# OFDM transmitter receiver

**URL:** <https://www.ruby-forum.com/t/ofdm-transmitter-receiver/231706>\
**Category:** GNU Radio\
**Created:** [August 25, 2014, 12:49pm UTC](https://www.ruby-forum.com/t/ofdm-transmitter-receiver/231706 "2014-08-25T12:49:26Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [August 25, 2014, 12:49pm UTC](https://www.ruby-forum.com/t/ofdm-transmitter-receiver/231706/1 "2014-08-25T12:49:26Z")

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Hi  
I used the ofdm transmitter receiver blocks to create a simple system as  
shown in the attachment. I used the system parameters as those used in  
the example transmitter and receiver grcs. Now I get error that  
‘Detected a packet larger than max frame size (80 symbols)’. I would  
like to know how the max frame size is set and should I add more  
information to the grc.

My transmitter- receiver parameters

fft length= 64  
cyclic prefix = 16  
packet length = 96  
no. of occupied carriers = 48  
no. of pilot carriers = 4

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**Author:** ![sreena\_p\_h](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/47e85d/32.png) [@sreena\_p\_h](https://www.ruby-forum.com/u/sreena_p_h)\
**Post date:** [August 25, 2014, 3:32pm UTC](https://www.ruby-forum.com/t/ofdm-transmitter-receiver/231706/2 "2014-08-25T15:32:14Z")

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What’s your kernel.shmmax value? (run sysctl kernel.shmmax)

M

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<div class="post-metadata">

**Author:** ![sreena\_p\_h](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/47e85d/32.png) [@sreena\_p\_h](https://www.ruby-forum.com/u/sreena_p_h)\
**Post date:** [August 26, 2014, 11:13am UTC](https://www.ruby-forum.com/t/ofdm-transmitter-receiver/231706/3 "2014-08-26T11:13:47Z")

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Try and not kill the context in a mailing list thread; these are also  
archived and are used by others for referral.

Max frame size depends on max\_output\_buffer(). 80 symbols at a 64-sized  
FFT would be ~40kB… that doesn’t seem unreasonable. Not sure if  
there’s a problem here. I suggest you have a look at the buffer sizes to  
track down this problem.

M