Single Channel Per Carrier Satellite Repeater Channel Capacity

This paper analyzes the performance of a number of modulation and speech processing techniques that have been considered for single voice channel per carrier transmissions via satellite. This transmission mode is applicable to demand assignment systems, which make possible the most efficient loading of the satellite transponder in applications where the traffic at individual Earth terminals is not sufficient to justify a substantial number of dedicated channels. The analysis basically determines the operating point for the satellite transponder which minimizes the required Earth terminal G/T. The fraction of the total link noise allocated to uplink noise is treated as a parameter, so that the cost of improving G/T may be traded against the cost of providing increased Earth terminal transmitter power. Both analog and digital modulation techniques are considered, together with various practical combinations of syllabic companding, voice-actuated carriers, and error-correcting codes. The results are presented in general analytic form, applicable to any modulation technique for which carrier-to-noise density ratio, channel width, and guardband width may be specified. Curves showing required G/T as a function of the total number of voice channels per transponder are also presented for the above-mentioned signal processing techniques, assuming "CCIR/CITT type" speech quality and transponder EIRP and bandwidth typical of current domestic satellite configurations.