Page 445 - Satellite Communications, Fourth Edition

Satellite Access 425

antenna and a parametric amplifier, which together provide a minimum
[G/T] of 37.5 dB/K.

14.3 Preassigned FDMA
Frequency slots may be preassigned to analog and digital signals, and to
illustrate the method, analog signals in the FDM/FM/FDMA format will
be considered first. As the acronyms indicate, the signals are frequency-
division multiplexed, frequency modulated (FM), with FDMA to the
satellite. In Chap. 9, FDM/FM signals are discussed. It will be recalled
that the voice-frequency (telephone) signals are first SSBSC amplitude
modulated onto voice carriers in order to generate the single sidebands
needed for the FDM. For the purpose of illustration, each earth station
will be assumed to transmit a 60-channel supergroup. Each 60-channel
supergroup is then frequency modulated onto a carrier which is then
upconverted to a frequency in the satellite uplink band.
Figure 14.2 shows the situation for three earth stations: one in
Ottawa, one in New York, and one in London. All three earth stations

Figure 14.2 Three earth stations transmitting and receiving simultaneously
through the same satellite transponder, using fixed-assignment FDMA.