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MIT16_36s09_lec06

MIT16_36s09_lec06 - MIT OpenCourseWare http/ocw.mit.edu...

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MIT OpenCourseWare http://ocw.mit.edu 16.36 Communication Systems Engineering Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .

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Lectures 6: Modulation Eytan Modiano Eytan Modiano Slide 1
Modulation Digital signals must be transmitted as analog waveforms Baseband signals Signals whose frequency components are concentrated around zero Passband signals Signals whose frequency components are centered at some frequency f c away from zero Baseband signals can be converted to passband signals through modulation Multiplication by a sinusoid with frequency f c Eytan Modiano Slide 2

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Baseband signals The simplest signaling scheme is pulse amplitude modulation (PAM) With binary PAM a pulse of amplitude A is used to represent a “1” and a pulse with amplitude -A to represent a “0” The simplest pulse is a rectangular pulse, but in practice other type of pulses are used For our discussion we will usually assume a rectangular pulse If we let g(t) be the basic pulse shape, than with PAM we transmit g(t) to represent a “1” and -g(t) to represent a “0” g(t) 1 S(t) = g(t) A 0 S(t) = -g(t) Tb Eytan Modiano Slide 3
M-ary PAM Use M signal levels, A 1 …A M Each level can be used to represent Log 2 (M) bits

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MIT16_36s09_lec06 - MIT OpenCourseWare http/ocw.mit.edu...

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