Doug Lung / 06.23.2011 12:00AM
LightSquared Proposes Plan to Prevent GPS Interference
After the tests and studies I reported on in last week's RF Report
, LightSquared apparently realized that concerns over interference to GPS will prevent it from building out its terrestrial network as planned. On Monday LightSquared proposed
a "comprehensive solution" which it said "ensures that tens of millions of GPS users won't be affected by LightSquared's launch." The solution appears to be partly based on RTCA test results outlined in a briefing on interference to aviation GPS from R. A. Frazier of RTCA. It noted that base stations involving only the lower 5 MHz of LightSquared's spectrum (centered on 1528.8 MHz) was "completely compatible" with aviation GPS operations. Note that this only referred to aviation GPS operations, not high-precision GPS, GPS surveying or other uses.
In the announcement, LightSquared acknowledged that early testing showed the 10 MHz block of spectrum it planned to use for its initial operation "poses interference to many GPS receivers." However, LightSquared said that based on the same early test results, "another 10MHz block of the spectrum did not create such an interference risk," explaining, "This block is lower on the spectrum band and located further away from the GPS frequencies, greatly reducing the risk for interference." This spectrum is currently controlled by Inmarsat, but LightSquared and Inmarsat have been working to consolidate the fragmented L-band spectrum held by the two companies to make it possible for both companies to offer higher speed broadband service. LightSquared said it has entered into negotiations with Inmarsat to accelerate the schedule for LightSquared to begin using the frequencies. See the ConnectedPlanetOnline.com article LightSquared swapping spectrum with Inmarsat
for more on the negotiations.
LightSquared also said it would modify its FCC license to reduce the maximum authorized power of its base-station transmitters by over 50 percent, noting, "This action will limit LightSquared to the power it was authorized to use in 2005, which will provide additional protection to GPS."
Jim Kirkland, vice president and General Counsel of Trimble and a founding member of the Coalition to Save Our GPS
, said, "This latest gambit by LightSquared borders on the bizarre. Last week LightSquared unilaterally delayed filing of the study report that culminated months of intensive work to evaluate interference to GPS, because they purportedly needed two more weeks to analyze the results. Days later, well before the report is scheduled to be filed, LightSquared unilaterally announces that it has found a 'solution.'" Kirkland continued, "LightSquared's supposed solution is nothing but a 'Hail Mary' move. Confining its operation to the lower MSS band still interferes with many critical GPS receivers in addition to the precision receivers that even LightSquared concedes will be affected. The government results submitted to date already prove this, and the study group report will also confirm this. It is time for LightSquared to move out of the MSS band."
I expect GPS users to demand further reduction in LightSquared base station power and more restrictions on frequencies. I wouldn't be surprised if LightSquared ends up agreeing to a compromise that would allow some limited operations. Once these are up and running, LightSquared will likely propose careful increases in spectrum and power in response to demand for its service. Wireless carriers are interested in LightSquared's operations, as shown in joint comments detailed elsewhere in this week's RF Report.