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Discussion Groups | Matlab DSP | Re: autocorrelation problem
Technical discussion about Matlab and issues related to Digital Signal Processing.
autocorrelation problem - t_katrina - Feb 22 19:24:00 2003
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Hi everyone, I need help in autocorrelation. I have generated a particular sequence code, C of period 15 and need to find its autocorrelation. I need to get the values at given lags from i = 0 to i = 15. For example when i = 0, it's a perfect autocorrelation (no lag) so I should get the peak value of the autocorrelation here. Theoretically, this value should be equal to 1. But what I got was more that. Subsequently, I got a constant value (which was lower than the peak) when there is lag. Theoretically, I should be getting a constant 0 value... What I did was multiply C by a cyclic shift of it for each lag. What did I do wrong or forgot? Really need suggestions.... Thanks in advance! Kat~ |
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Re: autocorrelation problem - Sergio Dominguez - Feb 24 9:32:00 2003
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Hi katrina, I do not really understand what you mean (my English is no that good). Could you send the sequence and describe a little more what you intend to do? What kind of process is it and what are you using to calculate the autocorrelation? I guess you are using xcorr, or have you done your own code? Sergio A las 07:24 del 22 de Feb de 2003, t_katrina <> <> dijo: > Hi everyone, > > I need help in autocorrelation. I have generated a particular > sequence code, C of period 15 and need to find its autocorrelation. > I need to get the values at given lags from i = 0 to i = 15. For > example when i = 0, it's a perfect autocorrelation (no lag) so I > should get the peak value of the autocorrelation here. > Theoretically, this value should be equal to 1. But what I got was > more that. Subsequently, I got a constant value (which was lower > than the peak) when there is lag. Theoretically, I should be > getting a constant 0 value... > > What I did was multiply C by a cyclic shift of it for each lag. > What did I do wrong or forgot? Really need suggestions.... > > Thanks in advance! > Kat~ > > _____________________________________ > /groups.php3 > -- Did you ever notice that everyone in favour of birth control has already been born? -- Benny Hill |
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Re: autocorrelation problem - Author Unknown - Feb 24 13:36:00 2003
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I'm just guessing here, but it sounds as if you have a non-zero average value in C when you expected C to be zero-mean. Is the constant value at lags not equal to zero positive or negative? Sincerely, Glen Ragan From: "t_katrina <>" <t_katrina on 02/22/2003 01:24 PM To: cc: Subject: [matlab] autocorrelation problem Hi everyone, I need help in autocorrelation. |
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I have generated a particular sequence code, C of period 15 and need to find its autocorrelation. I need to get the values at given lags from i = 0 to i = 15. For example when i = 0, it's a perfect autocorrelation (no lag) so I should get the peak value of the autocorrelation here. Theoretically, this value should be equal to 1. But what I got was more that. Subsequently, I got a constant value (which was lower than the peak) when there is lag. Theoretically, I should be getting a constant 0 value... What I did was multiply C by a cyclic shift of it for each lag. What did I do wrong or forgot? Really need suggestions.... Thanks in advance! Kat~ Yahoo! Groups Sponsor ADVERTISEMENT < http://rd.yahoo.com/M=246920.2960106.4328965.2848452/D=egroupweb/S=1705083376:HM\ /A=1464858/R=0/*http://www.gotomypc.com/u/tr/yh/cpm/grp/300_Cquo_1/g22lp?Target=\ mm/g22lp.tmpl > < http://us.adserver.yahoo.com/l?M=246920.2960106.4328965.2848452/D=egroupmail/S=:\ HM/A=1464858/rand=369070115 _____________________________________ /groups.php3 < http://www.dsprelated.com/groups.php3> >. |
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Re: autocorrelation problem - Predrag Valozic - Feb 25 7:48:00 2003
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Hi Katrina! It is all about a LFSR(4) sequence (I suppose) that (theoretically) has properties you are describing: normalized ACF(0) = 1, ACF(<>0) = 0. But it is only for bipolar sequence of infinit length. If the sequence is bipolar, length N then normalized ACF(<>0) = -1/N. If ACF(0) <> 1, then you have to normalize it. Predrag ----- Original Message ----- From: <> To: <> Sent: 2003. veljača 22 20:24 Subject: [matlab] autocorrelation problem > Hi everyone, > > I need help in autocorrelation. I have generated a particular > sequence code, C of period 15 and need to find its autocorrelation. > I need to get the values at given lags from i = 0 to i = 15. For > example when i = 0, it's a perfect autocorrelation (no lag) so I > should get the peak value of the autocorrelation here. > Theoretically, this value should be equal to 1. But what I got was > more that. Subsequently, I got a constant value (which was lower > than the peak) when there is lag. Theoretically, I should be > getting a constant 0 value... > > What I did was multiply C by a cyclic shift of it for each lag. > What did I do wrong or forgot? Really need suggestions.... > > Thanks in advance! > Kat~ > > _____________________________________ > /groups.php3 |
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