Re: Clear my fundamentals

[Alexander List]

discuss-gnuradio-request@... wrote:

Message: 2
Date: Sun, 01 Nov 2009 10:17:59 -0800
From: Josh Blum josh@...
Subject: Re: [Discuss-gnuradio] Clear my fundamentals :)
To: Blue Boy blueboy4444@...
Cc: discuss-gnuradio@...
Message-ID: 4AEDD0D7.1080403@...
Content-Type: text/plain; charset=ISO-8859-1; format=flowed



Blue Boy wrote:
  

Hello Everyone,
           My first post:
    I am a windows kernel programmer by profession.Recently my interest
has grown for SDR gnuradio.I an new to this field so I have newbie
doubts.I would welcome if you just point to some links for my answers.
 1] What is usrp cfile format? complex/float but whats stored in numbers
 like amplitude/intensity/phase difference etc.
    

Its a binary file containing 64-bit complex numbers where each 64 bit 
complex number is 2 32-bit floating point numbers corresponding to to 
the real and imaginary parts of a complex number.

  

 2] Is frequency also stored in the cfile ? or we have to assume
frequency from file name? How to reconstruct complete/sampled signal
from Cfile ?
    

You need to know the sampling rate and baseband frequency, the file is 
just raw data samples without any context.

Hi Josh,

I have a related question: Is there anything like an (upcoming) industry standard for recorded SDR samples, *including* the metadata? I guess that would make it a lot easier to exchange recordings between different platforms, and would also save people from the hassle of encoding metadata in the filename or an external data source.

I guess NetCDF would be one possible way - it's widely used e.g. in the geosciences:

http://www.unidata.ucar.edu/software/netcdf/usage.html
http://www.unidata.ucar.edu/software/netcdf/docs/faq.html#whatisit

Of course we would have to define the schema for SDR data...

Alex

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[Josh Blum-2]

>
> I have a related question: Is there anything like an (upcoming) industry
> standard for recorded SDR samples, *including* the metadata? I guess
> that would make it a lot easier to exchange recordings between different
> platforms, and would also save people from the hassle of encoding
> metadata in the filename or an external data source.
>

I would go with the vrt standard http://www.digitalif.org/
vrt gives you a standard for digitized if data and context/metadata.
Also we have a library for it in gnuradio :-)

Given libvrt and pmts in gnuradio, one could implement a
vrt_file_source/sink and use vrt as an interchange format for "saved"
digital if data as well as the live-streaming data.

Of course, a lot of development/polishing has to be done before we can
practically have these capabilities.

-Josh


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