[time-nuts] GPS-SDR-SIM

[Tim Lister]

On Sat, Mar 30, 2019 at 9:01 AM jimlux <jimlux at earthlink.net> wrote:
>
> On 3/27/19 11:49 AM, coderman via time-nuts wrote:
>
> Compiled the software, but...
>
> > he user specifies the GPS satellite constellation through a GPS broadcast ephemeris file. The daily GPS broadcast ephemeris file (brdc) is a merge of the individual site navigation files into one. The archive for the daily file is:
> >
> > ftp://cddis.gsfc.nasa.gov/gnss/data/daily/
>
> There's a ton of files under that.. broken down by year/day of year/ and
> then some subdirectories with dozens of files, that appear to be RINEX
> (the names are things like
>
> ftp://cddis.gsfc.nasa.gov/gnss/data/daily/2019/088/19f/USN700USA_R_20190880000_01D_CN.rnx.gz
>
> A casual browse did not find the brdc.
>

Yes the CDDIS holdings are not easy to find things in... The
organization from the data/daily/ is 4 digit year (e.g. '2019'), 3
digit day of the year. Then it's 2 digit truncated year, followed by
'n' (for 'n'avigation) e.g. '19n'. The brdc file is in there, and as
you say, is in RINEX format. The individual observations made by the
GNSS receiving sites live in the '19o' directories with a 4 letter
site code name.

For more precise work (probably not relevant for a GPS simulator), if
enough time has passed for the processing, you may want to the use the
post-processed products in ftp://cddis.nasa.gov/gnss/products/ which
are organized by GPS week number (for...reasons...) and documented at
https://cddis.nasa.gov/Data_and_Derived_Products/GNSS/orbit_products.html.
The precise orbits are in igsWWWWD.sp3.Z where 'WWWW' is the GPS week
number and 'D' the day in the week.

Hope this helps,

Tim

>
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