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Unformatted text preview: 1 1 EEN 404 EEN 404 Communication Systems Communication Systems Ch3.5: Analog Pulse Modulation Ch3.5: Analog Pulse Modulation 2 Ch2.8 Sampling Theory Ch2.8 Sampling Theory Sampling theorem: If a signal x(t) satisfies then the signal is completely described by instantaneous sample values with sampling frequency 2W: Nyquist frequency Sampled signal: Reconstruction: from samples to recover the signal x(t) The signal x(t) can be exactly reconstructed from the sampled signal by passing it through an ideal lowpass filter with bandwidth B where W<B<f s-W and f s =1/T s 3 FT: 3 lowpass filtering for reconstruction Spectrum of sampled signal Sampled signal: Eq. (2.136): reconstruction f s > 2W no overlap between spectra W<B<fs-W recover x(t) without distortion B 2 4 Aliasing if f s < 2W Non-ideal lowpass filter Possible distortion 5 Sampling bandpass signals: if a bandpass signal x(t) satisfies then the signal can be recovered by sampling at integer floor...
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- Spring '10