Signals and Systems Fall 2003 Lecture #15 28 October 2003 Complex exponential amplitude modulation 2. Sinusoidal am 3. Demodulation of Sinusoidal AM 4. Single-Sideband(SSB)AM 5. Frequency-Division Multiplexing 6. Superheterodyne receivers
Signals and Systems Fall 2003 Lecture #15 28 October 2003 1. Complex Exponential Amplitude Modulation 2. Sinusoidal AM 3. Demodulation of Sinusoidal AM 4. Single-Sideband (SSB) AM 5. Frequency-Division Multiplexing 6. Superheterodyne Receivers
The Concept of modulation Transmitted Signal Carrier Signal Why? More efficient to transmit E&M signals at higher frequencies Transmitting multiple signals through the same medium using different carriers Transmitting through "channels, with limited passbands Others How? Many metho Focus here for the most part on Amplitude Modulation(AM) X(1) y(t=X(tc(t) c()
The Concept of Modulation Why? • More efficient to transmit E&M signals at higher frequencies • Transmitting multiple signals through the same medium using different carriers • Transmitting through “channels” with limited passbands • O t h e r s... • Many methods • Focus here for the most part on A mplitude Modulation (AM ) How? x(t) Transmitted Signal Carrier Signal
Amplitude Modulation(AM)of a Complex exponential carrier c(t) Wc-carrier frequency jEct X(w)*clw) cga) 2丌 X u)* 2d(w-wc) 2TU X((-c) (Oc-OM)Oc(oc+OM)(
Amplitude Modulation (AM) of a Complex Exponential Carrier
Demodulation of Complex Exponential AM x(t) y() x(t) nwct cos wct+] sin wct Corresponds to two separate modulation channels( quadratures) with carriers 90 out of phase cOS (ct lmt
Demodulation of Complex Exponential AM Corresponds to two separate modu l ation channels (quadratures) with carriers 90 o out of phase
Sinusoidal am x(t) cOS O t X(j)米丌{6(u-uc)+6(u+c)} oXOw-wc))+eXo(w+wc) Drawn assuming (uc-oMωl(oc+uM (c)
Sinusoidal AM Drawn assuming ωc > ωM