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, ...
    MessageLength=K);
rsDecoder = comm.RSDecoder( ...
    BitInput=true, ...
    CodewordLength=N, ...
    MessageLength=K);
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);
    reset(errorRate)
    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);
    end
end

Unrecognized function or variable 'errorRate'.

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

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

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. ...
    

Could someone help me please fixing this issue. Thank you

Answer 1

[Balaji]

Hi Anour

I understand that you are facing an error in using the ‘comm.RSEncoder’.

When the ‘BitInput’ property is set to 1, the message length should be be an integer multiple of (MessageLength×M)  bits.

Where ‘MessageLength’ is ‘K’ and N = 2M -1. The current code doesn’t follow that property.

A group of M bits represents an integer in the range [0, (2M – 1)] that belongs to the finite Galois field gf(2M)

For more information on ‘comm.RSEncoder’ I suggest you refer to the following documentation:

https://www.mathworks.com/help/comm/ref/comm.rsencoder-system-object.html

Hope this helps

Thanks

Balaji