Differential GPS is an old thing, finnish FM stations
send out (local) corrections. (important where there
are temperature gradients between land, coast and
water, not just the earlier inaccuracy)
GPS signals come from high above, the mobile phone
signal from close by, more or less horizontically,
(also polarized) where there often is windows, and
if too deep into a commersial building, mall,etc one
must set up a picostation station inside and triangulation
is even easier.
And that pico station cannot be synchronized directly
with GPS anyway, no way the handset can be.
Ilmarinen
"Triangulation methods require the basestation network to be continuously figuring out the location of the handset"
The handset has to listen for incoming calls anyway,
wake up, every 0.125-4 second for a time slot or two,
but not transmit and waste battery.
Triangulation is done when a/the call is made, the inherent
delay information for positioning time slots (other
methods too possible) |
