GPS World, January 2018

OUT IN FRONT A GRAVE THREAT TO GPS AND GNSS by Karen VanDyke sponsored a very complete set of independent tests these are the most credible estimates of harmful interference The ABC results have been made public The PNTABs six points were published after DOT testing had begun but DOT expanded and modified their effort to satisfy the criteria The DOT conclusions based on modeling real world antennas and propagation patterns are shown in TABLE 1 At 100 meters all classes of receivers tested had results that would exceed the 1 dB threshold even for the reduced power level P2 1580 Watts that has been the most recent filing The shaded square is particularly troublesome It shows that for the most susceptible high precision receivers the Ligado proposed power exceeds the 1 dB threshold by over 200000 This result is particularly damning for the proposed repurposing because it is this class that produced the highest payoff in the recent Department of Commerce Study over 30 billion per year PNT OPERATIONS AT RISK These are examples of unintended and potentially hazardous consequences of repurposing UAVs Unmanned aerial vehicles drones will fly very close to the dense array of transmitters that Ligado would deploy They usually require GPS for flight control Even more important if we are to monitor them and keep them from collisions GPS offers the only viable techniques with 3D accuracy and almost 100 availability PRECISION SURVEY This is routinely used in urban areas for building construction and is a major source of productivity gains These survey receivers are all high precision and routinely make measurements to better than inch HELICOPTERS These are found in urban area at all altitudes They are FIGURE 1 Potential Impacts on High Performance receivers Red loss of lock of all satellites Yellow loss of lock of low elevation satellites Green 1 dB degradation used for law enforcement rescue and passenger transportation GPS is mainly used for general navigation PUBLIC SAFETY VEHICLES Fire police and ambulances use GPS for both navigation and dispatch tracking In a city they would drive in and out of susceptible high interference zones The PNTAB believes the DOT results are representative accurate and credible The National Coordinating Office for PNT also sponsored an evaluation of all testing to date A summary report is now in coordination as a combined Department of Defense DOD and DOT effort The DoD which uses GPS in the national airspace for routine flight testing training guiding rocket launches and for humanitarian rescue missions has opposed repurposing The Air Force reported Results from the DOD ABC Assessment support the conclusions drawn from Department of Transportations ABC Assessment NOVEMBER PNTAB MEETING At our November meeting the board invited Ligado to make a presentation 12 GPS WORLD WWW GPSWORLD COM JANUARY 2018 on its repurposing proposal The invitation said Specifically describe your implementation plan with a corresponding test plan addressing the issues we have openly raised We request you specifically focus on those regarding the potential for interfering with any GPS GNSS services that operate in the protected space to Earth L band 1559 1610 MHz Included should be all modes of operation and the use of all current and future GNSS signals Valerie Green executive vice president and chief legal officer of Ligado Networks represented Ligado In the run up to the meeting the Six Point Criteria had been sent to Ligado Green did not address the six points at all She did offer to reduce initial power to the safe power level in the 1526 1536 MHz channel ranges from 9 to 13 dBW EIRP nationwide not just near airports The 13 dBW corresponds to initial power levels of 1995 W However Ligado has made clear in its FCC filings that it ultimately still wants a full 32 dBW base station Continued from page 10 See Grave Threat page 34