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Wireless Networking

FCC Bars Lightsquared From Using Airwaves 178

Posted by Unknown Lamer
from the lightsquared-disputes-laws-of-physics dept.
New submitter mc6809e writes with news that Lightsquared might have just been killed. From the article: "A proposed wireless broadband network that would provide voice and Internet service using airwaves once reserved for satellite-telephone transmissions should be shelved because it interferes with GPS technology, the Federal Communications Commission said Tuesday. The news appears to squash the near-term hopes for the network pushed by LightSquared, a Virginia company that is majority-owned by Philip Falcone, a New York hedge fund manager." LightSquared, naturally, continues to deny that the interference is real.
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FCC Bars Lightsquared From Using Airwaves

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  • by ZaMoose (24734) on Wednesday February 15, 2012 @10:10AM (#39043825)

    The last time /. discussed this, it was pointed out that the spectrum L^2 was aiming for was intended for low-power satellite signals and was never intended to be used for (relatively) powerful ground stations. They were essentially trying to buy spectrum on-the-cheap and then repurpose it in a way that was virtually guaranteed to interfere with adjacent spectrum. So, while GPS devices could certainly be better-designed, this was more an incident of L^2 trying to abuse the system.

    Physics, alas, makes for a harsh mistress.

  • by FireFury03 (653718) <slashdot@nexusuk.oGAUSSrg minus math_god> on Wednesday February 15, 2012 @10:13AM (#39043887) Homepage

    It's my understanding* that Lightsquared's equipment was never the issue, but rather the GPS equipment that got interference were just poorly designed. If the GPS equipment was held to the standards it should have been, Lightsquared's equipment wouldn't have interfered. Yet Lightsquared are the ones being shafted, simply because GPS is "too important".

    That's not quite true. LS basically bought up a *satellite* band and tried to repurpose it for ground communications. It was then discovered that doing this caused some GPS equipment to malfunction. Whether or not you consider this GPS equipment to be "poorly designed", the fact remains that it was working absolutely fine for decades and LS's attempts to repurpose the ajacent band causes it to stop working. Expecting millions of GPS users to upgrade their GPS receivers just because LS wants to repurpose an existing band for a new use is ridiculous. On the other hand, if LS wants to buy shiny new GPS receivers for all these end-users...

    So no, LS isn't "being shafted" - they purchased a satellite band with the intention of using it for ground communications, rather than its existing use, badgered the FCC into letting them repurpose it and then cried when it was found that this repurposing wasn't compatable with millions of existing devices.

  • by heypete (60671) <pete@heypete.com> on Wednesday February 15, 2012 @10:14AM (#39043899) Homepage

    GPS receivers (and the filters in their electronics) were built with the assumption that neighboring frequencies would be used by other space-to-ground uses, and thus would have comparable signal strengths (that is, very low).

    Having ground-based stations blasting out signals that are brazillions of times more powerful than the weak space-to-ground signals on adjacent frequencies would overwhelm the relatively weak signal from GPS. Filters that can allow the weak GPS signals through while blocking out the immensely more powerful signals on neighboring frequencies would be bulky and expensive. Devices not equipped with those specialized filters (that is, essentially every GPS receiver ever made) would be screwed.

    I'm sure that if LightSquared wanted to use the frequencies they acquired for space-to-ground uses, the FCC would have very little trouble with it and the potential for interference with GPS would be essentially nil. Instead, LightSquared purchased (leased? I'm nowhere near an expert on this kind of thing.) these frequencies at a cheap price due to their being intended for space-to-ground use and was trying to change their classification to use them for ground-based transmitters (thus saving LightSquared tons of money acquiring spectrum). They gambled big and (rightfully) lost.

    Reliable GPS service is more important than the communication network LightSquared proposed, particularly in regards to safe navigation for aircraft and vessels.

  • by msauve (701917) on Wednesday February 15, 2012 @10:14AM (#39043901)
    Not quite. The spectrum adjacent to GPS frequencies was authorized for for use with other satellite services, which obviously have a very low signal level. GPS receivers were designed with that in mind. That's not unreasonable, in the real world there's no such thing as a perfect filter with vertical skirts.

    Lightsquared "bought" this spectrum, much cheaper than similar spectrum allocated for terrestrial use. They then fast tracked a petition through the FCC to get authorized to use that spectrum terrestrially. The problem is, that produces much stronger signals than GPS receivers were designed to deal with.

    If Lightsquared were to use the spectrum as originally intended, there would be no issue. Instead, they want to have their cake, and eat it too, by paying for relatively low cost satellite spectrum, but using it for terrestrial transmitters.
  • by worip (1463581) on Wednesday February 15, 2012 @10:15AM (#39043927)
    Actually, the spectrum was never intended for terrestrial use at all. Lightsquared applied for an exemption to apply the spectrum for terrestrial use, but they had to prove that it did not intefere with GPS. Most RF engineers would have told you that they where doomed from the start to fail, as the physics does not allow you to do this. All RF equipment have to contend with a thing call adjacent channel rejection - i.e. whilst tuned to its own channel a device must reject inteference from channels adjacent to its own by using a bandpass filter. Bandpass filters are not perfect (i.e. it is not a brickwall) and some interference always leaks through. The specific issue here is that the terrestrial signal would have been so large compared to the signal received from the GPS sattelite that the bandpass filters would have been unable to suppress the signal in the adjacent channel. This is akin to someone shouting in your ear, while you are trying to listing to someone whispering 20meters away.
  • by vlm (69642) on Wednesday February 15, 2012 @10:16AM (#39043935)

    "A proposed wireless broadband network that would provide voice and Internet service using airwaves once reserved for satellite-telephone transmissions should be shelved because it interferes with GPS technology, the Federal Communications Commission said Tuesday

    That's a massive simplification. They sell mobile satellite internet, and have done so for a long time, and will do so into the indeterminate future, this has nothing to do with that.

    The LS idea was to provide a backend carrier to local on ground cellular providers for internet traffic. Same as your off the shelf 3G service you now "enjoy" but instead of your greedy provider paying AT&T (or whoever) for fiber to the cell phone tower, they'd use the satellite service.

    Except... they didn't have an allocation for their ground network. Hmm. What if we reuse the satellite freqs, yeah that'll work. Well, except that the would ruin/destroy/eliminate the possibility of anyone on the ground hearing the satellites without a huge dish or technically impossible filtering. OK no problemo we'll dump all our satellite customers and focus on the ground guys, and use the marketing for satellite "as if" we're not a ground 3G provider. Whoops that'll kill all the adjacent satellite services too. Oh Oh, GPS is adjacent.

    Well, so much for that bad idea.

    Note there is no reason that instead of paying AT&T for fiber to a cell tower in the middle of nowhere, LS can't provide slow and high latency service RIGHT NOW to that cell tower... this FCC bar only stops them from setting up their own tower and using the satellite freqs to set up something like a 3G service.

    The standard /. car analogy is this is kind of like getting rid of the SUV exception where hyper obese ultra low MPG passenger cars are permitted under the legal fiction they are classified as trucks not cars. That takes care of the analogy "why the F are they installing 100 watt ground transmitters on an allocation for satellite transmitters only?". Or maybe a better analogy is LS thought it would be fun to build a network of hydrogen fueling stations, and figured no one would have any problem if they used an off the shelf gasoline filling nozzle instead of a technically correct solution that would not result in an infinite number of burnout fires. That takes care of the analogy "why the F are they installing 100 watt ground transmitters right next to satellite receivers and even daydreaming that won't knock out the receivers".

  • by msauve (701917) on Wednesday February 15, 2012 @10:46AM (#39044269)

    How do you think this spectrum came open in the first place? They forced consumers that were still using old TVs to receive analog TV signals to buy new equipment.

    Wow. You couldn't be more confused. Analog TV operated in 54-88 MHz, 174-216 MHz (VHF), and 470-890 MHz (UHF) bands. GPS is up above 1 GHz, 1.57542 GHz (L1 signal) and 1.2276 GHz (L2 signal) being the primary signals. The frequencies that Lightsquared wants to use have nothing to do with the any spectrum which was previously used for TV.

  • by tixxit (1107127) on Wednesday February 15, 2012 @10:51AM (#39044347)

    According to the actual 2003 decision by the FCC:

    Today we decide to permit flexibility in the delivery of communications by Mobile Satellite Service (MSS) providers [cut]. Specifically, we permit MSS licensees to integrate ancillary terrestrial components (ATCs) into their MSS networks

    ...

    We will authorize MSS ATC subject to conditions that ensure that the added terrestrial component remains ancillary to the principal MSS offering. We do not intend, nor will we permit, the terrestrial component to become a stand-alone service.

    That is, the decision was to let those offering mobile satellite services the ability to enhance their networks. This guy wanted to create a stand-alone cell phone network, which was explicitly not permitted in the 2003 decision.

  • by davros74 (194914) on Wednesday February 15, 2012 @10:54AM (#39044383) Homepage

    The GPS units are not faulty. The spectrum they use are reserved for SATELLITE reception, not terrestrial broadcast. The signal levels received are so incredibly weak, that it is quite difficult, certainly not cheap, to build filters to filter out a nearby signal that is several order of magnitude stronger than yours. The spectrum was reserved, by the FCC, such that the neighboring spectrum would be like weak signals, which makes building receivers with high sensitivity possible and affordable.

    I am sorry, but it was lightspeed who deceptively came in, got the spectrum, then changed from a mostly satellite based service (which would have been fine in that spectrum), to one consisting of tens of thousands of TERRESTRIAL transmitters in the L1 band, that simply overpower the nearby satellite downlink signals.

    You just cannot build a high sensitivity receiver with a filter strong enough to filter out that kind of interference.

    The FCC never should have granted them a go ahead in that frequency band in the first place.

  • by Muad'Dave (255648) on Wednesday February 15, 2012 @10:59AM (#39044443) Homepage

    Let's be clear - the FCC is not in the business of validating that any particular device is generally well-made or robustly-designed. Their one and only concern wrt to type acceptance is the RF _emissions_ of the device. They do not require testing of receivers for susceptibility to nearby carriers, intermodulation, desense or anything else, only their (in the case of a receiver, unintentional-) emissions. All not-otherwise licensed equipment carries the all-too familiar Part 15 warning [gpo.gov] about not causing and having to accept interference.

  • by davros74 (194914) on Wednesday February 15, 2012 @11:04AM (#39044509) Homepage

    I would also point out that the frequency band GPS and satellite signals are in are much cheaper than terrestrial frequencies. As such, Lightspeed abused a (poorly conceived) FCC ruling for filling in poor reception areas with local ground based transmitters, to take cheap satellite spectrum, and repurpose it for a very large and high-powered terrestrial network, without paying similar licensing fees other terrestrial providers have to pay for their spectrum.

    The whole loophole started by the FCC allowing ground based transmitters in the L1 band, but the intent was to supplement poor reception of satellite signals with some ground based ones. They never intended it to be repurposed for massive scale and high powered ground transmitters everywhere.

    The laws of physics don't work well with you here when you have very weak signals from space competing with local, very strong signals on the ground, and only a few MHz apart in the GHz range. That was the original reason satellite based signals have their OWN spectrum. While it stinks for Lightspeed, they should know they never should have really gotten that spectrum from the FCC in the first place. The FCC dropped the ball on this one, but perhaps that's not too surprising how much corporations can buy influence in Washington these days.

  • by Zcar (756484) on Wednesday February 15, 2012 @11:21AM (#39044759)

    so it becomes a competitive question here - why aren't GPS devices better designed?

    Because they were engineered with the constraints of their band in mind. If the rules of the band are such that you don't need to worry about a powerful signal on an adjacent frequency, designing a filter to deal with such an adjacent signal is unnecessary expense.

  • by farnz (625056) <slashdot@ f a r n z . o r g .uk> on Wednesday February 15, 2012 @11:32AM (#39044901) Homepage Journal

    And that's where the debate lies. LightSquared's license permits them two uses of the frequencies licensed:

    1. For satellite to earth communication, provided they ensure that the transmissions from the satellite do not leak out of their licensed bands.
    2. As a later waiver, made after the spectrum was initially licensed: For earth to earth and earth to space communication, provided that they ensure that their earth-based transmitters do not interfere with earth-based receivers designed to pick up satellite to earth transmissions in neighbouring bands.

    LightSquared's argument is that they have met the second term of their license if they ensure that their earth-based transmitters do not leak out of their licensed bands, even if they interfere with licensed users of neighbouring bands; note that the FCC has been clear that one way to meet the second requirement is to replace receivers of the neighbouring bands with ones that cope with your interference, an option LS has rejected as impractical, as they cannot find affordable receivers that have both the GPS abilities of the receivers they're replacing and better rejection of LS's signals.

  • by yourmommycalled (2280728) on Wednesday February 15, 2012 @11:36AM (#39044941)
    No the FCC isn't at fault. the FCC licensed the spectrum to American Mobile Satellite Corporation and later as Mobile Satellite Ventures after a merger between Motient Corporation and TMI Communications. It was most recently known as Skyterra, a company that provided mobile satellite communications services. There was also a cooperation agreement between Inmarsat and LightSquared. Had LightSquared continued to used the spectrum as it was licensed for this whole mess would have never occurred. The problem is LightSquared demanded a waiver from the FCC to use the spectrum for purposes the spectrum was not allocated for AFTER purchasing the companies who owned the spectrum for satellite-to-ground communications. Blaming the FCC in this case is like blaming Texas Instruments because their TI-89 calculator does not work very well as a ruler.
  • by CompMD (522020) on Wednesday February 15, 2012 @12:35PM (#39045655)

    You understand radio a bit it seems. Here's what you're ignoring though, so follow me here: a high-precision GPS receiver must pick up signal at -165 dBm. This is right about at the noise floor. Its incredibly easy to cause interference with a receiver that must operate with these conditions, and incredibly difficult to design a filter that would actually be useful. You're talking about transmitters with 10^5 W output interfering with other transmitters in the same class. Its apples and oranges.

  • by HornWumpus (783565) on Wednesday February 15, 2012 @12:36PM (#39045665)

    The rules upfront were clear; adjacent bands were for low power satellite use only.

    The fact is that Lightsquared thought it could buy the influence to screw everybody else while getting richer. There is a reason the band they bought was so cheap.

  • by Anonymous Coward on Wednesday February 15, 2012 @01:34PM (#39046495)

    Sometimes Slashdotters only see the technical arguments. Lightsquared has a somewhat-valid technical argument - if GPS receivers are intended to work on only one band they should take precautionary measures to reject potential interference from neighboring bands.

    That's not really a valid technical argument. The GPS receivers can very well reject the adjacent bands of relatively equal or slightly greater signal levels. LightSquared is essentially turning the technical details upside down by trying to use the band liscensed for non-terrstrial use for terrestial use.

    But, this was never a problem before, so nobody who makes civilian GPS receivers bothered to do so (I presume milspec receivers have decent filters).

    LightSquared interferance will actually have more impact on high precision devices. Those high precision devices need their high precision. Additional filtering for better sideband rejection can result in signal degredation. This is extremly harmful for those devices because they use the edges of those signals to estimate time of arrival of the signal.

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