6543216879455

Have you looked into using gyros for north-finding? There's been a lot of progress in recent years with MEMS gyros (which normally have too much zero-drift to work with traditional gyro north-finding techniques).

See, for example: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5464685/

> there's no communication happening, just reception.

Erm... In practice that's not quite true for many devices, depending on your definition of communication and the relevancy of side-channels (which may leak information).

So, first of all, Location Services is more than just GPS. It also uses cell and Wifi signals to estimate location (hence the pop-up that "enabling wifi improves location accuracy"). So using location services may affect the behavior of the cell and wifi radios.

Second, virtually all phones (and many other devices that expects to often have internet communications) use what's called "assisted GPS", which is where the satellite ephemerides and almanac are downloaded through a side channel and passed to the GPS chip (along with an estimate of the current time and location)

That greatly improves the time to first fix because the receiver knows exactly which satellites are above the horizon, and also doesn't have to wait for each satellite to broadcast its ephemeris data (ephemeris is only broadcast once per 30 second frame, and you aren't guaranteed to receive it correctly the first time).

Tangentially related to the above, there's a very interesting paper from Microsoft where they are able to recover the location of a very low duty-cycle receiver using only an estimate of the code phase relative to the internal clock (so the navigation message is never even decoded by the device).

They (of course) needed to record the ephemerides (at the "base station") during the periods where they wanted to know the receiver's position, and there are duty cycle minimums to avoid 'cycle slip' (because the receiver only knows the code phase to an ambiguity of n2pi).

Edit: Oh, here it is: https://www.microsoft.com/en-us/research/wp-content/uploads/...