Tucked away in the comments at the end of the article. Responding to how accuracy is achieved … It’s beautiful.
It is a radio wave. After 1500 waves the wave inverts if the PRN bit changes. At a particular epoch all we are identifying is
- – the millisecond interval a 1,000 bit PRN sequence is sent to give 1 millisecond accuracy (300 km)
- – the PRN bit that is current to give 1 microsecond accuracy (300 metre)
- – the particular wave in the 1,500 that represent the particular bit (ie the number of waves after the bit started) to give 1/15th of a nanosecond or 67 picosecond (20 cm accuracy)
- – alignment of the waveforms to give the point in the wave cycle which takes it down to 1 picosecond (3 mm).
Then it is a matter of how good your errors have been identified and fixed in your calculation!
Rather than 1 bit every 1500 waves wireless devices are utilizing phase changes 4 or 8 times in one single wave. Once a method is devised (say using 2 channels for one frequency, one 180° phase shifted) that id’s the actual wave when a bit changes we have cm accuracy.
whoops maths is wrong, is 1/1.5th of a nanosecond or 666 picoseconds, giving 10 picoseconds for 3mm