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

[Aditya Dhananjay]

Thanks for trying, Martin.

My OFDM Specs are:

FFT size = 64

CP length = 16

bandwidth = 2KHz

carrier freq: centered around 2.437GHz

It is easier to reproduce if I replace the noise block with one that adds CFO errors.

a) Increase this CFO error until header CRCs fail. Let this stand for a few seconds. 

b) Reduce CFO offset errors to 0.

c) Go to step a and repeat a few times.

I observe that after doing this a few times, the RX path freezes up.

In any case, thank you very much for trying to reproduce this error. I really appreciate your help. :)

best regards,

aditya

On Thu, Jan 16, 2014 at 10:11 AM, Martin Braun <address@hidden> wrote:

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

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