Complementary Code Keying ( 802.11b )

How can I find CCK code pairs length N on matlab? For example N = 4.
Check whether [-1 -1 -1 1] obeys the requirements of CCK codes or not.

[Guillaume]

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[Stephen23]

Original question (from Google Cache):

"Complementary Code Keying ( 802.11b )"

How can I find CCK code pairs length N on matlab? For example N = 4.

Check whether [-1 -1 -1 1] obeys the requirements of CCK codes or not.

[Rena Berman]

(Answers Dev) Restored edit

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Sriram Tadavarty]

Hi Alice,

This piece of code can check if the provided input obeys the CCK codes.

function flag = checkCCKCode(in)
% Returns 1, if obeys the requirement of CCK code

    % Get the length of in
    N = length(in);

    % Perform the circular shift for each location and check if the sum of all the elements of correlation is zero
    flag = 1;
    for i = 1:N-1
        shiftIn = circshift(in,i);
        if sum(in.*shiftIn) ~= 0
            flag = 0; % Implies input doesn't obey CCK code requirement
        end
    end
end

In command window,

>> checkCCKCode([-1 -1 -1 1])

ans =

1

Inorder to find all the CCK pairs of length N, you can just pass the inputs in a loop to this minor code and it would indicate what are the inputs that obey CCK codes.

Hope this helps.

Regards,

Sriram

[Alice Zurock]

Hi Sriram,

Thanks for your support, but I'am asking that for example, Whole length = 4, (-1,1) matrix that is 16x4 matrix because there is 2 possible value which is -1 and 1 then 4 different order so there is 16 possible length 4 rows. I need to look at this row pairs which obey the cck rules and ı need to count it...

[Sriram Tadavarty]

Hi Alice,

Sure that can be built up on the function placed in the answer and as suggested in the answer. Here is the snippet that does what is asked for.

function out = getCCKCodes(n)

    % Get the possible integer values for the length n
    intValue = 0:2^n-1;
    
    % Convert the integer values to binary values
    bits = de2bi(intValue);
    bits(bits==0) = -1;

    % Check if each bit vector is a CCK code and report accordingly
    cckFlag = false(1,2^n);
    for i = 1:2^n
        cckFlag(i) = checkCCKCode(bits(i,:));
    end
    out = bits(cckFlag,:);

end

In command window:

>> getCCKCodes(4)

ans =

1 -1 -1 -1

-1 1 -1 -1

-1 -1 1 -1

1 1 1 -1

-1 -1 -1 1

1 1 -1 1

1 -1 1 1

-1 1 1 1

Let me know if this helps and is the same you asked for.

Regards,

Sriram

[Sriram Tadavarty]

May i know if the third column in the table indicates the matrix multiplication of input Code 1 and shifted code(s). Implies is it code1*1-shifted, code1*2-shifted and so on?

[Sriram Tadavarty]

Hi Alice,

I did some further investigation and could figure out what the issue was. Initially, i interpreted the table in a different way. Here are the modified codes, which would help you to find the number of CCK codes for a given length.

function flag = checkCCKCode(in1,in2)
% Returns 1, if both obeys the requirement of CCK code(s)

    % Get the length of in
    N = length(in1);
    
    s1 = zeros(1,N);
    s2 = s1;
    for j = 0:N-1
        s1(j+1) = sum(in1.*circshift(in1,-j));
        s2(j+1) = sum(in2.*circshift(in2,-j));
    end

    flag = all((s1(2:end)+s2(2:end)) == 0);
end

And then the calling function

function out = getCCKCodes(n)

    % Get the possible integer values for the length n
    intValue = 0:2^n-1;

    % Convert the integer values to binary values
    bits = de2bi(intValue);
    bits(bits==0) = -1;

    % Check if each bit vector(s) obey CCK code(s) and report accordingly
    cckFlag = false(2^n,2^n);
    for i = 1:2^n
        for j = 1:2^n
            cckFlag(i,j) = checkCCKCode(bits(i,:),bits(j,:));
        end
    end
    out = nnz(cckFlag);
end

In the command prompt,

try >> getCCKCodes(4)

It provides the output as 64.

The code perform the same as you explained now.

Let me know if this helps.

Regards,

Sriram

[Sriram Tadavarty]

Hi Alice,

I will place this answer separately and do accept it so that it will be more accessible and will help the ones who are in need.

Yes, i have experience on C++. If you do have any issue with C++ and integration with MATLAB, please raise a new question.

Thanking you.

Regards,

Sriram

Answer 2

[Sriram Tadavarty]

Hi Alice,

Placing the working code separately. The function checkCCKCode will indicate if the provided inputs in1 and in2 satisfy the conditions of CCK code(s) and the function getCCKCodes provides the number of CCK codes possible for the given length N.

function flag = checkCCKCode(in1,in2)
% Returns 1, if both obeys the requirement of CCK code(s)

    % Get the length of in
    N = length(in1);
    
    s1 = zeros(1,N);
    s2 = s1;
    for j = 0:N-1
        s1(j+1) = sum(in1.*circshift(in1,-j));
        s2(j+1) = sum(in2.*circshift(in2,-j));
    end

    flag = all((s1(2:end)+s2(2:end)) == 0);
end

And then the calling function

function out = getCCKCodes(n)

    % Get the possible integer values for the length n
    intValue = 0:2^n-1;

    % Convert the integer values to binary values
    bits = de2bi(intValue);
    bits(bits==0) = -1;

    % Check if each bit vector(s) obey CCK code(s) and report accordingly
    cckFlag = false(2^n,2^n);
    for i = 1:2^n
        for j = 1:2^n
            cckFlag(i,j) = checkCCKCode(bits(i,:),bits(j,:));
        end
    end
    out = nnz(cckFlag);
end

In the command prompt,

try >> getCCKCodes(4)

It provides the output as 64.

Thanking you.

Regards,

Sriram