I wrote a matlab code for obtaining BER of ldpc codes using sum product algorithm. But its BER performance is relatively close to uncoded BPSK. What can I do to change this? What should be the dimension of parity check matrix, number of iterations???
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Questions: Range for noise power N0 when bit energy=1 using BPSK modulation? No'of iterations required for sum product algorithm for different parity check matrix? No'of frames required or total length of codeword required to have a coding gain compared with uncoded BPSK?
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OUDOMSACK PIERRE PASQUERO
2017-6-8
I also implemented a LDPC decoder based on Min-Sum algorithm, for 802.11ac in C language. The obtained BER is good, better than that of BCC decoder.
Then, I implemented the Sum-Product algorithm (a couple of lines to modify in my code). I have the same problem as you. The obtained performance is close to the case there is no channel coding.
After a deep analysis, I found where the problem comes from. The check-nodes messages values are very low compared to LLR. Without explaining to much in detail, it is due to the function f(x) = ln((e^x+1)/(e^x-1))... I don't manage to resolve the problem.
Have you found a solution ?
Aitor López Hernández
2017-7-22
Hello,
I am currently having the same issue. Were you finally able to solve it? If so, how?
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Tuong Nguyen Minh
2020-2-6
编辑:Tuong Nguyen Minh
2020-2-6
You might consider the log sum exp trick
when seeing this kind of function pop up f(x) = ln((e^x+1)/(e^x-1))
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