Talk:Barker code

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Why 2 codes of length 4 ?

I do not understand why there is two codes of length 4 in the table. The second is indeed a cycle shift of the first one, so they are identical. —Preceding unsigned comment added by 147.171.132.88 (talk) 13:13, 13 May 2011 (UTC)[reply]

Unlike maximum length sequences, Barker codes are not cyclic. They are generally transmitted in a very short short burst, with a long pause between each burst.

The first code of length 4 would be transmitted as the pattern .... 0 0 0 0 +1 +1 −1 +1 0 0 0 0 0 0 ...
The second code of length 4 would be transmitted as the pattern .... 0 0 0 0 +1 +1 +1 −1 0 0 0 0 0 0 ...

There is no way to "shift" that first pattern to make it identical to the second one.

All the known finite length codes that meet the low autocorrelation criteria are listed in that table. Cyclic shifts of those codes (except for the length-4 exception you pointed out) do not, in general, meet the low autocorrelation criteria necessary to be considered a Barker code. How can we edit the article to make this more clear? --DavidCary (talk) 04:15, 10 April 2012 (UTC)[reply]

no longer Barker codes exist?

Mathworld says it is conjectured that no longer Barker codes exist. Shouldn't the article be changed to reflect that, since mathworld is the only source listed? —Preceding unsigned comment added by 146.6.203.178 (talk) 22:37, 24 March 2009 (UTC)[reply]

+-+-+

i have a question of the barker code could we follow the rule to the barker code 5 (+-+-+)?

Alas, no. The sequence +-+-+ does not qualify as a Barker code. The autocorrelation of a Barker code is required to have all off-peak autocorrelations of either -1, 0, or +1. The autocorrelation coefficients of the +1 -1 +1 -1 +1 sequence are: ... 0 +1 -2 +3 -4 +5 -4 +3 -2 +1 0 0 0 0 0 ... The off-peak autocorrelations of -2, +3, and -4 indicate that +-+-+ is not a Barker code. --DavidCary (talk) 04:15, 10 April 2012 (UTC)[reply]

optimal Barker code

Currently this article states

Here is a table of all known optimal Barker codes, where negations and reversals of the codes have been omitted. Optimal is defined as having a maximum autocorrelation of 1 (when codes are not aligned).

That implies there exists some "Barker code" that is not an "optimal Barker code". I think that every Barker code is an "optimal" Barker code. So I am removing all mentions of "optimal". (If there exists some "Barker code" that is not an "optimal Barker code", please revert my edit and list that example in the article.) --68.0.124.33 (talk) 02:42, 1 August 2008 (UTC)[reply]

Method to verify codes

Maybe it would be usefull to add this simple method, by which it is posibble to verify a code if it is a Barker-code:

Let there be N numbers a1, a2, a3, ......, aN where every a equals either +1 or -1.

Pick a number k where 1 <= k <N.

Write down the first k a's, in order, then write down the last k a's in order. For k=3 you would write down

a1, a2, a3

a(N-2), a(N-1), aN.

Now multiply corresponding numbers and add (dot product):

a1 a(N-2) + a2 a(N-1) + a3 aN.

It's a Barker code if that sum is always (for every k) equal to 0, 1 or -1.

from: [1] --Grapestain (talk) 23:18, 26 May 2009 (UTC)[reply]

Mismatch between introduction and list of sequences

In the introduction it says that there are a total of eight Barker codes and three of them meeting the stronger condition

c_{v}=0,-1

.

A reference to a paper by Borwein and Mossinghoff is given.

But the next section lists nine sequences, and four of those meet the stronger condition. The reason for this mismatch is that in the given reference, the sequence [1 -1] is not listed as a Barker code. Since I don't have access to the original paper by Barker, I cannot tell who is "wrong" here, Wikipedia or Borwein/Mossinghoff. Consequently, I don't want to decide on my own what the correct modification to the article is: delete the sequence [1 -1] from the list (hence making wikipedia conformant to the cited article), or adding a note about this mismatch. Any suggestions? — Preceding unsigned comment added by 217.24.206.253 (talk) 14:04, 17 January 2013 (UTC)[reply]

better RMS performance?

In reference to the text

A Barker code has a maximum autocorrelation sequence which has sidelobes no larger than 2, and which thus has better RMS performance than the codes below.

How can a barker code have better RMS performance than the code below when the codes below are barker codes? Dsandber (talk) 11:27, 23 July 2013 (UTC)[reply]