First GPS Signal Received 40 Years Ago This Month

See https://spectrum.ieee.org/gps for description of a system being referred to as “SuperGPS” that conceivably deliver an accuracy of 2.2 cm or slightly less than an inch. Quoting from the article, “In experiments outdoors with six radio transmitters dispersed over 660 square meters, SuperGPS delivered a positioning accuracy pinpointing objects to within 7.4 to 10.2 cm, as well as sub-nanosecond timing. The researchers could improve the positioning accuracy to within 2.2 cm by taking advantage of information about the phase of the signals—that is, the fraction of a wave that the signal has completed at any given time.”

The full article points out that one cause of inaccuracy can be reflection of the signals off buildings. Accuracy of several devices was being discussed a few days ago on these forums.
http://www.poi-factory.com/node/53280

Multipath is indeed a source of GPS positioning error. From personal experience I can add a nearby rock face on the mountain to my East, and a cruise ship to clear cases of erroneous GPS position caused by signal reflection.

There is a polarization trick which makes this less likely than it would otherwise be, but it happens often enough anyway.

One of my female classmates in Grade School, Junior High School, and High School in West Virginia was a mathematician who worked on the first GPS system.

- Tom -