Autonomous power control algorithms for non-geostationary mobile satellite systems

The power control loop in a mobile satellite system is a regulatory type time-delay system. The aim of the receiver based controller is to compensate the channel gain disturbance and maintain a constant level of received signal strength. The investigation presented in this paper reports on the comparative performance of two power control algorithms. The rival policies are based on classical and predictive control methodologies respectively. The control schemes are appraised by observing their ability at compensating the propagation channel components such as diffuse and specular multipath. The paper also examines the effects of the time-delay within the control loop, which is due to the roundtrip delay of the considered satellite system. Computer simulations of the two algorithms reveal that the predictive scheme yields a superior performance. It is able to converge onto the cyclic specular fades by forward predicting the local mean of the channel gain signal. In comparison, the linear phase-lag integral controller suffers from amplification of the uncontrollable fast frequency components and so the power control error is high. Both control policies are severely limited by the amount of time-delay present within the control loop. Consequently, the quality of control at the LEO delay is markedly better than at the MEO delay.