OFDM Demodulation of Streaming Samples

This example shows how to use the OFDM Demodulator block in Wireless HDL Toolbox to demodulate complex time-domain OFDM samples to subcarriers for a vector input. This example model supports HDL code generation for the OFDMDemod subsystem.

Set Up Input Data Parameters

Set up these workspace variables for the model to use. You can modify these values according to your requirement.

rng('default');
numOFDMSym = 2;
maxFFTLen = 128;
DCRem = true;
RoundingMethod = 'floor';
Normalize = false;
cpFraction = 1;
fftLen = 64;
cpLen = 16;
numLG = 6;
numRG = 5;
if DCRem
    NullInd = [1:numLG fftLen/2+1 fftLen-numRG+1:fftLen];
else
    NullInd = [1:numLG fftLen-numRG+1:fftLen]; %#ok<UNRCH>
end
symbOffset = floor(cpFraction*cpLen);
vecLen = 2;

Generate Frames of Random Input Samples

Generate frames of random samples using the MATLAB function randn.

data = randn(fftLen,numOFDMSym)+1i*randn(fftLen,numOFDMSym);
dataIn = ofdmmod(data,fftLen,cpLen);

Convert Frames to Stream of Random Samples

Convert frames of random samples to a stream of random samples to provide them as input to the block.

data = dataIn(:);
valid = true(length(dataIn)/vecLen,1);
fftSig = fftLen*ones(length(dataIn),1);
CPSig = cpLen*ones(length(dataIn),1);
LGSig = numLG*ones(length(dataIn),1);
RGSig = numRG*ones(length(dataIn),1);
resetSig = false(length(data),1);
sampleTime = 1/vecLen;
stopTime = (maxFFTLen*3*numOFDMSym)/vecLen;

Run Simulink Model

Run the model to import the input signal variables to the block from the script and exports a stream of demodulated output samples from the block to the MATLAB workspace.

modelname = 'genhdlOFDMDemodulatorModel';
open_system(modelname);
out = sim(modelname);
simOut = squeeze(out.dataOut(:,1,out.validOut==1));

Demodulate Stream Samples Using MATLAB Function

Demodulate stream of random input samples using the ofdmdemod_baseline function.

[dataOut1] = ofdmdemod_baseline(dataIn,fftLen,cpLen,symbOffset,NullInd.',[],Normalize,RoundingMethod);
matOut = dataOut1(:);

Compare Simulink Block Output with MATLAB Function Output

Compare the output of the Simulink model against the output of ofdmdemod_baseline function.

figure('units','normalized','outerposition',[0 0 1 1])
subplot(2,1,1)
plot(real(matOut(:)));
hold on;
plot(real(simOut(:)));
grid on
legend('Reference','Simulink')
xlabel('Sample Index')
ylabel('Magnitude')
title('Comparison of Simulink block and MATLAB function - Real part')

subplot(2,1,2)
plot(imag(matOut(:)));
hold on;
plot(imag(simOut(:)));
grid on
legend('Reference','Simulink')
xlabel('Sample Index')
ylabel('Magnitude')
title('Comparison of Simulink block and MATLAB function - Imaginary part')

sqnrRealdB=10*log10(var(real(simOut(:)))/abs(var(real(simOut(:)))-var(real(matOut(:)))));
sqnrImagdB=10*log10(var(imag(simOut(:)))/abs(var(imag(simOut(:)))-var(imag(matOut(:)))));

fprintf('\n OFDM Demodulator: \n SQNR of real part is %.2f dB',sqnrRealdB);
fprintf('\n SQNR of imaginary part is %.2f dB\n',sqnrImagdB);

 OFDM Demodulator: 
 SQNR of real part is 47.77 dB
 SQNR of imaginary part is 42.69 dB