TABLE OF CONTENTS As seen in the preceding section, for small earth stations carrying digital signals at relatively low data rates, there is an advantage to be gained in terms of earth station power requirements by using FDMA. On the other hand, TDMA signals make more efficient use of the transponder because back-off is not required.
Market studies show that what is termed customer premises services (CPS) will make up a significant portion of the satellite demand over the decade 1990 2000 (Stevenson et al., 1984). Multiplexed digital transmission will be used, most likely at the T1 rate. This bit rate provides for most of the popular services, such as voice, data, and videoconferencing, but specifically excludes standard television signals. Customer premises services is an ideal candidate for the FDMA/TDM mode of operation mentioned in the preceding section. To operate in this mode requires the use of signal-processing transponders, in which the FDMA uplink signals are converted to the TDM format for retransmission on the downlink. It also should be noted that the use of signal processing transponders decouples the uplink from the downlink. This is important because it allows the performance of each link to be optimized independently of the other.
A number of signal-processing methods have been proposed. One conventional approach is illustrated in the simplified block schematic of Fig. 14.25a. Here the individual uplink carriers at the satellite are selected by frequency filters and detected in the normal manner. The baseband signals...
