# Channel Estimation in benchmark OFDM Code **URL:** \ **Category:** GNU Radio\ **Created:** [April 16, 2013, 8:23am UTC](https://www.ruby-forum.com/t/channel-estimation-in-benchmark-ofdm-code/228268 "2013-04-16T08:23:57Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Yahya\_E](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/858c86/32.png) [@Yahya\_E](https://www.ruby-forum.com/u/Yahya_E)\ **Post date:** [April 16, 2013, 8:23am UTC](https://www.ruby-forum.com/t/channel-estimation-in-benchmark-ofdm-code/228268/1 "2013-04-16T08:23:57Z")
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, ---
**Author:** ![Yahya\_E](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/858c86/32.png) [@Yahya\_E](https://www.ruby-forum.com/u/Yahya_E)\ **Post date:** [April 16, 2013, 9:22am UTC](https://www.ruby-forum.com/t/channel-estimation-in-benchmark-ofdm-code/228268/2 "2013-04-16T09:22:58Z")
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 ---
**Author:** ![Yahya\_E](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/858c86/32.png) [@Yahya\_E](https://www.ruby-forum.com/u/Yahya_E)\ **Post date:** [April 17, 2013, 2:37pm UTC](https://www.ruby-forum.com/t/channel-estimation-in-benchmark-ofdm-code/228268/3 "2013-04-17T14:37:45Z")
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 E. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) To: discuss-gnuradio [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) 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.