23 Aug
2010
23 Aug
'10
10:45 a.m.
Hello Andreas,
On Sun, 22 Aug 2010 23:35:17 +0200, "Andreas Schmidt-Dannert"
<aschmida(a)mail.tu-berlin.de> wrote:
So bringing ms-assisted positioning to work is also a goal of me.
Is it not possible to just transfer the acquired data from the GPS
receiver in the MS to a A-GPS server in the network and let te server
compute the acquisition assistance data? Probably I am thinking to naive
here. I know it should be a server not too far away from the asking MS.
My experience with two phones (BlackBerry, HTC with Qualcomm chipset)
is that if the phone already has the position (for example because a GPS
application is running on the phone) the phone will return the position
without asking for assitance data. However if there is no position, they
usually want the reference time, reference location and navigation model
(ephemeris) as assitance data.
One problem with this approach it that the size of those data are
quite large (around 800 bytes in my tests) if they have to be
transferred over a slow channel like the SDCCH during loacation
update, so this slows done the location update considerable.
Another problem which is most certainly related to the bad GSM receiver
in my test phones is that it take very long to get a fix, even with
the provided assitance data. In my experiments this was around 45 second,
nearly the same time as getting a fix without any RRLP data. Of course
there could be a problem with the assitance data so that getting a position
takes that long.
So I would like to try MS-assisted measurement where only a small amount
of data has to be transferred to the phone. I don't know if the measurement
will also be faster this way. I did not try it yet because the acquisition
assitance data have to be calculated, for example you need the doppler
shift of the satellite signal which has to be calculated from the satellite
postition. Probably no "black magic" but I would prefer to have ready and
tested code to avoid another source of possible errors (its a matter of
time, I don't want to spent too much on it ;-).
By the way there was for a while a rrlp-ephemeris tree
in openbsc. What
was it for and what happend with it? As i understood it one could
connect an external GPS device to a laptop to get data that is
needed..kind of an A-GPS server. Right?
I don't know where the tree is now. Its from Sylvain, maybe he can
tell you more. I used this code as a basis for my experiments.
Another tought: What about SUPL?
SUPL uses IP to get assistance data from a SUPL server...so maybe it is
possible to use a supl server from google or similar?
I don't have much experience with it. I guess that you can get the other
assitance data (e.g. ephemeris) this way. But I am not sure about the
acquisition assitance data.
Best regards,
Dieter
--
Dieter Spaar, Germany spaar(a)mirider.augusta.de