# Ofdm frequency offset **URL:** \ **Category:** GNU Radio\ **Created:** [June 24, 2015, 9:29am UTC](https://www.ruby-forum.com/t/ofdm-frequency-offset/242438 "2015-06-24T09:29:55Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\ **Post date:** [June 24, 2015, 9:29am UTC](https://www.ruby-forum.com/t/ofdm-frequency-offset/242438/1 "2015-06-24T09:29:55Z")
Dear all: Thank you in advance. 1. I want to ask a question about the new ofdm example.And I know the receiver have used the SCA(schmidl and cox algorithm) algorithm.Now in my application,maybe this algorithm isn’t enough.And I want to ask whether have other good frequency offset correction algorithm which have been implemented. 2.What is the algorithm used by the old version of the ofdm example?Thanks. Best regards, zs ---
**Author:** ![zszszs](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/5fc32e/32.png) [@zszszs](https://www.ruby-forum.com/u/zszszs)\ **Post date:** [June 25, 2015, 4:11am UTC](https://www.ruby-forum.com/t/ofdm-frequency-offset/242438/2 "2015-06-25T04:11:43Z")
Hi zs, this reminds me very much of OFDM radar technologies, as your problem boils down to finding a good estimator for the spectral properties of your OFDM frame as well as the time it reached you. I think you should have a look at chapter 3, “OFDM Radar Algorithms” of [1]; you might find that considering the unknown timing being a result of the time it took a OFDM signal to reach you (and hence an effect of range) a useful approach. You can find some shorter information on the accuracy of these estimates in [2]. The difference in the algorithms described in [1] and your problem is that you don’t a priori know the transmitted signal – you’ll have to figure that out by using something like S&C to receive and decode the OFDM symbol prior to “clean” reconstruction; you could then use the parameters (range == timing, doppler == frequency) that the radar estimators give you to model the symbol like you received it, and subtract it from your incoming signal. Of course, the mistakes you make when decoding the incoming symbol will have an influence on the accuracy of your estimates. Best regards, Marcus [1] Braun, Martin. /OFDM Radar Algorithms in Mobile Communication Networks/. Diss. Karlsruhe, Karlsruher Institut f??r Technologie (KIT), Diss., 2014, 2014; > **[OFDM Radar Algorithms in Mobile Communication Networks](https://publikationen.bibliothek.kit.edu/1000038892)** [2] Braun, Martin, Christian Sturm, and Friedrich Jondral. “On the single-target accuracy of OFDM radar algorithms.” /PIMRC/. 2011.; > **[PIMRC2011\_BraunSchuSturmJondral.pdf](https://www.cel.kit.edu/download/PIMRC2011_BraunSchuSturmJondral.pdf)** > > 104.56 KB ---
**Author:** ![zszszs](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/5fc32e/32.png) [@zszszs](https://www.ruby-forum.com/u/zszszs)\ **Post date:** [June 25, 2015, 4:49am UTC](https://www.ruby-forum.com/t/ofdm-frequency-offset/242438/3 "2015-06-25T04:49:41Z")
Dear Marcus M.: Actually my problem is: y=useful information+x\*h(channel)\*cfo(carrier offset due to the local oscillator between the interference and the radar)+noise. I want to turn y to new\_y=useful information+noise. So I need know the channel(h) and the cfo exactly(I know the x in advance while I don’t know the cfo and h.So I have to estimate them).The root question I faced is the cfo estimated from the SCA isn’t enough. Thank you so much. I will read the paper you mentioned.Maybe helpful.Thanks. Best regards, zs At 2015-06-24 17:08:16, “Marcus M.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: Hi zs, this reminds me very much of OFDM radar technologies, as your problem boils down to finding a good estimator for the spectral properties of your OFDM frame as well as the time it reached you. I think you should have a look at chapter 3, “OFDM Radar Algorithms” of [1]; you might find that considering the unknown timing being a result of the time it took a OFDM signal to reach you (and hence an effect of range) a useful approach. You can find some shorter information on the accuracy of these estimates in [2]. The difference in the algorithms described in [1] and your problem is that you don’t a priori know the transmitted signal – you’ll have to figure that out by using something like S&C to receive and decode the OFDM symbol prior to “clean” reconstruction; you could then use the parameters (range == timing, doppler == frequency) that the radar estimators give you to model the symbol like you received it, and subtract it from your incoming signal. Of course, the mistakes you make when decoding the incoming symbol will have an influence on the accuracy of your estimates. Best regards, Marcus [1] Braun, Martin. OFDM Radar Algorithms in Mobile Communication Networks. Diss. Karlsruhe, Karlsruher Institut fr Technologie (KIT), Diss., 2014, 2014; > **[OFDM Radar Algorithms in Mobile Communication Networks](https://nbn-resolving.org/urn:nbn:de:swb:90-388921)** [2] Braun, Martin, Christian Sturm, and Friedrich Jondral. “On the single-target accuracy of OFDM radar algorithms.” PIMRC. 2011.; > **[PIMRC2011\_BraunSchuSturmJondral.pdf](https://www.cel.kit.edu/download/PIMRC2011_BraunSchuSturmJondral.pdf)** > > 104.56 KB On 06/24/2015 10:29 AM, zs wrote: Dear Marcus M.: Thank you so much for your kindly reply. The SCA is adequate for a correct demodulation of the signal while maybe inadequate for estimate the precise frequency shift.I don’t have the synchroniztion device.In my application,I need to reconstruct one transmit signal in time domain,and remove it from the received signal.For example,y=x1+x2,and I want to remove x2 from the baseband recevied signal. Now my idea is no only used the SCA algorithm mentioned in the new ofdm example, but also use other similar finer carrier frequency estimation algorithm.I want to combined the algorithms.So I ask the question in the maillist. Thank you so much. Best regards, zs At 2015-06-24 15:54:30, “Marcus M.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: Dear zs, basically, Schmidl and Cox is a very good algorithm, because it can achieve the same quality of synchronization with half of the synchronization overhead compared to other approaches, or a better performance with the same amount. I must admit that from the top of my head, there’s probably not much that’s better than S&C in a real world OFDM receiver, but I must admit that I haven’t implemented many OFDM synchronizers myself. However, you say > Now in my application,maybe this algorithm isn’t enough. which means that you have a mathematical measure that’s not OK for S&C, I guess. So in what way doesn’t S&C suffice? What is it about your application that makes S&C insufficient or impossible to use? Best regards, Marcus On 06/24/2015 09:00 AM, zs wrote: Dear all: Thank you in advance. 1. I want to ask a question about the new ofdm example.And I know the receiver have used the SCA(schmidl and cox algorithm) algorithm.Now in my application,maybe this algorithm isn’t enough.And I want to ask whether have other good frequency offset correction algorithm which have been implemented. 2.What is the algorithm used by the old version of the ofdm example?Thanks. Best regards, zs ---
**Author:** ![zszszs](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/z/5fc32e/32.png) [@zszszs](https://www.ruby-forum.com/u/zszszs)\ **Post date:** [June 25, 2015, 4:34am UTC](https://www.ruby-forum.com/t/ofdm-frequency-offset/242438/4 "2015-06-25T04:34:30Z")
Dear Marcus M.: Thank you so much.So kindly of you.Thanks.I will read the papers you mentioned. Best regards, zs At 2015-06-24 17:08:16, “Marcus M.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: Hi zs, this reminds me very much of OFDM radar technologies, as your problem boils down to finding a good estimator for the spectral properties of your OFDM frame as well as the time it reached you. I think you should have a look at chapter 3, “OFDM Radar Algorithms” of [1]; you might find that considering the unknown timing being a result of the time it took a OFDM signal to reach you (and hence an effect of range) a useful approach. You can find some shorter information on the accuracy of these estimates in [2]. The difference in the algorithms described in [1] and your problem is that you don’t a priori know the transmitted signal – you’ll have to figure that out by using something like S&C to receive and decode the OFDM symbol prior to “clean” reconstruction; you could then use the parameters (range == timing, doppler == frequency) that the radar estimators give you to model the symbol like you received it, and subtract it from your incoming signal. Of course, the mistakes you make when decoding the incoming symbol will have an influence on the accuracy of your estimates. Best regards, Marcus [1] Braun, Martin. OFDM Radar Algorithms in Mobile Communication Networks. Diss. Karlsruhe, Karlsruher Institut fr Technologie (KIT), Diss., 2014, 2014; > **[OFDM Radar Algorithms in Mobile Communication Networks](https://nbn-resolving.org/urn:nbn:de:swb:90-388921)** [2] Braun, Martin, Christian Sturm, and Friedrich Jondral. “On the single-target accuracy of OFDM radar algorithms.” PIMRC. 2011.; > **[PIMRC2011\_BraunSchuSturmJondral.pdf](https://www.cel.kit.edu/download/PIMRC2011_BraunSchuSturmJondral.pdf)** > > 104.56 KB On 06/24/2015 10:29 AM, zs wrote: Dear Marcus M.: Thank you so much for your kindly reply. The SCA is adequate for a correct demodulation of the signal while maybe inadequate for estimate the precise frequency shift.I don’t have the synchroniztion device.In my application,I need to reconstruct one transmit signal in time domain,and remove it from the received signal.For example,y=x1+x2,and I want to remove x2 from the baseband recevied signal. Now my idea is no only used the SCA algorithm mentioned in the new ofdm example, but also use other similar finer carrier frequency estimation algorithm.I want to combined the algorithms.So I ask the question in the maillist. Thank you so much. Best regards, zs At 2015-06-24 15:54:30, “Marcus M.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: Dear zs, basically, Schmidl and Cox is a very good algorithm, because it can achieve the same quality of synchronization with half of the synchronization overhead compared to other approaches, or a better performance with the same amount. I must admit that from the top of my head, there’s probably not much that’s better than S&C in a real world OFDM receiver, but I must admit that I haven’t implemented many OFDM synchronizers myself. However, you say > Now in my application,maybe this algorithm isn’t enough. which means that you have a mathematical measure that’s not OK for S&C, I guess. So in what way doesn’t S&C suffice? What is it about your application that makes S&C insufficient or impossible to use? Best regards, Marcus On 06/24/2015 09:00 AM, zs wrote: Dear all: Thank you in advance. 1. I want to ask a question about the new ofdm example.And I know the receiver have used the SCA(schmidl and cox algorithm) algorithm.Now in my application,maybe this algorithm isn’t enough.And I want to ask whether have other good frequency offset correction algorithm which have been implemented. 2.What is the algorithm used by the old version of the ofdm example?Thanks. Best regards, zs