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Unformatted text preview: tput at time Ø ÑÌ to obtain the decision statistic for the symbol Ñ . At Ø ÑÌ , the output of the matched ﬁlter is ÞÑ Ò
Ñ £ Ú´ÑÌ ÒÌ µ · ÒÑ
Ò Ú £ Ú ´ÑÌ ÒÌ µ · ÒÑ
ÒÚ ÒÑ where ÒÑ is a zero-mean Gaussian random variable with variance (4.4) Æ¼ Ú ¾ ¾. The ﬁrst term in (4.4) is the desired signal contribution due to the symbol Ñ and the second term contains contributions
from the other symbols. These unwanted contributions from other symbols are called intersymbol
interference (ISI). 4.2 Wong & Lok: Theory of Digital Communications 4. ISI & Equalization 1.5 1 0.5 0 −0.5 −1 −1.5 5 10 15 20 25 30 Figure 4.1: Eye diagram of a BPSK signal with no ISI Ú ´Øµ were timelimited, i.e., Ú ´Øµ ¼ except for ¼
¼ except for Ì Ø Ì . Therefore, Ú £ Ú´ÑÌ ÒÌ µ Suppose Ú £ Ú´Øµ Ø Ì . Then it is easy to see that
¼ for all Ò Ñ, and there is no ISI. As a result, the demodulation strategy above can be interpreted as matched ﬁltering for each symbol.
Unfortunately, a timelimited waveform...
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- Spring '08