Design & Test

Innovation: GNSS and the Ionosphere

February 1, 2011By
Figure 4. Photo of red and green auroras observed near Fredericton, New Brunswick, Canada (46 degrees north latitude) early on October 31, 2003. (Courtesy of Richard and Marg Langley.)

What’s in Store for the Next Solar Maximum?
Although the sun can become disturbed at any time, solar activity is correlated with the approximately 11-year cycle of spots on the sun’s surface. We are just coming out of a minimum in the solar cycle and headed for the next maximum, predicted to occur around the middle of 2013. How significantly will GNSS users be affected? In this month’s column, two ionosphere experts tell us what might be in store. read more

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Innovation: The Distress Alerting Satellite System

January 1, 2011By
Cospas–Sarsat system.

Taking the Search out of Search and Rescue
In 1997, a Canadian government study determined that an improved search and rescue system would be one based on medium-Earth orbit satellites, which can provide full global coverage, can determine beacon location, and would need fewer ground stations. This month’s column examines the architecture of the GPS-based Distress Alerting Satellite System and takes a look at early test results. read more

Dynamic Duo: Combined GPS/GLONASS Receivers in Urban Environments

January 1, 2011By
Aerial view of downtown Calgary from the southwest, with test trajectory shown in red.

The impact of adding GLONASS to HS-GPS is assessed using a software receiver operating in an actual urban canyon environment. Results are compared with standard and high sensitivity GNSS receivers and show a significant improvement in the availability of position solutions when GLONASS is added. An assisted high sensitivity receiver architecture is introduced which enables high fidelity signal measurements even in degraded environments. read more

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GNSS RF Compatibility Assessment: Interference among GPS, Galileo, and Compass

December 1, 2010By

A comprehensive methodology combines spectral-separation and code-tracking spectral-sensitivity coefficients to analyze interference among GPS, Galileo, and Compass. The authors propose determining the minimum acceptable degradation of effective carrier-to-noise-density ratio, considering all receiver processing phases, and conclude that each GNSS can provide a sound basis for compatibility with other GNSSs with respect to the special receiver configuration. read more

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2010 Leadership Dinner: Recognizing GPS Heroes, Grand Game

November 1, 2010By

GPS World’s seventh annual Leadership Dinner, which took place during the ION-GNSS conference in Portland, Oregon, and was sponsored by Rockwell Collins, this year honored some of the surviving GPS Heroes (see May and June 2010 issues). PLUS: We invited 120 dinner guests to find out by walking a mile in someone else’s shoes, in the Grand Game of GNSS, a role-playing and negotiation exercise. Learn who won! read more

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Innovation: Record, Replay, Rewind

October 1, 2010By

Testing GNSS Receivers with Record and Playback Techniques
Is there a way to perform repeatable tests on GNSS receivers using real signals? This month’s column looks at how to use an RF vector signal analyzer to digitize and record live signals, and then play them back to a GNSS receiver with an RF vector signal generator. read more

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Letter to the Editor: History Articles Set Record Straight

October 1, 2010By

I was relieved to see that the facts related to the conception of GPS were clearly laid out in the two-part article “GPS Heroes” (May and June issues). During the past few years, erroneous information about the early years of GPS development has circulated in some military, engineering, and scientific circles.These stories centered on some version of the idea that GPS’ design originated with the Naval Research Laboratory (NRL) and within the patent submitted for Timation by the NRL’s Roger Easton; the U.S. Air Force and The Aerospace Corporation were conspicuously missing from the various scenarios that credited Roger Easton with “inventing” GPS. read more

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Spoofing Detection and Mitigation with a Moving Handheld Receiver

September 1, 2010By

A single spoofing source has a different spatial signal distribution from the authentic GPS signal. An antenna array can estimate the spatial distribution of the received signal and thus discriminate the spoofing signal from the authentic one. Moving a handheld receiver with a single antenna during signal capture snapshots produces a form of a synthetic array, highly effective in discriminating spoofing signals sourced from a point-source jammer. read more

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