Improvements in capacity of analog voice multiplex systems carried by satellite

Significant improvements in the voice capacities of satellite transponders have been made in the last few years. A major emphasis has been in improving the voice channel capacities of TDMA using techniques such as ADPCM and DSI. In domestic satellite systems, however, analog transmission of speech signals continues to be used heavily. This paper describes how the capacity of analog FDM-based systems has been improving in the last decade. The capacity improvements are made possible by the use of syllabic compandors. Using compandors, the capacity of a transponder can be increased by nearly threefold if the RF modulation is FM, and can be increased by sixfold if the RF modulation is SSB-AM. The latter is made possible by the availability of more linear satellite amplifiers and the realization that the average speech volumes are much lower than what are traditionally assumed.