Adaptive Sweeping Carrier Acquisition and Tracking for Dynamic Links with High Uplink Doppler

Abstract

In this paper, we propose an adaptive sweep signal acquisition and tracking algorithm that (1) takes into account high-order uplink signal dynamics (Doppler shift, Doppler rate, Doppler acceleration), (2) dynamically adapts the carrier search direction (positive or negative in frequency error) and (3) dynamically adapts the carrier search step. The combination of (2) and (3) are the main innovation of this paper, since radios do not need to restart at its initial search state when the carrier is missed. This, in turn, minimizes the time required for carrier lock and thus makes the system more robust to the loss of lock failures. Note that the proposed system improves upon the frequency sweeping algorithm used in current flight radios (e.g., JPL's Electra and IRIS) which use constant search direction and search step. There are three motivating applications for our proposed system: Proximity links at Mars or the Moon, support of Multiple Access per Antenna at the Deep Space Network, and generation of Doppler measurements for navigation purposes. As indicated later in the paper, all these scenarios require spacecraft to establish highly dynamic links for which no Doppler compensation can be performed on the ground. Therefore, the receiver's ability to properly acquire and track the received carrier is paramount for transfer of information, relative positioning and navigation.