Dear Ganeshaanand Rishi Balasubramanian ,

welcome!

I see that you have to continue your curve for higher signal to noise ration. You will find a rapid fall of the bit error rate at the threshold value of S/N ratio.

You have to compare the bit error rate with and without LDPC.

You can compare your results with the results in the paper:Article Implementation for Two-Stage Hybrid Decoding for Low Density...

Best wishes

Yes, but shouldn't I be getting error rate more than 10^-5 just for 5dB itself. I'm using Sum Product Decoding which has highest error rates apparently.

clear;

clc;

[bb, Ha] = qcldpc(3, 5, 2, 5, 31); %Creates PCM.

H = alt(Ha); %Rearrange PCM to ALT form for Encoding

[N1, N2] = size(H);

k = N2-N1;

pcs =1;

while (pcs ~= 0)

y = round(rand(1, N2-N1));

encode = enc(H,y);

msg = [y encode];

cs = mod(msg * H', 2); %to detect a proper codeword

pcs = sum(cs);

end

[~, bits] = size(msg);

dB = 1:5; % range of SNR values in dB

R = k/N2; % code rate

iter = 10; %Iterations

N0 = (10.^(-dB/10)); %Variance values

for i = 1 : length(dB)

ber1(i) = 0; ber2(i) = 0;

for j = 1:bits

mod = bpsk(msg); %bpsk modulation

bp = mod';

tx = bp + sqrt(N0(i)/2) * randn(size(bp)); %Transmitted with AWGN

dp(i,:) = dbpsk(tx); %Demodulated

Li = -dp(i,:);

vhat1(i,:) = SPA(tx, Ha, N0(i), iter); %Decoding Using Sum Product Algorithm

vhat2(i,:) = MSA(Li, Ha, iter); %Decoding Using Min Sum Algorithm

[n1, r1] = biterr(vhat1(i,:), msg);

[n2, r2] = biterr(vhat2(i,:), msg);

ber1(i) = ber1(i) + r1;

ber2(i) = ber2(i) + r2;

end

BER1(i) = ber1(i) / (bits * length(dB)); %BER Calculation

BER2(i) = ber2(i) / (bits * length(dB));

end

figure('Name','BER vs SNR','NumberTitle','off');

semilogy(dB, BER1, 'o-');

hold;

semilogy(dB, BER2, 'o--');

legend('SPA','MSA')

grid on;

hold off;

My Y axis is not a semilog because my error rates are low. Now after some work, My Sum Product works perfectly, but my min sum is still showing errors.

That is proprietary, but I am trying to run the QC Tanner Code [155, 64, 20] for your reference...

Thank you to everyone who tried helping me with this question. I figured out that my encoding was wrong and I have corrected it.