Tandy, Michael J. (2011) Ambiguity resolution of single frequency GPS measurements. PhD thesis, University of Warwick.

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Abstract

This thesis considers the design of an autonomous ride-on lawnmower, with particular
attention paid to the problem of single frequency Global Navigation Satellite System
(GNSS) ambiguity resolution.
An overall design is proposed for the modification of an existing ride-on lawnmower for
autonomous operation. Ways of sensing obstacles and the vehicle's position are compared.
The system's computer-to-vehicle interface, software architecture, path planning
and control algorithms are all described. An overview of satellite navigation systems is
presented, and it is shown that existing high precision single frequency GNSS receivers
often require time-consuming initialisation periods to perform ambiguity resolution.
The impact of prior knowledge of the topography is analysed. A new algorithm is proposed,
to deal with the situation where different areas of the map have been mapped
at different levels of precision. Stationary and kinematic tests with real-world data
demonstrate that when the map is sufficiently precise, substantial improvements in
initialisation time are possible. Another algorithm is proposed, using a noise-detecting
acceptance test taking data from multiple receivers on the same vehicle (a GNSS com-
pass configuration). This allows a more demanding threshold to be used when noise
levels are high, and a less demanding threshold to be used at other times. Tests of this
algorithm reveal only slight performance improvements. A final algorithm is proposed,
using Monte Carlo simulation to account for time-correlated noise during ambiguity
resolution. The method allows a fixed failure rate configuration with variable time,
meaning no ambiguities are left floating. Substantial improvements in initialisation
time are demonstrated.
The overall performance of the integrated system is summarised, conclusions are drawn,
further work is proposed, and limitations of the techniques and tests performed are
identified.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	T Technology > T Technology (General)
Library of Congress Subject Headings (LCSH):	Global Positioning System, Autonomous robots, Algorithms
Official Date:	April 2011
Institution:	University of Warwick
Theses Department:	Warwick Manufacturing Group
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Young, K. (Ken)
Sponsors:	Engineering and Physical Sciences Research Council (EPSRC); Ransomes Jacobsen Ltd.; Warwick Innovative Manufacturing Research Centre
Extent:	xvii, 177 leaves : illustrations.
Language:	eng

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