High Precision Uplink Time and Frequency Calibration in Cognitive Space Communications

Being cognitive is important to future space communications for improved energy and spectrum efficiency. A fundamental challenge therein is calibrating timing and frequency offsets brought by the long distance and rapid relative movement between communications satellites and ground terminals. In this work, we proposed a high-precision time and frequency calibration algorithm for communications between satellites and ground user terminals, with the ideas of recursive short-term satellite state prediction and iterative transmitting time and frequency calculation. The proposed method models and corrects the bias of satellite position and velocity prediction, and improves the precision of transmitting time and frequency calibration. Simulations are conducted for different types of satellite orbits, and the results show that the proposed calibration method significantly outperforms existing methods.