JultikaUniversity of Oulu repository

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.