gpsd and AGPS

Ken Yale kyale at
Fri Sep 28 21:21:54 CEST 2007

Hello Alexey,

You have 4 great ideas to discard or supplement the location cache:
1)  CellID database inside the phone.
2)  Power-on after a long timeout with a prompt to discard location.
3)  Flight mode with no destination typing.
4)  Change cell network.

Each of these sparks additional ideas and opportunities for improving
autonomous GPS:
- invalidate location cache from sort of "travel manager" application
that knows you're flying because of schedule, change of timezone,
invoking "flight mode", etc.  Could tie into the airport destination
planning to get a rental car, directions, local information, etc.
- the cellID and cell network information has a lot of potential.

Ken Yale

-----Original Message-----
From: Alexey Feldgendler [mailto:alexey at] 
Sent: Friday, September 28, 2007 08:14
To: List for OpenMoko community discussion
Subject: Re: gpsd and AGPS

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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