How is GPS free?

Ben Lawrence

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Mar 2, 2011
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I was driving around the other day having issues with my Tom Tom connecting to GPS. I started to wonder dang I got this thing a while ago and its crazy how there is no subscription fee. I dont even think they make Tom Tom units anymore. I mean the GPS satellite infrastructure must be pricey to keep functioning. What do vendors pay a one time fee or is it just a universal no cost signal.
 
I was driving around the other day having issues with my Tom Tom connecting to GPS. I started to wonder dang I got this thing a while ago and its crazy how there is no subscription fee. I dont even think they make Tom Tom units anymore. I mean the GPS satellite infrastructure must be pricey to keep functioning. What do vendors pay a one time fee or is it just a universal no cost signal.

Ben,

GPS isn't free. Your taxes pay for it as part of overall US military spending, and elements of its development have been intimately tied to government work (and war) since the turn of the 20th century.

GPS and its competitors (e.g. GLONASS, Galileo) require nation-state levels of infrastructure for satellite construction, launch, and timing synchrony. Further, GPS required the discovery and characterization of the physic of general relativity: (https://physics.stackexchange.com/questions/1061/why-does-gps-depend-on-relativity)

GPS also uses a highly robust data transmission scheme to convey satellite location called direct sequence spread spectrum. Practical modern spread spectrum techniques (though not DSSS) can more or less be traced to the use of SIGSALY during WW2 for encrypted communications between the allies:
(https://en.wikipedia.org/wiki/SIGSALY)

Prior to SIGSALY, things like multiplexing (US patent 745,734 from 1903) and quantizing (U.S. Patent 2,272,070 in 1937) helped lay the ground work. Also in this time frame Hartley and Nyquist worked to figure out some of the principles around sampling rates and data rates.

This work was put together as a cohesive system by a man named Claude Shannon in 1948, in a paper (then book) called "A Mathematical Theory of Communication" in the Bell Laboratory Technical Journal. Shannon started the field of information theory and he is one of the most central figures in communications, cryptography, and computing in the 20th century
 
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And this is why you are an "Honorary PhD" on here! Very interesting information. I see how the original use was military use so understand how the government backs the infrastructure. Here is one thing I am willing to contribute some tax dollars to.
 
And this is why you are an "Honorary PhD" on here! Very interesting information. I see how the original use was military use so understand how the government backs the infrastructure. Here is one thing I am willing to contribute some tax dollars to.
Ben,
Back from GPS start in the 1970's the military used "selective availability" to reduce the accuracy of the GPS signal available to non-military receivers, instead of being as little as 1 meter from your absolute global position, you could be as much as a 50 meters horizontally off to 150 meters vertically off, so was of little use as an enemy missile guidance system, but also of limited use for aircraft . It also made commercially available units not effective for wartime use, and selective availability was turned off for a while during the Gulf War.
May of 2000, President Clinton removed the selective availability, and the FAA was able to not have to rely on their own system of location so much, reducing costs maintaining stations far away from airports.

As a historical tidbit, LORAN continued to be preferable to many fishermen over GPS in the early days. Even with selective availability randomly creating location inaccuracies, it was far more accurate overall than LORAN, but LORAN could precisely return you to a little outcropping of coral or some other invisible feature that would be difficult to pinpoint with GPS and a paper chart.

Recently purchased a Garmin Oregon 600 GPS loaded with complete street maps of Canada, USA and Mexico. My first GPS units from the mid-1980's and early 1990s just showed Latitude and Longitude, requiring buying paper Lat/Long maps or charts of every location you wanted to sail to or visit with accuracy- and those paper maps were only as accurate as the cartographers could measure bit by bit, and one's own lining up on the cross-hairs.

I probably have recycled 25 pounds of paper maps and charts that cost hundreds of dollars, though still have quite a few- never know when a big EMP might knock out the GPS ;^).

Cheers,
Art

 
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I wonder if they still have the option to go back to the selective availability or if the infrastructure is too far along where it would cause havoc.
As far as you recycling your maps Those gazetteer State map books are amazing. Full detail on class four roads etc that I feel allow you a way better view than the GPS units. From point A to point B ok a GPS wins but for leisure planning I would have to go with the gazatteer
 
I wonder if they still have the option to go back to the selective availability or if the infrastructure is too far along where it would cause havoc.

You GPS receiver has a estimate of the accuracy of the GPS fix. So assuming you mean that if you don't have enough satellites or that you are in a location where you aren't getting good signal from the satellites, your receiver can let you know. No need to degrade the signal.