mimo ofdm system outputioing snr vs ber grapj performing qpsk mod manually and selective fading in matlab

main.m
% number of transmit antennas
numTx = 2;

% number of receive antennas
numRx = 2;

% cyclic prefix length
cpLen = 16;

% FFT size
fftSize = 64;

% channel parameters
maxDopplerShift = 30;
numPaths = 1;
channel = [
    0.8+0.6i -0.6+0.8i 0 0;
    0 0 0.9+0.4i -0.4+0.9i;
    0 0 0 0;
    0 0 0 0
];
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main.m
numBitsPerSym = 2;
data = randi([0 1], numTx*fftSize*numBitsPerSym, 1);
qpskModulator = comm.QPSKModulator();
txSym = qpskModulator(data);
txSymMat = reshape(txSym, numTx, []);
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main.m
txOFDM = ifft(txSymMat, fftSize, 2);
txCP = [txOFDM(:, end-cpLen+1:end) txOFDM];
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main.m
rxCP = zeros(size(txCP));
for i = 1:numRx
    for j = 1:numTx
        rxCP(i, :) = rxCP(i, :) + sqrt(numTx)*sqrt(numRx)*conv(txCP(j, :), squeeze(channel(i,j,:)));
    end
    rxCP(i, :) = awgn(rxCP(i, :), snr, 'measured');
end
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main.m
rxOFDM = rxCP(:,cpLen+1:end);
rxSymMat = fft(rxOFDM, fftSize, 2);
rxSym = rxSymMat(:);
qpskDemodulator = comm.QPSKDemodulator();
dataRx = qpskDemodulator(rxSym);
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main.m
numErrs = sum(dataRx ~= data);
ber = numErrs/(numTx*fftSize*numBitsPerSym);
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main.m
semilogy(snr, ber)
xlabel('SNR (dB)')
ylabel('BER')
title('MIMO OFDM QPSK in Selective Fading')
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