Comm Toolbox Turbo Coding - Not Systematic

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Hello, I do not find the turbo coding implementation to match the description, which clearly shows that the systematic bits should appear at the output : https://www.mathworks.com/help/comm/ref/turboencoder.html. If I execute the following :
b1 = rand(1,100) > 0.5;
intrlvrIndices = 1 : length(b1);
hTEnc = comm.TurboEncoder('TrellisStructure', poly2trellis(4,[13 15],13), 'InterleaverIndices', intrlvrIndices);
b2 = step(hTEnc, double(b1)')';
plot(conv(2*b2-1,2*b1(end:-1:1)-1));
There is no trace of the systematic bits at the output. This renders both the encoder and decoder not useful for me. What am I missing ?
  4 个评论
Walter Roberson
Walter Roberson 2018-1-30
At the bottom of the documentation page, there is a button to choose whether the documentation was useful or not. If you click on No then it brings up a form that allows you to input remarks for consideration by the documentation writers.
Stephen Carsello
Stephen Carsello 2018-1-30
编辑:Stephen Carsello 2018-1-30
Next finding. Apparently, the way to ensure the systematic bits appear is that the first set of feed-forward taps match the feedback taps. The constituent code is rate 1/n, where n is the number of sets of feed-forward taps. It appears to be implied that the interleaved bits are fed through feed-forward tap sets 2 through n. You really have to dig into the convolutional encoder details, and examples, in order to realize how this is supposed to work. OK ... next topic ... tail bits.

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