The carrier signals have the same frequency, fc, but they are out of phase by 90◦
Since the signals are orthogonal, they do not interfere with each other
One of the carriers is called the I carrier (in-phase signal) and the other is called the Q signal (quadrature signal)
recall that:
At the receiver side, the composite modulated signal will be mixed with two demodulating signals
they are identical in frequency but out of phase with each other by 90