Too many signals not enough spectrum
February 7, 2011 7:37 AM Subscribe
Like the GPS features of your smartphone? Like your high speed wireless internet connection? You may not be able to have both. A company called Lightsquared has proposed a service to provide high speed internet using satellite feeds. However, some tests show that the the signal from Lightsquared's system may interfere with GPS. The FCC has granted a waiver allowing Lightsquared to proceed, with the caution that issues with GPS must be resolved. The GPS world is concerned.
Dear FCC,
WTF?
Yours,
Pretty much everybody
posted by Threeway Handshake at 7:41 AM on February 7, 2011 [8 favorites]
WTF?
Yours,
Pretty much everybody
posted by Threeway Handshake at 7:41 AM on February 7, 2011 [8 favorites]
Where would we be without GPS?
posted by memebake at 7:46 AM on February 7, 2011 [17 favorites]
posted by memebake at 7:46 AM on February 7, 2011 [17 favorites]
The FCC has now completed their shift into bureaucratic uselessness by being tough on nipples and otherwise ignoring real threats to the radio spectrum they were designed to protect.
posted by adipocere at 8:01 AM on February 7, 2011 [10 favorites]
posted by adipocere at 8:01 AM on February 7, 2011 [10 favorites]
The next generation of Air Traffic Control is going to use GPS. Maybe the FAA can lay the smack down appropriately while we figure out exactly who was asleep at the wheel in the FCC?
posted by Xoder at 8:06 AM on February 7, 2011 [2 favorites]
posted by Xoder at 8:06 AM on February 7, 2011 [2 favorites]
I can't tell, so this is just satellite internet? I've used (very expensive) satellite internet and the latency was horrible. Even things like gmail felt absolutely sluggish. I would imagine that the average consumer would interpret this as slow and unusable, or at least not what they'd expect from a high speed internet provider.
Perhaps this is meant to go where broadband simply isn't available, which would be pretty much the entire rural US. Better than nothing, but given the trend for more and more web services to expect low latency connections ... not exactly what you'd want to use for daily life.
posted by geoff. at 8:06 AM on February 7, 2011 [1 favorite]
Perhaps this is meant to go where broadband simply isn't available, which would be pretty much the entire rural US. Better than nothing, but given the trend for more and more web services to expect low latency connections ... not exactly what you'd want to use for daily life.
posted by geoff. at 8:06 AM on February 7, 2011 [1 favorite]
I love GPS. For those who aren't aware, Garmin, TomTom, and your iPhone all use a US government signal for free -- the GPS satellite network was one of those massively expensive DOD research/engineering boondoggles that Bill Clinton, in a fit of charity, decided to give away to anyone who wanted it. Of course, now it's completely taken for granted by everyone on the planet, and for some reason this incredibly important information bounty is regulated by the same morons who won't let you say "bullshit" on the radio. I wouldn't expect some fly by night 4G operator with no revenue to shut down an existing billion-dollar operation with significant military, industrial, commercial, and personal applications, but weirder things have happened.
(Bonus fact: the people who maintain the GPS network get to wear a special patch that says MASTER OF SPACE and has a picture of a griffin.)
posted by theodolite at 8:06 AM on February 7, 2011 [8 favorites]
(Bonus fact: the people who maintain the GPS network get to wear a special patch that says MASTER OF SPACE and has a picture of a griffin.)
posted by theodolite at 8:06 AM on February 7, 2011 [8 favorites]
The way I see it, the U.S. Armed Forces use GPS, and, by and large, you don't fuck with them. This will blow over.
posted by reductiondesign at 8:13 AM on February 7, 2011 [6 favorites]
posted by reductiondesign at 8:13 AM on February 7, 2011 [6 favorites]
Where would we be without GPS?
Fewer places less quickly.
posted by edguardo at 8:15 AM on February 7, 2011 [1 favorite]
Fewer places less quickly.
posted by edguardo at 8:15 AM on February 7, 2011 [1 favorite]
(Bonus fact: the people who maintain the GPS network get to wear a special patch that says MASTER OF SPACE and has a picture of a griffin.)
They're also tenth-level paladins with +5 Holy Avengers.
posted by Mr. Bad Example at 8:18 AM on February 7, 2011 [2 favorites]
They're also tenth-level paladins with +5 Holy Avengers.
posted by Mr. Bad Example at 8:18 AM on February 7, 2011 [2 favorites]
Ummmm, what about the impact on mobile E911? I had a recent experience at work when the police showed up when a customer accidentally activated a 911 call while in the parking lot.
posted by Samizdata at 8:20 AM on February 7, 2011
posted by Samizdata at 8:20 AM on February 7, 2011
I can't tell, so this is just satellite internet?
No, this is satellite Internet “supplemented” by terrestrial service to increase speeds. The trick here is that while supplemental terrestrial antennas are usually only used when satellite reception is bad, LightSquared will be using them everywhere, to increase speeds and lower latency.
posted by smammy at 8:21 AM on February 7, 2011 [1 favorite]
No, this is satellite Internet “supplemented” by terrestrial service to increase speeds. The trick here is that while supplemental terrestrial antennas are usually only used when satellite reception is bad, LightSquared will be using them everywhere, to increase speeds and lower latency.
posted by smammy at 8:21 AM on February 7, 2011 [1 favorite]
Geoff, no: The idea is that they got access to this portion of the spectrum by buying and operating a satellite, but that it'll be augmented with ground stations. The ground stations are what people are worried about, because it means that
On the latency issue, the reason your satellite connection sucked was that it was in geostationary orbit, 35,786 km above the equator, which means the minimum time for a signal to be in transit is .119 seconds up, and another .119 seconds back. The Iridium satellite phones do better because they use a network of satellites much closer to the earth. Wikipedia tells me this is 781km, which would mean a latency (if the satellite were directly overhead) of roughly .0026 seconds each way.
Xoder, modern avionics use GPS, in fact the WAAS (Wide Area Augmentation System) network, which provides an error signal from ground reference stations rebroadcast back up to the satellites and then out to receivers to narrow the typical GPS accuracy of 15 meters or so (for 95% of samples) down to < 3 meters (similarly measured), is maintained by the FAA already.
And many cheap civilian receivers use this signal.
Samizdata, a lot of the cell phone positioning is augmented by triangulation from terrestrial towers. It's hard to say how much for any given device, but it's possible to find a cell phone without GPS.
posted by straw at 8:22 AM on February 7, 2011 [1 favorite]
On the latency issue, the reason your satellite connection sucked was that it was in geostationary orbit, 35,786 km above the equator, which means the minimum time for a signal to be in transit is .119 seconds up, and another .119 seconds back. The Iridium satellite phones do better because they use a network of satellites much closer to the earth. Wikipedia tells me this is 781km, which would mean a latency (if the satellite were directly overhead) of roughly .0026 seconds each way.
Xoder, modern avionics use GPS, in fact the WAAS (Wide Area Augmentation System) network, which provides an error signal from ground reference stations rebroadcast back up to the satellites and then out to receivers to narrow the typical GPS accuracy of 15 meters or so (for 95% of samples) down to < 3 meters (similarly measured), is maintained by the FAA already.
And many cheap civilian receivers use this signal.
Samizdata, a lot of the cell phone positioning is augmented by triangulation from terrestrial towers. It's hard to say how much for any given device, but it's possible to find a cell phone without GPS.
posted by straw at 8:22 AM on February 7, 2011 [1 favorite]
I think that claiming that the FCC wish to destroy GPS is more than paranoid -- it's illogical. As pointed out above, GPS was developed by and continues to be heavily used by the American military. Imagining that the FCC is conspiring to disable something very important to a very significant and powerful branch of the US govt does not even pass a simple logic test. They don't care about whether your tweets can be posted with your location, but I'm sure that they do care than the military knows where they are and can map things correctly.
And, slightly off-topic, may I say that the U.S. geological survey (USGS) is one of the finest and most wonderful branches of any government on the planet? They make all those lovely accurate maps and GIS datasets, and then share them with the world. They put the British OS to shame (great maps, until recently evilly locked away from scholars and the public).
posted by jb at 8:34 AM on February 7, 2011 [3 favorites]
And, slightly off-topic, may I say that the U.S. geological survey (USGS) is one of the finest and most wonderful branches of any government on the planet? They make all those lovely accurate maps and GIS datasets, and then share them with the world. They put the British OS to shame (great maps, until recently evilly locked away from scholars and the public).
posted by jb at 8:34 AM on February 7, 2011 [3 favorites]
And, slightly off-topic, may I say that the U.S. geological survey (USGS) is one of the finest and most wonderful branches of any government on the planet?
I've long thought the US government is fantastic when it comes to releasing information into the public domain. It still blows my mind that in the U.K., the postal code database isn't free or open.
posted by reductiondesign at 8:40 AM on February 7, 2011 [1 favorite]
I've long thought the US government is fantastic when it comes to releasing information into the public domain. It still blows my mind that in the U.K., the postal code database isn't free or open.
posted by reductiondesign at 8:40 AM on February 7, 2011 [1 favorite]
I love GPS. For those who aren't aware, Garmin, TomTom, and your iPhone all use a US government signal for free -- the GPS satellite network was one of those massively expensive DOD research/engineering boondoggles that Bill Clinton, in a fit of charity, decided to give away to anyone who wanted it.
The excess tax money earned by extra economic activity created by GPS has probably paid for the satelites, I would bet.
But the thing is, the signals are just out there, there is zero cost in letting people use it, and there is no way to charge for it. The point of GPS was to be used for guiding missiles and so-forth.
posted by delmoi at 8:40 AM on February 7, 2011
The excess tax money earned by extra economic activity created by GPS has probably paid for the satelites, I would bet.
But the thing is, the signals are just out there, there is zero cost in letting people use it, and there is no way to charge for it. The point of GPS was to be used for guiding missiles and so-forth.
posted by delmoi at 8:40 AM on February 7, 2011
And yeah, it's 100% impossible that the government would deliberately fuck up GPS.
posted by delmoi at 8:42 AM on February 7, 2011
posted by delmoi at 8:42 AM on February 7, 2011
But the thing is, the signals are just out there, there is zero cost in letting people use it, and there is no way to charge for it.
Technically the government retains the ability to randomly fuck up the signal for anyone who doesn't have the password. They haven't done that for ten years, and they probably never will, but they could charge for GPS use if they really wanted to.
posted by theodolite at 8:45 AM on February 7, 2011
Technically the government retains the ability to randomly fuck up the signal for anyone who doesn't have the password. They haven't done that for ten years, and they probably never will, but they could charge for GPS use if they really wanted to.
posted by theodolite at 8:45 AM on February 7, 2011
If one wants to be charitable towards the FCC (which may not be advisable on a regular basis) it may not be cluelessness. It may be they want to see if this is doable and are letting Lightsquared and the GPS community duke it out. Either way, its probably important for people who rely on GPS to keep an eye on developments.
I'm torn because I think the GPS system has become so woven into modern society that it would be close to catastrophic if it failed or was disrupted. I also think that wide access to the internet is just as important.
As for the military issue, the military grade GPS signal operates independent of the civilian signal (or at least it used to), so I'm not sure this proposed plan would interfere with military uses.
posted by cptspalding at 8:53 AM on February 7, 2011
I'm torn because I think the GPS system has become so woven into modern society that it would be close to catastrophic if it failed or was disrupted. I also think that wide access to the internet is just as important.
As for the military issue, the military grade GPS signal operates independent of the civilian signal (or at least it used to), so I'm not sure this proposed plan would interfere with military uses.
posted by cptspalding at 8:53 AM on February 7, 2011
And yeah, it's 100% impossible that the government would deliberately fuck up GPS.
Yes, but it's also extremely likely that no one working at the FCC understands the technology.
posted by fuq at 9:43 AM on February 7, 2011 [1 favorite]
Yes, but it's also extremely likely that no one working at the FCC understands the technology.
posted by fuq at 9:43 AM on February 7, 2011 [1 favorite]
You have arrived at your destination.
posted by dougrayrankin at 9:47 AM on February 7, 2011
posted by dougrayrankin at 9:47 AM on February 7, 2011
You have arrived at your destination.
Your destination, 1983, is on the left. Enjoy living in the past.
posted by GuyZero at 10:01 AM on February 7, 2011
Your destination, 1983, is on the left. Enjoy living in the past.
posted by GuyZero at 10:01 AM on February 7, 2011
I haven't had either internet or GPS on a cell phone yet.
Meh.
posted by Doohickie at 10:33 AM on February 7, 2011 [1 favorite]
Meh.
posted by Doohickie at 10:33 AM on February 7, 2011 [1 favorite]
Route recalculation.
Route recalculation.
Route recalculation.
posted by kmz at 10:35 AM on February 7, 2011
Route recalculation.
Route recalculation.
posted by kmz at 10:35 AM on February 7, 2011
and there is no way to charge for it
Well, that's certainly not true. The signal is encrypted and could be subject to paid licensing. As I understand that encryption ensures it a portion of the signal is in fact not available to civilian applications so that the highest accuracy information is limited to authorized users.
posted by The Bellman at 10:38 AM on February 7, 2011
Well, that's certainly not true. The signal is encrypted and could be subject to paid licensing. As I understand that encryption ensures it a portion of the signal is in fact not available to civilian applications so that the highest accuracy information is limited to authorized users.
posted by The Bellman at 10:38 AM on February 7, 2011
It's not just navigation that relies on GNSS (GPS's proper name). GPS units generate a very accurate pulse every second, synchronized with microsecond precision. Broadcasters, internet time servers, electrical utilities and air hazard warning lights all rely on it for synchronization.
posted by scruss at 10:51 AM on February 7, 2011
posted by scruss at 10:51 AM on February 7, 2011
The way I see it, the U.S. Armed Forces use GPS, and, by and large, you don't fuck with them. This will blow over.
Is the military side transmitted in the same bands as the civilian side? Because if not and it's possible to interfere with the free stuff w/o getting the military, I can easily see the argument that a private profit-driven enterprise doesn't deserve to have to worry about interfering with a free public service flying in a lot of circles these days.
It still blows my mind that in the U.K., the postal code database isn't free or open.
Is it in the U.S.? Every time I've looked into it, what I've come away with is that the USPS sells the information in an obtuse format and it's the census bureau that gives away a pretty good but incomplete sorta-zip database as part of its results.
posted by weston at 10:52 AM on February 7, 2011
Is the military side transmitted in the same bands as the civilian side? Because if not and it's possible to interfere with the free stuff w/o getting the military, I can easily see the argument that a private profit-driven enterprise doesn't deserve to have to worry about interfering with a free public service flying in a lot of circles these days.
It still blows my mind that in the U.K., the postal code database isn't free or open.
Is it in the U.S.? Every time I've looked into it, what I've come away with is that the USPS sells the information in an obtuse format and it's the census bureau that gives away a pretty good but incomplete sorta-zip database as part of its results.
posted by weston at 10:52 AM on February 7, 2011
Scruss is right, the timing component of GPS (GNSS) is extremely important. All told, between the navigation and timing uses of the system, it is a critical part of the global infrastructure.
It's miraculous actually, the U.S. spent billions on developing this system and billions maintaining it and makes it available to the world for free! Even more miraculous, the US recently reiterated its commitment to "provide continuous, world wide access". That gives me some hope.
Despite this, my fear is the solution offered by Lightsquared would be for the company to offer a WAAS type local area corrective signals in the locations where they have set up their systems, using their ground stations. This would give them (and any other company with a similar approach) defacto control over GPS in an area. What would stop them from deciding to degrade their corrective signal and then offer a more accurate signal they charge for? They could call it "GPS HD" or some other catchy name, market it to both businesses and consumers.
posted by cptspalding at 11:35 AM on February 7, 2011
It's miraculous actually, the U.S. spent billions on developing this system and billions maintaining it and makes it available to the world for free! Even more miraculous, the US recently reiterated its commitment to "provide continuous, world wide access". That gives me some hope.
Despite this, my fear is the solution offered by Lightsquared would be for the company to offer a WAAS type local area corrective signals in the locations where they have set up their systems, using their ground stations. This would give them (and any other company with a similar approach) defacto control over GPS in an area. What would stop them from deciding to degrade their corrective signal and then offer a more accurate signal they charge for? They could call it "GPS HD" or some other catchy name, market it to both businesses and consumers.
posted by cptspalding at 11:35 AM on February 7, 2011
the USPS sells the information in an obtuse format and it's the census bureau that gives away a pretty good but incomplete sorta-zip database as part of its results.
Not to derail too far, but the answer depends on the level of detail you want. It's relatively easy to get a file of all ZIP codes and the cities they contain, if you want to do some minimal validation of user input, for instance. I've set up systems using this file, which is periodically updated and you have to cache locally, to automatically choose city/state from a ZIP code, to save data-entry time. There's some minimal agreement I think you need to go through to get the file directly from the USPS, but it's not that hard to get.
The USPS is more restrictive about the really granular data, like street level and ZIP+4. In part this is because it's valuable and they see it as a source of income (important because by statute they have to break even), but I also think it's because you could do some really spammy/abusive stuff with it if you wanted to.
The street-level data is what Amazon et al use to validate and normalize delivery addresses (e.g. "123 Main Street / Suite 102" becomes "123 MAIN ST STE 102" and if there really isn't a 123 Main Street as a deliverable address, it'll suggest nearby alternatives). The USPS basically gives the information to a few vendors and then most users subscribe to feeds or validation services from these vendors. Thus the USPS is kept out of the web services business.
As someone who's had to develop software that uses their information I wish they were a little more open with it, but honestly they're not bad especially compared to some other countries' postal services.
posted by Kadin2048 at 12:02 PM on February 7, 2011
Not to derail too far, but the answer depends on the level of detail you want. It's relatively easy to get a file of all ZIP codes and the cities they contain, if you want to do some minimal validation of user input, for instance. I've set up systems using this file, which is periodically updated and you have to cache locally, to automatically choose city/state from a ZIP code, to save data-entry time. There's some minimal agreement I think you need to go through to get the file directly from the USPS, but it's not that hard to get.
The USPS is more restrictive about the really granular data, like street level and ZIP+4. In part this is because it's valuable and they see it as a source of income (important because by statute they have to break even), but I also think it's because you could do some really spammy/abusive stuff with it if you wanted to.
The street-level data is what Amazon et al use to validate and normalize delivery addresses (e.g. "123 Main Street / Suite 102" becomes "123 MAIN ST STE 102" and if there really isn't a 123 Main Street as a deliverable address, it'll suggest nearby alternatives). The USPS basically gives the information to a few vendors and then most users subscribe to feeds or validation services from these vendors. Thus the USPS is kept out of the web services business.
As someone who's had to develop software that uses their information I wish they were a little more open with it, but honestly they're not bad especially compared to some other countries' postal services.
posted by Kadin2048 at 12:02 PM on February 7, 2011
I suspect that the FCC wants them to figure it out together because only the GPS companies know what their user base has in terms of hardware and how interference tolerant it is. How many units have really great band pass filters and how many cheaped out expecting little to no interference on adjacent bands? Is Garmin the best at filtering? There's a lot of questions that the FCC shouldn't even try to answer without the data. A provisional waiver forces the GPS companies to take this seriously.
posted by BrotherCaine at 12:14 PM on February 7, 2011
posted by BrotherCaine at 12:14 PM on February 7, 2011
According to the Wikipedia, the military code (the P code) is transmitted on both L1 (the frequency in question here, which is also used for civilian receivers) and L2 (1227.60 MHz). Therefore, I would assume that military GPS receivers would still work, however, they do need the L1 frequency as well for "ionospheric delay correction".
posted by Xoder at 1:26 PM on February 7, 2011 [1 favorite]
posted by Xoder at 1:26 PM on February 7, 2011 [1 favorite]
scruss wrote: "It's not just navigation that relies on GNSS (GPS's proper name). GPS units generate a very accurate pulse every second, synchronized with microsecond precision. Broadcasters, internet time servers, electrical utilities and air hazard warning lights all rely on it for synchronization"
Some cell phone networks, too, ironically enough..
Also, the government is in the (long term) process of rolling out another civilian frequency. Supposedly it'll be good for accuracy down to about a foot most of the time and since it'll be open, unlike L2, it won't cost several thousand dollars for a receiver like it does for a current dual-frequency receiver.
posted by wierdo at 1:53 PM on February 7, 2011
Some cell phone networks, too, ironically enough..
Also, the government is in the (long term) process of rolling out another civilian frequency. Supposedly it'll be good for accuracy down to about a foot most of the time and since it'll be open, unlike L2, it won't cost several thousand dollars for a receiver like it does for a current dual-frequency receiver.
posted by wierdo at 1:53 PM on February 7, 2011
Oh..I should have mentioned that I think it's highly unlikely there will be any significant interference from this. That's the whole point of CDMA modulation, which GPS uses. What it will do is degrade the signals ever-so-slightly, so if you're in an already very marginal situation and near one of this company's transmitters, you might have a problem.
This will mainly be an issue for folks with crappy cellphone GPSes, which all have terrible antennas. Built-in navigation in an auto will, thanks to the good external antenna, be much less affected unless the transmit power on the ground stations is incredibly high and you're very close.
posted by wierdo at 1:56 PM on February 7, 2011
This will mainly be an issue for folks with crappy cellphone GPSes, which all have terrible antennas. Built-in navigation in an auto will, thanks to the good external antenna, be much less affected unless the transmit power on the ground stations is incredibly high and you're very close.
posted by wierdo at 1:56 PM on February 7, 2011
CDMA is hardy a panacea for noise rejection. It's very, very good at it, but it would be trivially easy to muck it up.
posted by GuyZero at 2:01 PM on February 7, 2011
posted by GuyZero at 2:01 PM on February 7, 2011
This involves up to 40,000 high-power (15 KW, IIRC) transmitters spread out all over the country, operating in a frequency band just adjacent to the GPS signal's band. The issue isn't a simple ever-so-slight signal degradation, it's massive front-end overloading of receivers meant to receive signals which are very low-level. If this goes through, it's gonna be nasty.
Some of the data in this article from GPSWorld is purdy scary.
Good thing I haven't removed the ADF from my bird. Might have to put the LORAN back in.... if they don't completely tear down all the transmitters!
posted by drhydro at 3:30 PM on February 7, 2011
Some of the data in this article from GPSWorld is purdy scary.
Good thing I haven't removed the ADF from my bird. Might have to put the LORAN back in.... if they don't completely tear down all the transmitters!
posted by drhydro at 3:30 PM on February 7, 2011
Breaking GPS would make US aviation very difficult now and impossible in 9 years with the full transition to ADS-B. It won't happen.
The FCC waiver gives me the impression the approval to LightSquared is contingent on them verifying GPS isn't disrupted.
posted by Nelson at 3:33 PM on February 7, 2011
The FCC waiver gives me the impression the approval to LightSquared is contingent on them verifying GPS isn't disrupted.
posted by Nelson at 3:33 PM on February 7, 2011
I know people at both the FCC and Lightsquared and I think it's important to separate intent from reality. Neith the FCC nor Lightsquared intend for any GPS degradation. The FCC intends to hold Lightsquared's feet to the fire until it is assured that there is no issue with GPS. Lightsquared intends to do everything it can to make sure it doesn't interfere with GPS. The cost of making sure there's no issue on the front end is minuscule compared to any issue found post-deployment, so it is in Lightsquared's best interest to ensure there's no interference to GPS.
That's the intent. The reality is that sometimes things don't go as intended, and that's the issue that needs addressing - making sure intents are followed through with evidence based facts that clearly demonstrate GPS behavior in a Lightsquared environment. And it's incumbent upon *Lightsquared* to demonstrate this. Proving a negative is a high hurdle, but its one they are (rightfully) saddled with.
For the record, I think that if Lightsquared can get past deployment hurdles (and assuming no GPS interference issues) that they will provide some needed services currently missing (in the US) for high-speed wireless data. Their business is to essentially sell wireless access to the internet. They do not have any GPS business, and the satellite system they have is to provide wireless access to remote areas (whether it's cost effective with adequate performance for rural use remains to be seen though).
PS. I seem I have parentheses to spare, if anybody needs any I've got more out on the curb, feel to take as many as you like.
posted by forforf at 8:22 AM on February 8, 2011
That's the intent. The reality is that sometimes things don't go as intended, and that's the issue that needs addressing - making sure intents are followed through with evidence based facts that clearly demonstrate GPS behavior in a Lightsquared environment. And it's incumbent upon *Lightsquared* to demonstrate this. Proving a negative is a high hurdle, but its one they are (rightfully) saddled with.
For the record, I think that if Lightsquared can get past deployment hurdles (and assuming no GPS interference issues) that they will provide some needed services currently missing (in the US) for high-speed wireless data. Their business is to essentially sell wireless access to the internet. They do not have any GPS business, and the satellite system they have is to provide wireless access to remote areas (whether it's cost effective with adequate performance for rural use remains to be seen though).
PS. I seem I have parentheses to spare, if anybody needs any I've got more out on the curb, feel to take as many as you like.
posted by forforf at 8:22 AM on February 8, 2011
forforf, thanks for the insight. I'm glad to hear that this is an attempt to try and sort out how to accomplish two laudable goals (increased access to high-speed internet and preserving GPS signal integrity). It would be great if Lightsquared (or someone else) gets it figured out.
P.S. I borrowed a couple of your spare parentheses, hope you don't mind
posted by cptspalding at 11:17 AM on February 8, 2011
P.S. I borrowed a couple of your spare parentheses, hope you don't mind
posted by cptspalding at 11:17 AM on February 8, 2011
15kW? Nobody runs cell towers at that kind of output. Try 150 watts EIRP. (that is, after antenna gain)
Realistically, a GPS receiver might see -50dBW of interfering signal at the absolute most, at least in a place one can reasonably expect a GPS receiver to function...
posted by wierdo at 5:12 PM on February 8, 2011
Realistically, a GPS receiver might see -50dBW of interfering signal at the absolute most, at least in a place one can reasonably expect a GPS receiver to function...
posted by wierdo at 5:12 PM on February 8, 2011
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posted by crapmatic at 7:41 AM on February 7, 2011