A quadrature amplitude modulation (QAM) system is a communication system capable of transmitting two messages m₁(t), m₂(t) at the same time. The transmitted signal s(t) is

s(t) = m₁(t) cos(Ω_ct) + m₂(t) sin(Ω_ct)

Carefully draw a block diagram for the QAM system.

(a) Determine if the system is time-invariant or not.

(b) Assume m₁(t) = m₂(t) = m(t), i.e., we are sending the same message using two different modulators. Express the modulated signal in terms of a cosine with carrier frequency Ω_­c, amplitude A and phase θ. Obtain A and θ. Is the system linear? Explain