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To: Clarksterh who wrote (13930)	7/18/2001 8:54:22 AM
From: LarsA	Read Replies (2) \| Respond to of 34857

Partly OT Ilmarinen, Clark Hare: I'm a big GPS fan and I have several units, one of which is this one: garmin.com that I carry at all times in my pocket when I'm travelling. It and many other brands now features the new WAAS correction that gives it a precision of 3m or less (in the U.S.) - better than differential GPS. It also boots up and finds the satellites in a few seconds. Works great under foliage and in deep, narrow canyons etc. It's rare that you don't get at least a 2D position. Doesn't work deep inside buildings but most often in a car with regular big windows. Now that said I don't understand the need to, by mandating a Snaptrack kinda system- if they have a monopoly, to get a really good fix inside a house. Aren't we overreacting to the need of people to call 911 and be found with very high precision? If a network based system can get you within 100 m most of the time and helped by a regular GPS can pinpoint you within 10 m? Call me paranoid but it wouldn't surprise me if this FCC location push is really about the war on drugs or something similar rather than ambulances. Maybe within a few years we learn that the little red button to activate your cell phone GPS is really only symbolic.... Or what do you think JohnG?

To: Clarksterh who wrote (13930)	7/18/2001 10:46:32 AM
From: S100	Respond to of 34857

<accuracy is about 10 meters.> I was around some GPS groups years ago. I recall some pretty good numbers using some tricks (read big bucks) like differential GPS. Numbers were similar to these that I found on the net. I believe that surveyors now use GPS. snip IGDG (Internet-based Global Differential GPS) is a uniquely powerful and flexible C-language software package that provides a complete end-to-end system capability for GPS-based real-time positioning and orbit determination 10 cm horizontal and 20 cm vertical real time positioing accuracy with dual frequency GPS receivers snip gipsy.jpl.nasa.gov The official dogma is snip In most cases civilian users (whose receivers can read only unencrypted, intentionally corrupted GPS signals) can expect navigation accuracy on the order of 50-100 meters. The advertised accuracy for users with military receivers, which read the encrypted GPS signals, is 16 meters. Coalition forces in Desert Shield / Desert Storm relied heavily on GPS, and U.S. military authorities praised GPS effusively for its effectiveness as a force multiplier in that conflict snip A site with info on GPS is oreillynet.com Gives one reason SA was turned off.

To: Clarksterh who wrote (13930)	7/18/2001 12:29:45 PM
From: 49thMIMOMander	Read Replies (1) \| Respond to of 34857

Differential GPS is an old thing, finnish FM stations send out (local) corrections. (important where there are temperature gradients between land, coast and water, not just the earlier inaccuracy) GPS signals come from high above, the mobile phone signal from close by, more or less horizontically, (also polarized) where there often is windows, and if too deep into a commersial building, mall,etc one must set up a picostation station inside and triangulation is even easier. And that pico station cannot be synchronized directly with GPS anyway, no way the handset can be. Ilmarinen "Triangulation methods require the basestation network to be continuously figuring out the location of the handset" The handset has to listen for incoming calls anyway, wake up, every 0.125-4 second for a time slot or two, but not transmit and waste battery. Triangulation is done when a/the call is made, the inherent delay information for positioning time slots (other methods too possible)