pskmod output is complex, I expect out = I*cos(2*pi*fc*t) - Qsin(2*pi*fc*t)

I am trying to understand what parts of I/Q modulation are being performed by the pskmod function. To me modulation includes taking the input data and processing it into an I stream and a Q stream. The I stream is then mulitplied by cos and the Q stream by sin. The two streams are then added together. Therefore the output is in the form of I*cos(2*pi*fc*t) - Qsin(2*pi*fc*t). But the pskmod is giving me a matrix with values of x + yi. Is the pskmod function not multiplying the I and Q streams by cos and sin? Is the pskmod function actually just creating I + Q values?

Regards,

Mark

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/instrument/creating-and-downloading-an-iq-waveform-to-a-rf-signal-generator.html

 IQData = Iwave+1i*Qwave;

Notice that 1i. That is inherent in how IQ is created: you have two independent real channels multiplexed together by making one an imaginary component.

[Mark Bailly]

I am thinking of things from an RF Modulator point of view. This block diagram is what I envision as a QPSK modulator.

From what I can tell, the MATLAB pskmod does not implement this block diagram. It provides I and Q data, but it does not upconvert and combine the I and Q streams into one modulated signal. Is that correct?

I am trying to create a poor-man's vector sig gernerator by using an IQ waveform from MATLAB, fed into an arb generator and then upconverted using an analog generator. The arb is a 33622A. I can load it with pulse shaped IQ data from MATLAB. The arb has two outputs that can be used as I and Q. I would then use an external modulator to RF upconvert. Or I can create a signal in MATLAB that is already "modulated" in baseband. This combined waveform can be fed into a mixer for up conversion.