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Abstract
Global Navigation Satellite System’s (GNSS) known shortcomings in difficult radio-environments – signal obstructions and jamming vulnerability – could pose significant risks in critical location based services (LBS) applications. Off-the-shelf systems such as ‘Spot Satellite Messenger’ are not compliant for E911 and other emergency response requirements. Despite considerable research and engineering efforts, few techniques have demonstrated promising results. Multiple sensor-based techniques and systems based on Assisted-GNSS (AGNSS) have been proposed in order to improve the performance of stand-alone GNSS. Improved time-to-first-fix (TTFF), system availability and positioning accuracy are the notable performance gains.
Many AGNSS techniques employ proprietary protocols which limit further academic research or pre-deployment testing. The Open Source GNSS Reference Server (OSGRS) – on the other hand uses a Hyper Text Transfer Protocol (HTTP) based stateless GNSS Reference Interface Protocol (GRIP). For the research described in this thesis, a hardware based GNSS receiver was first used to acquire assistance data. Subsequent versions of OSGRS have seen alternative acquisition approaches using numerous GNSS Casters available over Internet Protocol. A variety of data formats are available, hence OSGRSv2 is capable of Multiple Assisted GNSS (MAGNSS). Client and server integration, testing and performance benchmarking against competing technologies appeared promising. The system tracked the highest number of satellites, availability and higher accuracy with low TTFF values. Three configurations of multi-GNSS assistance servers allow flexible operation independent of the presence of Virtual Private Networks (VPNs) – a limitation of OSGRSv1.
Iteratively, the server has been augmented with Long Term Evolution (LTE) Positioning Protocol (LPP) and the associated extensions (LPPe) to develop the third generation OSGRSv3. Interconnection of multiple networks is provided through Internet Protocol (IP) data control gateways for user-specific information exchange. Assistance Model Portfolio of OSGRSv3 has been expanded with the development of mobile communications interworking criteria. A real network implementation in a controlled mobile network laboratory has been configured. The architecture exploits LTE Radio Access Network (RAN), Transmission, Core and GNSS elements to test the performance of the system. Performance graphs demonstrate that Radio Resource Location Protocol (RRLP) based system lowered the TTFF and improved the satellite availability and positioning accuracy over OSGRSv1 or OSGRSv2. Options of selectively choosing which GNSS to use is managed through a source selector switch.
Presence of basic networking infrastructure has been a critical limitation of Multiple Assisted GNSS systems. A low infrastructure strategy to augment GNSS with adhoc Wireless Sensor Nodes (WSN) has been presented. Pre-programmed fixed sensor nodes are deployed in the test area where a rover sensor node is connected to a GNSS-capable mobile device. Based on the received signal strength, signature indices are generated and autonomous proximity calculations of the rover are performed. The localization information is transferred to GNSS via assistance messages. Experiments were conducted to simulate a reduction in navigation search space, competitive TTFF and improved availability and accuracy. Link quality indicators can effectively provide pre-processed frequency offset, range and coordinate assistance in the absence of IP network, in building coverage (IBC) repeaters or GNSS. Stand-alone sensors based localization demonstrated cm-level accuracy, response sensitivity and reliability. System robustness against partial node malfunction in instances of clocking, time syncing, thermal noise, coordinate decoding and processing issues, was observed. Such errors can arbitrarily eventuate in erroneous localization.
Reference Server, Caster and Sensor Networks and MAGNSS can provide cost effective alternatives for generic and specific AGNSS localization applications. The contributions of this thesis can be summarized as follows:
a. GPS, GNSS, AGNSS, RNSS, SBAS and alternative positioning technologies have been reviewed. Several LBS variants have been investigated and shortcomings listed. Alternative navigation, communication and logging techniques have been suggested to BWRS, NSW Police and the VRA. SPOT GNSS Messenger has been performance evaluated. Architecture for a Multiple Sensor based hybrid Multi-GNSS has been developed.
b. An NTRIP capable OSGRS has been developed. System efficiency has been improved and the system has been integrated with an IP and mobile data network. Several configurations of the OSGRS have been developed to suit varying scenarios. Such configurations have been performance tested and benchmarked.
c. OSGRSv3 has been developed by upgrading the previous version of server. The system has been augmented with SMLC, GMLC, RRLP 3GPP LPP and OMA LPPe functionality. Performance of the OSGRSv3 vis-à-vis the OSGRSv2 has been evaluated. The design and architecture of the OSGRSv4 has been developed.
d. An autonomous positioning method employing the WSN-enabled AGNSS has been developed and tested. The stand-alone WSN-based positioning method which can mitigate the associated communication, energy-cycle and radio limitations has been developed and employed to benchmark the WSN-enabled AGNSS.