GPS soft baseband processing
joerg at openmoko.org
Sat Sep 13 03:39:28 CEST 2008
Am So 7. September 2008 schrieb quatrox at gmail.com:
> On 2008-09-07, Al Johnson <openmoko at mazikeen.demon.co.uk> wrote:
> > On Sunday 07 September 2008, Andy Green wrote:
> >> Somebody in the thread at some point said:
> >> | On 9/7/08, Flemming Richter Mikkelsen <quatrox at gmail.com> wrote:
> >> |> "Our automatic geotagging technology solves these
> >> |> problems. A fragment of RAW GPS RF data is captured
> >> |> in 0.2 seconds and then stored alongside the digital image
> >> |> and the processing is performed later on a PC. Because
> >> |> we separate the GPS capture from the GPS processing,
> >> |> our technology maintains the traditional "instamatic" user
> >> |> experience we are all used to and then pulls consumers
> >> |> to experience a far more interesting way to search and
> >> |> share photographs later."
> >> |
> >> | Interesting.
> >> | Around 1995 I used about the same technique to sync spectrometer
> >> | data to an external authoritative timesource ( in that case the DCF77
> >> | signal encoded into 10ms dataframes ) time recovery could achieve
> >> | better than 100us
> >> It sounds like a fine technique, but it pushes the whole issue into
> >> license of the host CPU software then. They don't seem to mention if
> >> they provide it or it is liberally licensed, etc.
> > There appear to be several open source GPS projects around, including a
> > that do correlation in software.
> > http://gnuradio.org/trac/wiki/GlobalPositioningSystem
> > http://gnuradio.org/trac/wiki/GlobalNavigationSatelliteSystem
> The article I read mentioned all the details of what the chip does and
> what is left for software. IIRC, it is basically an FFT and a reverse
> transfer function which is needed. There is free implementations of
> FFT. It looks like the only problem is that calculating everything each
> second might take much CPU, but then again, we can choose to only
> calculate every n'th second or so.
GPS chip has xxKunits of hardware correllators. I don't see benefit of moving
all this to main CPU.
You might take a photo in 1 second, where you might be able to caculate later
on where the photo has been taken.
But IIGTR you trade that in for ability to get a fast realtime first fix.
probably not what we want to deliver with any Neo.
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