Inside GNSS Media & Research

MAR-APR 2018

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38 InsideGNSS M A R C H / A P R I L 2 0 1 8 supporting customers over a diverse range of applications and geographic locations for more than twenty years. "As we all know, GNSS offers amazing position- ing and timing capabilities. But its predicated on a very weak signal and a complex processing chain with multiple entry points for interference. So serious GNSS users need a way to identify and deal with interference on their own." Kennedy shared a story of one of her first ex- periences of interference with a customer, an instance in 2005 when Sportvision was using GPS and Real-Time K inematic (RTK) posi- tioning to enhance a television broadcast of a NASCAR race. The Sportvision team working at the Daytona track noticed that on Turn 1, they always lost RTK positioning and also often lost GPS positioning. NovAtel and Sportvision ran several tests, looking into telemetry links and RTK correc- tions, swapping receivers and systems around, and everything appeared to be operating prop- erly. Finally, Sportvision, savvy GNSS users with a strong background in RF, used a spectrum analyzer attached to an active GPS antenna to find their interferer. Turns out a luxury RV in the camping area around the track had a satellite TV antenna that had a design defect that made it an accidental emitter on GPS L1. "It was an unexpected thing to find," Kennedy said. "Satellite T V should have been OK; it should not have been a problem with our part of the spectrum. But like I said, it was an unin- tentional interferer that was a design defect that was creating a fairly effective jammer on Turn 1. I remember then thinking there really has to be a better way to do this." Now there is. With NovAtel's OEM7 generation, the company introduced the Interference Toolkit with two major areas of functionality: detection and mitigation. This behind the scenes workshop illustrates how to use ITK and how to solve typi- cal problems users may encounter on the detec- tion side of things. "I have to remind everybody that prevention is a better cure than any medicine," she said. "Being able to characterize your RF environment is a re- ally powerful tool, especially when you're design- ing a system." The systems today that people are using GNSS in are shrinking in size, and they usually include telemetry, data storage or other data processing components, and they're likely operating in an uncontrolled environment that has inadvertent or possibly unintentional interferers. "Telling the future is a really tricky business but I'm pretty sure one bet that you can make is that wireless communication and spectrum usage is only increasing and never decreasing," Kennedy added. "Which means interference threats are increas- ing and never decreasing. It's never getting qui- eter out there in an RF sense." SELF-INTERFERENCE Schleppe provided a section of the webinar on "Solving self-interference using the Interference Toolkit." Self-interference can come from the onboard processors or data loggers in your system, the motors and controllers on your Unmanned Aerial Vehicle (UAV), or the radio WiFi systems used for data exchange. "Self-interference is especially annoying since you take it with you wherever your system is deployed," Schleppe said. "If it's present while tracking in clear sky conditions it can be a real problem when you're in an attenuated environ- ment such as under trees, indoors and especially if you're experiencing external interference or jamming." Schleppe ex pla ined how power spec tra l density graphs and IT Spectral Analysis com- mands are used to "hunt down self-interfer- ence in your system," and also showcased the importance of comparing a clean spectrum vs. self-interference. CASE STUDIES The ITK has been proven to help detect and miti- gate interference in a variety of applications and environments. Alves shared success stories where WEBINAR RECAP ยป INTERFERENCE DETECTION AND MITIGATION NovAtel's Interference Toolkit was able to identify a weather station antenna as the source for interference at a university in India. After relocating the antenna, the interference issue was corrected.

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