Wednesday, October 05, 2011

Invention of the Day: GPS

GPS is one of the very few inventions that was created with an explicit goal to have an infinite number of users, and, consequently, provide infinite benefits to the world. On January 29, 1974 Roger L. Easton was awarded US patent 3,789,409 for Navigation System Using Satellites and Passive Ranging Technologies.

Here's how Easton describes the problem he wants to solve:
A new order of accuracy has become possible with the introduction of artificial earth satellite navigation systems wherein the instantaneous location of the satellites is precisely known.
Unfortunately, the measurement of range has hitherto required the navigator to radiate an interrogation signal (and thereby betray his presence) and also raises the possibility that the satellite transponder will saturate from a plurality of simultaneous interrogations by different navigators.
In other words, direct communications between many ships and the satellites may become a bottleneck in the navigation system. Further, a request for information may betray the position of the ship. Therefore, the inventor proposes a solution:
...the present invention allows the navigator to passively determine his position by measuring the distance, or range, to one or more satellites. Each satellite transmits multi-frequency signals which are derived from extremely precise oscillators. Similar multi-frequency signals are derived by the navigator's equipment from an extremely precise oscillator which is phase synchronized with the oscillators on the satellites. By measuring the phase differences between the signals received from the satellites and the locally produced reference signals, the navigator obtains an indication of the distance to the satellites and, therefrom, of his own location. The navigator's presence is not betrayed since no interrogation signal transmission is required.
As a result we get the best of both worlds: precise positioning with unlimited number of users and maintaining secrecy of location.

In 2010, Roger L. Easton was inducted into the National Inventors Hall of Fame.

tags: trade-off, dilemma, solution, problem, system, information, detection

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