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Unformatted text preview: will work with this discrete-time model in all the following sections. ¯ Finally, the equalizing circuit (we simply call it the equalizer from now on) attempts to remove ´Þµ. The focus of our coming discussion is the design of this equalizer.
Suppose that the equalizer is also an LTI ﬁlter with transfer function À ´Þ µ and corresponding ISI from the output of impulse response . Then the output of the equalizer is given by Á Á (4.18) Ideally, Á contains only contributions from the current symbol Á and the AWGN sequence with
small variance. 4.3.2 Zero-forcing equalizer
First, let us consider the use of a linear equalizer, i.e., we employ an LTI ﬁlter with transfer function À ´Þ µ as the equalizing circuit. The simplest way to remove the ISI is to choose À ´Þ µ so that the
output of the equalizer gives back the information sequence, i.e., Á
Á for all if noise is not
present. This can be achieved by simply setting the transfer function À ´Þ µ ½ ´Þ µ. This method
is called zero-forcing equalization since the ISI component at the equalizer output is forced to zero.
4.12 Wong & Lok: Theory of...
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- Spring '08