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function code_interleaver = CreateDvbInterleaver(Nbits)
% CreateDvbInterleaver intializes an interleaver for use with the duobinary
% tailbiting turbo code from the DVB-RCS standard
%
% The calling syntax is:
% code_interleaver = CreateDvbInterleaver(Nbits)
%
% code_interleaver = a structure with the following members
% code_interleaver.subblk_intl = subblock bit-wise interleaver, 1 by Nbits/2 vector
% code_interleaver.info_intl = information interleaver over GF(2),
% a row vector of length Nbits.
%
% Nbits = number of bits (i.e. twice the number of couples)
% valid range = {48 64 212 220 228 424 432 440 848 856 864 752}
%
% Copyright (C) 2007, Matthew C. Valenti and Shi Cheng
%
% Last updated on Oct. 12, 2007
%
% Function CreateDvbInterleaver is part of the Iterative Solutions Coded Modulation
% Library (ISCML).
%
% The Iterative Solutions Coded Modulation Library is free software;
% you can redistribute it and/or modify it under the terms of
% the GNU Lesser General Public License as published by the
% Free Software Foundation; either version 2.1 of the License,
% or (at your option) any later version.
%
% This library is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
% Lesser General Public License for more details.
%
% You should have received a copy of the GNU Lesser General Public
% License along with this library; if not, write to the Free Software
% Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
% USA
N = Nbits/2; %% N is the number of couples
NN= [ 48, 64, 212 220, 228, 424, 432, 440, 848, 856, 864, 752].';
PP=[11, 24, 0, 24;
7, 34, 32, 2;
13, 106, 108, 2;
23, 112, 4, 116;
17, 116, 72, 188;
11, 6, 8, 2;
13, 0, 4, 8;
13, 10, 4, 2;
19, 2, 16, 6;
19, 428, 224, 652;
19, 2, 16, 6;
19, 376, 224, 600];
Nindex = find( NN== N);
if (length(Nindex) ~= 1)
disp('Wrong interleaver size of WiMax CTC');
end
P0 = PP(Nindex, 1);
P1 = PP(Nindex, 2);
P2 = PP(Nindex, 3);
P3 = PP(Nindex, 4);
x= zeros(2,N);
x(1:2*N) = 1:2*N;
%% intra-couple shifting
t = 1:2:N;
x(1,t) = 2*t;
x(2,t) = 2*t -1;
y= zeros(2,N);
for index = 0: N-1
if mod(index,4) == 0
P = 0;
elseif mod(index,4) ==1
P = N/2 +P1;
elseif mod(index,4) ==2
P = P2;
else
P = N/2 +P3;
end
i = mod( P0* index + P +1, N);
y(:, index+1) = x(:,i+1);
end
code_interleaver.info_intl = reshape(y, 1, Nbits);
% create subblock interleaver
code_interleaver.subblk_intl= [];
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