Application of open-loop uplink power control in Ka-band satellite links

Propagation impairments impose a limit on the use of the 20/30-GHz frequency band for satellite communication applications. Power control is one of the techniques that can be used to mitigate such impairments. Results of an experiment conducted using the Advanced Communications Technology Satellite (ACTS) to evaluate the efficacy of open-loop uplink power control are presented. A power control system is required to maintain the power flux received at the satellite at a constant level irrespective of the fading along the propagation path. The control parameter for the power controller was derived from the fading and enhancements observed on a downlink beacon signal thus requiring frequency translation of the propagation effects to the uplink frequency. In this scheme, the controller performance is largely a function of the frequency translation accuracy, which is determined by the prevailing propagation conditions. In addition, equipment-induced variations in the control parameter can produce power control errors. To maintain the control accuracy within reasonable limits, an algorithm that can differentiate various propagation factors as well as equipment effects was devised. It was found that under most conditions, the power control accuracy could be maintained within ±2.5 dB