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

[Michael Dickens]

Hi Francisco - If you read through "gr-digital/python/ofdm.py" carefully (lines 
68:81), you'll find that the number of "occupied tones" cannot be more than 
4512 because of the way the known preamble symbols are pre-generated; feel free 
to regenerate these symbols to as many as you want, but make sure to use the 
new symbols on both the Tx and Rx for proper transmission.  There is no check 
for this value, and the Python script will set the resulting preamble to length 
4512 when the number of occupied tones is greater than 4512.  So, even if you 
set in GRC to not use preambles, one is always created through the known 
symbols.  It wouldn't be too difficult to tweak this Python script to properly 
expand the known symbols' part of the preamble to be of the correct length; 
please feel free to do this tweaking & submit a patch.  Good luck. - MLD

On Jul 16, 2012, at 4:17 AM, frankist wrote:

> Thanks for the response. I am using the GRC and I let the preamble size=0.
> When I use a lower number of occupied tones this error doesn't occur.
> However if I used the values specified in the first post that message
> appears