GPS World, September 2018

SYSTEM SYSTEMS OF Policy and System Developments GPS Galileo GLONASS BeiDou PNT Board Opposes Ligado Lite Proposal O n Aug 10 the National Space Based Positioning Navigation and Timing PNT Advisory Board the governments GPS expert board sent a letter to the National Executive Committee for Space Based PNT a multi agency body that steers GPS policy that concluded We strongly recommend your opposition to the Ligado proposal The letter sprang from a unanimous vote five days earlier to oppose allowing Ligado Networks to use spectrum neighboring the GPS band for terrestrial communications Ligado possesses licenses to broadcast on two satellite bands located adjacent to the GPS frequencies The company has been seeking permision from the Federal Communications Commission FCC to repurpose these licenses from satellite based use to ground based use from powerful tower transmitters Ligado said in May it would lower the power in its proposal for the 1526 1536 MHz band to 998 dBW to avoid interference with certified aviation receivers However the PNT Advisory Board reiterated its opposition saying that even if the transmissions power was lowered to just under 10 watts it will create totally unacceptable interference for a great number of GPS users in the United States From the Letter This risk is far too great and far too many questions remain for Ligados proposal to be approved While there are many broadband alternatives Ligado would be a very small percentage of this national asset there is only one GPS Any impairment to current and future uses is clearly contrary to the national interest Therefore implementation of their recently proposed 10 watt Figure 1 The PNTAB strongly believes that 90 is the minimum Area Protection Criterion maximum 10 degradation operating scheme will create totally unacceptable interference for a great number of GPS users in the United States In fact despite power limits in their current amended application it is probable they could still be allowed to increase this power over time This would be even more destructive to GPS users While there are many broadband alternatives there is only one GPS Any impairment to current and future uses is clearly contrary to the national interest We believe avoiding degradation over at least 90 of the region near Ligado transmitters is the absolute minimum protection for GPS receivers in each class This would be a hypothetical 90 Protection Evaluation This is not an endorsement of this level since of course all users would prefer 100 protection The Department of 10 GPS WORLD WWW GPSWORLD COM SEPTEMBER 2018 Transportation DOT Adjacent Band Compatibility ABC study is the only validated test to verify degradation at various received power levels Those results inform that to insure degradation not exceed 10 of the Region 90 Protection for High Performance receivers either Ligado maximum power can be no more than 0036 watts at the 400 meter spacing they had earlier planned Tolerable power would be 3 10ths of 1 of their proposed 10 watts Or the closest spacing of Ligado transmitters is 20000 meters over 12 miles for their proposed 10 watt power level see FIGURE 1