Convolutional Coding/Decoding Using Matlab Functions

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.

[amjad ali]

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]

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.

Answer 1

[Amit Kansal]

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

[anees rafeh]

hello is using convenc function and vitdec function free in matlab.

if no is there any alternatives.

i would really appreciate your help

[anees rafeh]

i am using matlab R2019a

[Amit Kansal]

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

Answer 2

[Muhammad Haris Khan]

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)

[Amit Kansal]

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.

Answer 3

[selva ganesh]

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]