Convolutional Coding/Decoding Using Matlab Functions
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I'm trying to perform convolutional coding/decoding using built in Matlab functions. I'm trying to implement (2,1,3) code.
K=3;
G1=7;
G2=5;
msg=[1 1 0 0 1 0];
trel=poly2trellis(K,[G1 G2]);
coded=convenc(msg,trel);
decoded=vitdec(coded,trel,5*K,'cont','hard');
coded=[1 1 0 1 0 1 1 1 1 1 1 0]
decoded=[0 0 0 0 0 0]
As you would expect, the decoded message should be the same as msg, which it is not. I don't see where I have gone wrong in this simple example.
2 Comments
amjad ali
on 14 Nov 2015
Edited: Walter Roberson
on 14 Nov 2015
use the following :
K=3;
G1=7;
G2=5;
msg=[1 1 0 0 1 0]
trel=poly2trellis(K,[G1 G2]);
coded=convenc(msg,trel);
tblen = length(msg);
decoded=vitdec(coded,trel,tblen,'trunc','hard')
Amit Kansal
on 9 Jun 2021
Edited: Amit Kansal
on 9 Jun 2021
Amjad's response above is right for the case highlighted.
For the vitdec function, the "cont" (continuous) mode of operation incurs a delay which is why the decoded output has zeros. In the "trunc" (truncated mode), each frame is treated independently and there is no delay incurred in the output. Depending on ones use case (streaming or batch mode), either operation mode may be applicable.
Accepted Answer
Amit Kansal
on 24 Jun 2021
For the vitdec function, the "cont" (continuous) mode of operation incurs a delay which is why the decoded output has zeros.
In the "trunc" (truncated mode), each frame is treated independently and there is no delay incurred in the output.
Therefore, use the following instead:
K = 3;
G1 = 7;
G2 = 5;
msg = [1 1 0 0 1 0]
trel = poly2trellis(K,[G1 G2]);
coded = convenc(msg,trel);
tblen = length(msg);
decoded = vitdec(coded,trel,tblen,'trunc','hard')
For outputs to match the input msg as shown below.
msg =
1 1 0 0 1 0
decoded =
1 1 0 0 1 0
3 Comments
Amit Kansal
on 2 Aug 2021
Hello Anees,
Both convenc and vitdec functions are offered with Communications Toolbox. As a result, to be able to use these functions, you would need to have the Communications Toolbox as well on top of base MATLAB.
Hope this helps,
Amit
More Answers (2)
Muhammad Haris Khan
on 26 Nov 2019
I'm trying to perform convolutional coding. Kindly share MAtlab code for Part 1. Conv Encoder.
This block encodes the random bit vector u into a (longer) bit vector c. We assume that the convolutional
encoder is not zero-terminated. In this project, we use the following different encoders:
• E1: Rate-1/2 convolutional encoder, generator polynomial G = (1 + D2, 1 + D + D2)
![Conv .JPG](https://www.mathworks.com/matlabcentral/answers/uploaded_files/250425/Conv%20.jpeg)
1 Comment
Amit Kansal
on 9 Jun 2021
You can use
trellis = poly2trellis(3, [5 7]);
convenc(msg, trellis)
to encode a binary msg. In the trellis specification, the [5 7] corespond to the [1+D2, 1+D+D2] polynomials in octal notation.
selva ganesh
on 13 Sep 2022
K=3;
G1=7;
G2=5;
msg=[1 1 0 0 1 0];
trel=poly2trellis(K,[G1 G2]);
coded=convenc(msg,trel);
decoded=vitdec(coded,trel,5*K,'cont','hard');
coded=[1 1 0 1 0 1 1 1 1 1 1 0]
decoded=[0 0 0 0 0 0]
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