Open-loop signal tracking of AltBOC-Modulated GNSS signals
Abstract
Global Navigation Satellite Systems (GNSS) such as the United States' GPS and Europe's upcoming Galileo system provide unique signals-of-opportunity for atmos\-pheric sounding. When a planetary atmosphere occults a radio-frequency (RF) signal, its physical properties cause measurable changes in the signal. Therefore, at any time we can track a GNSS signal that is propagating along a path that intersects the atmosphere, we can measure various properties of the atmosphere along that path. Researchers have successfully demonstrated this radio occultation (RO) technique with GPS signals, and the National Research Council has recommended widespread deployment of RO receivers on future Earth-observing satellites. In the coming years, Europe's new Galileo navigation system's deployment will double the number of GNSS satellites in orbit. An RO receiver that can track both GPS and Galileo signals will be able to observe roughly twice as many RO events, doubling its measurement density in space and time for minimal additional cost. Additionally, open-loop (OL) signal tracking has proven to be an effective method for tracking occulted signals through low altitudes where strong refractivity gradients often overwhelm traditional closed-loop (CL) trackers. The OL method predicts the character of the signal ahead of time and measures the prediction error upon arrival of the actual signal. In contrast, the CL method relies on error feedback to fully characterize the signal in real time. This thesis provides an overview of the Galileo GNSS and its AltBOC-modulated E5 signal, introduces and compares several AltBOC tracking discriminators and develops two prototype RO receivers for E5 employing an open-loop signal tracking approach to decrease the minimum altitude at which we can observe RO events. The Galileo constellation does not yet exist, so it is not possible to test a fully representative RO receiver. To provide initial validation of the E5 OL tracking algorithms, these prototypes—operating from a fixed location on the ground—track signals from the Galileo In-Orbit Validation Element B (GIOVE-B) test satellite and synthesize aspects of OL tracking that would normally require a full GNSS constellation.
Degree
M.S.E.
Advisors
Krogmeier, Purdue University.
Subject Area
Aerospace engineering|Electrical engineering
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