In Quadrature Phase Shift Keying (QPSK) modulation, the modulator takes two input signals (I and Q) and modulates them onto the carrier signal. In this case, the inputs given are I=0 and Q=1, and the carrier signal is cos(w_ct).
The QPSK modulation process involves modulating the I and Q signals onto the carrier signal at the same time. The I signal is used to modulate the in-phase component and the Q signal is used to modulate the quadrature component.
Given:
I = 0
Q = 1
Carrier signal = cos(w_ct)
The modulation process can be represented as:
s(t) = I*cos(w_ct) + Q*sin(w_ct)
Substitute the given values into the equation:
s(t) = 0*cos(w_ct) + 1*sin(w_ct)
s(t) = sin(w_ct)
Therefore, the output signal of the QPSK modulator with the given inputs and carrier signal is sin(w_ct).
Now, let's analyze the options provided:
A. -sin(w_ct) + cos(w_ct)
B. sin(w_ct) - cos(w_ct)
C. -sin(w_ct) - cos(w_ct) <<<< Correct option
D. sin(w_ct) + cos(w_ct)
Comparing the output signal sin(w_ct) obtained from the modulation with the options:
- The correct option is C, -sin(w_ct) - cos(w_ct).
Therefore, option C is correct because it matches the output signal obtained from the QPSK modulation process with the given inputs and carrier signal.
