A State-Based Method to Jointly Estimate Code Delay and Carrier Phase of Short Segment GNSS Signals Using Complex Waveforms from Open-Loop Tracking: A Simulation Study

This paper presents a complex waveform filtering (CWF) algorithm to jointly estimate dual frequency code delays and carrier phases directly using complex correlation values from short segments of global navigation satellite system (GNSS) open-loop (OL) tracking output. Compared to the code delay, carrier phase measurements have higher precision and are used in high-accuracy navigation and remote sensing applications. However, carrier phase measurements are prone to cycle slips and have integer ambiguity that needs to be resolved. To resolve the integer ambiguity and mitigate cycle slips, pseudorange leveling method is often used but requires a relatively long averaging time to suppress the code delay noise. This limits the use of short phase-coherent data segments which are prevalent under challenging conditions when signals have low signal-to-noise ratio or high phase dynamics. Examples include signals propagating through the ionospheric irregularities, moist troposphere, urban/indoor environment with rich multipath effects, or signals transmitted from or received on low Earth orbiting (LEO) satellites. Carrier phase filtering algorithms such as the simultaneous cycle slip and noise filtering (SCANF) algorithm can mitigate cycle slip and suppress the noise to some extent, but they use phase measurements from only one correlation value. The CWF algorithm takes all complex correlation values generated from an OL tracking as input and uses short segments of precise phase measurements to assist the filtering of code delay. This paper presents simulated correlation values to assess the precision and bias of the carrier phase estimations for CWF and SCANF algorithms. We also present a case study using short segments of actual GNSS reflection signals collected on a low Earth orbiting (LEO) platform. Future refinement of the CWF algorithm is also presented.