LightSquared's Threat to GPS

http://freegeographytools.com/2011/how-the-fcc-plans-to-destroy-gps-a-simple-explanation

I don't know if this is old (I don't think so) or 205 but it seems a pretty credible threat if it were to go through. Still it's better to know about it than not, and it's a good, rational explanation of a company's plans to offer wireless broadband on a frequency that would interfere with GPS operation.

Now back to figuring out the difference between routes and tracks

Sorry not going to read the whole thing but based on a quick skimming....not happening, at least in a form that would derogate GPS performance.

Bruce

Give that airliners are soon going to be exquisitely sensitive to GPS signals for separation, this sounds like a non-starter. The FCC has done some pretty bone-headed things, like forbidding broadcasts of emergency locator beacons on 121.5.

In a nutshell, depending on the modulation methods employed, it's still entirely possible for multiple transmissions on even a single frequency to operate without interacting with one another.

If from the same source. If from entirely separate/unrelated senders, very doubtful.

http://en.wikipedia.org/wiki/Single-frequency_network

No difference between routes and tracks. Routes is American; tracks is British.

theKite

And then there is GPS lingo, where they are not synonyms.

Yeah, big but:
the last paragraph of that article:

In a Single Frequency Network, the transmitters and receivers are usually synchronized with the others, using GPS or a signal from the main station or network as a reference clock. For example, the DVB forum specifies (TS 101 191) the use of a special marker, the Mega-frame Initialization Packet (MIP) that is inserted in the bit stream at a central distribution point, and signals the SFN transmitters the absolute time (as read from a GPS receiver) at which this point in the data stream is to be broadcast.

Seems that system (SFN) would also be negatively impacted by LightSquared's plan as it uses GPS to work.

That's all wonderful and may be true but now the the FAA has approved Differential GPS for some aspects of aircraft flight navigation (I believe in some instances including airfield approach/glide-path) they are going to allow the system to be degraded?

Edit; Just checked with my neighborer an FAA controller, and if I understood him correctly WAAS GPS is FAA approved for precision approaches. They have worked to hard getting the precision necessary to dump it now.

Bruce

Not going too deeply into the intricacies or even the actual proprietary format employed by ANY particular system (may be top secret to Joe anyway), my main purpose was simply to explain that a channel is NOT rendered unuseable just because two or more transmitters were used on a single frequency. It is only in the article's example that GPS be one of the originating sources of the control bit as well as the emanation in question with respect to LightSquared's dilemma.

Even just employing standard coding techniques including CDMA, TDMA, etc. and especially if integrating spread spectrum, any amount of bandwidth can still be utilized (albeit, necessarily with corresponding speed degradation). Since all users still need FCC coordination anyway, control codes might just as easily be required to be integrated into their transmissions so as to enable frequency sharing.


An excerpt from CDMA:

"An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can communicate."

http://en.wikipedia.org/wiki/Cdma

Data Shows Disastrous GPS Jamming from FCC-Approved Broadcaster | GPS World

An excerpt from CDMA:

"An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can communicate."

http://en.wikipedia.org/wiki/Cdma[/QUOTE]


In this case rejected means it is not decoded. You can't simply reject signal energy with no loss of some sort... It is noise. Noise degrades performance... always, just to varying degrees. How much tolerance does your device have????

Of course. There will always be degradation even if only versus shot noise. One always wants to be the only one using the highway (or restroom, natural resources, etc.) but it's getting to be a crowded world so compromises have to be implemented.

Not sure if this is just a late April fools joke,,,or something vastly bigger:

http://freegeographytools.com/2011/how-the-fcc-plans-to-destroy-gps-a-simple-explanation

Steve

I think the big problem is the difference in power of signals at close frequency proximity. GPS signals are at very low power relative to the Lightsquared signals. Those new signals will jam our GPSes because our GPS receivers use high gain amplifiers in the signal path and the noise caused by the Lightsquared signal will render our GPSes paper weights. I seriously doubt this is going to happen because the physics just don't work and consumers will demand their GPSes continue to work. I'd short LIghtsquared if I was a gambling man.

DEADLINE is July 30, TODAY. Act now!

I just learned that the FCC is considering granting permission to an outfit called Lightsquared to use their satellite frequency band, which is right next to the GPS frequency band, for terrestrial service. They would have towers rather like cell phone towers. The government's own studies have shown that the much-stronger Lightsquared signals would overwhelm GPS receivers, in some cases rendering them useless.

Read about it here and here, and many other places on the web.
Speak out here. BE SURE TO INCLUDE PROCEEDING NUMBER 11-109.

Not really a "new" thing, there's been talk of this for several years now.

Personally I don't see it going very far, too much of today's infrastructure relies on GPS. Not just your phone or the GPS in your car, but marine/aircraft navigation systems, PLB/SPOT beacons, emergency comm systems (Nearly every police/fire/med vehicle has a GPS receiver that relays its position to dispatch's CAD terminal)....

There's plenty of other bands open, especially since the analog TV shutdown.

Lightsquared will develop the technology/solution for these potential problems. But don't worry, them nor anyone else will turn on anything that will render GPS useless, and the birds will keep singing.

Invest wisely.

Isn't that nice of them:
"After recent tests that confirmed interference, LightSquared has proposed GPS device makers use filtering technology to avoid problems."
http://www.washingtonpost.com/blogs...re-you-hiding/2011/07/27/gIQAugeIdI_blog.html

The FCC won't tell Sen. Chuck Grassley (R-Iowa) why they fast-tracked LightSquared's application:
http://grassley.senate.gov/news/Article.cfm?customel_dataPageID_1502=36226

Here's Garmin's position:
https://support.garmin.com/support/searchSupport/case.faces?caseId={d8f631e0-3ac0-11e0-d39a-000000000000}

If you don't want to have to buy a new GPS to support LightSquared, now may be a good time to write your congress-critters.
http://senate.gov/
http://house.gov/

Chris