Pseudorange bias from inter-signal interference: the QZSS L5-L5S case

Analysis of the bias between Quasi-Zenith Satellite System (QZSS) L5-Q and L5-I pseudoranges reveals decimeter-level variations over the satellite passes, a phenomenon that is not observed on any other GNSS signal. The paper provides a study of this QZSS peculiarity. It is shown that the bias depends on the orientation of the line-of-sight vector with respect to the transmit antenna panel of the QZSS satellite, and that the amplitude of its variation is satellite dependent. The cause of the L5 bias is identified as interference from the L5S signal transmitted by QZSS satellites at the same frequency and from a different antenna. The interference introduces a distortion of the correlation peak dependent on the primary and secondary code selected for the L5 and L5S signals and on the relative delay and phase between the received L5 and L5S signals. This distortion induces tracking biases affecting pseudoranges produced using the pilot signal component. A theoretical model of the interference is provided, and it is shown that the bias variation can be accurately modeled and compensated for if L5 and L5S measurements are available.