NovAtel: Proposed Ligado wireless network a concern for high-precision positioning

May 22, 2016  - By
Image: GPS World

NovAtel Inc. has submitted comments to the Federal Communications Commission (FCC) regarding Ligado Networks LLC’s (formerly New LightSquared LLC) License Modification Applications. NovAtel raises deep concerns about the testing methodology used and conclusions presented by Ligado regarding the impact of its proposed usage of L-band frequencies for a terrestrial wireless network.

In its filing, NovAtel identified serious flaws in the testing methodology used to evaluate high precision receivers. Although high-precision receivers were used during the testing, the high-precision position modes that are used to achieve centimeter-level positioning accuracy required by many professional and safety-critical applications were not evaluated. The study shows a lack of understanding of the uses of the GPS by assuming that all applications require the same positioning accuracy, NovAtel said.

The filing also raises a number of concerns about the potential harmful interference impact on GPS receiver performance. NovAtel is particularly concerned that Ligado has moved away from what it understood to be an agreed upon standard that interference tolerance should be limited to a received interference signal power level that causes no more than 1-dB degradation in the received C/No level. NovAtel disagrees with the conclusion in the RAA Study that there is no meaningful correlation between a 1-dB change and GPS performance. NovAtel submits any interference must not exceed 1-dB degradation in received C/No if robust, precise positioning is to be maintained. Ligado has not yet proven that its use of the spectrum will not be detrimental to high-precision users of the Global Navigation Satellite System (GNSS), which is what the 1-dB C/No degradation metric ensures.

“To date, Ligado has not proven that its use of the proposed spectrum can be made compatible with high-precision GNSS,” NovAtel said in a press release. “The interference impact on the other GNSS constellations such as Galileo, GLONASS and Beidou has not been addressed. These constellations are increasingly used in combination with GPS for many high-precision applications. Proposed, unverified mitigation methods such as narrowband antennas are presented in the Ligado filing without explanation of who will be responsible for the cost of such design modifications and retrofit programs.”

To view NovAtel’s FCC filing in its entirety, visit the FCC website.

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