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comm.ViterbiDecoder performing worse than vitdec

조회 수: 6 (최근 30일)
Marian Keller
Marian Keller 2023년 2월 13일
댓글: Marian Keller 2023년 3월 6일
I'm trying to get a simple "Hello World" example of convolutional coding and decoding to work. For some reason, the comm.ViterbiDecoder won't ever correctly decode the data, no matter which options I tried, while vitdec works just fine.
trellis = poly2trellis(7,[171 133]);
encoder1 = comm.ConvolutionalEncoder(trellis);
data = randi([0 1],70,1);
codedData = encoder1(data);
tbdepth = 34;
commDecoder = comm.ViterbiDecoder(trellis, 'TracebackDepth', tbdepth, 'InputFormat','Hard','TerminationMethod','Terminated');
decodedData1 = vitdec(codedData,trellis,tbdepth,'trunc','hard');
decodedData2 = commDecoder(codedData);
BER1 = biterr(data,decodedData1)
BER1 = 0
BER2 = biterr(data,decodedData2)
BER2 = 5

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Nadia Shaik
Nadia Shaik 2023년 3월 6일
Hi Marian,
I understand that "comm.ViterbiDecoder" is not decoding the data as compared to "vitdec". The different termination methods could explain why the bit error rate differs between the two decoders.
In your case, you are using the "Terminated" method for "comm.ViterbiDecoder", and "trunc" for "vitdec". Consider setting the termination method "Truncated" for "comm.ViterbiDecoder" instead.
Here is the updated code snippet:
trellis = poly2trellis(7,[171 133]);
encoder1 = comm.ConvolutionalEncoder(trellis);
data = randi([0 1],70,1);
codedData = encoder1(data);
tbdepth = 34;
commDecoder = comm.ViterbiDecoder(trellis, 'TracebackDepth', tbdepth, 'InputFormat','Hard','TerminationMethod','Truncated');
decodedData1 = vitdec(codedData,trellis,tbdepth,'trunc','hard');
decodedData2 = commDecoder(codedData);
BER1 = biterr(data,decodedData1)
BER1 = 0
BER2 = biterr(data,decodedData2)
BER2 = 0
I hope this helps!
  댓글 수: 1
Marian Keller
Marian Keller 2023년 3월 6일
Thank you very much. Could've sworn I also tried that, apparently not. The alternative solution my professor suggested was to append a few zeros to the data.

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