On-Board Signal Acquisition Strategies for Deep Space Transponders

On-board signal acquisition is a fundamental task for deep space missions when telecommand and/or ranging functions must be implemented Local oscillator frequency instabilities and Doppler contribution cause a frequency offset of the carrier at the receiver input. Two different strategies to allow carrier loop acquisition are reported and compared: on-ground sweeping and on-board frequency aided acquisition. A trade-off based on the acquisition time and the acquisition probability addresses the on-ground sweeping procedure as less efficient with respect to the frequency aided solution for the case of weak signal and wide frequency offset. As regards frequency aided acquisition, two different frequency estimation algorithms are considered, one is based on the classical Fast Fourier Transform (FFT), the other one on an Auto Regressive (AR) Estimation for power spectrum evaluation. Theoretical evaluations via analysis and simulation are proposed together with the experimental results obtained both on the Ka Translator for the Cassini mission and the Huygens Receiver for the Cassini-Huygens mission.