[Discuss-gnuradio] Channel Estimation in benchmark OFDM Code

[Yahya Ezzeldin]

Dear All,

Does the benchmark OFDM Code perform Channel synchronization ?
I am moving through the code however I can't seem to get the part where
this is done ?

Can anyone give any pointers regarding this ?
The number of pilots ? Estimation technique used ?

Best Regards,
--
Yahya Ezzeldin
 
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Re: [Discuss-gnuradio] Channel Estimation in benchmark OFDM Code

[Martin Braun (CEL)]

On Tue, Apr 16, 2013 at 08:21:54AM +0200, Yahya Ezzeldin wrote:
> Does the benchmark OFDM Code perform Channel synchronization ?
> I am moving through the code however I can't seem to get the part where this 
> is
> done ?
> 
> Can anyone give any pointers regarding this ?
> The number of pilots ? Estimation technique used ?

Hi Yahya,

check out my previous email on OFDM. Also, have a look at the blocks in
gr-digital/lib.

MB

-- 
Karlsruhe Institute of Technology (KIT)
Communications Engineering Lab (CEL)

Dipl.-Ing. Martin Braun
Research Associate

Kaiserstraße 12
Building 05.01
76131 Karlsruhe

Phone: +49 721 608-43790
Fax: +49 721 608-46071
www.cel.kit.edu

KIT -- University of the State of Baden-Württemberg and
National Laboratory of the Helmholtz Association


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Re: [Discuss-gnuradio] Channel Estimation in benchmark OFDM Code

[Bogdan Diaconescu]

Since you mentioned this, the code in gr-digital performs channel estimation 
base on known pilots. It is in the 
./gr-digital/lib/digital_ofdm_frame_acquisition.cc

Channel estimation is based on preamble which contains known pilots each second 
carrier. Therefore the unknown carrier channel estimation is calculated by 
linear interpolation between the adjacent values. 
But before that, the module does a coarse frequency estimation in frequency 
domain, by shifting the freq domain so that the correlation of the known pilots 
with the received signal after FFT is maximum. The result will be a number of 
FFT bins to shift the signal with.

I was looking at this before and one question was always unanswered in my mind: 
why the factor gr_expj(-M_TWOPI*freq_delta*d_cplen/d_fft_length*symbol_count) 
is used for frequency correction, after finding out the frequency offset? I'm 
especially interested in the role of cp_len in this.

Thanks,
Bogdan
 





 From: Yahya Ezzeldin 
To: discuss-gnuradio  
Sent: Tuesday, April 16, 2013 9:21 AM
Subject: [Discuss-gnuradio] Channel Estimation in benchmark OFDM Code
 

Dear All,

Does the benchmark OFDM Code perform Channel synchronization ?
I am moving through the code however I can't seem to get the part where this is 
done ?

Can anyone give any pointers regarding this ?
The number of pilots ? Estimation technique used ?


Best Regards,
--
Yahya Ezzeldin
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