High-Precision Carrier Tracking Algorithm for Extremely Weak and High-Dynamic Signals

Obtaining high-precision Doppler frequencies for very weak and high-dynamic signals in deep space exploration is challenging. Such signals are commonly encountered, including in soft landing of lunar probes and the entry, descent, and landing (EDL) phase of Mars probes. Phase-locked loop (PLL) is a widely used method for measuring high-precision Doppler frequencies. In this study, two major improvements are applied to PLL. The first is that high precision estimation of initial frequency is achieved by open loop maximum amplitude search algorithm. Second, a novel denoising method is proposed and a new type of phase detector is designed based on this new denoising method. By replacing arctangent phase detector with the novel phase detector, the tracking accuracy and weak-signal tracking abilities of the PLL are improved. The actual data processing results of soft landing process of lunar probe further verify the excellent performance of the improved PLL.