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[Discuss-gnuradio] Possible bug with PATH/gr-channels/lib/cfo_model_impl

From: Aditya Dhananjay
Subject: [Discuss-gnuradio] Possible bug with PATH/gr-channels/lib/cfo_model_impl.h
Date: Wed, 5 Feb 2014 14:40:20 -0500

Dear All,

I suspect there is a bug in cfo_model_impl.h, where calling set_std_dev to set the std_dev back to 0 causes undesirable effects.

How to reproduce the bug:

a) Standard OFDM TX-RX example in GRC. Connect the TX block to the RX block through this channel model block.

b) Use a variable slider to control the std_dev of the CFO model block.

c) Start the flowgraph, with 0 as the initial value of the std_dev. All should be fine.

d) Bump up the std_dev and observe high packet errors.

e) Drop the std_dev back to 0. While we expect the packet error rate to drop back to 0, but that does not happen.

Reason: The value of d_cfo might be a high non-zero value. Even though we drop std_dev back to 0, d_cfo remains high, and continues to create CFO.

How to fix it:

In the function set_std_dev, reset the value of d_cfo to 0.

If someone could verify that this is indeed a bug, that would be very helpful. Thank you in advance for your help.

Best regards,

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