Thread: LDPC Decoding:Looking for logic using algorithm.

  1. #1
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    LDPC Decoding:Looking for logic using algorithm.

    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 languageLDPC Decoding:Looking for logic using algorithm.-algo-png for decoding procedure. Please give me logic.

    Code:
     Procedure D
    Code:
    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

  2. #2
    and the hat of int overfl Salem's Avatar
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    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.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
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    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.

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