# OFDM receiver error, FATAL: Missing a required length tag on port 0 at item #0

**URL:** <https://www.ruby-forum.com/t/ofdm-receiver-error-fatal-missing-a-required-length-tag-on-port-0-at-item-0/230710>\
**Category:** GNU Radio\
**Created:** [June 30, 2014, 3:22pm UTC](https://www.ruby-forum.com/t/ofdm-receiver-error-fatal-missing-a-required-length-tag-on-port-0-at-item-0/230710 "2014-06-30T15:22:30Z")\
**Posts on this page:** 4\
**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:** [June 30, 2014, 3:22pm UTC](https://www.ruby-forum.com/t/ofdm-receiver-error-fatal-missing-a-required-length-tag-on-port-0-at-item-0/230710/1 "2014-06-30T15:22:30Z")

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Hi,

I implemented OFDM receiver on USRP E110 using the OFDM receiver in  
examples in gnuradio’s files 3.7

and I added to it a chain to create OFDM transmitter: random source,  
OFDM  
transmitter, channel model, throttle, USRP sink

But when I executed the flow graph. It generated “UOOOOOOOOOOOOOOOOOO”  
and  
I got an error :

FATAL: Missing a required length tag on port 0 at item #0  
thread[thread-per-block[21]: \<gr\_block crc 32\_bb (9)\>]: Missing length  
tag.

and tag debug didn’t show anything.

Have you an idea how to fix this error ?

Thanks in advance

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**Author:** ![wafa\_e](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/b4bc9f/32.png) [@wafa\_e](https://www.ruby-forum.com/u/wafa_e)\
**Post date:** [June 30, 2014, 4:37pm UTC](https://www.ruby-forum.com/t/ofdm-receiver-error-fatal-missing-a-required-length-tag-on-port-0-at-item-0/230710/2 "2014-06-30T16:37:34Z")

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On 06/30/2014 09:20 AM, Wafa E. wrote:

> Hi,
> 
> I implemented OFDM receiver on USRP E110 using the OFDM receiver in  
> examples in gnuradio’s files 3.7
> 
> and I added to it a chain to create OFDM transmitter: random source, OFDM  
> transmitter, channel model, throttle, USRP sink
> 
> But when I executed the flow graph. It generated “UOOOOOOOOOOOOOOOOOO” and  
> I got an error :

Slow the data rate until this message stops. Then worry about the next  
message.

Philip

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<div class="post-metadata">

**Author:** ![wafa\_e](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/b4bc9f/32.png) [@wafa\_e](https://www.ruby-forum.com/u/wafa_e)\
**Post date:** [July 1, 2014, 3:16pm UTC](https://www.ruby-forum.com/t/ofdm-receiver-error-fatal-missing-a-required-length-tag-on-port-0-at-item-0/230710/3 "2014-07-01T15:16:07Z")

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Hi, thank you for your response.

In fact, I still have the same error:  
FATAL: Missing a required length tag on port 0 at item #0  
thread[thread-per-block[21]: \<gr\_block crc 32\_bb (9)\>]: Missing length  
tag.  
and UOOOOOOOOOOOOOO  
I put the usrp sink and usrp source 's sample rate to 1M.

What is the suitable sampling rate to put ?

Thanks in advance

2014-06-30 16:36 GMT+02:00 Philip B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

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<div class="post-metadata">

**Author:** ![wafa\_e](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/b4bc9f/32.png) [@wafa\_e](https://www.ruby-forum.com/u/wafa_e)\
**Post date:** [June 30, 2014, 4:47pm UTC](https://www.ruby-forum.com/t/ofdm-receiver-error-fatal-missing-a-required-length-tag-on-port-0-at-item-0/230710/4 "2014-06-30T16:47:06Z")

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On 06/30/2014 03:20 PM, Wafa E. wrote:

> FATAL: Missing a required length tag on port 0 at item #0  
> thread[thread-per-block[21]: \<gr\_block crc 32\_bb (9)\>]: Missing length tag.

Add a stream to tagged stream converter.

M