Comparison of modulation methods for multiple-access synchronous satellite communication systems

Single-sideband modulation, multicarrier phase modulation, interleaved-pulse p.c.m., multicarrier p.c.m. and asynchronous p.c.m. are considered as possible modulation techniques. Fluctuation-noise and intermodulation-noise effects are analysed to derive comparative performance curves. A subjective comparison of performance and of technical problems is made. It is observed that, for systems having only one power-limited transmitter, bandwidth expansion by p.c.m. is less effective in reducing fluctuation and intermodulation noise than volume companding of the analogue voice signal. In addition, timing problems associated with interleaved-pulse systems appear beyond the state of the art. It is recommended, therefore, that attention be given to the development of improved volume compandors so that flexible, high-capacity, multiple-access systems using single-sideband modulation can link existing common-carrier ground networks without noticeable service degradation.