Page 430 - Satellite Communications, Fourth Edition

410 Chapter Thirteen

TABLE 13.1 Summary of Single-Entry Interference Objectives Used in FCC/OST R83-2,
May 1983
[S/I ] objectives:
FDM/FM: 600 pW0p or [S/I ] 62.2 dB (62.2 dB). Reference: CCIR Rec. 466–3.
TV/FM (broadcast quality): [S/I ] 67 dB weighted (67 dB; 65.5 dB). References:
CCIR Rec. 483–1, 354–2, 567, 568.
CSSB/AM: (54.4 dB; 62.2 dB). No references quoted.
[C/I ]pb objectives:
TV/FM (CATV): [C/I]pb = 20 dB (22 dB; 27 dB). Reference: ABC 62 FCC 2d 901 (1976).
6
Digital: [C/I ]pb [C/N] (at BER 10 ) 14 dB (20 to 32.2 dB). Reference: CCIR
Rec. 523.
SCPC/PSK: (21.5 dB; 24 dB). No references quoted.
SCPC/FM: (21.2 dB; 23.2 dB). No references quoted.
SS/PSK: (11 dB; 0.6 dB). No references quoted.

13.2.8 Protection ratio
In CCIR Report 634–2 (1982), the International Radio Consultative
Committee (CCIR) specifies the permissible interference level for TV car-
riers in terms of a parameter known as the protection ratio.The pro-
tection ratio is defined as the minimum carrier-to-interference ratio at
the input to the receiver which results in “just perceptible” degradation
of picture quality. The protection ratio applies only for wanted and inter-
fering TV carriers at the same frequency, and it is equivalent to [C/I] pb
evaluated for this situation. Denoting the quality impairment factor by
Q and the protection ratio in decibels by [PR ], the equation given in
0
IF
CCIR Report 634–2 (1982) is
[PR ] 12.5 20 loga Dv b Q 1.1Q 2 IF (13.9)
IF
0
12
Here Dv is the peak-to-peak deviation in megahertz.

Example 13.5 An FM/TV carrier is specified as having a modulation index of
2.571 and a top modulating frequency of 4.2 MHz. Calculate the protection ratio
required to give a quality impairment factor of (a) 4.2 and (b) 4.5.
Solution The peak-to-peak deviation is 2 2.571 4.2 21.6 MHz. Applying Eq.
(13.9) gives the following results:

(a) [PR 0 ] 12.5 20 loga 21.6 b 4.2 1.1 4.2 2
12
22.6 dB

(b) [PR 0 ] 12.5 20 loga 21.6 b 4.5 1.1 4.5 2
12
25.2 dB