Since its introduction in the early 1980??s, the Global Positioning System (GPS) has become an important worldwide resource. Although the primary use of GPS is for position location, the inherent timing accuracy built into the system has allowed it become an important synchronisation resource for other systems. In most cases the GPS end user only requires a position estimate without awareness of the timing and synchronisation aspects of the system. A low accuracy position (at the several-metre level) with a low update rate of about 1Hz is often acceptable. However, obtaining more accurate position estimates (at the sub-metre level) at higher update rates requires the use of differential correction signals (DGPS) and greater processing power in the receiver. Furthermore, some extra challenges arise when simultaneously gathering information from a group of independently moving remote GPS receivers (rovers) at increased sampling rates (10Hz). This creates the need for a high bandwidth telemetry system and techniques to synchronise the position measurements for tracking each rover. This thesis investigates and develops an overall solution to these problems using GPS for both position location and synchronisation. A system is designed to generate relative position information from 30 or more rovers in real-time. The important contributions of this research are as follows: a) A GPS synchronised telemetry system is developed to transport GPS data from each rover. Proof of concept experiments show why a conventional RF Local Area Network (LAN) is not suitable for this application. The new telemetry system is developed using Field Programmable Gate Array (FPGA) devices to embed both the synchronising logic and the central processor. b) A new system architecture is developed to reduce the processing load of the GPS receiver. Furthermore, the need to transfer the DGPS correction data to the rover is eliminated. Instead, the receiver raw data is processed in a centralised Kalman filter to produce multiple position estimates in real-time. c) Steps are taken to optimise the telemetry data stream by using only the bare essential data from each rover. A custom protocol is developed to deliver the GPS receiver raw data to the central point with minimal latency. The central software is designed to extract and manage common elements such as satellite ephemeris data from the central reference receiver only. d) Methods are developed to make the overall system more robust by identifying and understanding the points of failure, providing fallback options to allow recovery with minimal impact. Based on the above a system is designed and integrated using a mixture of custom hardware, custom software and off-the-shelf hardware. Overall tests show that efforts to minimise latency, minimise power requirements and improve reliability have delivered good results.
| Identifer | oai:union.ndltd.org:ADTP/257715 |
| Date | January 2008 |
| Creators | Parkinson, Kevin James, Surveying & Spatial Information Systems, Faculty of Engineering, UNSW |
| Publisher | Publisher:University of New South Wales. Surveying & Spatial Information Systems |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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