Speaking before the Space-Based Position Navigation and Timing (PNT) advisory board and a room full of visitors, Javad Ashjaee, president and CEO of Javad GNSS, explained on Nov. 9 how his filter technology protects GPS receivers from LightSquared broadband network interference. Through a series of charts and illustrations, he showed that GPS as currently designed is open to all types of interference, and that the filter system he developed-which essentially consists of a ceramic filter followed by a series of surface acoustic wave (SAW) filters-resolves the problem by providing a solid wall against 10L and 10R signals, which are most likely to cause interference on either side of the GPS signal.
He further explained that extensive testing done in his company’s labs has demonstrated no signal loss at the 10L power of -10dBm, which he said is the highest theoretical power level the LightSquared signal could generate. He also showed that the filter technology did not affect the performance of the receivers. When subjected to what he described as the “ultimate test,” in which they were placed on a tall building with multipath from both above and below, the receivers were accurate to .2 millimeters-well above the level of accuracy needed for precise positioning applications.
Javad GNSS has already begun manufacturing LightSquared-compatible TRIUMPH GNSS receivers in its San Jose, Calif., facility. To emphasize this point, 40 boxed and stacked units were in the background as Ashjaee spoke, along with several open units that were available for demonstration. Ashjaee said the company will begin manufacturing LightSquared-integrated receivers in May 2012, which he believes will substantially improve RTK positioning by taking full advantage of the anticipated high speed, low cost and wide availability of the proposed LightSquared broadband network.
Ashjaee’s presentation was part of a panel discussion on LightSquared compatibility with GPS. Other participants on the panel included Jim Kirkland, vice president and general counsel for Trimble Navigation; Martin Harriman, executive vice president of LightSquared; Scott Burgett, software engineering manager for Garmin International, and Mark Sturza, president of 3C Systems Co.. The panel was moderated by Thomas Stansell of Stansell Consulting, who noted in his introduction that Ashjaee is “one of the single most innovative people in his field, bringing out products that make his competitors unhappy and uncomfortable at times because he is a leader.”
No one on the panel debated the technical aspects of Ashjaee’s presentation. However, Kirkland pointed out that the reason modern GPS devices are open to interference is because the manufacturers’ contracts with mobile satellite service (MSS) providers said that the receivers needed to be able to receive signals anywhere within the band due to international coordination treaties. He conceded that other manufacturers could also develop filters that would block those signals, but he noted that such filters would only be a potential solution for high-precision receivers and likely wouldn’t work for other GPS devices.
Questions were presented to the panel in a written format and primarily revolved around the issues of cost and LightSquared’s potential use of the upper band of the spectrum in the future-issues Stansell said would not be resolved in the panel discussion. Kirkland reiterated the general concern that even if the filter solution does prove viable at the lower 10 mHz of the spectrum-an issue he said still needs to be definitively resolved through independent testing-retrofits would be costly, both in terms of upfront cost and lost productivity. He said he believes the $300 to $800 retrofit costs cited by Ashjaee are on the low end when considering the broad range of receivers currently in use. He also said the possibility of LightSquared later being able to expand its use of the spectrum into the higher bands casts a pall over any potential solution at the lower bands. In a follow-up question, Harriman was asked whether LightSquared intends to develop the upper bands, but he didn’t provide a direct answer.
Stansell closed the discussion by summarizing the key issues. “I think we learned, thanks to Javad, about a very clever solution to a particular problem for a particular range of products-the products he is most familiar with,” he said. “It may or may not fit in some of the other applications. What we have not addressed is sort of the elephant in the living room. That is the cost, and time delay, and changeover process if LightSquared is allowed to go forward. Will it be the lower 10, upper 10? That has to be resolved. There are very large questions remaining to be discussed, and [they] may or may not be fully solved in a short period of time."
At the same time, he said, everyone should appreciate the work that is being done on all sides. “I have never seen so much dedication and energy, and people extended in cooperation, not only within the GPS community but also with LightSquared,” Stansell said. “It’s a massive effort that’s been going on. We have a lot still to learn and to do, and we certainly appreciate the innovation of solutions and thoughts that are coming to us."