On: Lockheed is now tracking phones and walkie-talkies from space

[fatboy]

Can anyone explain how this works? Are these satellites in a similar orbit to GPS satellites? Do signals from cell phones etc include timestamps? Or is there a high resolution way of detecting the direction of a signal?

[livueta → fatboy]

modern DoA algs like https://en.m.wikipedia.org/wiki/MUSIC_(algorithm) can use a small phase coherent array of antennas to estimate DoA by, in grossly simplified terms, measuring minute phase differences across the array as a signal arrives: https://www.diva-portal.org/smash/get/diva2:724272/FULLTEXT0...

[Gare → fatboy]

Maybe just plain old triangulation? The constellation consists of 21 satellites. If multiple satellites receive the same signal, the difference in arrival can be used to precisely locate the source.

[spoonfeeder006 → fatboy]

You'd need unique signature of cell phone signal to separate it from other cell signals

In terms of timestamp, when multiple satellites measure different times of receipt from same cell signal they could reverse compute the location

Could probably incorporate differences in received signal strength as well

At least thats my guess

I don't think you'd wanna use timestamp info from the sender, since you have no control over the accuracy of that, even if it was available

[DenisM → fatboy]

Iirc, SAR satellites in polar orbits measure Doppler effect of distress beacons to compute coarse latitude. It’s been working for decades, so I imagine recent advances in signal processing might be able to significantly improve precision.