Space-Time Processing Methods to Enhance GNSS Signal Robustness under Electronic Interference

Abstract

Open access GNSS signals have enabled the development of receivers that find their use spanning multitude of user segments. Owing to the long distance travel from the satellite to the user, the received signal level is very weak on or near earth. This is due to the free-space loss and, to a small extent, atmospheric losses. The signals arriving at the RF front-end can be affected by the presence of signals from other communication systems. Since GNSS has to coexist with other such systems, it is not abnormal to expect that even in normal operations, receivers experience interference. Additionally, undesirable signals can appear in the GNSS frequency band due to other man-made high power signal transmissions. The levels of these disturbing signals will determine the impact that they may have on the performance metrics of the receiver. Antenna array processing techniques are studied in GNSS as effective tools to mitigate interference in spatial and spatiotemporal domains. Analyzing the performance of array based mitigation methods involves many challenges, such as prohibition to propagate test interference signals and the challenge involved with the design and execution of cost-effective experimental setups. To reduce this burden, a new approach is proposed and developed and tested herein. Without specific filter design considerations, the array space-time processing (STP) results in distortions. This research also focuses on characterizing these degradations for different controlled signal scenarios and for live data from an antenna array. The capability of antenna array STP to mitigate the interference from near zone pseudolites and provide subsequent enhancements is studied in the latter part of the thesis. An array simulator is developed during the research and is effectively used for assessing STP measurement distortions. The characterization results show that distortions due to STP are significant and can lead to erroneous pseudorange measurements. From the simulation results, it is concluded that the antenna array STP methods are beneficial for interference mitigation in GPS-pseudolite combined signal environments.