GPS L1CA/BDS B1I Multipath Channel Measurements and Modeling for Dynamic Land Vehicle in Shanghai Dense Urban Area

Global navigation satellite system multipath channel modeling is important for signal simulation and error mitigation in urban scenarios. However, there have not been sufficient studies on channel statistical models for dynamic land vehicles in eastern Asian cities. This paper presents both MULTIPATH and non-line-of-sight (NLOS) channel models for GPS L1CA and BDS B1I signals. They are based on an extensive field dataset collected in the Shanghai-Lujiazui area. In addition, a method is developed to estimate multipath components and NLOS signal parameters in a dynamic channel environment. It is found that the Gamma function best fits the distribution of MULTIPATH channel delays while the exponential function is better suited for the distribution of NLOS channel delays. Both MULTIPATH and NLOS channel signals follow a linear decline average power-delay trend and a zero-mean Gaussian distribution power scattering model. The Doppler fading frequency distribution for MULTIPATH and NLOS channels can be modeled by the Gaussian function except for the MULTIPATH channel signal at the low velocity range (0∼3 km/h), where an absolute exponential distribution is a better fit. The lifetime distribution for MULTIPATH and NLOS channels is represented by the generalized Pareto distribution function. These findings offer insights into the GNSS signal models in urban propagation channels and are essential to the development of accurate urban navigation systems.

I. Introduction

Amajor challenge imposed in urban environments to global navigation satellite system (GNSS) receivers is the multipath interference caused by the addition of reflected signals from nearby objects, thereby resulting in significant range measurement errors and ultimately positioning errors. There are three multipath effects, i.e., reflection, diffraction, and scattering, based on the physics of the signal interactions with an object in the signal propagation channel. Reflection occurs when an electromagnetic wave impinges on an object that has a large dimension compared to the wavelength of the propagating wave. Diffraction occurs when the radio path between the transmitter and the receiver is obstructed by a surface that has sharp edges. If the dimensions of reflection objects are smaller compared to the wavelength, scattering usually happens [1]–[3]. Each multipath component has a certain amount of delay when compared to the line-of-sight (LOS) signal, and the strength of this delayed signal depends on the reflection coefficient of the surface and the amount of excess delay. The carrier frequency of the multipath signal is possibly different from that of the LOS signal. This difference is termed the multipath Doppler fading frequency, or fading frequency for the sake of simplification. The fading frequency is caused by the relative geometry change between the satellite, reflector, and receiver due to the movement of receiver and satellite.