Estimate BER of QPSK in AWGN with Reed-Solomon (240,224) Coding

I want to make a BER estimate of QPSK in AWGN with RS(240.224) as depicted in this paper. So I began with something working like the MATLAB example and I just made parameter changes as follows:

rng(1993);     % Seed random number generator for repeatable results
M = 4;         % Modulation order
bps = log2(M); % Bits per symbol
N = 240;         % RS codeword length
K = 224;         % RS message length
rsEncoder = comm.RSEncoder( ...
    BitInput=true, ...
    CodewordLength=N, ...
rsDecoder = comm.RSDecoder( ...
    BitInput=true, ...
    CodewordLength=N, ...
ebnoVec = (3:0.5:8)';
ebnoVecCodingGain = ...
    ebnoVec + 10*log10(K/N); % Account for RS coding gain
errorStats = zeros(length(ebnoVec),3);

for i = 1:length(ebnoVec)
    awgnChannel.EbNo = ebnoVecCodingGain(i);
    while errorStats(i,2) < 100 && errorStats(i,3) < 1e7
        data = randi([0 1],1500,1);
        encData = rsEncoder(data);
        modData = pskmod(encData,M,InputType='bit');
        rxSig = awgnChannel(modData);
        rxData = pskdemod(rxSig,M,OutputType='bit');
        decData = rsDecoder(rxData);
        errorStats(i,:) = errorRate(data,decData);

berCurveFit = berfit(ebnoVecCodingGain,errorStats(:,1));

semilogy(ebnoVecCodingGain,errorStats(:,1),'b*', ...
xlabel('Eb/No (dB)')
legend('RS coded BER','Curve Fit')

I keep getting this error:

Error using comm.RSEncoder/setupImpl
the dimensions of the Input X must be consistent with the BitInput property value, the message and Codeword lengths, and primitive polynomial. ...


  • Your snippet is missing lines from the MATLAB example. The actual reference code is here: Estimate BER of QPSK in AWGN with Reed-Solomon Coding.

    However, the key fix is data = randi([0 1],224*8,1);

    Excerpt from help comm.RSEncoder/BitInput:"When you set this property to true, X must be a column vector of bits with an integer multiple of MessageLength*M bits."

    M = 8 in the case of your choice of (N,K) since you are using Galois Field GF(2^M). I would also recommend subtracting 3 from the SNR range ebnoVec = (0:0.5:5)'; so you have some bit errors at all of the SNRs or else berfit will return an curve that is not the same length as the simulation snr range.