36. BeiDou Satellite Multipath Characteristics Research-From the “Micro” Parameters Point of View

Multipath is one of the most important factors that affect the positioning accuracy of GNSS receivers. Traditionally, the Code-Minus-Carrier Multipath Observable (CMO) is used to study the characteristics of GPS multipath errors, which takes on period fluctuations. However, BeiDou System comprises of three types of satellite—MEO, IGSO and GEO, the orbits of which differ a lot with each other. The standing multipath observed in GEO multipath causes the fluctuation phenomenon obscure, making the research with CMO technique hard to continue. Up till now, only a few literatures focused on studying the characteristics of multipath ‘micro’ parameters like delay, attenuation, carrier phase and number with real-world signal data. Those parameters indeed reflect the behavior of multipath more straightforward. Therefore, the Code Amplitude Delay Lock Loop (CADLL) technique is used at this paper to decompose the multipath at its signal parameter level. The experiment results reveal that even the GEO multipath can also vary slowly because of the satellite perturbation. The GEO multipath fading period can be a few hours. However, the IGSO and the MEO multipath do not show much distinct difference. The specular multipath fading period of both IGSO and MEO is normally a few minutes, while the diffused multipath parameters take on steady behavior but last very short time. It is found as well that the multipath signal of all kinds of satellites bears the nature of limited existing time. Thus, the concept of multipath life-time is proposed in this paper to describe the statistical distribution of multipath lasting time as well as the multipath power variation feature during its life-time. Those models are useful for simulator design to emulate more precise multipath scenario.