ABSTRACT
This chapter focuses on propagation effects on navigation signals. It reviews the fundamentals of propagation effects relevant to Global Navigation Satellite Systems (GNSS), including state-of-the-art modeling and characterization for ionospheric, tropospheric, and environmental effects. Signals from the modern GNSS are based on direct-sequence spread spectrum, based on high symbol rate pseudorandom sequences modulated with a given spreading shape. Applications based on GNSS positioning for difficult environments, such as urban canyons, indoor environments, or forests, requires a rigorous modeling of the electromagnetic radio channel in order to be able to assess receiver performances in controlled laboratory conditions with respect to their target conditions. In order to estimate the ionospheric delay contribution using GNSS observations, dual-frequency observations are required since the ionosphere is a dispersive media. For GNSS single-frequency receivers, correction algorithms based on empirical or climatological models are driven by broadcast parameters in the navigation message.
