Frequent loss or attenuation of signals in urban areas and integrity (or reliability of
system performance) are two principal challenges facing the Global Navigation Satellite
Systems or GNSS today. They are of critical importance especially to safety or
liability-critical applications where system malfunction can cause safety problems or has
legal/economic consequences. To deal with the problem of integrity, algorithms called
integrity monitors have been developed and fielded. These monitors are designed to
raise an alarm when situations resulting in misleading information are identified. However,
they do not enhance the ability of a GNSS receiver to track weak signals. Among
several approaches proposed to deal with the problem of frequent signal outage, an
advanced GNSS receiver architecture called vector tracking loops has attracted much
attention in recent years.
While there is an extensive body of knowledge that documents vector tracking’s
superiority to deal with weak signals, prior work on vector loop integrity monitoring is
scant. Systematic designs of a vector loop-integrity monitoring scheme can find use in
above-mentioned applications that are inherently vulnerable to frequent signal loss or
attenuation. Developing such a system, however, warrants a thorough understanding of the workings of the vector architecture as the open literature provides very few
preliminary studies in this regard.
To this end, the first aspect of this research thoroughly explains the internal
operations of the vector architecture. It recasts the existing complex vector architecture
equations into parametric models that are mathematically tractable. An in-depth
theoretical analysis of these models reveals that inter-satellite aiding is the key to
vector tracking’s superiority.
The second aspect of this research performs integrity studies of the vector loops.
Simulation results from the previous analysis show that inter-satellite aiding allows easy
propagation of errors (and faults) among satellite loops in vector tracking mode. Hence, the basic single fault requirement of the traditional Receiver Autonomous Integrity
Monitoring or RAIM is violated with the pseudorange measurements of the vector
architecture. This work develops a vector loop RAIM scheme that addresses above
limitation. The designed vector loop RAIM algorithm is validated via a high fidelity
simulation of an aircraft making an instrument approach.
University of Minnesota Ph.D. dissertation. April 2012. Major: Aerospace engineering. Advisor: Demoz Gebre-Egziabher. 1 computer file (PDF); xi, 235 pages, appendices A-D.
Performance and integrity analysis of the vector tracking architecture of GNSS receivers.
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