- SPECIAL REPORTS
- THE MAGAZINE
Tests of the broadband communications system being proposed by the firm LightSquared found that every sector and applications area of the Global Positioning System (GPS) industry experienced significant levels of interference from LightSquared signals, according to a report filed today by the Technical Working Group (TWG) formed to study the interference issue at the request of the Federal Communication Commission (FCC).
The report also indicated that there are no satisfactory fixes to the interference effects that can work across the broad range of GPS receiver designs and applications areas. The TWG that prepared the report was co-chaired by Chairman of the United States GPS Industry Council Charles R. Trimble, and LightSquared Executive Vice President for Regulatory Affairs and Public Policy Jeff Carlisle.
“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 Trimble. “In the end, the laws of physics won out.”
He 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, Trimble 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.”
Receivers: The report identified seven categories of receivers that are representative of the non-military use of GPS in the United States: aviation, cellular, general location/navigation, high precision, timing, networks, and space-based receivers. The report said significant interference effects were experienced in each of the categories.
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, it was found that damaging interference existed at times at very long distances for the LightSquared transmitters. NovAtel Inc. 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.”
Damaging interference also occurred with GPS timing receivers, which are widely used to provide precise time synchronization in applications such as wireless, wireline, fiber optic telecommunications networks, electric power grids, paging systems, public safety radio systems, and financial networks.
The report concluded that for high-precision and timing receivers, “We know of no currently available receiver, filter, antenna or other mitigation technology that would enable the construction of future wideband High Precision, Timing or Network GPS receivers that are compatible with the Phase 0, 1, or 2 LightSquared rollout plans.” The report also stated, “We know of nothing feasible that can be done to make currently fielded High Precision, Timing, and Network receivers operate properly when in the vicinity of a LightSquared base station, with respect to either GPS or augmentation systems.”
Regarding general location/navigation receivers, the report concluded that all phases of the LightSquared deployment plan will result in widespread harmful interference to GPS signals and service and that mitigation is not possible.The report noted that lab testing revealed that many devices suffered from harmful interference from the lower 10 MHz channel (the use of which LightSquared has proposed as a “solution” to the GPS interference problem); specifically, the report stated that 20 out of 29 devices tested experienced harmful interference from the lower 10 MHz channel. Commenting on the report, Andrew Etkind, Vice President and General Counsel of Garmin International, Inc.,said, “Today’s report demonstrates that the only practical way of protecting general location and navigation receivers is to move LightSquared to another part of the spectrum.”
Possible Mitigation Options: The report also studied possible mitigation options that could be adopted by GPS receiver manufacturers and/or LightSquared. Said Trimble, “There were no magic bullets that emerged despite some very creative thinking on both sides of the question.” Currently available filters to screen GPS receivers from the LightSquared signals were found to be inadequate in meeting the stringent demands of current receiver designs for size, power consumption and other technical parameters. Even proposed filter designs for future generations GPS receivers were found to be uncertain in terms of actual performance and delivery times and could take years to be made available and integrated into new products.
Trimble also raised the major issue of the huge already-installed base of several hundred million GPS devices that simply cannot be retrofitted. These devices are not simply or easily replaced either, with consumer GPS products lasting over eight years, and even longer life spans for more sophisticated and expensive aviation products.
Deployment Modifications: The report also considered modifications to LightSquared’s deployment plan for its system that proposed a partial initial deployment using only a portion of the original proposed spectrum. Here, too, the results were largely unsatisfactory. Trimble noted, “While we appreciate the flexibility and creativity shown by LightSquared in the proposed modifications to their deployment scenario, in the end this is little more than a temporary band-aid to the larger question of trying to find ample separation of the GPS and LightSquared signals. There simply is not enough room in the spectrum adjacent to GPS for safe and reliable operation of both services together.”
Regarding future GPS and broadband developments, Trimble stated, “We hope that the FCC will understand and appreciate the comprehensive work that the TWG has done to define the interference effects of the LightSquared signals in scientific and engineering fact. GPS and broadband are two very valuable elements of today’s information infrastructure, but the report shows clearly that they cannot operate in adjacent spectrum. Finding new areas of spectrum where sharing is possible to accommodate the LightSquared requirements is a difficult regulatory question. However, the FCC needs to consider other options for the LightSquared signals where they do not run up against the laws of physics.”