FCC pulls the plug on LightSquared radio interference with GPS

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sardog1

sardog1

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From CNET Daily News -- FCC suspends LightSquared waiver over GPS interference

"LightSquared suffered a possibly fatal blow today when the FCC said it would indefinitely suspend the company's effort to build a national wireless broadband network using satellite spectrum.
"The National Telecommunications and Information Administration, a Department of Commerce agency tasked with overseeing military and government spectrum use, determined that LightSquared's interference with other devices, including GPS devices, was unavoidable."
 
...problem documented (CNN) that GPS has strayed from their defined spectrums into that LightSquared wants to use. Problem is not with the new guy but with the existing not being held to standards.
 
Stash said:
...problem documented (CNN) that GPS has strayed from their defined spectrums into that LightSquared wants to use. Problem is not with the new guy but with the existing not being held to standards.
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No--the CNN reporter is obviously not an electrical engineer...

(Attribution? The above statement sounds like a quote from LightSquared...)

In practice, receiving filters have to be wider than the signal and the skirts (sides) cannot drop off infinitely quickly. Thus a strong signal at a nearby frequency can overwhelm a receiver attempting to receive a weak signal at the desired frequency. (The filters in high-precision survey-grade GPSes have to be even wider than the filters in consumer GPSes to maintain the higher accuracy and are thus at even greater risk.)

For services like AM radio, FM radio, and TV, there are guard bands (empty zones) between channels to minimize adjacent channel interference. In the case of GPS, the spectrum just below the L1 GPS band was assigned to weak satellite downlinks (GPS is also a weak satellite downlink) which do not interfere with normal GPS receivers. LightSquared proposed a system (and obtained an ill-considered FCC waver* to do so) using terrestrial high-power transmitters in this satellite downlink band. These high-power transmissions would have interfered with every current GPS in much of the country and made aircraft navigation by GPS unusable.

* This waver includes a provision that this new service not interfere with GPS.

In other words, at best every existing GPS receiver would have to be upgraded or replaced to work in the new environment. (A company claims to have designed such a filter but it likely costs more than many current GPSes and would require many years of testing to be qualified for aircraft and military use. I don't know whether such a filter is compatible with high-accuracy use.) At worst, the new environment could destroy the use of GPS in this country.

A ref to the FCC announcement with rebuttal by LightSquared: http://www.businessweek.com/news/20...ked-by-fcc-after-u-s-interference-report.html

The full history is long and complicated starting back in 2001 with an allocation which would likely have been compatible with GPS. LightSquared obtained the controversial waver in 2010. There is lots of discussion (and links to articles) in Sci.geo.satellite-nav which may be found at your favorite Usenet news server or at http://groups.google.com/group/sci.geo.satellite-nav/topics?lnk There is also an overview at http://en.wikipedia.org/wiki/Lightsquared

IMO-1, LightSquared will ultimately be denied permission to use the high-power transmitters in the L1 band, but they continue to fight

IMO-2, LightSquared should never have been given the conditional waver in the first place and it should be withdrawn.

Doug
 
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The statement was not meant to indicate that there would be no interference with GPS. The statement was to provide clarity that there was no direct impact to the defined spectrums but to those on the "fringe". I wouldn't say that the post or the CNN report was incorrect. More a matter of wording and perception.
 
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There was lots of screaming about the amount of "interference" that would be generated or need to be tolerated long before the FCC accepted lightsquared's application to try this. As I remember NTIA was against it from the beginning and didn't want them to get the permit to try. Thank god it has been squashed.

Why a company thought that this would work, or why the FCC thought it would work, when everyone else was screaming what a problem it was going to be during the public comment phase, is beyond me. Their is no one at the time that I was reading about the application that could have possibly thought that the impact would have been non-existent or even small. Almost everyone told the FCC that. The FCC did the right thing - eventually. But why a company, with real engineers would think this would work is beyond me.

Keith
 
SAR-EMT40 said:
Why a company thought that this would work, or why the FCC thought it would work, when everyone else was screaming what a problem it was going to be during the public comment phase, is beyond me.
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They were claiming that they had permission to transmit in the particular frequency bands (close to GPS) and any interference was the fault of the GPS receivers and therefore it was the GPS receiver's job to get out of their way.

LightSquared was trying to carve out a mobile broadband network and was hoping they could use these particular frequency bands--the realities of physics and the enormous cost to others "weren't their problems...".

Background for the non-technically oriented: radio frequency space suitable for mobile (eg cellphone) use is very scarce, very valuable, and finite. Any organization hoping to start a new mobile network has to get access to some appropriate radio band to function.

Doug
 
DougPaul said:
They were claiming that they had permission to transmit in the particular frequency bands (close to GPS) and any interference was the fault of the GPS receivers and therefore it was the GPS receiver's job to get out of their way.



Doug
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That is the point. Neither are part 15 devices that would need to accept whatever interference it received. Knowing that, Lightsquared would be responsible to fix the problem if they caused it to the GPS service, up to and including turning their equipment off. So knowing that LightSquared would absolutely interfere with the GPS service. Why did the FCC even give them permission to try? And like I wrote, why did LightSquared see this as even remotely possible that this would work. Unless they intended to apply liberal amounts of graft and corruption money to keep this abortion afloat?

Keith
 
SAR-EMT40 said:
That is the point. Neither are part 15 devices that would need to accept whatever interference it received. Knowing that, Lightsquared would be responsible to fix the problem if they caused it to the GPS service, up to and including turning their equipment off. So knowing that LightSquared would absolutely interfere with the GPS service.
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LightSquared presumably took what they thought was a calculated risk: they hoped they could manipulate the regulatory system to their benefit.

Why did the FCC even give them permission to try? And like I wrote, why did LightSquared see this as even remotely possible that this would work. Unless they intended to apply liberal amounts of graft and corruption money to keep this abortion afloat?
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There are charges of campaign contributions and favors by people in high places. However, this forum is not the place to explore this issue (politics, etc).

Doug
 
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