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5.2 Precoding and bandlimited signals

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A description of various ways to deal with the problem of intersymbol interference which occurs in bandlimited channels.

Precoding

The data symbols are manipulated such that

y k k T a k u 0 ISI k T

Design of bandlimited modulation signals

Recall that modulation signals are

X t n ∞ ∞ a n s t n T
We can design s t such that
u n T large n 0 zero or small n 0
where y k T a k u 0 n ∞ ∞ a n u k T n T k T (ISI is the sum term, and once again, n k .) Also, y n T s g h opt n T The signal s t can be designed to have reduced ISI.

Design equalizers at the receiver

Linear equalizers or decision feedback equalizers reduce ISI in the statistic y t

Maximum likelihood sequence detection

y k T n ∞ ∞ a n k T n T k T
By observing y T y 2 T the date symbols are observed frequently. Therefore, ISI can be viewed as diversity to increase performance.
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Source:  OpenStax, Digital communication systems. OpenStax CNX. Jan 22, 2004 Download for free at http://cnx.org/content/col10134/1.3
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