From: Jack Smith
Subject: Re: Extracting time from GSM / mobile phone transmissions?
X-Newsreader: Forte Agent 1.92/32.572
Date: Sat, 21 Sep 2002 14:30:56 GMT
NNTP-Posting-Date: Sat, 21 Sep 2002 10:30:56 EDT
Organization: Cox Communications
GSM synch signal uses frame numbers, not absolute time.
Also, base stations need not be synchronized to each other, although
it can be done to reduce handover times. Hence, measuring arrival
times from multiple BTSs (assuming you know where the BTSs are
located) won't necessarily let you locate yourself.
That being said, there are some interesting locating schemes that have
been developed for locating the handset, as required by rules in USA
for emergency call location finding (enhanced 911). In addition to GPS
chip in the receiver, someone (Ericsson?, can't recall now) is
producing a system that measures time of arrival of MS uplink at
several Base Stations and thereby can locate the MS to within the
On Thu, 19 Sep 2002 17:49:13 +0100, firstname.lastname@example.org (Peter) wrote:
>I have in the past asked about a cheap way of extracting *accurate*
>time from GPS (not possible), or timecode signals (possible).
>What about doing it from mobile phone signals. These are everywhere in
>the developed world, although AFAIK the standards differ between e.g.
>the USA and Europe.
>Also this needs to work in a light aircraft, say 20000ft, so the
>reception might not be too great.
>Is it easy to extract the time from this type of signal? Presumably
>one would be listening to the base stations rather than the phones