# OFDM RX Script Recovery After Interference

**URL:** <https://www.ruby-forum.com/t/ofdm-rx-script-recovery-after-interference/240575>\
**Category:** GNU Radio\
**Created:** [April 21, 2014, 9:03pm UTC](https://www.ruby-forum.com/t/ofdm-rx-script-recovery-after-interference/240575 "2014-04-21T21:03:53Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\
**Post date:** [April 21, 2014, 9:03pm UTC](https://www.ruby-forum.com/t/ofdm-rx-script-recovery-after-interference/240575/1 "2014-04-21T21:03:53Z")

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Hey list, another OFDM question.

I have this simple OFDM script I have used before and in between USRPs I  
have VHF handheld radio I am using as an interferer (also have plenty of  
attenuation, between USRPs it is about 30 dB and the handset is  
attenuated  
by 55 dB). So with interefering signal around -23 dBm in between the the  
transmission 80 kHz channel which is at -32 dbm as according to my  
handheld  
Spectrum Analyzer, GNU Radio’s FFT plot on the RX side gives a  
transmission  
of -90 dB and an interference at -50 dB.

Whenever the handheld goes off, the receiver predictably loses the  
transmitted message and freezes up or the scope goes blank. Depending on  
the duration of the interference of the handheld (just a simple click of  
the tx) usually causes the receiver to lock up and not receive/never  
recover transmitted comms again.

So why does the RX never recover and how can this be mitigated? I am  
still  
learning OFDM so I am thinking this is related to the channel estimator,  
is  
my line of thinking correct?

Thanks for the help,

Jon

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**Author:** ![jfaulkenberry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c2a13f/32.png) [@jfaulkenberry](https://www.ruby-forum.com/u/jfaulkenberry)\
**Post date:** [April 28, 2014, 3:48pm UTC](https://www.ruby-forum.com/t/ofdm-rx-script-recovery-after-interference/240575/2 "2014-04-28T15:48:33Z")

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Thanks for responding. No, everything is from the master branch, other  
than  
I split the ofdm\_loopback script into tx and rx scripts but the blocks  
went  
unchanged.

Jon

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**Author:** ![jfaulkenberry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c2a13f/32.png) [@jfaulkenberry](https://www.ruby-forum.com/u/jfaulkenberry)\
**Post date:** [April 26, 2014, 6:11pm UTC](https://www.ruby-forum.com/t/ofdm-rx-script-recovery-after-interference/240575/3 "2014-04-26T18:11:57Z")

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On 04/21/2014 09:02 PM, Jonathan F. wrote:

> Whenever the handheld goes off, the receiver predictably loses the  
> transmitted message and freezes up or the scope goes blank. Depending on  
> the duration of the interference of the handheld (just a simple click of  
> the tx) usually causes the receiver to lock up and not receive/never  
> recover transmitted comms again.
> 
> So why does the RX never recover and how can this be mitigated? I am  
> still learning OFDM so I am thinking this is related to the channel  
> estimator, is my line of thinking correct?

The channel estimator holds no state, so I doubt that’s the problem. Are  
you working off of master?

Martin