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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ASWATHY G P 2015-12-11

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编辑： Tuong Nguyen Minh 2020-2-6

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