo development phases, such as the real-time synchronization process with sub-nanosecond accuracy (below 0.5 ns).

The main objective of this paper is to present the navigation and integrity algorithms for Galileo and to briefly describe the development approach which is being followed including aspects such us: