201011 November/December 2010

Measuring GNSS Signal Strength

Q: What is the difference between SNR and C/N0?

A: GPS receivers built for various applications, such as handhelds, automobiles, mobile phones, and avionics, all have a method for indicating the signal strength of the different satellites they are tracking. Some receivers display the signal strength in the form of vertical bars, some in terms of normalized signal strength, and others in terms of carrier-to-noise density (C/N0) or signal-to-noise ratio (SNR).

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By Inside GNSS

Modeling Phase Noise Effects on Receivers: A History

Return to main article: Local Oscillator Phase Noise

In 1966 D.B. Leeson proposed an empirical linear model for the noise spectrum of an oscillator, which has been extensively cited in the  literature since then. G. Sauvage generalized this model to other resonant circuits in 1977, providing a deeper mathematical background. In 1998 A. Hajimiri and T.H. Lee proposed a linear time variant model (LTV) to explain the effect of each of the noise sources of an oscillator on its phase noise.

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By Inside GNSS

World Wide GNSS

GNSS and the Internet. Less than a generation has passed since these two pervasive, global systems first became practical realities for the Earth’s citizens, and now it seems as though they have always been here, connected to everything. The Internet’s warp to GNSS’s woof.

Throw in two nearly simultaneous developments — mass-market wireless communications and mobile computing — and we have sketched the technological matrix of the modern world.

Where did these game-changers come from? How far back do they go?

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By Inside GNSS

Frank Czopek

Frank & Jeanine at the Wild Animal Park

SIDEBAR: Frank Czopek’s Compass Points

Frank Czopek and his brothers used to go to the 1970s Detroit version of Craigslist — Trading Times — to buy two or three non-functioning Chevrolet Corvairs (air-cooled rear engine-mounted) cars, at $25 apiece.

They hoped to turn the junkers into a single functioning automobile over a weekend. Unfortunately, the results did not last long; so, the process was repeated often. But they sure had fun!

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By Inside GNSS
October 31, 2010

China Launches Another Compass/Beidou-2 GEO Satellite

Compass G4 satellite and Long March rocket on Xichang launch pad displays new Beidou logo.

[UPDATED Oct. 31, 2010) China has launched its fourth Compass/Beidou-2 satellite this year, shortly after midnight today (November 1, 2010, local time) from the Xichang Satellite Launch Center in Sichuan Province.

This is the sixth satellite in the second-generation Beidou constellation. The spacecraft will join three other GEOs, a middle Earth orbiting spacecraft, and an inclined geosynchronous orbiting (IGSO) satellite.

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By Inside GNSS
October 25, 2010

Galileo Master, Winner of the 2010 European Satellite Navigation Competition

A Salzburg, Austria–based start-up company, Mobilizy, took home the €20,000 grand prize in the European Satellite Navigation Competition 2010 (ESNC 2010) for its revolutionary navigation system Wikitude Drive, which uses augmented reality (AR) to superimpose driving directions over live street video on smartphones.

Wikitude Drive also won the prize for the best application leveraging EGNOS, the European satellite-based augmentation system that aims to add even more speed, precision, and reliability to GPS. The European GNSS Agency (GSA) sponsored the EGNOS prize.

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By Inside GNSS

Local Oscillator Phase Noise

FIGURE 1: Block-diagram of a GNSS direct-conversion receiver


For the complete story, including figures, graphs, and images, please download the PDF of the article, above.

GNSS systems rely on direct sequence spread spectrum (DSSS) transmissions to achieve high receiver sensitivity. Typically, GNSS user equipment compares the signal received from a satellite with an internally generated replica of its corresponding code until the maximum correlation for a given delay is achieved. This provides an indirect measurement of the satellite-receiver range.

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By Inside GNSS