Optimized carrier tracking loop design for high dynamic and low CNR conditions

Abstract

The carrier tracking loop face extreme difficulty in entering a locked-in state for high dynamic and low carrier-to-noise ratio (CNR) environment. To address this issue, this paper presents an improved Frequency-Locked Loop (FLL) serially assisted Phase-Locked Loop (PLL). The improved carrier tracking loop design consists of a high-dynamic frequency discriminator and a high-dynamic loop filter based on second-order FLL serially assisted third-order PLL. In particular, this proposed frequency discriminator executes an adaptive switching mechanism between the maximum likelihood estimation (MLE) discriminator and the conventional frequency discriminator. Once the Doppler frequency estimation error begins to accumulate, the MLE discriminator will be selected which can pull the Doppler frequency into the working range of the conventional frequency discriminator. Thus, a wider pull-in range can be obtained to provide good frequency discrimination capabilities under high dynamic conditions. The experimental results and comparative analysis demonstrate that the improved FLL serially assisted PLL can achieve an improved tracking performance under high dynamic and low CNR conditions.