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In BAE’s system, everyday signals like TV, Wi-Fi, radio or cell phone are used to triangulate the location of a person or vehicle. NAVSOP gets the position exact within several feet with this signal-scavenging approach. It uses all sorts of other signals as well, from GPS satellite to air traffic control. The system can even learn and evolve by taking signals that were originally unidentified and using them to build increasingly reliable and more exact fixes on location.
Because Navsop uses a number of signals (sometimes hundreds, depending on your location), it's resistant to jamming devices. In fact, in certain situations, it can even use the signal from a GPS jammer as one of its location beacons. It also shrugs off spoofing, where a bogus signal tricks a device into misidentifying its location.
Those are different technologies. GPS is satellite, typical cell phone is not. Iridium has satellite phones but few people use them due to cost.
Originally posted by PaperbackWriter
reply to post by watchitburn
Why would cell and GPS service ever be "spotty" if they are truly linked by satellites that "blanket" the Earth?
This does not surprise me that they would say that they can use "radio signals" instead.
Does this help?
Originally posted by PaperbackWriter
reply to post by Arbitrageur
If GPS were " satellite" based, why would the signal NEED to travel through mountains?
Mountains would only be a hindrance to ground based relay systems.
If GPS were " satellite" based
Originally posted by PaperbackWriter
Here's my central thesis question.
If you are standing with a transponder in your backpack broadcasting a signal, how do you know if the signal
will travel to a satellite 500 miles above you, 1000 miles above you, 10,000 miles above you, or 25,000 miles above you, then bend and return?
Or simply bounce off the ionosphere and return to Earth?
What determines this?
If we are talking about GPS, the signal is coming from the GPS satellites.
Originally posted by PaperbackWriter
Here's my central thesis question.
If you are standing with a transponder in your backpack broadcasting a signal, how do you know if the signal
will travel to a satellite 500 miles above you, 1000 miles above you, 10,000 miles above you, or 25,000 miles above you, then bend and return?
Or simply bounce off the ionosphere and return to Earth?
What determines this?
The reason it does, is you need more than one or two satellites for GPS to work. If you're at the floor of the canyon and can only find one satellite, GPS won't work. Ideally you'd like to have contact with at least 4 satellites to get a fix on your position and elevation. This is easiest to do if canyon walls aren't blocking some satellites from reaching your GPS unit.
Originally posted by PaperbackWriter
It shouldn't matter how much of the sky is blocked if a satellite system is in effect.
Originally posted by Arbitrageur
If we are talking about GPS, the signal is coming from the GPS satellites.
Originally posted by PaperbackWriter
Here's my central thesis question.
If you are standing with a transponder in your backpack broadcasting a signal, how do you know if the signal
will travel to a satellite 500 miles above you, 1000 miles above you, 10,000 miles above you, or 25,000 miles above you, then bend and return?
Or simply bounce off the ionosphere and return to Earth?
What determines this?
This diagram may help to illustrate. It shows a hypothetical position on the Earth's surface, and how the different satellites pass above. They are all around the same altitude, around 12,600 mi (20,200km):
en.wikipedia.org...
As you see, everything is moving, the earth and the satellites.edit on 2-12-2012 by Arbitrageur because: clarification