“Based on the analysis performed, LightSquared should not be permitted to use the L-Band spectrum for a densely-deployed, non-integrated terrestrial-only network. Such a network would cause unacceptable interference to GPS operations, wiping out an installed base of over 500 million units used in a wide array of public safety, aviation, industrial and consumer applications. While mitigation techniques utilizing filters were discussed in theory, they could not be tested as part of the WG effort because filters do not exist, even in prototypes. No information considered by the WG demonstrated that any mitigation techniques — other than relocation of the proposed terrestrial network to an alternative band — would be successful.” (From the U.S. GPS Industry Council’s overview of the WG report)
The final report to the Federal Communications Commission (FCC) on three months of research by the technical working group (TWG) tasked to investigate and analyze effects of powerful terrestrial L-band transmitters on the GPS signal and services finally appeared on June 30, nearly two weeks after its assigned date. LightSquared had requested an extension, and apparently the lawyers on its staff used the extra time to write many pages of self-justification and further argumentation of the company’s case. But the facts are clear: the LightSquared signal would devastate services for users of all GPS receivers tested.
The final report is not easy to find on the FCC’s labyrinthine website. Read the full “final report of the Working Group (WG) that was formed to study the GPS overload/desensitization issue as described by the Federal Communications Commission (FCC) in DA 11-133” here.
See also four appendices:
one, “Appendix A.1: MOPS Based Procedure for Minimum Recommended Testing of LightSquared RFI to GPS Aviation Receivers”
two, “Appendix G.2: from Alcatel-Lucent Labs, LightSquared L-Band GPS Receiver Equipment Impact Evaluation Testing”
three, “Appendix H.1.1: JPL/NASA Report on Laboratory Testing of Receivers for the Space-Based Sub-Team and the High Precision Sub-Team”
and four, “Appendix H.1.10: High Precision Receivers – NAVAIR Anechoic Chamber Test Results.”
Full data for all device tests conducted by the Working Group is available for download at: ftp://twg:firstname.lastname@example.org
GPS World readers may also be interested in the thoughtful and intelligible analyses provided by the U.S. GPS Industry Council (“Overview of the Final Report of the Working Group”) and the Coalition to Save Our GPS (“FCC-Mandated Working Group Report Documents Pervasive Harmful Interference with GPS“).
The TWG conclusions of widespread disruption and harm to GPS services are consistent with those reached by third parties that have reported independent analyses: RTCA, Inc., a Federal Advisory Committee that evaluates aviation, and the National Public Safety Telecommunications Council (NPSTC).
“The TWG faced an extraordinary challenge of trying to determine if the laws of physics would allow the high-power LightSquared signals to co-exist in adjacent radio spectrum with the low-power satellite signals of GPS over and above the complex regulatory challenges of managing spectrum sharing,” said Charles Trimble, chairman of the U.S. GPS Industry Council. “In the end, the laws of physics won out.”
Trimble, who co-chaired the TWG, added, “There is no single, simple solution that can eliminate interference for all classes of GPS receivers in the near term. GPS touches every aspect of our lives. It goes beyond the most widely known navigation applications such as car navigation and cell phones to hugely important applications such as agriculture, electric power grids, communications networks, infrastructure monitoring and construction.”
Regarding possible effective solutions, he offered the view that “greater separation of the LightSquared signals and those of GPS are necessary if the value of GPS is to be protected and broadband communications can grow to its potential over the long term.”
In the area of high-precision receivers used for precision agriculture, survey, construction, machine control, mining, geographic information systems (GIS), structural deformation monitoring, and science, the group found that damaging interference existed at times at very long distances for the LightSquared transmitters. NovAtel president and CEO Michael Ritter said, “Allowing LightSquared to interfere with the utilization of these high precision receivers would eliminate the productivity improvements provided to these industries and applications during the past 20 years and will result in significantly higher prices for goods and services from these industries to the consumer.”
Key Results and Findings from the WG Report:
1. The LightSquared Terrestrial Broadband Service Will Cause Harmful Interference to Nearly All GPS Receivers and GPS-Dependent Applications
2. Limited Testing of LightSquared Terrestrial Broadband Operations in the “Lower” 4G LTE Channel Does Not Eliminate Harmful Interference to GPS Receivers and GPS-Dependent Applications.
3. Increasing Filtering on GPS Receivers Is Not an Available Mitigation Technique.
- No Suitable Filters Exist;
- Even if Filters Were Available, They Have Undesirable Performance Impacts on GPS Receivers That Have Not Been Evaluated.
- Increased Filtering Does Not Mitigate Interference to Hundreds of Millions of GPS Users in the Installed Base.
4. The Only Feasible Solution to the Harmful Interference Effects LightSquared’s Proposed 4G LTE Terrestrial Broadband Service Will Cause to GPS Receivers and GPS-Dependent Applications Is to Relocate the LightSquared Service to Spectrum that is Not Adjacent to GPS/RNSS, outside of the L-Band.