Where do Brits go abroad?

> <tims_new_home.TakeThisOut@yahoo.co.uk> wrote:
>
>>And even if I did, the majority of them don't have a GPS chip in.
>
> see my reply to Roland
> --
> Lansbury (Retired)


It's a bit of everything really ; (from wikipedia)
A second phase of Enhanced 911 service is to allow a wireless or mobile
telephone to be located geographically using some form of radiolocation from
the cellular network, or by using a Global Positioning System built into the
phone itself.

Radiolocation in cellular telephony uses base stations. Most often, this is
done through triangulation between radio towers. The location of the caller
or handset can be determined several ways:

a.. Angle of arrival (AOA) requires at least two towers, locating the
caller at the point where the lines along the angles from each tower
intersect.
b.. Time difference of arrival (TDOA) works like GPS using
multilateration, except that it is the networks that determine the time
difference and therefore distance from each tower (as with seismometers).
c.. Location signature uses "fingerprinting" to store and recall patterns
(such as multipath) which mobile phone signals are known to exhibit at
different locations in each cell.
The first two depend on a line of sight, which can be difficult or
impossible in mountainous terrain or around skyscrapers. Location signatures
actually work better in these conditions however. TDMA and GSM networks such
as AT&T Wireless Services and T-Mobile use TDOA. [1]

CDMA networks tend to use handset-based radiolocation technologies, which
are technically more similar to radionavigation. GPS is one of those
technologies. Verizon Wireless and Sprint PCS use Assisted GPS.[1]

Hybrid solutions, needing both the handset and the network include:

a.. Assisted GPS (wireless or television) allows use of GPS even indoors
b.. Advanced Forward Link Trilateration (A-FLT)
c.. Timing Advance/Network Measurement Report (TA/NMR)
d.. Enhanced Observed Time Difference (E-OTD)
The purpose of any of these in mobile phones is twofold - first, the
wireless system must know to which PSAP it should route the call, and
second, the PSAP that answers the call should know where the caller is and
exactly where to send emergency services.

Mobile phone users may also have a selection to permit the location
information gathered to be sent to other phone numbers or data networks, so
that it can help people who are simply lost or want other location-based
services. By default, this selection is usually turned off, to protect
privacy.



Liam
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