GPS

[g***@lycos.co.uk]

My current phone does not have GPS but I had thought.

Surely if your phone gets a signal from more than one mast using
triangulation it should give you a similar geographical results.

Any comments?

[Andreas Wenzel]

Post by g***@lycos.co.uk
My current phone does not have GPS but I had thought.
Surely if your phone gets a signal from more than one mast using
triangulation it should give you a similar geographical results.

Not new at all.

http://www.google.com/search?hl=en&q=gsm+positioning&btnG=Google+Search

Andreas

[John Henderson]

Post by g***@lycos.co.uk
My current phone does not have GPS but I had thought.
Surely if your phone gets a signal from more than one mast
using triangulation it should give you a similar geographical
results.
Any comments?

This will work only if:

1) you can get the information about signals out of the phone,
and

2) you know where the BTS (base transceiver station) sites are
that those signals are coming from.

The two useful information sets you might be able to read from
the phone are TA (timing advance) and NMR (network measurement
results).

TA is calculated by the BTS whenever the phone is interacting
with it, and the value is passed to the phone so that the phone
can adjust the timing of its transmission bursts (so that they
arrive at the BTS to exactly coincide with your allocated
timeslot opening).

TA values range from 0 to 63, representing distances from the
serving cell of between 0 and 35 km.

You may be able to read the last negotiated TA value from the
phone. If the phone is idle and moving, you'd need to force an
interaction with the BTS to get a fresh value. This can be
done easily and for free by using a supplementary services
command.

NMR is calculated by the phone at all times (not just when
interacting with a BTS). It gives the BSIC (base transceiver
station identity code) and signal strength of the 6 strongest
neighbouring cells (other than the serving cell - usually the
strongest). NMR is passed to the BTS during any interaction so
that the network can manage handovers between your phone and
those BTSs.

TA and NMR are not readable by standard GSM 07.07 "AT" commands.
But they may be readable by proprietary extensions on some
phones. They are also usually available to the SIM application
toolkit interface (as part of the "provide local information"
proactive SIM command).

References: GSM 04.08, 11.14.

John

[matt weber]

Post by g***@lycos.co.uk
My current phone does not have GPS but I had thought.
Surely if your phone gets a signal from more than one mast using
triangulation it should give you a similar geographical results.
Any comments?

That's pretty much how most GSM phones in the USA do it, although
triangulation is not very useful because the antennae are fairly broad
beamed. They do however derive position based upon the timing
differences at the 3 antennae. Timing advance will only give you
position +/- about 500 yards, but you can actually signal arrival with
much more precision than timing advance provides, and get the distance
from the BTS down to about +/- 15 meter or so. The intersection of 3
circles of known diameter is a single point. So if you can hear the
signal from 3 BTS that have the timing software, you can determine
position of the phone with satisfactory accuracy even when a GPS
signal isn't available.

[John Henderson]

Post by matt weber

Post by g***@lycos.co.uk
My current phone does not have GPS but I had thought.
Surely if your phone gets a signal from more than one mast
using triangulation it should give you a similar geographical
results.
Any comments?

That's pretty much how most GSM phones in the USA do it,
although triangulation is not very useful because the antennae
are fairly broad beamed. They do however derive position based
upon the timing differences at the 3 antennae. Timing advance
will only give you position +/- about 500 yards, but you can
actually signal arrival with much more precision than timing
advance provides, and get the distance from the BTS down to
about +/- 15 meter or so. The intersection of 3 circles of
known diameter is a single point. So if you can hear the
signal from 3 BTS that have the timing software, you can
determine position of the phone with satisfactory accuracy
even when a GPS signal isn't available.

This method is described in GSM 03.71. But I was under the
impression that it's implementation is the exception rather
than the rule.

Is it widely used? And in which countries?

John