Main Content

OFDM Modulation of LTE Resource Grid Samples

Open Script

This example shows how to use the LTE OFDM Modulator block to modulate LTE resource grid samples to an equivalent time-domain signal output. You can generate HDL code from this block.

Generate the input resource grid using LTE Toolbox™ function.

enb = lteRMCDL('R.6');
enb.CyclicPrefix='Normal';
enb.TotSubframes = 1;
% --------------------------------------------------------------
%      NDLRB              |   Sampling Rate (MHz)
% --------------------------------------------------------------
%       6                  |   R.4
%       15                 |   R.5
%       25                 |   R.6
%       50                 |   R.7
%       75                 |   R.8
%       100                |   R.9
% --------------------------------------------------------------

[~,LTEGrid,info] = lteRMCDLTool(enb,[1;0;0;1]);
[eNodeBOutput,~] = lteOFDMModulate(enb,LTEGrid);

Convert the LTEGrid sample frames to a stream of samples with control signals for input to the Simulink® model.

NDLRB=info.NDLRB;
if strcmp(enb.CyclicPrefix,'Normal')
    CPType=false;
else
    CPType=true;
end

sampling_time=1/30.72e6;
stoptime=enb.TotSubframes*(30720+4137+2048*2)*sampling_time;

idlecyclesbetweensamples = 0;
idlecyclesbetweenframes  = 0;

[dataIn,ctrl] = whdlFramesToSamples(mat2cell(LTEGrid(:),numel(LTEGrid),1),...
    idlecyclesbetweensamples,idlecyclesbetweenframes);
validIn = logical(ctrl(:,3));

Run the Simulink model.

modelname = 'OFDMModulatorModelExample';
open_system(modelname);
sim(modelname);

Save the output of the Simulink model and then compare the output of the model against the output of the lteOFDMModulate function.

rxgridSimulink=dataOut(validOut);

figure('units','normalized','outerposition',[0 0 1 1])
subplot(2,1,1);
plot(real(eNodeBOutput));
hold on
plot(squeeze(real(rxgridSimulink)));
legend('Real part of behavioral waveform','Real part of HDL-optimized waveform');
title('Comparison of LTE Time-Domain Downlink Waveforms from Behavioral and HDL-Optimized Algorithms');
xlabel('OFDM subcarriers');
ylabel('Real part of the time-domain waveform');

subplot(2,1,2)
plot(imag(eNodeBOutput))
hold on
plot(squeeze(imag(rxgridSimulink)))
legend('Imag part of behavioral waveform','Imag part of HDL-optimized waveform');
title('Comparison of LTE Time-Domain Downlink Waveforms from Behavioral and HDL-Optimized Algorithms');
xlabel('OFDM subcarriers');
ylabel('Imag part of the time-domain waveform');

See Also

Blocks