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530
Performance of Communication Systems Corrupted by Noise Chap. 7
80
(S/N) pk out= peak signal power to average noise power out (dB)
70
60
50
40
30
20
M=4096 (n=12)
M=1024 (n=10)
M=256 (n=8)
M=64 (n=6)
M=8 (n=3)
M=4 (n=2)
10
0
10 7
10 6 10 5 10 4 10 3 10 2 10 1 1.0
P e
Figure 7–17 (SN) out of a PCM system as a function of P e and the number of quantizer steps M.
7–8 OUTPUT SIGNAL-TO-NOISE RATIOS
FOR ANALOG SYSTEMS
In Chapters 4 and 5, generalized modulation and demodulation techniques for analog and digital
signals were studied. Specific techniques were shown for AM, DSB-SC, SSB, PM, and
FM signaling, and the bandwidths of these signals were evaluated. Here we evaluate the output
signal-to-noise ratios for these systems as a function of the input signal, noise, and system
parameters. Once again, we find that the mathematical analysis of noncoherent systems is
more difficult than that for coherent systems and that approximations are often used to obtain
simplified results. However, noncoherent systems are often found to be more prevalent in