Page 328 - Satellite Communications, Fourth Edition

308 Chapter Ten

The [C/N ] ratio is then used in the link budget calculations, as described
0
in Chap. 12.
With purely digital systems, the BER will be directly reflected in
errors in the data being transmitted. With analog signals which have
been converted to digital form through PCM, the BER contributes to the
output signal-to-noise ratio, along with the quantization noise, as
described in Sec. 10.3. Curves showing the contributions of thermal
noise and quantization noise to the signal-to-noise output for analog
systems can be seen in Fig. 10.19. The signal-to-noise power ratio is
given by (Taub and Schilling, 1986)

2
S Q
(10.25)
2
N 1 4Q P e

Figure 10.19 (a) Use of optimum terminal filter to maximize the signal-to-
noise voltage ratio; (b) plot of Eq. (10.25).