A method for the numerical representation of the nonlinear properties of amplifiers is developed. It is designed for use in computer models, and results in efficient and accurate computation of important properties of the output signal for a wide range of input signals. The single-carrier nonlinear transfer characteristic is split into two parts, one of which is chosen for analytical convenience and the other of which is approximated over a finite interval by a Fourier-Bessel expansion. Numerical values for a typical traveling wave tube are included in the paper; these values can be used as a basis for simulation programs for satellite communication systems.

The output EIRP or the available bandwidth of a satellite in general limits the amount of traffic which can be handled by SATCOM systems. As the frequency congestion drives future SATCOM systems to higher frequencies, the former constraint will be the more important one because of the severe fades caused by precipitation. Rather than using fixed fade margins, the link power can be dynamically allocated from a common pool of satellite EIRP. By judicious, adaptive allocation of the satellite EIRP among the various users, the traffic supported can be maximized while maintaining the link availability. This paper reports techniques and statistical results of four different ways of allocating the EIRP. By using adaptive centralized control of the terminals transmit power and a variable satellite transmit antenna adaptively controlled by ground commands to compensate for link fades, most efficient use of the satellite EIRP is made. The performance of this technique is derived and compared with others of less complexity and that of a system with fixed satellite antenna and transmit power levels.

A dynamic mathematical model of rain attenuation has been developed and is presented in this paper. This model permits the expression of analytic relationships between parameters commonly used to describe the properties of interest for communication. The dynamic model is based on the lognormal distribution of rain attenuation and utilizes a memoryless nonlinear device to transform attenuation and rain intensity into a one-dimensional Gaussian stationary Markov process. Hence, only one parameter is required to introduce the dynamic properties of rain attenuation into the model. Experimental results and the known properties of rain have been used to derive and to verify the model; comparative results are presented and demonstrate good correspondence. The application of the model to the statistical analysis of the performance of communications systems is illustrated in the paper. The use of a dynamic rain attenuation model is necessary in order to analyze radio communication systems with transmit power control to offset the effects of rain attenuation, and where the finite response time of the control system affects the performance. An advantage of the model is the simplicity with which it allows simulation of communication link performance under the influence of rain attenuation. Such simulations are of great interest for complex models of adaptive networks where several deteriorating effects, including finite response times, are present.