[Discuss] GPS feature in cellphones?

[bogstad at pobox.com (Bill Bogstad)]

On Fri, Jun 6, 2014 at 7:00 AM, Jerry Feldman <gaf at blu.org> wrote:
> Actually triangulation is used in GPS also. It is a very old tried and
> true method.

Very true.   Some difference are:

1. GPS is triangulation from satellites rather then cell towers
2. GPS was designed explicitly to provide location information and is
available anywhere the sky is sufficiently visible.
3. GPS triangulation is done in the endpoint while the cell tower one
is done cooperatively by the cell network as a whole.
4. GPS can be done passively by anyone anywhere, while cell tower
triangulation requires endpoints that transmit (and as a result
identify themselves.)

I think that #4 is particularly interesting.   I had a recent
discussion with my father-in-law about Google's driverless cars and he
was concerned that this meant that people would be trackable via their
vehicle.   He didn't seem to realize that it was perfectly possible to
do driverless cars with GPS and offline maps in a way that was
untrackable.   Of course, I pointed out that we all
now carry personal tracking devices (cellphones) anyway so there is no
need to track our cars.

Bill Bogstad

Note to #4:  I could conceive of a system that worked via network
triangulation where the endpoint broadcast a random token
which was used by the cell towers to triangulate the anonymous
endpoint.   I'm pretty sure that isn't the way it is done and even if
it was the network would still know SOME device was at a particular
location.  It's interesting to note that because GPS was intended for
dual civilian/military use, it was a design requirement that silent
endpoints could determine their location.   Privacy (of location) was
obviously mandatory for military users.