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All posts from GPS World staff

  • Parkinson Prescribes Remedy for GAO Report Alarm

    May 26, 2009 1 Comment

    Brad Parkinson, the first GPS Program Office Director, chief architect and advocate for GPS, submitted written testimony to Congress on mitigation options for possible GPS brownouts. His presentation comes in reference to the recent GAO report highlighting the risk that the GPS constellation may fal...

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  • Loran Study Finally Unleashed: Says Keep It, Best Option

    May 12, 2009 1 Comment

    Withheld from the public for two years, since its completion in March 2007, the Independent Assessment Team (IAT) report has been let out of detention, just in time to counter recent efforts by the Obama administration, the Department of Homeland Security, and the U.S. Coast Guard to throttle the pr...

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  • GPS at Risk: Doomsday 2010

    May 12, 2009 1 Comment

    The United States Government Accountability Office (GAO) issued on May 7 an alarming report on the future of GPS, characterizing ongoing modernization efforts as shaky. The agency appears to single out the IIF program as the weak link between current stability and ensured future capability, calling ...

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  • New GPS Satellite’s Problems Indicated

    May 04, 2009 1 Comment

    Lt. Col. David Goldstein, chief engineer for the GPS Wing, told the plenary session at the European Navigation Conference in Naples, Italy, that the Wing is experiencing some “out of family” measurements from the recently launched IIRM (20) satellite. This appears to corroborate some unofficial ...

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  • Assessing the Spoofing Threat

    Jan 01, 2009 1 Comment

    A portable spoofer implemented on a digital signal processor mounts a spoofing attack, characterizes spoofing effects, and suggests possible defense tactics. GNSS users and receiver manufacturers should explore and implement authentication methods against sophisticated spoofing attacks. By Todd E. H...

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  • Integer ambiguity validation: Still an open problem?

    Jul 30, 2007 No Comments

    By Sandra Verhagen High-precision Global Navigation Satellite System (GNSS) positioning results are obtained with carrier phase measurements, once the integer cycle ambiguities have been successfully resolved. The position solution is obtained in four steps: 1. Float solution:least-squares, discardi...

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  • Antenna-induced biases in GNSS receivers May 17, 2007

    May 17, 2007 No Comments

    By Inder Jeet Gupta It is well known that the phase center of a GNSS antenna can vary with the satellite direction. This phase center movement leads to aspect dependent carrier phase and code phase biases in the satellite signal. For precise geo-location, one needs to characterize the antenna-induce...

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  • GPS Transmitter Frequencies

    Jan 16, 2007 No Comments

    Why are the two GPS Transmitter frequencies (1575.42 and 1227.6 MHz) coherently selected integer multiples of 10.23 MHz master clock? Question posted on CANSPACE on October 30, 2006, by Sivaraman Ranganathan. The document defining the GPS signal, IS-GPS-200, states that “The carrier frequencie...

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