Slashdot Mirror
FCC Bars Lightsquared From Using Airwaves
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.
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.
I wish I had a kryptonite cross, because then you could keep Dracula and Superman away.
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.
http://blog.nexusuk.org
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.
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.
"National Security is the chief cause of national insecurity." - Celine's First Law
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.
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 about not causing and having to accept interference.
Tiller's Rule: Never use a word in written form that you've only heard and never read. You will end up looking foolish.
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.
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.
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.
John McAfee 'It was like that time I hired that Bangkok prostitute; to do my taxes, while I fucked my accountant'