[aprssig] indoor tracking.

[Chris Kantarjiev]

I recently learned a little more about the "assisted GPS" that is
being deployed in cell phones. The basic idea is that the
chipset in the phones is not smart enough to completely decode
the GPS satellite information and compute a posit, so it 
"makes a call" to equipment in the central office to assistance
in computing the posit.

What I didn't know is that at least one of the chipsets that's
out there (don't know which one, I was getting a second-hand story)
also mixes cell tower id/location into the computation. So
even if you're deep in a building where the GPS signal won't
penetrate, but signals from two cell towers will, you can
compute an accurate position.

Very interesting. Unfortunately, I don't think the data will
be accessible in any meaningful way (like a serial connector
spitting out NMEA sentences :-)

chris