Re: [Discuss-gnuradio] Fwd: Questions on rx_ofdm example in GR 3.7.1

[Martin Braun]

On Wed, Jan 15, 2014 at 07:55:45PM -0500, Aditya Dhananjay wrote:
> There is a variant of this issue that I discovered and would like to point
> it out to the community.
> 
> Synopsis: After the first time the header CRC fails, *all* subsequent
> packets fail.
> 
> Setup:
> 
> - GRC examples of Tx/Rx OFDM
> - Noise source with a variable slider to control the amount of noise. The
> output of the Tx block is added with the output of the noise source.
> - The output of this adder is connected to the Rx block.
> 
> Procedure:
> 
> - Start the experiment with 0 noise. We see that the packets are
> successfully decoded.
> - Increase the noise, and we observe that the packet success rate begins to
> drop (payload CRC failures)
> - Further increase the noise to force a header CRC failure.
> - Decrease the noise back to 0. Notice that the packet success rate remains
> 0, even though the noise is 0.
> 
> This is highly repeatable. Any help would be greatly appreciated.

Hm, can't repeat it. I used the loopback example. Increasing noise does
make packets drop (as expected), but setting it back makes them come
again. A noise amplitude of ~2 causes most packets to fail, but some
come through. What are your OFDM specs?

MB