GPS interference: Who knew it would get this bad?

Posted in LightSquared, Operators, Regulatory, Spectrum at 9:04 am by timfarrar

As more information starts to emerge from real world testing into whether LightSquared’s terrestrial network will interfere with GPS receivers, the news appears to be fairly bad for LightSquared on both the technical and political fronts. In addition to Qualcomm’s comments last week, suggesting that the filters in their A-GPS chipsets might need to be upgraded, New Mexico state officials have submitted a letter stating that their testing “substantiate[s] concerns that the LightSquared network will cause interference to GPS signals and jeopardize 911 and public safety nationwide”. Meanwhile the FCC has been asked by Sen. Chuck Grassley (R-Iowa) “for more information on its review” of LightSquared’s plans, including “all communications between the FCC and Falcone or any other Harbinger Capital and LightSquared employees [and] all internal FCC communications regarding LightSquared or Harbinger Capital” and language has been included in the National Defense Authorization Act (NDAA) that “requires the U.S. Secretary of Defense to notify Congress if he determines that widespread interference with the military’s use of the GPS is caused by a commercial communications service”.

What I’ve always found intriguing is that this issue apparently came out of nowhere to potentially derail the whole LightSquared buildout plan. LightSquared has highlighted that terrestrial use of the L-band has been anticipated since 2003, and that the GPS Industry Council negotiated several agreements with LightSquared (previously SkyTerra and before that MSV) on out-of-band emissions into the 1559-1610MHz band, starting in 2002 and extending right up until August 2009. Indeed in March 2004, the GPS Industry Council urged “the Commission to grant the above referenced [ATC] applications of Mobile Satellite Ventures Subsidiary LLC (“MSV”), and to do so as soon as possible”, commending MSV “for its proposal to use its spectrum in a responsible manner that ensures the continued utility of GPS receivers operating in the vicinity of MSV ATC stations”.

However, it appears that the GPS Industry Council never recognized the potential for GPS receiver overload from transmissions within LightSquared’s own L-band frequencies. Given their comments above, it seems plausible that they were lulled into a false sense of security by LightSquared’s cooperation over out-of-band interference, including limiting the PSD to -100dBW/MHz or less, a very aggressive commitment, giving a high level of protection to GPS receivers. Of course, LightSquared also benefited from that commitment, because to filter LightSquared’s emissions to this level requires about 3-4MHz of separation between the edge of the GPS band at 1559MHz and LightSquared’s terrestrial transmissions at 1550-1555MHz. When similarly challenging constraints were imposed on Globalstar at 1610MHz, it meant that Globalstar would be less able to operate high power terrestrial transmissions at the bottom edge of its L-band frequencies, restricting Globalstar’s ability to support ATC in its more limited Big LEO L-band allocation (and thereby hampering potential competition to LightSquared).

Given the complexity of these issues and how critical their resolution was in obtaining LightSquared’s ATC license, it is hard to believe that no-one at LightSquared was aware of the possibility of GPS overload interference until it was raised in December 2010. Indeed, in an offhand comment in March 2011, even Mr. Falcone’s wife apparently suggested that “this type of interference has always been a potential issue for GPS”. Nevertheless, it appears that no mention is made of such problems in the risk factors section of SkyTerra’s 10-K filings with the SEC, and the 2009 10-K filing basically states the opposite, noting that “We have also agreed to comply with requirements on our user terminals and base stations that we negotiated with the GPS industry to provide additional protection to GPS receivers, beyond existing mandatory limits. Our compliance with these limits is a condition of our ATC license. All of our broadband wireless system designs take into account these requirements and specifications. We believe that they do not materially limit our network deployment or our ability to achieve our business plan”.

Summing up, it seems that the GPS Industry Council clearly dropped the ball when it came to analyzing the potential impact of LightSquared on GPS receivers. However, they may very well feel that they were the victim of a bait and switch play, thinking that MSV/SkyTerra was being extremely cooperative with its expressed intent to “ensure the continued utility of GPS receivers operating in the vicinity of MSV ATC stations”, when in reality out-of-band interference was not most important issue to consider.

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