Channel capacity extension via FDMA/PSK/DSI

The paper studies an FDMA system which uses phase-shift keyed carriers with digital speech interpolation (DSI) of the input voice channels for use in the Intelsat IV-A system. The system is expected to provide the following advantages: (1) a channel capacity advantage of approximately 2:1 over FDMA/FM/FDM due to DSI; (2) compatibility with FDMA/FM/FDM signals in a transponder; (3) selective transition to either an all-digital or a mixed FM and digital system; (4) operation requiring neither network synchronization nor coordination on a global basis; (5) partial reuse of equipment for future TDMA operation through proper design; (6) low risk entry into digital operation; and (7) a tradeoff between DSI and coding gains and G/T in small earth terminal applications.