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Global Differential GPS System
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System Description - Overview

Employing a large global real-time tracking network, the Global Differential GPS (GDGPS) System tracks the GNSS civil signals on the L1, L2, and L5 frequencies. Highly redundant satellite coverage (for example, 25 fold for GPS, 18 fold for GLONASS, on average) ensures seamless and robust global coverage. The raw measurements are streamed via redundant communication paths to three geographically-separate GDGPS Operation Centers (GOC). At the GOCs the data is processed by the RTGx software to estimate the real-time GNSS orbit and clock states, and derive the differential corrections to the GNSS broadcast ephemerides, as well as many by-products and services. Our state-space approach to orbit determination, pioneered by JPL, 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, and modems.

Extreme high reliability has been accomplished through an extremely high level of end-to-end redundancy, without any single points of failure. Innovative software ensures automatic fault detection and seamless failover between various redundant components of the system, resulting in uninterrupted service to customers.

Global Differential GPS System Overview
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