Communication - Topic 5

Question 1

Baseband vs Passband: What is the difference.

Answer 1

Baseband sends the signal as it is without frequency shifting (i.e. modulation). On the other hand, Passband transmission shifts the frequency of the signal to a higher frequency and then transmits it, the transmitted signal is then shifted back at the receiver.

Question 2

What is the generic setup of a Passband Digital Transmission?

Answer 2

Question 3

What happens to the frequency spectrum of a signal when you multiply the time domain by a sine wave?

Answer 3

The frequency domain is shifted.

It gets shifted to the frequency of the sine wave that was multiplied.

Question 4

How do you determine that e^j*π/2 = j ?

Answer 4

Through Eulers Formula which states that:

e^x*j = cos(x) +jsin(x)

Question 5

Passband Digital Transmission: What is the phase shift for each of these symbols?

Answer 5

These are complex symbols, the phase shift for each of the symbol is determined by π and its associated coefficient values.

So in this case, e^π*j leads to a phase shift of pi or 180º.

e^3π*j/2 leads to a phase shift of 3π/2 or 270º, etc.

Question 6

Passband Transmission: What do we achieve by making the symbols complex?

Answer 6

It allows for more phase differences in the passband digital signal.