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Optimization of system design parameters, such as onboard antenna diameter, number of beams, and number of onboard transponders, is of great importance to decide system capacity of subscribers in a multi‐beam mobile satellite communication system. This paper describes an optimization method of important system design parameters to maximize system capacity of subscribers under limited weight budget and dissipation power of satellite mission and limited service area. First, the concept of aquivalent weight, which is defined by a linear combination of weight and dissipation power of satellite mission is proposed. Next, the optimization of above design parameters, giving the maximum system capacity of subscribers, is made under the constant equivalent weight of the total satellite mission. As a result, it is found that the optimized conditions are simply expressed and universal.

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In SCPC satellite systems intermodulation (IM) noise is generated due to transponder nonlinearity. It is known that this noise can be reduced by proper signal frequency allocation. In the conventional method the signal frequencies are allocated at integral multiples of a basic interval, that is, the minimum signal frequency separation. This paper is concerned with offset frequency allocation in which the signal frequencies are not necessarily integral multiples of a basic interval. Specifically, the IM noise power spectrum is analyzed for 2‐phase PSK signals and studies are made for the IM power reduction characteristics after passing the receiving filter, specific signal frequency allocations with reduced IM noise and IM noise improvement over equal‐interval frequency allocation. Also, starting with the Babcock allocation, offset frequency allocations are derived and their IM characteristics and frequency bandwidth are evaluated.

Mobile satellite communication systems employ the wide area accessibility of a satellite. Digital signal transmission systems which enable communication by highly efficient voice encoding techniques and error correcting techniques, even on low C/N channels, are being studied and developed in many countries. This paper studies error rate monitoring for application to antenna tracking control and transmitting power control in mobile satellite communication systems. A soft decision error correction method, which is expected to be available in a wide range of C/N, is proposed and its performance is clarified theoretically and experimentally. Considering the application to ship antenna tracking control, the monitoring accuracy on fading channels is evaluated experimentally. A simulation experiment is carried out for an electronic tracking control with switching arrays, and the reception level degradation due to tracking error is clarified. Simulation results of transmitting power control against rain attenuation are also given.