Global Navigation Satellite Systems Engineering, Policy, and Design
Global Navigation Satellite Systems Engineering, Policy, and Design
Integrity denotes the measure of trust placed in the correctness of the information provided by navigation systems. Safety critical applications require integrity measures to indicate with what level of confidence the navigation information may be used.
By Alan Cameron
Q: Are C/N0 Algorithms Equivalent in All Situations?
A: Fundamental to determining the status of GNSS tracking subsystems and controlling a GNSS receiver, the measure of C/N0 (carrier-to-noise ratio) provides satellite signal health information in addition to the PVT (position, velocity, time) information. For example, tracking loops experience a rapid increase of tracking errors at low C/N0, e.g., below 30 dBHz, until they completely lose lock.
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A frequently asked question about GPS is: How accurate is a GPS-based position? The experienced GPS user knows that a big difference lies between using pseudoranges alone or combining pseudoranges and carrier phases.
The following analysis is partly based on an idea raised in the book, Global Positioning System: Signals, Measurements, and Performance, by P. Misra and Per Enge (See Additional Resources section at the end of this article).
By Alan Cameron
Back in 1999, the European Union decided to set up a global satellite navigation system (GNSS), known as Galileo, for civil and commercial use. Early 2010 the European Commission awarded the contracts for Galileo’s first satellites, launchers and support services. In 2011 the European system will finalize its validation phase. As a result, the initial service provision of Europe’s satellite navigation system could start as of early 2014.
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The New Year’s festivities had ended and satellite operators at the 2d Space Operations Squadron (2 SOPS) at Schriever Air Force Base, Colorado, were hard at work conducting routine operations on the GPS satellites. At around 11:30 in the morning local time (1830 UTC) on January 1, 2004, range errors for space vehicle number (SVN) 23 began to rapidly drift above the 30-meter threshold.
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