GPS problems, summary

[Yorick Moko]

question:
does the lower signal also effect accuracy?

On Wed, Jul 16, 2008 at 10:56 PM, Marcus Bauer <marcus.bauer at gmail.com> wrote:
> On Wed, 2008-07-16 at 21:38 +0200, Alasal wrote:
>
>> What is the problem?
>>  - The Openmoko Freerunner have a long TTFF with the SD card in the
>> phone. So it takes a long time (10min+) before you get your first GPS
>> data.
>
> More specific: the GPS signal level drops by -20dBm, i.e. factor 100.
> Signal strength of a GPS satellite above your head is around -127dBm.
> Needed strength for a first fix is -145dBm with a minimum of three
> satellites. Once the GPS chip has a fix, it can operate at signal levels
> of -157dBm, thus making it possible to operate while there is data
> transfer from/to the SD card.
>
>
>> So if we have a first fix, the SD card isn't blocking the GPS anymore?
>>  - yes, the SD card isn't blocking the GPS if we have a first fix.
>> (Some people even claim it's more stable)
>
> The FR's GPS performance is definitely top notch without the SD card.
>
>
>> But we can't read of the SD card when the GPS is on?
>>  - Wrong, you will be able to read the SD card when the GPS is on. You
>> will probably not be able to read the SD card when you're starting the
>> GPS (appr. 30 sec), because the GPS will only block the SD card when
>> it's searching it's first fix. After that you will be able to read the
>> SD card again.
>
> You can always read the SD card. As said above the GPS signal
> temporarily drops by -20dBm during i/o.
>
> The kernel patch is a pragmatic and well working solution and should not
> effect daily use.
>
>> Summary of the summary:
>> You will be able to use the SD card in the same time of the GPS except
>> for the first appr 30 seconds. (And that's the worst case, because
>> maybe Openmoko can find better hacks/fixes)
>
> With the help of AGPS you can shorten it probably to 15 seconds.
>
>
>
>
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