Investigating Delay Compensation within the Context of Frequency-Aided PLL

The transition from analog GNSS receivers to digital ones has spurred the emergence of various GNSS baseband signal processing algorithms. Among these, Frequency-aided PLL has been widely investigated in different forms, including FLL-assisted PLL, VFLL, etc. Great contributions have been made in the practical implementation and evaluation of different forms of Frequency-aided PLLs, but the impact of frequency aid information delay has not been thoroughly analyzed quantitatively. To date, only preliminary impact analysis in S domain is available in few literature sources. This paper mainly addresses the problem in Z domain that is more aligned with practical implementations. Two distinct types of Frequency-aided PLL are firstly proposed and a quasi-FLL-assisted PLL considering the frequency aid delay is chosen to be analyzed. Additionally, delay compensation is also derived using the Controlled-Root method to counteract the impact of delay, providing a valuable insight into the problem of frequency aid delay in other models.