GPS soft baseband processing

Joerg Reisenweber 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 
few
> > that do correlation in software.
> >
> > 
http://sourceforge.net/project/showfiles.php?group_id=91538&package_id=271229
> > 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.

/j
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 194 bytes
Desc: This is a digitally signed message part.
Url : http://lists.openmoko.org/pipermail/hardware/attachments/20080913/705c7359/attachment-0001.pgp 


More information about the hardware mailing list