Comments on: Frequency offset estimation using 802.11a short preamble http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/ Signal Processing for Communication Fri, 10 Feb 2012 01:03:15 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: srikant http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-101181 srikant Thu, 09 Feb 2012 04:09:45 +0000 http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-101181 respected experts, can anyone send me the matlab codings for estimation of frequency offset in awgn channel using ofdm technique respected experts,
can anyone send me the matlab codings for estimation of frequency offset in awgn channel using ofdm technique

]]> By: Krishna Sankar http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-56091 Krishna Sankar Sun, 22 May 2011 21:07:54 +0000 http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-56091 @Baal Hadad: Well, the idea in this post is not doing cross-correlation. Its correlating the received signal with a delayed version of itself. @Baal Hadad: Well, the idea in this post is not doing cross-correlation. Its correlating the received signal with a delayed version of itself.

]]> By: Baal Hadad http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-56038 Baal Hadad Sun, 22 May 2011 09:41:53 +0000 http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-56038 Hi Krishna; Thank you for you post. One thing that I wanted to check was if what you were trying to do there is a cross-correlation between the transmitted signal and the offset-ed one since the offset here is affecting the whole OFDM symbol and not an Inter carrier offset. So it was in this order: 1. Cross-correlation between the transmitted (after applying the ifft) and the offseted signal, 2. Applying the fft of the result to estimate the delay ? Thx Hi Krishna;

Thank you for you post. One thing that I wanted to check was if what you were trying to do there is a cross-correlation between the transmitted signal and the offset-ed one since the offset here is affecting the whole OFDM symbol and not an Inter carrier offset. So it was in this order: 1. Cross-correlation between the transmitted (after applying the ifft) and the offseted signal, 2. Applying the fft of the result to estimate the delay ?

Thx

]]> By: Krishna Sankar http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-40218 Krishna Sankar Fri, 19 Nov 2010 00:39:07 +0000 http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-40218 @Erick: Oh, ok. Having zeros in the time domain samples is not a good idea. @Erick: Oh, ok. Having zeros in the time domain samples is not a good idea.

]]> By: Erick http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-40185 Erick Thu, 18 Nov 2010 09:46:41 +0000 http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-40185 @Krishna: My case is that for some of the sample points, the estimate FO is zero, which is not the case cause we set the FO to be 200Hz. I checked the code and preambles, I found one problem that by changing the first “1+j” to “1-j” and the last “1+j” to “-1+j”, some sample points become zero. That is why the estimate FO is zero, because when you multiply the zero's conjugate by zero, the results are zeros and then the angle are zeros. Anyway, I think this is not related with the estimate time. But it is related with the design of the preambles. The preamble, which is 160 samples, has 10 repeated short preambles and none of the 160 samples should be zero. Am I right? @Krishna: My case is that for some of the sample points, the estimate FO is zero, which is not the case cause we set the FO to be 200Hz.

I checked the code and preambles, I found one problem that by changing the first “1+j” to “1-j” and the last “1+j” to “-1+j”, some sample points become zero. That is why the estimate FO is zero, because when you multiply the zero’s conjugate by zero, the results are zeros and then the angle are zeros.

Anyway, I think this is not related with the estimate time. But it is related with the design of the preambles. The preamble, which is 160 samples, has 10 repeated short preambles and none of the 160 samples should be zero.

Am I right?

]]> By: Krishna Sankar http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-40153 Krishna Sankar Wed, 17 Nov 2010 23:31:04 +0000 http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-40153 @Erick: I think once you give the estimate the time to settle (16 samples), find that the estimation is accurate. Is that the case with you too? @Erick: I think once you give the estimate the time to settle (16 samples), find that the estimation is accurate. Is that the case with you too?

]]> By: Erick http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-40133 Erick Wed, 17 Nov 2010 17:08:48 +0000 http://www.dsplog.com/2008/03/03/frequency-offset-estimation-using-80211a-short-preamble/#comment-40133 @Krishna: ok, I see. Thanks very much. One further question :) One out of four subcarriers are populated in the frequency domain for the “inputFFTShortPreamble”. These 12 subcarriers are set to either "1+j" or "-1-j". I think this is for the purpose of having low PAPR. But when I changed the first "1+j" to "1-j" and the last "1+j" to "-1+j", the result curve is totally incorrect. The estimated FO becomes zero for every 8 samples numbers. What's the reason? @Krishna: ok, I see. Thanks very much.
One further question :)
One out of four subcarriers are populated in the frequency domain for the “inputFFTShortPreamble”. These 12 subcarriers are set to either “1+j” or “-1-j”. I think this is for the purpose of having low PAPR. But when I changed the first “1+j” to “1-j” and the last “1+j” to “-1+j”, the result curve is totally incorrect. The estimated FO becomes zero for every 8 samples numbers.
What’s the reason?

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