ldpc using matlab function

Hi,

here my matlab code for 16-QAM over AWGN channel using LDPC matlab function. I get a BER which is worse than the one without code. Does somebody have any idea about what is wrong with my code?

% Set the simulation parameters.
clear; close all
rng default
M = 16;                 % Modulation order
k = log2(M);            % Bits per symbol
EbNoVec = (0:10)';      % Eb/No values (dB)
numSymPerFrame = 1000;  % Number of QAM symbols per frame
rate=1/2;

% Set LDPC coding and decoding
hEnc = comm.LDPCEncoder;
hDec = comm.LDPCDecoder;

for n = 1:length(EbNoVec)
    n
    % Convert Eb/No to SNR
    snrdB = EbNoVec(n) + 10*log10(k*rate);

          % Generate binary data and convert to symbols
          dataIn = (randi([0 1],32400,1));

          % Convolutionally encode the data
          dataEnc    = step(hEnc, dataIn);

          % QAM modulate
          txSig = qammod(dataEnc,M,'InputType','bit');

          % Pass through AWGN channel
          rxSig = awgn(txSig,snrdB,'measured');

          % Demodulate the noisy signal using hard decision (bit) and
          % approximate LLR approaches
          rxDataSoft = qamdemod(rxSig,M,'OutputType','approxllr', ...
              'NoiseVariance',10.^(snrdB/10));

          % LDPC decoding
          receivedBits   = step(hDec, rxDataSoft);

          % Ber computation
          [umErrsInFrameSoft, BER(n)] = biterr(receivedBits,dataIn);

end

semilogy(EbNoVec,BER,...
    EbNoVec,berawgn(EbNoVec,'qam',M),'-*')
legend('LDPC','Uncoded')
grid
xlabel('Eb/No (dB)')
ylabel('Bit Error Rate')

[Rostislav Shaniiazov]

All theoretical boards are for rate = 1. You used rate =1/2.

[Rishi Balasubramanian]

check SNRdB calculation

[ikram DAANOUNE]

@Thomas Larhzaoui did you solve this problem?

Answer 1

[Raed Abd-Alhameed]

Remove the noise variance in the qamdemod function. The errors will be zero for most of teh EbNo values... I meant water falling approach occurs. Please try it and let me know, otherwise if you have another solution please let me know.