# How can I add freq. offset(related to time index) after IFFT in data symbol in ofdm example? **URL:** \ **Category:** GNU Radio\ **Created:** [July 25, 2013, 5:28pm UTC](https://www.ruby-forum.com/t/how-can-i-add-freq-offset-related-to-time-index-after-ifft-in-data-symbol-in-ofdm-example/245895 "2013-07-25T17:28:03Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\ **Post date:** [July 25, 2013, 5:28pm UTC](https://www.ruby-forum.com/t/how-can-i-add-freq-offset-related-to-time-index-after-ifft-in-data-symbol-in-ofdm-example/245895/1 "2013-07-25T17:28:03Z")
Hi guys, Thanks in advance. Since freq. offset is time related, like exp(2pi \* f \* t), how can I generate freq. offset in gnuradio? Normally, freq. offset exists due to mismatched oscillators between transmitter and receiver. Is that possible get the same freq. offset effect mentioned above, merely through modifying some code in GunRadio but not modifying the RF hardware in USRP. For example, if I want to add 1KHZ offset in sender in data symbol(not preamble part,to avoid freq. offset correction), to see if the receiver can still succeed to decode the data, how should I do? Which part should I locate at after IFFT moving the samples to base band? Thanks again. Best, Kay ---
**Author:** ![Yingjie\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f14d63/32.png) [@Yingjie\_C](https://www.ruby-forum.com/u/Yingjie_C)\ **Post date:** [July 25, 2013, 5:32pm UTC](https://www.ruby-forum.com/t/how-can-i-add-freq-offset-related-to-time-index-after-ifft-in-data-symbol-in-ofdm-example/245895/2 "2013-07-25T17:32:44Z")
Kay, Freq offset can be added by multiplying the baseband data with complex-exponential. In GR this can be done by any of the following ways 1. Sine Source and Multiply block or 2. Freq Translating FIR Filter 3. Channel Model -Adeel