In Turbo Encoder/decode if we give encoder output to decoder (without adding noise) we are getting errors

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Ideally if we give encoder output to decoder (without adding noise) then we are supposed to get zero bit errors right? but in the following code we are getting BER as non-zero. Can any one help with this?
hTEnc = comm.TurboEncoder('TrellisStructure', poly2trellis(4, [13 15 ], 13), 'InterleaverIndices', intrlvrIndices);
hTDec = comm.TurboDecoder('TrellisStructure', poly2trellis(4,[13 15 ], 13), 'InterleaverIndices', intrlvrIndices,'NumIterations', 4);
data = randi( [0 1], 1024, 1);
encodedData = step(hTEnc, data);
receivedBits = step(hTDec, encodedData );
  2 Comments
Jakub Hoferek
Jakub Hoferek on 4 May 2018
I have also this problem. Could anyone help us? .. Or give some tips.
With (4,[13 15 17], 13) it work OK. But with (4,[13 15 ], 13) is about 20% errors in output BITs.
Jakub Hoferek
Jakub Hoferek on 4 May 2018
frmLen = 1024;
rng default
intrlvrIndices = randperm(frmLen);
obj.hTEnc = comm.TurboEncoder('TrellisStructure',poly2trellis(4, ...
[13 15 ],13),'InterleaverIndices',intrlvrIndices);
obj.hTDec = comm.TurboDecoder('TrellisStructure',poly2trellis(4, ...
[13 15 ],13),'InterleaverIndices',intrlvrIndices, ...
'NumIterations',4);
in = randi([0 1],frmLen,1);
coded = step(obj.hTEnc, in(:, 1));
out = step(obj.hTDec, coded);
eval = sum(in-out) % output is cca 3% bit error
Ok there is 2.7% error, but it is still to much. (if setting is 4,[13 15 ],13 - error = 0 )

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Answers (1)

Jakub Hoferek
Jakub Hoferek on 10 May 2018
Thanks to Jan H., he found that problem is in format between coder and decoder. Because decoder need at the input soft bits between -1 and 1. And at the codet output are just normal bits like 0 and 1.

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