If you've ever wondered what goes on inside a GPS receiver, here's a superb writeup by a guy who built his own:
It doesn't matter if you know the difference between a Costas loop and a bang-bang discriminator; it's well written and will give you a good idea of what's going on.
Waiting for my eyes to clear.
"With over bar denoting conjugation, the cross-correlation function y(Τ) of complex signal s(t) and code c(t) shifted by offset Τ is:"
Now I can go to sleep knowing all is right in the GPS world.
thank the Gods there are people that know this stuff, and, I might add, people that understand it!
this was good but clear as mud. I will stick with my 660.
Look over the pictures and diagrams, skim over the words -- ignore the math.
That first picture is the analog front end -- clean and simple -- not a lot of parts.
From there things move to the digital realm, and yeah, they get more complex.
Looking at the diagrams, he's got that front end, a specialized digital block, and a general purpose computer.
Guess what's in our portable units? A similar analog front end, a digital block, and the power of a modern general purpose computer, running some very specialized software!
All that work he goes through gets him lat/long/time, using a maximum of four satellites! That's all his hardware will track at once!
None of us would buy a GPS receiver that only had a 4 channel receiver!
Layer on top of that all the mapping stuff, and the non-trivial computation involved in running through that map database to find a route from where you are to where you want to go that our small portable units do!
And if you skim over the text, you'll spot remarks like the fact that GPS receivers are essentially recognizing signals that are well below the noise level... Now there's a bit of technological magic for you! And also a clue as to how susceptible GPS can be to outside noise sources (such as LightSquared).
Some times it's useful to peek behind the curtain and take a look at the machinery that powers the things we use every day -- even if all you do is whistle in amazement and let go of the curtain.
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