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    Re: GPS Interference
    From: Frank Reed
    Date: 2011 Sep 15, 21:47 -0700

    Gary,

    There is still a fair amount of controversy over the technical aspects here as well as the bureaucratic machinations at the FCC and elsewhere. I don't think there's any evidence that the Obama Administration cheated or engaged in corruption, but they do consider national wireless broadband a major policy objective so they have asked the FCC to fast-track the approvals process. The LightSquared system uses frequencies which are outside but adjacent to the GPS signal band. The exceedingly weak GPS satellite signals are susceptible to the slightest overlap from the "tails" of other signals. LightSquared claimed a couple of months ago in their report that the vast majority of GPS receivers including, according to them, one-hundred percent of the GPS circuitry in smartphones (by far the largest commercial users of GPS) are not affected by this interference. They also claim that very cheap filtering circuitry could have made all GPS hardware immune to this interference if it had been designed and built according to specs. That latter claim is nice in theory, but seems rather weak in practice. Then again, if they're right, then the makers of those devices should perhaps have to pay to retrofit or replace them any which depended on empty spectrum outside the standard GPS range.

    It is worth noting that LightSquared received licensing to use that spectrum adjacent to the GPS band in 2004. Note the year. That's smack in the middle of the Bush Administration, not the Obama Administration. This tends to dilute the argument that there is some sort of political corruption at work here. Of course, their plans are a work in progress, and the usages envisioned in 2004 are very different from the current plans. There have been many modifications to the licensing in the past two years. Those can legitimately be questioned for political influence.

    Incidentally, the primary interference concern at this point apparently applies almost exclusively to high-precision GPS which yields positions accurate to some few centimeters.

    -FER


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