Expert Advice & Leadership Talks

Expert Advice: The Strategic Significance of Compass

December 1, 2010By

On November 1, 2010, China’s state news agency reported that the sixth Compass satellite was launched from the Xichang Satellite Launch Center. This was the fourth Compass satellite put into orbit this year, following launches in January, June, and August. Joining the United States, Russia, and the European Union, China is deploying is own global navigation satellite system of five geosynchronous satellites, 27 in medium Earth orbit (MEO) and three in highly inclined geosynchronous orbits (IGSO). Sometimes referred to as Beidou-2, Compass is a global RNSS (radio-navigation satellite system) that broadcasts one-way precision time signals to enable receivers to calculate their position. An earlier Chinese satellite navigation system, Beidou-1, was an RDSS (radio-determination satellite system) that provided regional coverage and required two satellites to get a position fix using two-way communications with a centralized ground station. read more

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Galileo from the Top: Interview with the EC’s Paul Verhoef

November 20, 2010By

Paul Verhoef, the European Commission’s program manager for European Union (EU) satellite navigation programs — namely Galileo — discussed current issues at some length with GPS World, in a conversation on November 10. He addressed aspects of interoperability with GPS and prospects for further development in that area, the need for an ongoing political commitment by the EU to Galileo, the challenges of financing, the prospects for an 18-satellite constellation (which he dismisses as unrealistic), military considerations for both Galileo and GPS, and the recent uncertainty around Galileo’s Public Regulated Service. read more

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Expert Advice: Block IIR Lifetimes and GPS Sustainment

November 1, 2010By

In 2009, a Government Accountability Office (GAO) report claimed that the GPS constellation was extremely vulnerable to failure, and a recent September 2010 GAO follow-up continues to make that assertion. In this article, we present the technical data to contradict some of the GAO report conclusions. read more

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Expert Advice: An EPIC Start for Coordination

October 1, 2010By

The new European Positioning, Navigation, and Timing (PNT) Industry Council (EPIC) will be a forum for organizations with an interest in all PNT systems including Global Navigation Satellite Systems (GNSS). EPIC shall serve as an information and distribution portal between all stakeholders in the PNT community. Its mandate includes all GNSS constellations and related augmentation systems worldwide, both operational and in development/modernization. read more

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Expert Advice: Remembering. And Resolving

August 1, 2010By

Few outside the position, navigation, and timing (PNT) community will also recall that the day before the 9/11 attacks, the U.S. government released a landmark document that described the vulnerabilities of services provided by GPS to disruption, whether by attack or inadvertent interference. The Department of Transportation Volpe Center’s GPS vulnerability assessment recommended that services utilizing GPS-provided PNT seek alternative sources of these services. What decisions and actions have the findings and recommendations of this report promoted? The answer is most disturbing. read more

Expert Advice: Moore’s Law and GNSS

July 1, 2010By

I started my relationship with GNSS and Moore’s Law in 1985, writing software for GPS tracking loops on the Advanced Range Instrumentation Aircraft program at the Applied Physics Laboratory of Johns Hopkins University for the U.S. Air Force. The project’s purpose was to navigate a large jet to accurately fly a pattern to drop buoys into the ocean. That receiver had seven circuit boards (six trackers and one navigator) mounted on a VME backplane in a 19-inch rack mount in the back of a C-130, and was about the size and weight of suitcase. read more

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Expert Advice: Quasi-Coherent Delay Lock Loop Tracking and Generalized Binary Coded Symbols in Multipath

May 1, 2010By

The original GPS signals, and indeed most GPS signals including L5, utilize conventional pseudonoise (PN) signal code division multiple access (CDMA), some with both in-phase and quadrature-phase modulation. In the late 1990s, I generalized Manchester PN symbol-spreading by defining split-spectrum binary square wave symbol-spreading, in a series of limited-distribution papers for the Air Force GPS Independent Review Team (IRT). These split-spectrum signals have been developed and analyzed much more fully by many others, and they are now termed binary offset carrier (BOC) modulation. The BOC codes can provide a noise-error advantage by placing more of their spectral energy at an offset frequency, thereby increasing the Gabor bandwidth. They can also provide spectral separation from other GNSS signals in the same frequency band, for example, L1. read more

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Expert Advice: Jamming: A Clear and Present Danger

April 1, 2010By

A packed audience attended the National Physical Laboratory in the United Kingdom for a February 23 meeting titled, “GPS Jamming and Interference: A Clear and Present Danger,” organized by the Digital Systems Knowledge Transfer Network. In his keynote address, David Last described a dark, silent and dangerous world without GPS. His final insight was this: “Navigation is no longer about how to measure where you are accurately. That’s easy. Now it’s how to do so reliably, safely, robustly.” read more

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