OFDM modulation how to apply in real application

I am looking to generate and QAM-16 OFDM signal and apply it to a LED to control the amplitude.

When I create the OFDM modulated signal as follows, it outputs complex numbers in modData. Can I simply take the real portion of this complex value to convert to a voltage to amplitude modulate the diode? Or is there some other way to convert the modulated data into a summation of sinusoids?

On the receiving end, I have a detector attached to a scope which will change the sampling rate. Can I use the corresponding demodulator with this signal or will I have to adjust the sampling rate, assuming I can find the correct start of the signal or will it fail because I don't have a complex input?

FFTlen = 256;
Guard = [28;28];
DC = false;

pilotIdx = [-88,-63,-38,-13,13,38,63,88]';
pilotIdx = pilotIdx+129;

CP = FFTlen * 0.25;
nSymb = 30;

%QAM
M = 16;

%PILOT
p1 = [0 1 0 1 1 1 0 0];
p2 = [1 0 1 0 0 0 1 1];
pilot1 = pskmod(p1,2)';
pilot2 = pskmod(p2,2)';


%OFDM MOD
ofdmMOD = comm.OFDMModulator('FFTLength',FFTlen,'NumGuardBandCarriers',Guard, ...
    'InsertDCNull',DC, 'CyclicPrefixLength', CP, ...
    'PilotInputPort', true, 'PilotCarrierIndices', pilotIdx,...
    'NumSymbols',nSymb);

modDim = info(ofdmMOD);


%DATA
inSig = randi([0 M-1],modDim.DataInputSize(1),modDim.DataInputSize(2));
dataIn = qammod(inSig,M,'UnitAveragePower',true);

pilotIn = [repmat(pilot1,1,8), repmat(pilot2,1,9), ...
            repmat(pilot1,1,2), repmat(pilot2,1,7), ...
            repmat(pilot1,1,4)];
        
modData = step(ofdmMOD,dataIn,pilotIn);

[Akira Agata]

Before jumping into a solution, I would recommend learning a basics on IQ modulator, such like the following page.

What is I/Q Data?

Regards,

Akira

[Kaitlyn Morgan]

Thank you, I do understand IQ modulation, the summation of orthogonal frequencies was throwing me off. So if I use the same code as above, but set only one bit of the input data to one, I get a constant sinusoid over one OFDM symbol only.

I am currently trying to verify the sinusoidal frequencies using the fourier-transform method, I don't seem to be getting the correct frequencies. Is my definition of f below incorrect?

%% CONVERT TO OPTICAL SIGNAL and verify
RHO = abs(modData);
PHI = angle(modData);

Fc = 1.1e9; % center frequency at 1.1 GHz
dt = 1/Fc;
t = (0:dt:dt*length(PHI)-dt)';

% OPTICAL SIGNAL
OPT_sig = RHO .* cos(2*pi*Fc*t + PHI);

   %%Time specifications:
   N = size(t,1);
   
   %%Fourier Transform:
   X = fftshift(fft(OPT_sig));
   %%Frequency specifications:
   dF = Fc/N;                      % hertz
   f = -Fc/2:dF:Fc/2-dF;           % hertz
   %%Plot the spectrum:
   figure(1)
   hold on
   plot(f/1e9,abs(X)/N);
   xlabel('Frequency (GHz)');
   title('Magnitude Response');
   hold off