Efficient Adaptive Carrier Tracking for Mars to Earth Communications During Entry, Descent and Landing

In the Mars rover missions the signals transmitted back to Earth travel under low SNR conditions in highly non-stationary channels [1, 2]. During the entry, descent and landing phase (EDL), the spacecraft high dynamics yields severe Doppler effects. We propose a robust and low complexity scheme to estimate and track carrier frequency from the received signals at the Earth end. The method employs a hierarchical arrangement of convex linear prediction cells that is dynamically adapted to respond to the channel conditions. The adaptive combination is able to outperform the best individual estimator in the set, leading to a universal scheme for frequency estimation and tracking. In order to compensate the lag error effect, we explore an efficient forward and backward aggregation scheme that improves considerably the frequency RMS error as compared to the original method [3].