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Pocket GPS World :: View topic - Making sure a device is in Cold Start
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Making sure a device is in Cold Start

 
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TUGAdmin
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PostPosted: Sun Jul 04, 2010 10:46 am    Post subject: Making sure a device is in Cold Start Reply with quote

Hi,
I hve a mobile phone with internal GPS and need to test the device's Time To First Fix.

How can I make sure that the device is in cold start.
Will pulling the battery and letting the device just sit or 3 days do the trick?
Is there any faster way?

Thanks
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mikealder
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Location: Blackpool , Lancs

PostPosted: Sun Jul 04, 2010 11:37 am    Post subject: Reply with quote

Does it use Quick GPS or assisted GPS, if so TTF should be fairly quick as it will have some of the data it needs to acquire the signal before it even switches the hardware on, if its got neither aGPS or qGPS take the battery out and leave the phone off for a few days.

Which phone have you got? - Mike
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TUGAdmin
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PostPosted: Sun Jul 04, 2010 12:32 pm    Post subject: Reply with quote

Hi Mike,
Thanks for the quick response.

I'm testing both BlackBerry (9700 or 9000) and iPhone 3G.
I don't think either are using aGPS or qGPS.

Will 3 days without the battery do the trick?
tks
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mikealder
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PostPosted: Sun Jul 04, 2010 12:39 pm    Post subject: Reply with quote

The iPhone 3G uses assisted GPS and without assistance I am not too sure my own 3G iPhone would ever find where it is as the receiver isn't very good.

BB 9700 uses assisted GPS but not too sure about the 9000 as the BB web site tech info doesn't mention it in the text (it does for the 9700 though).

Three days without the battery for the BB devices will be OK but not too sure how you would do that with an iPhone as there is no way to remove the battery - Mike
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robertn
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PostPosted: Mon Jul 05, 2010 2:33 am    Post subject: Reply with quote

It would be wrong assuming that the main battery is the only source of power for the GPS memory (and other) backup. All it needs is a tiny supercap to keep the memory good for months. Many devices use this as it's common for the main battery to run flat, or be removed. Alternately the data may be stored in flash. The only way to ensure a cold start would be to instruct the GPS to perform one in software. Even if 3 days is gaurenteed, how many cold starts are you going to do - one or two is not enough to draw a statistically reliable conclusion.

I wonder why you want TTFF. It used be a reasonable poormans way to determine overall GPS performance, however more recently I have found it has little bearing on post-fix performance. If you have assited GPS, TTFF is really not a worth while measure of anything useful. This is likely because with Assited start, theres no need to waste money and effort improving TTFF for unassited starts. What happens if you are talking on the phone while doing the TTFF test. Some phone may be better than others at this kind of multitasking. I know when starting up the phone is busy - what about TTFF 3 minutes are the phone if turned on.

Given the lenghts you need to go to to do your tests, what practical information does it provide?

The tests I am interested in are
1) TTFF from starting up the GPS application, with Assited GPS if avalible, from a phone that has been on for some time.
2) Tenacity to hold the signal once found.
3) Accuracy of the fix in marginal signal conditions (HDOP < say 15 meters)
4) Time to reestablish fix (in marginal conditions) (HDOP < say 15 meters).

These more accurately reflect the reallife use of a GPS.
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