This thesis is concerned with the modelling of Global Positioning System (GPS) phase multipath. GPS is increasingly used for very high precision (centimetre level) engineering surveying applications such as setting out on construction sites and the control of major civil engineering plant (e.g. bulldozers, graders and pavement layers). In such applications the phase of the carrier signal is the basic observable and the dominant error source is muldpath (electromagnetic reflections of the carrier waves from surfaces in the surroundings of the antennas). The work contained in the thesis has been carried out in collaboration with the LCPC (Laboratoire Central des Ponts et Chaussees) in Nantes, France, which made available its test facility and Leica Geosystems, Heerbrugg, Switzerland, a GPS manufacmrer, which funded the work and which made available modified equipment for testing. The specific subject of the research is the assessment and improvement of the capabilities of a Phase Multipath Mitigation Window correlator (PMMW) to model GPS multipath phase errors. The phase window correlator is a new sampling technique dedicated to the estimation of multipath errors in phase measurements. The thesis contains background material on GPS multipath mitigation and on several existing patents related to the PMMW technique. The main contribution of the work relates to:The rigorous mathematical modelling of multipath, starting from the physics of the phenomenon, right through to the phase measurement process itself, particularly that based on the PMMW correlator. The design of a general testing methodology in a controlled environment to assess the efficacy of multipath mitigation techniques. The carrying out of full-scale experiments at the LCPC in both static and kinematic modes and the assessment of the performances and limitations of the PMMW correlator. Initial investigations into the design of a new real-time correction strategy for phase multipath phase errors based on a combination of multipath observables including the signal-to-noise ratio, the output from the PMMW correlator and an estimation of the code multipath errors from dual frequency phase data. A key feature of the new strategy is its ability to overcome the major limitation of the PMMW technique, i.e. its insensitivity to multipath caused by very close reflectors. It enables the multipath corrupted phase measurements to be improved by 10 % in average in this case, whereas the PMMW corrections on their own had almost no effect.

Wayfinding is a fundamental spatial activity that people experience in their daily lives. Human wayfinding is often assisted by external aids. Recent developments in mobile information and telecommunication technologies are stimulating demand for services that can deliver, to individuals on the move, location-specific information to assist wayfinding. Such services are known as Location-Based Services (LBS). This research aims to investigate the interaction and information transactions between individuals, urban environments and mobile technologies for individuals engaged in pedestrian wayfinding. A novel conceptual model is proposed which explicitly focuses on these interactions and transactions. One of the challenges is to objectively record the overt information transactions and behavioural responses when individuals use mobile technologies for wayfinding in urban settings. Therefore, in this research, an immersive virtual reality approach has been proposed and implemented for capturing data in real-time in a dynamic environment. This test environment integrates three main components: urban VR models that allow individuals to 'walk around' at street level, a mobile device as information source which simulates LBS applications, and software for recording participant actions and reactions within the test environment. Multi-source data were collected regarding movement tracking, information accessed through the mobile device and observations of participants' actions using a combination of automated and semi-automated methods. This has provided a rich data source detailing individual overt behaviour in space and time for pedestrian wayfinding tasks. Contrasting urban models were constructed having their own distinctive layouts and mix of architectures. A series of detailed empirical wayfinding experiments have been carried out using this controlled setting and research design. Detailed analyses, both quantitative and qualitative, are performed on the integrated data sets. One key focus has been on establishing patterns of spatial information usage preferences in terms of types of information, frequency of access, and time spent in consulting the information. A classification of spatial information usage groups has been developed. Characteristics of these groups in terms of their spatial abilities and information usage during wayfinding are explored. It has also been possible to confirm certain effects of urban layout on behaviour and has highlighted key spatial loci for information demand and decision making. An integrated picture of participant behaviour and spatial information preferences is thus constructed through the analyses.

An ever growing demand for ‘location based services’ and the unprecedented growth of wireless local area networks (WLAN) has, in the past few years, attracted the focus of the research community to investigate and develop accurate indoor geolocation systems. Performance of any geolocation system is based upon the reported distance error . The accuracy required varies from application to application. For example an accurate geolocation system is required to apprehend a rogue client (illegitimate connection) inside a building in a dense wireless environment. At present this is possible only through wireless radio frequency (RF) interception of signals. The received signal strength (RSS) of a signal can be used to report the position of a client by triangulation. The hostile indoor environment presents many challenges including multipath and wall attenuation that needs to be considered for determining accurate indoor location. In this thesis a novel method to reduce the variation in RSS values is demonstrated by exploiting the frequency diversity existing across multiple channels of devices equipped with the IEEE 802.11 a/b/g wifi (wireless fidelity) standards. Absorption of the RF signal due to walls is observed and identified as one of the major factors that influence location estimation. RSS from different directions and within different environments is also studied. The processed RSS values are then applied to location estimation using a novel RSS threshold algorithm based upon a RF propagation model. The algorithm is designed based on the room dimensions where location sensors are placed. The algorithm’s main feature is to correctly identify the walls existing between the sensors and client. Correct determination of walls together with a data fusion process produces accurate location results. For a set of example locations, the algorithm gives an accuracy of 3m for 75% of the locations and in terms of mean location error, is shown to be 2.16m for 100% of the locations. The reported accuracy is superior to the most accurate existing systems. The research trend for indoor geolocation has recently focused upon a ‘finger-printing’ technique, which is environment dependant and time consuming. The results achieved and presented in this thesis revive the use of simple propagation modelling for indoor geolocation applications.

No description available.

The European GNSS system Galileo is being designed to operate 30 satellites in MEO. The design of these satellites requires a thorough understanding of the radiation environment. To this end a pair of radiation monitors, CEDEX and Merlin, were carried on the precursor mission GIOVE-A. These collected data on electrons, protons and heavy ions over the nominal mission life of 27 months. This work was aimed at understanding the response of the instruments and therefore understanding the radiation environment in MEO to determine if existing models of the environment are accurate enough for the design of the Ml Galileo constellation.

Global Navigation Satellite Systems (GNSS) have an endless number of applications in industry, science, military, transportation and recreation & sports. Two systems are currently in operation namely GPS (the USA Global Positioning System) and GLONASS (the Russian GLObal NAvigation Satellite System), and a third is planned, the European satellite navigation system GALILEO. The potential performance improvements achievable through combining these systems could be significant and expectations are high. Computer software can be used to simulate the overall process of GNSS (signal transmission and reception) and produce realistic simulated GNSS measurements. Using such simulated measurements, current and future GNSS systems and possible new applications of GNSS can be investigated. Thus data simulation is the perfect research tool in GNSS fields. Oceanography, is one application of GNSS, which requires position determination with a high accuracy. LEO satellites are used to measure the precise height of the sea surface for studying the dynamics of the world's oceans. Achieving maximum benefit from the altimetric data collected by LEO satellites requires a radial orbit accuracy of 10 cm, or better. It is in determining this orbit where GNSS may be utilised. GPS already delivers high quality position information for LEO satellite orbits such as Topex/Poseidon (1992- present). However LEO satellite orbits determination can still benefit from using GPS combined with GALILEO as there will be more visible satellites and a higher quality of measurements. Investigation of LEO satellite orbit determination using GPS or GALILEO or both systems requires GPS and GALILEO measurements. Due to the lack of real GALILEO measurements, as the system is still in development, the simulation of GPS and GALILEO measurements is required. In order to generate realistic simulated GPS and GALILEO data, the errors, which predominate in GNSS measurements, must be accurately modelled. During this research, it has been shown that it is possible to generate realistic simulated GPS data through the more realistic simulation of the ionospheric, tropospheric and multipath delays. Models with a high spatial resolution have been implemented to simulate the real behaviour of the ionosphere and troposphere. The behaviour of the resulting simulated GPS data is shown to follow the behaviour of real GPS data with a strong agreement. It has also been possible to generate GALILEO simulated data through modifying the simulation software using the GALELEO Design technical specifications. The potential impact of using GPS and GALILEO on LEO satellite orbit determination could be investigated on Topex/Poseidon mission which real GPS data was available from the beginning of this study. The performance of GPS, GALILEO, combined GPS/GALILEO and combined GPS-modernised/GALELEO constellations have been investigated in relation to the reduced dynamic orbit determination of the LEO satellite Topex/Poseidon. It can be concluded that the GALILEO constellation will provide high quality real time LEO satellite orbits compared with GPS. GALELEO constellation will provide slightly better quality real time LEO satellite orbits over the combined GPS-present/GALELEO constellation. However the best quality real time LEO satellite orbits will result from the combined GPS-modernised/GALILEO constellation.

The use of genetic methods for the optimisation of propulsion and heading controllers for marine vessels is presented in this thesis. The first part of this work is a study of the optimisation, using Genetic Algorithms, of controller designs based on a number of different time-domain control methodologies such as PID, Sliding Mode, H8, and Pole Placement. These control methodologies are used to provide the structure for propulsion and navigation controllers for a ship. Given the variety in the number of parameters to optimise and the controller structures, the Genetic Algorithm is tested in different control optimisation problems with different search spaces. This study presents how the Genetic Algorithm solves this minimisation problem by evolving controller parameters solutions that satisfactorily perform control duties while keeping actuator usage to a minimum. A variety of genetic operators are introduced and a comparison study is conducted to find the Genetic Algorithm scheme best suited to the parameter controller optimisation problem. The performance of the four control methodologies is also compared. A variation of Genetic Algorithms, the Structured Genetic Algorithm, is also used for the optimisation of the H8 controller. The H8 controller optimisation presents the difficulty that the optimisation focus is not on parameters but on transfer functions. Structured Genetic Algorithm incorporates hierarchy in the representation of solutions making it very suitable for structural optimisation. The H8 optimisation problem has been found to be very appropriate for comparing the performance of Genetic Algorithms versus Structured Genetic Algorithm. During the second part of this work, the use of Genetic Programming to optimise the controller structure is assessed. Genetic Programming is used to evolve control strategies that, given as inputs the current and desired state of the propulsion and heading dynamics, generate the commanded forces required to manoeuvre the ship. Two Genetic Programming algorithms are implemented. The only difference between them is how they generate the numerical constants needed for the solution of the problem. The first approach uses a random generation of constants while the second approach uses a combination of Genetic Programming with Genetic Algorithms. Finally, the controllers optimised using genetic methods are evaluated through computer simulations and real manoeuvrability tests in a laboratory water basin facility.

Στο πλαίσιο αυτής της διπλωματικής εργασίας μελετήθηκε το σύστημα του πλοίου και η απόκρισή του σε διάφορες εισόδους και αναπτύχθηκε κατάλληλη μέθοδο ελέγχου σύμφωνα με τη δεδομένη πειραματική διάταξη. Ο στόχος του ελεγκτή είναι από ένα αρχικό τυχαίο σημείο με αρχικό τυχαίο προσανατολισμό το πλοίο να προσεγγίσει ένα τελικό επιθυμητό σημείο και να σταθεροποιηθεί σε όσο δυνατόν μικρότερη απόσταση από αυτό.Για την επίτευξη αυτού του στόχου υλοποιήθηκε εμπειρικός ελεγκτής πρόσω δράσης. / This thesis adresses the control of a ship vessel. To accomplish this goal, the response of a model vessel to several control actions was recorded and a control algorithm based on this response was developed. The final goal was to approach a desired point on the horizontal plane having started from a random point and having random orientation at the starting point .