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chap_2Discrete-time and continuous-time AWGN channelsChapter 2
Discrete-time and continuous-time AWGN channels
In this chapter we begin our technical discussion of coding for the AWGN channel. Our purpose is to show how the continuous-time AWGN channel model Y (t) = X (t) + N (t) may be reduced to an equivalent discrete-time AWGN channel model Y = X + N, without loss of generality or optimality. This development relies on the sampling theorem and the theorem of irrelevance. More practical methods of obtaining such a discrete-time model are orthonormal PAM or QAM modulation, which use an arbitrarily small amount of excess bandwidth. Important parameters of the continuous-time channel such as SNR, spectral eciency and capacity carry over to discrete time, provided that the bandwidth is taken to be the nominal (Nyquist) bandwidth. Readers who
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