GPS World, December 2011

THE SYSTEM PNT Board Hears Proposal for LightSquared Solution The November 9 meeting of the National Space Based Position Navigation and Timing PNT Advisory Board in Alexandria Virginia got several earfulls regarding the LightSquared GPS controversy One of seven speakers on a two hour panel Javad Ashjaee president and CEO of JAVAD GNSS demonstrated his companys newly developed filter technology that he said could protect GPS receivers from LightSquared broadband network interference As Ashjaee stated the proposed solution does not protect against interference from the so called high 10 signals one of two bands the other is known as the low 10 for which LightSquared has received a conditional waiver Unless and until a solution for the terrestrial high 10 signals is found LightSquared transmissions in that band will still interfere with the GPS signal The technical solution proposed by JAVAD GNSS addressed only the low 10 band The JAVAD GNSS proposed fix consists in simplified form of a ceramic filter followed by a series of surface acoustic wave SAW filters A PDF of Ashjaees 76 slide Powerpoint demonstration without his verbal explanations and commentary along with other presentations from the board meeting are available at www pnt gov advisory 2011 11 A December 8 GPS World webinar reprised the same presentation and the download at www gpsworld com webinar includes audio of Ashjaees remarks Ashjaee said that his companys testing of its own filter methodology found no GPS signal loss due to a low 10 10L signal power of 10 dBm An Ultimate Test Special Zero Baseline put receivers on a Moscow skyscraper with multipath from both above and below One antenna fed two receivers zero baseline One receiver used PROPOSED FILTER to harden high precision GPS receivers against Lightsquared Lower 10 standard filtering and the other the new filters He said that over 15 hours of testing the average carrier phase error between the two receivers was 02 millimeters and the average code difference was about 5 centimeters JAVAD GNSS has started production of what Ashjaee calls LightSquaredcompatible Triumph GNSS receivers He brought 40 units to the PNT Board meeting The company will begin manufacturing LightSquaredintegrated receivers in May 2012 for RTK positioning using the proposed LightSquared broadband network for high speed communication if and when it is deployed Fellow presenter Jim Kirkland vice president and general counsel for Trimble Navigation pointed out that such filters represented a potential solution only for one class of high precision receivers Whether it would work for other classes of high precision receivers had yet to be verified Kirkland said that even if further independent testing shows that the filter solution is viable at the lower 10 MHz of the spectrum retrofits would be costly and time consuming Questions regarding cost and responsibility of retrofit should the solution prove practical were not discussed at length at the meeting nor was any solution proposed LightSquared executive vice president Martin Harriman did not directly answer a question as to whether his company intends to develop the upper 10 MHz for which it has been given a conditional waiver Scott Burgett software engineering manager for Garmin International said It is almost impossible to design new products compatible with LightSquareds proposed system without knowing its technologys end state He estimated 10 15 years to properly retrofit Garmin devices which are widely distributed in general aviation personal navigation car navigation and other sectors so that they could coexist with LightSquared The panel was moderated by Tom Stansell of Stansell Consulting who concluded 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 It may or may not fit in some of the other applications What we have not addressed is the elephant in the living room Stansell continued 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 www gpsworld com December 2011 GPS World 17