Abstract:
Employing the largest global real-time tracking network, the Global Differential GPS (GDGPS) System tracks the GPS civil signals on the L1 and L2 frequencies. Highly redundant satellite coverage (25 fold, on average) ensures seamless and robust global coverage. The raw measurements are streamed via redundant communication paths to multiple GDGPS Operation Centers (GOC) (3 centers as of October
... 2006). At the GOC the data is processed by the award-winning software, Real Time GIPSY (RTG), to derive the real-time differential corrections to the GPS orbit and clock states, as well as many by-products and services. Our state-space approach to orbit determination ensures that all the products are globally and uniformly valid.
The fundamental latency of the system is ~5 seconds from reception of the navigation signal by the tracking receiver to the production and dissemination of the differential corrections and the other real-time by-products. Lower latency for certain products, such as integrity monitoring, is supported.
The data products are disseminated to customers through a variety of channels. Customers are encouraged to access multiple GOCs and use multiple communications channels to ensure end-to-end redundancy for mission-critical products and services. Supported channels include: internet, VPN over internet, T1, Frame Relay, modems, and satellite broadcast.
Extremely high reliability has been accomplished through an extremely high level of end-to-end redundancy, without any single point of failure. Innovative software ensures automatic fault detection and seamless failover between various redundant components of the system, resulting in uninterrupted service to customers.
[Summary provided by NASA.] 
