GPS World, January 2018

OUT IN FRONT A GRAVE THREAT TO GPS AND GNSS of the area would be in violation But the ABC test results reveal a much graver situation They show that for the current Ligado proposal 1580 watts the degradation radius is over 14 kilometers for high precision receivers See FIGURE 2 CONCLUSIONS The 1 dB criterion is the correct accepted and somewhat generous allocation of interference that can be accepted by the PNT community We would hope that the FCC would continue to insist on this standard PNT users must yet again defend the spectrum vigorously Most of us are scientific and technical people We are not used to discussions that deliberately avoid the technical issue or deny scientific evidence We reject arguments that violate the fundamental laws of physics The currently filed proposal 1580 Watts at spacing of mile is unacceptable It will do grave harm to many important PNT applications We must be very leery of the new proposal by Ligado of 9 13 dBW It still would violate the 1 dB criterion at 100 meters for many PNT users Moreover the company history has been to bait and switch it has an authorization for MSS Ancillary Terrestrial Component MSS ATC stations to fill the gaps in satellite coverage with ground transmitters These must operate in conjunction with the space to ground link that made them effectively self limiting However in 2011 it almost succeeded in switching this to a ground only system which would have achieved a huge financial windfall OPEN AIR VERIFICATION If the FCC continues to consider this proposal there is one step that it should take before granting it It should require Ligado to deploy an array of transmitters in its advocated configuration and run realworld open sky testing to assess the harm that may result particularly to high precision accuracy Such testing was done when the issue was first raised in 2011 and conclusively demonstrated unacceptable interference Nothing has really changed from the baseline that was tested and found unacceptable then The company should carry the full financial burden of such a verification under PNT supervision The government having already spent millions of dollars to defend the spectrum should not bear the cost of such retesting Without this confirmation it is hard to conceive of putting GPS and PNT at significant risk to satisfy investors who want to flip a company after gaining rezoning permission for their spectrum FROM 20000 FEET ALTITUDE If we examine the situation without the technical details we have this Fundamentally Ligado wants to provide service using its allocated frequency band for an unlimited number of 36 GPS WORLD WWW GPSWORLD COM JANUARY 2018 Internet of Things installations It is not proposing a small fixed number of transmitting towers located in isolated regions but rather an accelerating deployment of private networks many of which will be close to commercial and essential infrastructure where GPS use is critical It seems unrealistic that Ligado can or will reliably guarantee that these widespread installations will be continually adjusted and monitored to avoid GPS interference I believe the concept of allowing the installation of transmitting towers that by design will interfere with normal GPS use at some distance away opens the door to tacit approval of short range or not so short range GPS jammers Whil e I can commend the entrepreneurial spirit the Ligado proposal seems very reckless indeed The incremental value of an additional broadband transmitting system when there are at least five already in existence seems trivial compared to the potential damage done to the modern utility named GPS I sincerely hope the FCC can find a spectrum swap or deny outright the current Ligado application Continued from page 14 FIGURE 2 macro urban transmitter high precision receiver 1530 MHz