This model generates baseband and IF BPSK signal and plots its waveform(time-domain) and FFT(frequency-domain).
First, a random bit stream is given to a BPSK baseband modulator.
The output of modulator XL is a complex-valued stream which is called lowpass equivalent or complex envelope.
The lowpass equivalent is a baseband signal which is converted to IF signal X based on this transformation:
X=real(XL)*cos(2*pi*Fc*t)-Imaginary(XL)*sin(2*pi*Fc*t),
where Fc is the carrier frequency and is the frequency of sine and cosine generator.
for more info about the lowpass equivalent look this book:
Digital communications by J.G.Proakis & M.Salehi.(5th edition, McGrawHill 2008)
The IF signal is given to a scope to plot the waveform. you have to double click on the scope to view the waveform.
The purple one is the IF BPSK signal and the yellow one is the bit stream.
The IF signal is also given to a spectrum scope in order to plot its FFT.
The Frequency domain shows that the FFT is located around
this frequency: Fc*sample_time
sample_time is given in sine and cosine generator. |