GPS is stuck with a set of satellites - how to remove them from memory?

[tichi]

I seem to know why SOMETIMES it takes forever
to get a satellite lock with GPS.
(I learn that many users experience this problem, including those on Bell, and including those with NSFSAN's ROM 1.10, like me).

After you get a successful lock, a few satellite numbers (like those 4,2,9,12,22 etc, that you see in GPSViewer) are stored
somewhere on the phone.

Next, when after some time (overnight, let's say), you try to get another lock, the OLD satellites moved, they are not available anymore,
but the phone tries to use them anyway, WITHOUT UPDATING...

(my highly subjective perception after some observations is that if there's is one-two OLD satellites still avaialble, it may be still OK for the phone to find the new ones, but if NONE of the old satellites are available,
the phone is stuck, and may sit forever looking for them..

what helps is a SOFT-RESET (which clears some memory, I suppose) - after that - ther's a A FAST (10ns) LOCK, with NEW SET OF SATELLITES (e.g .13. 15. 3. 7 etc )..

so my question is WHERE those satellite are stored, and how to clean them without doing a soft-reset?

("HTC GPS Tool" that has some "clear-memory" button does not seems to help, maybe because it is for another phone model?)

EXPERTS, PLEAAASE!

[flatspin]

That doesn't make sense. GPS satellites don't move. They are geo-synchronous.

YOU move however. If you move a certain distance, GPS's have to go through a search process again. It's taken 20 minutes before with my Garmin handheld GPS to get a lock after traveling a couple thousand miles.

[tichi]

Originally Posted by flatspin

That doesn't make sense. GPS satellites don't move. They are geo-synchronous.

YOU move however. If you move a certain distance

they are not geosync, afaik..

and.. for old man Galileo and for old man Einstein it is all the same anyway..

I suppose, for the GPS chip too ..

[taidan]

Your wrong, GPS sats are in MEO (medium earth orbit). They Move and You move. Stop talking out of your @$$.

OP is correct, the chip does recall sats based on recently downloaded stattelite location information or Almanac. Thats why right after you get a lock its easier to get another one right after. But if you move, or they move, it still thinks the sats are their.

That is also why HTC quick GPS data expires after a while.

Now as to how to fix it, I have no IDEA

[tichi]

Originally Posted by taidan

...the chip does recall sats based on recently downloaded stattelite location information or Almanac. Thats why right after you get a lock its easier to get another one right after. But if you move, or they move, it still thinks the sats are their.

Now as to how to fix it, I have no IDEA

thnx a lot! the POSITIONS too... yes of course...
and then from the old positions, it ( either the software or GPS chip itself?) tries to predict the new positions, somehow, I suppose?
based on time difference? (because it cannot account for your movement)..
Also I wonder if some info from the internet / third parties is used here (like that AssistedGPS etc?)

And then, the problem is
- why some ROM`s / some carriers' phones are able to
update the sat positions correctly, and also use new sats if available,
while SOME others (like Bell phones) are stuck with old useless sats/positions,
and never search for the new ones before soft-reset..

hmmmm.. I've also seen around here written
that there's a dedicated GPS area in memory, somewhere in the "radio" section?
but the "radio" must be ROM, is not it?
and this are must bes flashed often while GPS works... or only when it stops working?
or GPS chip has some RAM/ROM itself?

[mithodge]

The sats are not geo-synchronous. That is why they need to have location data (ephemeris) uploaded every 4 hours.

"Each satellite in the GPS constellation orbits at an altitude of about 20,000 km from the ground, and has an orbital speed of about 14,000 km/hour (the orbital period is roughly 12 hours - contrary to popular belief, GPS satellites are not in geosynchronous or geostationary orbits). The satellite orbits are distributed so that at least 4 satellites are always visible from any point on the Earth at any given instant (with up to 12 visible at one time)." http://www.astronomy.ohio-state.edu/...Unit5/gps.html

[flatspin]

You're right, of course. I was thinking of the WAAS satellites.

Originally Posted by mithodge

The sats are not geo-synchronous. That is why they need to have location data (ephemeris) uploaded every 4 hours.

"Each satellite in the GPS constellation orbits at an altitude of about 20,000 km from the ground, and has an orbital speed of about 14,000 km/hour (the orbital period is roughly 12 hours - contrary to popular belief, GPS satellites are not in geosynchronous or geostationary orbits). The satellite orbits are distributed so that at least 4 satellites are always visible from any point on the Earth at any given instant (with up to 12 visible at one time)." http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

[tichi]

useful info for those interested:

Almanac and Ephemeris Data as used by GPS receivers
(4 July 199

The satellites broadcast two types of data, Almanac and
Ephemeris. Almanac data is course orbital parameters for all
SVs. Each SV broadcasts Almanac data for ALL SVs. This Almanac
data is not very precise and is considered valid for up to
several months. Ephemeris data by comparison is very precise
orbital and clock correction for each SV and is necessary for
precise positioning. EACH SV broadcasts ONLY its own Ephemeris
data. This data is only considered valid for about 30 minutes.
The Ephemeris data is broadcast by each SV every 30 seconds.

When the GPS is initially turned on after being off for more than
30 minutes, it "looks" for SVs based on where it is based on the
almanac and current time. With this information, appropriate
SVs can be selected for initial search.

When the GPS receiver initially locks onto a SV, the Garmin
display then shows "hollow" signal strength bars. At this time,
the Ephemeris data has yet to be completely collected. Once the
ephemeris data is collected from EACH SV in turn, the associated
signal strength bar will turn "solid" black and then the data
from that SV is considered valid for navigation.

If power is cycled on a GPS unit, and when turned back on, the
Ephemeris data is less than 30 minutes old, lock-on will be very
quick since the GPS does not have to collect new Ephemeris data.
This is called a "warm" start.

If it is later than 30 minutes, this is considered a "cold"
start and all Ephemeris data will have to be recollected.

If the GPS has moved more than a few hundred miles or accurate
time is lost, the Almanac data will be invalid and if you are
far enough off, none of the SVs that the Almanac thinks should
be overhead will be there. In such case, the GPS will have to
"sky search" or be reinitialized so it can download a new Almanac
and start over.

(Note: Yes! We know this is somewhat simplified information.
Yes, we know that the Ephemeris data may not have to be updated
as often as the G-12XL does it to get data to the G-12XL
accuracy.)

Joe Mehaffey
================================================== ==============


http://gpsinformation.net/main/almanac.txt

[jethro_static]

Originally Posted by flatspin

You're right, of course. I was thinking of the WAAS satellites.

WAAS is not a satelite. LMFAO. It's a server developed by garmin for a more acurate position. 3 feet range as oppose to non WAAS enabled GPS chips, The range can be up to 3 meters.

[tichi]

I have another example of weird behavior of my phone, when it is stuck
forever and never gets a lock.. maybe someone knowledgeable may
tell me what's this about?

For a few hours I had fast locks with 5 satellites - 3, 7, 25, 27, 28 (seen in GPSview)

then, while I was moving 15 km away on the way,
(it does not matter, I may have just powered it off and then on)

it loses the lock, and the new set of satellites shows up
6,8,11,19,26, all in the range of 20-30 dB signal strength,
but NEVER gets a lock,
no soft power on heaven and earth can make it lock,
I tried HTC GPS Tool, switch on and off Location setting,
switch on and off AGPS in registry, etc etc..

What's funny, while it is stuck on those satellites, sometimes, almost instantaneously , another 4 show up, 28,27, 7,25, they blink, and disappear...

Soft reset helps, though..
it Cold Locks with 1,2,5,9,12,28,30 in a minute or two..

any ideas? Anyone else experiences this, probably with different ROM?