# Ofdm\_sync\_sc\_cfb missing square operation in "delay path"

**URL:** <https://www.ruby-forum.com/t/ofdm-sync-sc-cfb-missing-square-operation-in-delay-path/231309>\
**Category:** GNU Radio\
**Created:** [August 2, 2014, 10:31am UTC](https://www.ruby-forum.com/t/ofdm-sync-sc-cfb-missing-square-operation-in-delay-path/231309 "2014-08-02T10:31:10Z")\
**Posts on this page:** 2\
**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 2, 2014, 10:31am UTC](https://www.ruby-forum.com/t/ofdm-sync-sc-cfb-missing-square-operation-in-delay-path/231309/1 "2014-08-02T10:31:10Z")

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Hi Martin,  
I was looking ofdm\_sync\_sc\_cfb block, I found in delay path,  
“delay\_magsquare” directly connect to “delay\_normalize”, but according  
S&C’s paper, “delay\_magsquare” need do square operation like “Energy  
Path”.  
M(d)=|P(d)|^2/(R(d))^2

Seems in your code that numerator P(d) missing ^2,  
but when I add a square operation in P(d), the ofdm\_loopback’s result  
was wrong.

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**Author:** ![Tiankun\_Hu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/46a35a/32.png) [@Tiankun\_Hu](https://www.ruby-forum.com/u/Tiankun_Hu)\
**Post date:** [August 2, 2014, 11:08am UTC](https://www.ruby-forum.com/t/ofdm-sync-sc-cfb-missing-square-operation-in-delay-path/231309/2 "2014-08-02T11:08:02Z")

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Sorry, I got a mistake, magsquare has done a square operation

output[0][m] = Re{input[0][m]}^2 + Im{input[0][m]}^2

在 2014年08月02日 16:29, Tiankun Hu 写道:

> –  
> Thanks  
> Tiankun
> 
> * * *
> 
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–  
Thanks  
Tiankun