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550
Performance of Communication Systems Corrupted by Noise Chap. 7
70
60
Ideal
(B T /B) = 12
FM with deemphasis
ı f = 5, (B T /B) = 12
50
FM no deemphasis
ı f = 5, (B T /B) = 12
(S/N) out (dB)
40
30
20
PCM with BPSK signaling
Baseband
(B T /B) = 12
DSB
SSB
10
AM
(envelope
detection)
0
0
Figure 7–27
AM
(product detection)
5 10 15
20
(S/N) baseband (dB)
Comparison of the noise performance of analog systems.
25 30 35
But
a S N b in
= P s
N 0 B T
= a P s
N 0 B ba B B T
b = a B B T
ba S N b baseband
(7–145)
where Eq. (7–84) was used. Thus, Eq. (7–144) becomes
a S N b out
= c1 + a B ba S B T /B
B T N b d - 1
baseband
(7–146)
Equation (7–146), which describes the ideal system performance, is plotted in Fig. 7–27
for the case of B T B = 12. As expected, none of the practical signaling systems equals the
performance of the ideal system. However, some of the nonlinear systems (near threshold)
approach the performance of the ideal system.