B. P. Lathi, Zhi Ding - Modern Digital and Analog Communication Systems-Oxford University Press (2009)

Fi g ure 12.22
Scatter plots of
signal samples
before (a) and
after (b) linear
equalization at
Eb/N = 26 dB
demonstrate
effective ISi
mitigation by the
linear equalizer.
0.
>-,
·en "'
3
2
0
-1
-2
-3
--4
--4 -2 0 2 4
Real part
(a)
.. -.
12.12 MATLAB Exercises 72 1
4 ....---....------.----,----,
3 ..,
.: ..
#,·. : .
2
., .
.!fl_ 111'£''
..
--4 ..___ .......__ ......___ _..___ _,
--4 -2 0 2 4
Real part
(bJ
Fi g ure 12.23
Symbol error
rate (SER)
comparison
before and after
linear
equalization
demonstrates its
effectiveness in
combating
multipath
channel ISi.
-- Analytical
1 o --4 -a-without equalizer
With Linear equalizer . ·::.
1 0-S '-----------------'---'----'--------'-
0 5 10 15
20 25
E/N, dB
We can suppress a significant amount of ISI by applying the linear equalizer to the sampled matched
filter output. Figure 12.22 compares the "scatter plot" of signal samples before and after equalization
at E 1, / /If = 26 dB. The contrast illustrates that the equalizer has effectively mitigated much of the ISI
introduced by the multipath channel.
The program lineareq .rn also statistically computes the symbol error rate (SER) at different
SNR levels. It further computes the ideal SER according to ISI-free AWGN channel (Chapter 10) and,
for comparision, the SER without equalization. The results shown in Fig. 12.23 clearly demonstrate the
effectiveness of linear equalization in this example.