Channel Estimation in benchmark OFDM Code

GNU Radio
1

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,

2

On Tue, Apr 16, 2013 at 08:21:54AM +0200, Yahya E. 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 B.
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

3

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_TWOPIfreq_deltad_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 E. [email protected]
To: discuss-gnuradio [email protected]
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 E.