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My assumption was that GPS doesn't use dead reckoning to get a fix (other than the satellite paths). Do receivers use the Doppler effect to directly measure velocity?

Edit: this article seems to support my view that they don't start with velocities: https://insidegnss.com/wp-content/uploads/2018/01/marapr15-S... "How does a GNSS receiver estimate velocity?"



Dead reckoning isn't really the right term- there are broadcast and published ephemera (ephemeris-es) for the satellites of various qualities. (Both predicted and observed and then even levels of correction days or weeks later, for high precision/accuracy or strictly static obvs. stuff.)

The doppler mostly comes into play with the small delta-t errors, but again, more math magic cancels most of it out in most cases, or what remains is negligible.

It's more of a signals/sync thing that gets into antenna design and (to simplify) getting all signal cycles from the various satellites working within a single aligned synced cycle, if that makes sense.

One reason the old gps units needed a long time to get an initial fix was waiting to download the broadcast, in ~bits/sec. This can now be downloaded much quicker via internet or other methods.

And there are dozens of other similar shortcuts possible depending on receiver capabilities/ connectivity/ observervation methods.

Which is to say that there's no one 'right' way to get a fix- and the 'most' correct original design was the ~hour long broadcast download. And no one does that anymore.

But just about every method (I'm aware of) is derived one way or another from the general eqns I gave above.

(But my exposure is almost entirely geodesy, engineering, and surveying, and my military (encrypted) knowledge comes from my PLS instructor being ex army intelligence, not hands on. But which is also why I am at least aware of so much of the missile tie-in issues.)

And there are signals processing and CS tricks also, which I only barely grasp.

But if something says it starts with baseline (propagating signal path) lengths to get position, it's skipping the step of how it measures/ estimates those initial baseline lengths.




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