gpsd and AGPS

Alexey Feldgendler alexey at
Fri Sep 28 17:14:05 CEST 2007

On Fri, 28 Sep 2007 16:39:43 +0200, Ken Yale <kyale at> wrote:

> Sure, the cell operators won't gladly share this data with anybody, but
> there's still something that could be done: the phone could learn the
> CellID <-> area association and use it later (if we are registered at  
> some cell we've already been at, we can't be miles away from where we
> were last time at this cell).
> [Ken]  Exactly!  This would be a good feature for an Open SUPL server.
> The Broadcom SUPL server has this feature also.

Wow, I didn't think about that! I was thinking about accumulating the  
learned CellID <-> area data in the phone, but storing it on an open  
server would take it one step further, so that the users can benefit from  
each other's contributions.

> [Ken[ Your second point:  presumed proximity based on most recent
> location is hard-coded into the GTA01 GPS already.  However, the GPS
> must derate the accuracy of the position as a function of time.  Most
> GPS receivers have this feature already.  One problem is when you've  
> flown across an ocean, and a 1-or-2 day old (or even 8 hour old) position
> would actually be a negative assistance.

To avoid this, my Garmin does the following: if you turn it on after not  
having used it for quite some time AND satellite reception is difficult at  
the moment (happens when I turn it on before driving out of the garage),  
it asks you: "Have you moved hundreds of miles/km since the last time?"

> [Ken]  This could be a feature to be added to the GLLIN by FIC:  detect
> this large position change.  Some ideas:
> - "flight mode"  - tap the city (or airport code) your flying to.

Typing should be optional, of course. So if you just enable flight mode  
without typing the destination, it should invalidate the recent location  

Change of the cell network ID (not the cell ID), i.e. roaming, is also an  
indication that we have probably travelled far. However, this one should  
be used with care because some networks in urban areas have poor coverage  
so that the phone enters roaming now and then and connects to some other  
local cell network.

Alexey Feldgendler <alexey at>
[ICQ: 115226275]

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