Page 436 - Satellite Communications, Fourth Edition

416 Chapter Thirteen

where U is the maximum power spectral density transmitted by S,
S
G TS is the transmit gain of S in the direction of E, and G RE is the receive
gain of E in the direction of S. It is assumed that the uplink and down-
link propagation losses, L and L , are the same as those used for the
U
D
interference signals.
The transmission gain for network R is then defined as
] [U ] (13.16)
[ ] [U RE RS
Note that this is the same transmission gain shown in Fig. 12.9.
Using the transmission gain, the interference I at the satellite may
2
be referred to the earth-station receiver as I , and hence the noise-
2
temperature rise at the satellite receiver input may be referred to the
earth-station receiver input as T . This is illustrated in Fig. 13.9b.
S
Expressed in decibel units, the relationship is
[ T S E ] [ ] [ T ] (13.17)
S

13.4.3 Resulting noise-temperature rise
The overall equivalent rise in noise temperature at earth-station E as
a result of interference signals B and B is then
1
2
T T S E T E (13.18)

In this final calculation the dBK values must first be converted to
degrees, which are then added to give the resulting equivalent noise-
temperature rise at the earth-station E receive antenna output.

Example 13.6 Given that L U 200 dB, L D 196 dB, G E G′ E 25 dB, G S G′ S
9 dB, G TE G RE 48 dB, G RS G TS 19 dB, U S U′ S 1 J, and U′ E 10 J;
calculate the transmission gain [ ], the interference levels [I 1 ] and [I 2 ], and the
equivalent temperature rise overall.
Solution Using Eq. (13.14) gives
[U RS ] 50 48 19 200

183 dBJ
Using Eq. (13.15) gives
[U RE ] 60 19 48 196
189 dBJ
Therefore,

[ ] 189 ( 183)
6 dB