Effect of shadowing and diffraction on the received GNSS signal

Abstract. The characteristics of the GNSS received signal depend on the propagation medium environment. Typically, the transmitted signal interacts with several numbers of obstacles which leads to the multipath propagation to receiver end. In such cases, diffraction over the edges or wedges of the obstacles in the propagation path should be considered. The effects of diffraction and shadowing are the important elements in radio wave propagation because of their strong influence on the received signal quality. Especially, received signal strength and characteristics are very significant for GNSS applications. This master’s thesis investigates the effect of knife-edge diffraction model and shadowing environment on the received GNSS signal. Characterization of the received signal is investigated both theoretically and experimentally. In the measurement, a dual circular polarized antenna has been used to receive the multipath GPS signal in the shadow region in which antenna was placed in the zenith direction. The measurement was performed for two scenarios 1) the receiver was in the static position, and 2) in motion for the second measurement. Measurement results show that, the received signals following the Knife-edge diffraction pattern for both measurements case. In the first measurement case, knife-edge diffraction has been identified in received signal attenuation whereas the interference pattern in the LoS propagation can be observed because of multipath effect. In the deep shadow region, a linearly polarized signal has been received in both antennas because the incident RHCP signal turned into a linearly polarized signal after diffraction. For the second measurement case, knife-edge attenuation pattern is also visible. A clear agreement between the measured and theoretical aspects has been achieved in the case of knife-edge diffraction

Transient convection flow in super-imposed fluid and porous layers

This paper is aimed at investigating the effects of combined Marangoni and Rayleigh convections in a porous layer, underlain by a fluid layer. The two-dimensional transient numerical model represents a dual rectangular cavity system in which the porous cavity is located below the fluid cavity. Both cavities are saturated with hexane. The problem consists of studying the combined Marangoni and Rayleigh effects on the flow. The interaction between the Marangoni and the Rayleigh convection is investigated in detail. The porous cavity is heated at the bottom while the top liquid cavity has a free surface and is maintained at a room temperature. In addition, the role of the aspect ratio of the porous layer over the fluid layer in determining the convection pattern was studied. Results indicate that the Marangoni convection enhances the flow in the porous layer for high aspect ratio while the Rayleigh number suppresses the Marangoni convection at the free surface for a low aspect ratio. At a critical aspect ratio above 3, the Marangoni convection becomes dominant over the Rayleigh convection in the liquid layer. Copyright © 2000 Society of Automotive Engineers, Inc.SCOPUS: cp.jinfo:eu-repo/semantics/publishe