LDPC Decoding:Looking for logic using algorithm.

[SarasMuthu]

I am working LDPC encoding and decoding for mini project work. With my effort i have completed LDPC encoding but struggling with LDPC decoding.

Message-passing on the binary erasure channel

Code word =[1 0 0 1 0 1]

Y= [1 0 0 x x 1] // x = missing bit, need to find out the missing bit through Message-passing decoding algorithm.

Can anyone help me in writing C language for decoding procedure. Please give me logic.

 Procedure D

ECODE(Y)
 
I= 0                        //Initialization
For i= 1 :n do
Mi=yi
end for
repeat
 
for j= 1 :m do               //Step 1: Check messages
for all i ∈Bj do
if all messages into check j other than M i are known then
[IMG]file:///C:\Users\OPTICS~1\AppData\Local\Temp\msohtmlclip1\01\clip_image002.gif[/IMG]
end if
end for
end for
 
for i= 1 :n do //Step 2: Bit messages
if Mi= ‘unknown’then
[IMG]file:///C:\Users\OPTICS~1\AppData\Local\Temp\msohtmlclip1\01\clip_image004.gif[/IMG]
Mi=Ej,i
end if
end if
end for
 
if all Mi known or I =Imax then                                 //Test
Finished
else
I=I+ 1
end if
 
until Finished
 
end procedure

[Salem]

Previewing your post so that it doesn't include links to images on your hard drive might help.

> for decoding procedure. Please give me logic.
You're already given the procedure, you need to have a go at turning it into C code.

Start by thinking about what data structures M, E, are.

[SarasMuthu]

Actually i am not getting about the type of decoder concerned with partially parallel or fully serial bcoz I have to implement the LDPC decoder with the help of belief propagation algorithm.In that process i have been provided with a H matrix,code word like [0 0 1 0 1 1] for a 4*6 matrix.The received word is r=[1 0 1 0 1 1] with a cross over probability of p=0.2.

Now the steps which i have to follow for computation is as follows:-

1.in the first step using logp/1-p i have to find out the received word and it comes like
r=[-1.3863,1.3863,-1.3863,1.3863,-1.3863,1.3863]

2.Since it is a 4*6 matrix
M11=r1=-1.3863 and M31=r1=-1.3863
for i=2,M12=r2=1.3863 and M22=r2=1.3863
.
.
.
.
for i=6 M36=r6=-1.3863 and M46=r6=-1.3863

3.Extrensic information.It is calculated by using formula

E11=log(1+tanh(M12/2)tanh(M14/2)/1-tanh(M12/2)tanh(M14/2))
Like that i have to calculate for eacha nd every node and finally a E matrix has been formed

4.calculation of LLR
L1=r1+E11+E31=some value
.
.
.
.
L6=some value
finally on the basis of BPSK scheme
Z=[0 0 1 0 1 1]

5.To check if Z is a valid codeword
S=Z.H transpose
if it comes like [0 0 0 0] then my code word is correct otherwise have to go for next iteration.

Please tell me how should i proceed.Its a total mathematical calculation.I am stuck with the point of taking matrix as a input.If i take it as an array also then how should i calculate that tanh calculation.