Re: [Discuss-gnuradio] Problem with OFDM Mod block

[Michael Dickens]

Hi Francisco - The code in question is, as the error says, at line 106 of the 
Python file "ofdm.py":

self.preambles = digital_swig.ofdm_insert_preamble(self._fft_length,
                                                   padded_preambles)

This code calls the C++ code found in the file digital_ofdm_insert_preamble.cc, 
which throws an error when any valid preamble's length is not equal to the FFT 
size.  This throwing has nothing to do with the cyclic prefix length or # 
occupied tones.  You should be able set no preambles, according to the code, by 
sending in a zero-length vector (I think).  The preamble must be a vector of 
vectors, with the first dimension being the number of preambles and the second 
dimension must be the FFT length.  Check out which preamble you're using would 
be my recommended next step.  Good luck. - MLD

On Jul 11, 2012, at 2:54 PM, frankist wrote:
> I was trying to use the OFDM Mod block to create a OFDM signal with FFT
> size=8192, occupied tones=6818 and CP=2048
> 
> However I keep getting this error:
> 
> File "/usr/local/lib/python2.7/dist-packages/gnuradio/digital/ofdm.py",
> line 106, in __init__
>    padded_preambles)
>  File
> "/usr/local/lib/python2.7/dist-packages/gnuradio/digital/digital_swig.py",
> line 4517, in ofdm_insert_preamble
>    return _digital_swig.ofdm_insert_preamble(*args, **kwargs)
> RuntimeError: digital_ofdm_insert_preamble: invalid length for preamble
> symbol
> 
> If I use a lower number of occupied tones this error disappears but I was
> interested in this number because it is close to the DVB-T 8k mode.
> 
> Can you explain me what am I doing wrong or if there is a workaround for
> this problem