Frequency Division Multiplexing
In a FDM communication system, the transmitted baseband signal is
x(t) = m₁ (t) cos ω₁t + m₂ (t) cos ω₂t
this system has a second-order nonlinearity between the transmitter input and receiver output. Thus the received baseband signal y(t) can be expressed as
y(t) = ₁x(t) +₂x(t)
assuming that the two message signals, m₁ (t) and m₂ (t), have the fourier transforms
M₁ (f) = M₂ (f) = rect(2f/W)
Sketch the Fourier transform of y(t). Discuss the difficulties encountered in demodulating the received baseband signal. In many FDM sustems, the subcarrier frequencies ω₁ and ω₂ are harmonically related (meaning one frequency is then integer multiple of the other). Describe any additional problems this presents.