201011 November/December 2010

Measuring GNSS Signal Strength

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

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
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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
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China Launches Another Compass/Beidou-2 GEO Satellite
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
Galileo Master, Winner of the 2010 European Satellite Navigation Competition
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

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
Military PNT — The Way Ahead

Military PNT — The Way Ahead

FIGURE 1: The three foundations of C2 and how they are “changing the game” in an electronic battlespace: spectrum (communications media), yellow; computers (digital data), green; PNT (precise position and timing), blue.

With thanks to Yogi Berra, it’s “déjà vu all over again” for the Global Positioning System, but this time with a twist.

Twenty-five years ago, the question asked by U.S. military commanders and combat personnel in the field was, “Why should I go to the trouble to use this space-based system called GPS?” Today, the question being asked is, “GPS is vital to the success of my mission; so, why are you asking me to consider using something else?”

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By Inside GNSS
eVOTZ: Mobilizing Voters

eVOTZ: Mobilizing Voters

Figure 1: An overview of the eVOTZ location-based voter solution architecture

The votes are in and the USA Challenge 2010 award goes — appropriately enough — to eVOTZ, a mobile electronic balloting technology.

According to eVOTZ founder Elliot Klein, the winning application in the North American portion of the European Satellite Navigation Competition (ESNC) is designed to solve the problems of authentication and verification that have stalled previous attempts to create a secure and trustworthy e-voting solution.

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By Inside GNSS
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