Three different databases for gsm celltower locations

[Jan Lübbe]

On Tue, 2009-04-07 at 23:49 +0100, Joerg Reisenweber wrote:
> Am Sa  4. April 2009 schrieb Stefan Schmidt:
> > OpenBmap likes to have more fields
> > for quality informations about GPS and GSM. 
> 
> I strongly suggest to include fields for TimeAdvance values for each BTS.
> TA is a much better and more reliable value for distance to Base Transmitter 
> Sation than dB signal strength.
> See:
> http://lists.openmoko.org/pipermail/openmoko-kernel/2008-April/002434.html
> and
> http://lists.openmoko.org/pipermail/openmoko-kernel/2008-June/002987.html

As Jörg said, the timing advance is only valid while a channel to the
BTS is open. An active GPRS connection is enough, but the TA for that is
sent in the EM command for GPRS. When it is invalid 255 is sent,
otherwise the actual value. You may need to create traffic to see a
vaild TA here.

The TA field for voice calls uses '0' for invaild, so it's not as nice
for getting proper readings.

-- 
Jan Lübbe <jluebbe at lasnet.de>            http://sicherheitsschwankung.de
 gpg-key      1024D/D8480F2E 2002-03-20
 fingerprint  1B25 F91F 9E7B 5D4F 1282  02D6 8A83 8BE4 D848 0F2E