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Unformatted text preview: 1 Modulation and demodulation transmission media coaxial line twisted pair optical fiber free space (EM wave) usually more than one stream of information channel = region of the transmitted frequency spectrum assigned to particular users or services Some definitions baseband signal- the original low-frequency signal modulation- translation to the channel frequency demodulation- recovery of baseband signal f ( t ) = baseband signal e ( t ) = transmitted or modulated signal c = frequency corresponding to center of channel 2 Frequency/ phase modulation generalization of the concept of phase- if we write then if ( t ) = t + then and We can modulate the phase or frequency according to the baseband signal f ( t ) . Note that the amplitude stays constant! )) ( cos( ) ( t t x = ) cos( ) ( + = t t x c dt d = Frequency/ phase modulation Phase modulation Frequency modulation )) ( cos( ) ( t Af t t e c + = = = dt t f A dt d ) ( ) ) ( cos( ) ( + = dt...
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- Fall '08