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Backing Up GNSS with Laser Radar & INS, RAIM in the City, Antenna Phase Wind-Up

Urban test location WEB.jpgHigh-sensitivity receivers were tested in these urban canyons.

“GNSS Solutions” is a regular column featuring questions and answers about technical aspects of GNSS. Readers are invited to send their questions to the columnists, Professor Gérard Lachapelle ( and Dr. Mark Petovello (, Department of Geomatics Engineering, University of Calgary, who will find experts to answer them.

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Q: What are the benefits of combining laser radar (ladar) and inertial data for navigation?

A: Indoor and urban outdoor areas still pose a very challenging environment for most GNSS receivers. In such areas, buildings and other obstacles generally introduce a significant GNSS signal attenuation and create a variety of multipath reflections. Although man-made obstacles represent a significant challenge for GNSS-based localization, they can be efficiently used as localization reference points if their navigation-related features are detected and feature parameters are estimated.

(For the rest of Andrey Soloviev’s answer to this question, please download the complete article using the PDF link.)

Q: Is fault detection/RAIM useful in areas of severe signal degradation, such as urban environments?

A: In the navigation message transmitted from its satellites, the GPS system provides users with some basic integrity information regarding the “health” or usability of the signals. However, this information is not current enough for some applications. Timely integrity monitoring is especially essential in safety-critical applications in order to ensure a certain degree of confidence in the navigation function.

(For the rest of Heidi (Sandström) Kuusniemi’s answer to this question, please download the complete article using the PDF link.)

Q: What is carrier phase wind-up? What is its effect on GNSS performance/operation?

A: Carrier phase wind-up refers to the change in measured carrier phase by a GNSS receiver caused by variations in the relative orientation between the transmitting and receiving antennas. This phenomenon is of concern for positioning, navigation, and timing applications because the observed change does not represent a variation of transmitter/receiver range and, hence, will result in carrier phase-based ranging errors.

(For the rest of Sunil Bisnath’s answer to this question, please download the complete article using the PDF link.)


The data generated for figures 1 and 2 in the laser radar/INS "solution" used a Systron Donner Digital Quartz Inertial Measurement Unit (DQI) from BEI Technologies, Inc., San Francisco, California USA, and an LMS-200 ladar from SICK AG, Waldkirch, Germany.

Author Profiles

Andrey Soloviev, Ph.D., is a senior research engineer at the Ohio University Avionics Engineering Center. He has been involved in navigation-related research since 1996.

Heidi (Sandström) Kuusniemi received her M.Sc. and doctor of technology degrees from Tampere University of Technology, Tampere, Finland. Her doctoral studies on reliability and quality monitoring in personal satellite navigation were partly conducted at the Department of Geomatics Engineering at the University of Calgary, Canada. Since October 2005, she has been working in research and development as Fastrax Ltd, Vantaa, Finland, where her current interests include high-sensitivity GNSS and reliability enhancement techniques.

Sunil Bisnath is an assistant professor of geomatics engineering in the Department of Earth and Space Science and Engineering at York University in Toronto, Canada. He has been involved in GNSS research since 1996, and his interests include long-range RTK, precise point positioning, crustal deformation monitoring, and spaceborne GNSS.

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