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    Re: GPS Interference
    From: Richard B. Langley
    Date: 2011 Sep 16, 09:39 -0300

    �Based on the test results and analysis to date, the LightSquared  
    network would effectively jam vital GPS receivers,� General William L.  
    Shelton, commander of U.S. Air Force Space Command, told the members  
    of the House Subcommittee on Strategic Forces [yesterday]. �And to our  
    knowledge thus far, there are no mitigation options that would be  
    effective in eliminating interference to essential GPS services in the  
    United States.�
    
    More: http://www.insidegnss.com/node/2779
    
    -- Richard Langley
    
    
    On 16-Sep-11, at 1:47 AM, Frank Reed wrote:
    
    > 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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    -----------------------------------------------------------------------------
    | Richard B. Langley                            E-mail:  
    lang---.ca         |
    | Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/ 
      |
    | Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506  
    453-5142   |
    | University of New Brunswick                   Fax:      +1 506  
    453-4943   |
    | Fredericton, N.B., Canada  E3B  
    5A3                                        |
    |        Fredericton?  Where's that?  See: http:// 
    www.fredericton.ca/       |
    -----------------------------------------------------------------------------
    
    
    
    
    

       
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