LTE Symbol Demodulation of Complex Data Symbols

This example shows how to use the LTE Symbol Demodulator block to demodulate complex LTE data symbols to data bits or LLR values. The workflow follows these steps:

1. Set up input data parameters.

2. Generate frames of random input samples.

3. Convert framed input data to a stream of samples and import the stream into Simulink®.

4. Run the Simulink® model, which contains the LTE Symbol Demodulator block.

5. Export the stream of demodulated samples from Simulink to the MATLAB® workspace.

6. Demodulate data symbols with lteSymbolDemodulate function to use its output as a reference data.

7. Compare Simulink block output data with the reference MATLAB function output.

Set up input data parameters.

Map modulation names to values. The numerical values are used to set up the LTE Symbol Demodulator block. The strings are used to configure the lteSymbolDemodulator function.

rng(0);
framesize = 10;

% 0 - BPSK
% 1 - QPSK
% 2 - 16-QAM
% 3 - 64-QAM
% 4 - 256-QAM
% others - QPSK
modSelVal = [0;1;2;3;4];
modSelStr = {'BPSK','QPSK','16QAM','64QAM','256QAM'};

decType = 'Soft';

numframes = length(modSelVal);
dataSymbols  = cell(1,numframes);
modSelTmp = cell(1,numframes);
lteFcnOutput = cell(1,numframes);

Generate frames of random input samples.

for ii = 1:numframes
    dataSymbols{ii} = complex(randn(framesize,1),randn(framesize,1));
    modSelTmp{ii} = fi(modSelVal(ii)*ones(framesize,1),0,3,0);
end

Convert the framed input data to a stream of samples and input the stream to the LTE Symbol Demodulator Simulink block.

idlecyclesbetweensamples = 0;
idlecyclesbetweenframes  = 0;
[sampleIn, ctrl] = whdlFramesToSamples(dataSymbols,idlecyclesbetweensamples,...
    idlecyclesbetweenframes);
[modSel, ~] = whdlFramesToSamples(modSelTmp,idlecyclesbetweensamples,...
    idlecyclesbetweenframes);
validIn = logical(ctrl(:,3)');

sampletime = 1;
samplesizeIn = 1;
simTime = size(ctrl,1)*8;

Run the Simulink model.

modelname = 'ltehdlSymbolDemodulatorModel';
open_system(modelname);
set_param([modelname '/Demod/LTE Symbol Demodulator'],'DecisionType',decType)
sim(modelname);

Export the stream of demodulated samples from Simulink to the MATLAB workspace.

lteHDLOutput = sampleOut(validOut).';

Demodulate data symbols with lteSymbolDemodulate function and use its output as a reference data.

for ii = 1:numframes
 lteFcnOutput{ii} = lteSymbolDemodulate(dataSymbols{ii},modSelStr{ii},decType).';
end

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

lteFcnOutput = double(cell2mat(lteFcnOutput));

figure(1)
stem(lteHDLOutput,'b')
hold on
stem(lteFcnOutput,'--r')
grid on
legend('Reference','Simulink')
xlabel('Sample Index')
ylabel('Magnitude')
title('Comparison of Simulink Block and MATLAB Function')