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The Basement
How is GPS free?
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<blockquote data-quote="Phil Graham" data-source="post: 207457" data-attributes="member: 430"><p>Ben,</p><p></p><p>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.</p><p></p><p>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: (<a href="https://physics.stackexchange.com/questions/1061/why-does-gps-depend-on-relativity" target="_blank">https://physics.stackexchange.com/questions/1061/why-does-gps-depend-on-relativity</a>)</p><p></p><p>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:</p><p>(<a href="https://en.wikipedia.org/wiki/SIGSALY" target="_blank">https://en.wikipedia.org/wiki/SIGSALY</a>)</p><p></p><p>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.</p><p></p><p>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</p></blockquote><p></p>
[QUOTE="Phil Graham, post: 207457, member: 430"] 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: ([url]https://physics.stackexchange.com/questions/1061/why-does-gps-depend-on-relativity[/url]) 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: ([url]https://en.wikipedia.org/wiki/SIGSALY[/url]) 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 [/QUOTE]
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