NAVSOP Navigation System Rivals GPS 135
dangle writes "BAE Systems has developed a positioning solution that it claims will work even when GPS is unavailable. Its strategy is to use the collection of radio frequency signals from TV, radio and cellphone masts, even WiFi routers, to deduce a position. BAE's answer is dubbed Navigation via Signals of Opportunity (NAVSOP). It interrogates the airwaves for the ID and signal strength of local digital TV and radio signals, plus air traffic control radars, with finer grained adjustments coming from cellphone masts and WiFi routers. In any given area, the TV, radio, cellphone and radar signals tend to be at constant frequencies and power levels as they are are heavily regulated — so positions could be calculated from them. "The real beauty of NAVSOP is that the infrastructure required to make it work is already in place," says a BAE spokesman — and "software defined radio" microchips that run NAVSOP routines can easily be integrated into existing satnavs. The firm believes the technology could also work in urban concrete canyons where GPS signals cannot currently reach."
Re:Doesn't sound that accurate (Score:1, Informative)
Its not using signal strength. Its using position. You have a set of internal antennas, that are tenths of a degree apart arrayed in a circle. You get a strongest signal from the set of elements that are orthogonal (at right angles in 3 dimensions) to the source. You can calculate based on signal strengths of two 'strongest' sets of elements the direction (accurate to perhaps 1 second of arc), the direction to one source. Then you switch frequencies and determine the location to a second source (again, accurate to 1 second of arc). Where those two points intersect is your location (really its not that different from receiving GPS signals, except the frequencies are different). You can use multiple sources to refine your position. Your initial position can be determined by perhaps the TV frequencies in use at a given locale. Since digital television broadcasts time also, you can very quickly determine the time zone. A digital magnetic compass can give you magnetic north. All of these things can be combined to help refine your location. If you have determined your city, celll tower locations can further refine your location. Its only good to within a few meters, good enough for flying bombs. Of course, any radio signal can be jammed, but how many do you want to have to jam? You had a better/cheaper solution to loss of GPS signal? At sea its not that useful, unless you could send up a balloon to say 3000 meters, at which point, you could still direction find and find your location, provided you are within about 276 km of a coastal TV transmitter. Its difficult to get higher frequencies to refract off the ionisphere, so you are then stuck receiving long range transmissions from low frequency AM/SSB radio signals. Direction finding these is difficult because of the physics involved (you need physically very large equipment, such as a Plessy "Elephants cage" such as might be used by a national governments signals intelligence agency). Clearly its not a universal solution. Its effective for aircraft, not so much for people on the ground or at sea (although dead reckoning is still used for aircraft, and even getting to within 300-400 km of a destination can give location information --further with increased altitude). We started talking about drone aircraft. For drones, this is would be a very useful method of direction finding.
Re:Doesn't sound that accurate (Score:5, Informative)
Whenever a program is looking-up the location of a smartphone, that phone is very probably also beaming back a list of all the Wifi APs in-range, their signal strength, and approximate location. Everyone who makes navigation software for smartphones is guaranteed to have such a database, and is continually keeping it up-to-date.
Not only is it practical to do this, and it has been for years and years, it's done because you're likely to get much better accuracy, and a much quicker location fix. You can prove this out by running a navigation app on a tablet that has wifi but lacks a GPS chip. You'll find that Google Maps or anything else has no problem at all pinpointing your location.
And BTW, moving one AP won't cause a problem... Triangulation requires several APs in range, and it'll try to use everything in-range to get a more precise fix so... Short of conspiring to have everyone in an area to move their APs in unison for a significant distance, you're not going to significantly fool the algorithm that handles all of this.
What's more... Before wifi was widespread, the previous fallback was a database with the GPS coordinates, altitudes, power levels, etc., of all of a telco's cell towers. It works, but not as well as the horde of prolific wifi APs these days. And for the record, I am speaking from first-hand knowledge.