Automotive applications of high precision GNSS

This thesis aims to show that Global Navigation Satellite Systems (GNSS) positioning can play a significant role in the positioning systems of future automotive applications. This is through the adoption of state-of-the-art GNSS positioning technology and techniques, and the exploitation of the rapidly developing vehicle-to-vehicle concept. The merging together of these two developments creates greater performance than can be achieved separately. The original contribution of this thesis comes from this combination: Through the introduction of the Pseudo-VRS concept. Pseudo-VRS uses the princples of Network Real Time Kinematic (N-RTK) positioning to share GNSS information between vehicles, which enables absolute vehicle positioning. Pseudo-VRS is shown to improve the performance of high precision GNSS positioning for road vehicles, through the increased availability of GNSS correction messages and the rapid resolution of the N-RTK fixed solution. Positioning systems in the automotive sector are dominated by satellite-based solutions provided by GNSS. This has been the case since May 2001, when the United States Department of Defense switched off Selective Availability, enabling significantly improved positioning performance for civilian users. The average person most frequently encounters GNSS when using electronic personal navigation devices. The Sat Nav or GPS Navigator is ubiquitous in modern societies, where versions can be found on nomadic devices such as smartphones and dedicated personal navigation devices, or built in to the dashboards of vehicles. Such devices have been hugely successful due to their intrinsic ability to provide position information anywhere in the world with an accuracy of approximately 10 metres, which has proved ideal for general navigation applications. There are a few well known limitations of GNSS positioning, including anecdotal evidence of incorrect navigation advice for personal navigation devices, but these are minor compared to the overall positioning performance. Through steady development of GNSS positioning devices, including the integration of other low cost sensors (for instance, wheel speed or odometer sensors in vehicles), and the development of robust map matching algorithms, the performance of these devices for navigation applications is truly incredible. However, when tested for advanced automotive applications, the performance of GNSS positioning devices is found to be inadequate. In particular, in the most advanced fields of research such as autonomous vehicle technology, GNSS positioning devices are relegated to a secondary role, or often not used at all. They are replaced by terrestrial sensors that provide greater situational awareness, such as radar and lidar. This is due to the high performance demand of such applications, including high positioning accuracy (sub-decimetre), high availability and continuity of solutions (100%), and high integrity of the position information. Low-cost GNSS receivers generally do not meet such requirements. This could be considered an enormous oversight, as modern GNSS positioning technology and techniques have significantly improved satellite-based positioning performance. Other non-GNSS techniques also have their limitations that GNSS devices can minimise or eliminate. For instance, systems that rely on situational awareness require accurate digital maps of their surroundings as a reference. GNSS positioning can help to gather this data, provide an input, and act as a fail-safe in the event of digital map errors. It is apparent that in order to deliver advanced automotive applications - such as semi- or fully-autonomous vehicles - there must be an element of absolute positioning capability. Positioning systems will work alongside situational awareness systems to enable the autonomous vehicles to navigate through the real world. A strong candidate for the positioning system is GNSS positioning. This thesis builds on work already started by researchers at the University of Nottingham, to show that N-RTK positioning is one such technique. N-RTK can provide sub-decimetre accuracy absolute positioning solutions, with high availability, continuity, and integrity. A key component of N-RTK is the availability of real-time GNSS correction data. This is typically delivered to the GNSS receiver via mobile internet (for a roving receiver). This can be a significant limitation, as it relies on the performance of the mobile communications network, which can suffer from performance degradation during dynamic operation. Mobile communications systems are expected to improve significantly over the next few years, as consumers demand faster download speeds and wider availability. Mobile communications coverage already covers a high percentage of the population, but this does not translate into a high percentage of a country's geography. Pockets of poor coverage, often referred to as notspots, are widespread. Many of these notspots include the transportation infrastructure. The vehicle-to-vehicle concept has made significant forward steps in the last few years. Traditionally promoted as a key component of future automotive safety applications, it is now driven primarily by increased demand for in-vehicle infotainment. The concept, which shares similarities with the Internet of Things and Mobile Ad-hoc Networks, relies on communication between road vehicles and other road agents (such as pedestrians and road infrastructure). N-RTK positioning can take advantage of this communication link to minimise its own communications-related limitations. Sharing GNSS information between local GNSS receivers enables better performance of GNSS positioning, based on the principles of differential GNSS and N-RTK positioning techniques. This advanced concept is introduced and tested in this thesis. The Pseudo VRS concept follows the protocols and format of sharing GNSS data used in N-RTK positioning. The technique utilises the latest GNSS receiver design, including multiple frequency measurements and high quality antennas

A Hansel and Gretel approach to cooperative vehicle positioning

There is little doubt in the benefit gained from cooperative modes of road transport, as agents working together generally perform better. In simple terms, this is the holistic idea that the whole is greater than the sum of its parts, commonly known as synergy. On top of this clear advantage, the complex systems theory of emergence suggests that novel strategies will develop from the as-yet-undefined patterns and structures. It is clear, however, that to facilitate this development certain technological advances need to be achieved. In this case, individual road agents need to accurately identify their location, and communicate easily and safely with other agents. This is a shift away from protective and passive systems toward preventative and active transport safety

A fairy tale approach to cooperative vehicle positioning

This paper outlines an innovative approach to the cooper-ative positioning of road vehicles by sharing GNSS informa-tion. Much like the children’s fairy tale Hanzel and Gretel by the Brothers Grimm, GNSS receivers on road vehicles generate detailed VRS-like “breadcrumbs” as they accurately position themselves (in this case using a Network RTK GNSS technique). These breadcrumbs can then be shared with other vehicles in the locality to help position themselves, much like traditional RTK GNSS positioning. Similar to the breadcrumbs in the fairy tale that are eaten by birds shortly after being dropped, the VRS-like correction information is only valid for a short period of time. By using this technique, off-the-shelf GNSS receivers can be used without any major hardware or software adjustments, including those of different receiver brands or legacy receivers. The techniques employed in this paper aim to deliver absolute positions, to enable high-accuracy ITS applications that involve road agents and infrastructure alike. A much anticipated development in ITS technology is the use of vehicle to vehicle or vehicle to infrastructure commu-nication (collectively called V2X). Driven partly by the need to increase road safety, and perhaps heavily influenced by the infotainment needs of drivers and passengers, V2X technology will allow local vehicles to communicate with each other and with other road agents and fixed infrastructure. In the US, the National Highway Traffic and Safety Administration (NHTSA) recently commented that connected vehicle technology “can transform the nation’s surface transportation safety, mobility and environmental performance”, with industry experts pre¬dicting the widespread uptake of the technology within 5-6 years. This provides an opportunity for road vehicles to share GNSS information. (As the V2X technology is not under test in this paper, any V2X communication is made using a local Wi-Fi P2P network). This is demonstrated in this paper by directly sharing Network RTK correction information for one receiver (in this case Virtual Reference Station (VRS) corrections) with a second receiver on a separate vehicle. This is done using an NTRIP client running on an Android cellular device at the end-user distributing the VRS corrections from the NTRIP server to both the primary and secondary receivers (in the same locality). Network RTK corrections are not always available, not least because it requires a subscription to a service provider. However, if a GNSS receiver on a road vehicle has access to raw GNSS observations and is capable of calculating its absolute position to a reasonable accuracy (perhaps using an integrated sensor approach), then it has the necessary ingredients to generate its own VRS-like RTK corrections. These VRSs are left like breadcrumbs in the road, ready for any other GNSS receiver in the vicinity to use. Any received VRS correction information will continue to be valid for up to 10 seconds. By utilising the open source RTKLIB GNSS processing software, and the most recent RTCM standard messages (RTCM v3.1) generated through software provided by BKG, one receiver can perform the task of a VRS or a moving base station. The position of the receiver is processed whilst separately recording the raw RINEX information, in order to generate an RTCM stream that simulates that of a Network RTK VRS correction service. Additional information about the source of the correction information is also transmitted, in-cluding the self-assessed quality of the position and hardware used, using the RTCM message types reserved for proprietary information from service providers. Sharing GNSS information between vehicles is shown to significantly increase the availability of ambiguity fixed so-lutions, for both dual and single frequency receivers; and improves the performance of DGNSS receivers. However there needs to be caution, as the use of a single epoch of raw observations from a moving base station is less reliable than traditional static base station Network RTK GNSS positioning. Fixing the integer ambiguity is more likely to be successful (passing the ratio test), but also more likely to be incorrect, and relies heavily on the initial position of the moving base station (i.e. the relative position or baseline may be accurate, but not necessarily the absolute position). Three control solutions are used to assess the performance of the cooperative positioning techniques in real world tests: An RTK GNSS control solution provided by a local static continuously operating reference station (CORS); a Network RTK GNSS solution based on the MAC standard; and an Applanix POS/RS dual frequency GPS inertial navigation system. The processing parameters are adjusted to assess the optimum configuration for successful cooperative positioning (delivering accuracy and reliability), and the limitations of the technique are addressed. It is shown that although the cooperative position may not match the positioning accuracy of the initial moving base station vehicle (<5 centimetre), the solution is valid for sub-decimetre accuracy for up to one minute using dual frequency GPS observations. A cooperative DGNSS solution is accurate to 20 centimetres over the same period

UWB/GNSS-based cooperative positioning method for V2X applications

Limited availability of GNSS signals in urban canyons is a challenge for the implementation of many positioning-based traffic safety applications, and V2X technology provides an alternative solution to resolve this problem. As a key communication component in V2X technology, Dedicated Short Range Communication (DSRC) not only allows vehicles to exchange their position, but also traffic safety related information such as real-time congestion, up-to-date accident details, speed limits, etc. This position and traffic information could underpin various traffic safety applications - for instance, lane departure warnings, potential collision avoidance, and traffic congestion warnings. By taking advantage of DSRC, a vehicle in a GNSS denied environment is able to calculate its position using the assistance of other vehicles with sufficient GNSS signals to fix their locations. The concept of cooperative positioning, which is also called collaborative positioning, has been proposed to achieve this goal

A fairy tale approach to cooperative vehicle positioning

This paper outlines an innovative approach to the cooper-ative positioning of road vehicles by sharing GNSS informa-tion. Much like the children’s fairy tale Hanzel and Gretel by the Brothers Grimm, GNSS receivers on road vehicles generate detailed VRS-like “breadcrumbs” as they accurately position themselves (in this case using a Network RTK GNSS technique). These breadcrumbs can then be shared with other vehicles in the locality to help position themselves, much like traditional RTK GNSS positioning. Similar to the breadcrumbs in the fairy tale that are eaten by birds shortly after being dropped, the VRS-like correction information is only valid for a short period of time. By using this technique, off-the-shelf GNSS receivers can be used without any major hardware or software adjustments, including those of different receiver brands or legacy receivers. The techniques employed in this paper aim to deliver absolute positions, to enable high-accuracy ITS applications that involve road agents and infrastructure alike. A much anticipated development in ITS technology is the use of vehicle to vehicle or vehicle to infrastructure commu-nication (collectively called V2X). Driven partly by the need to increase road safety, and perhaps heavily influenced by the infotainment needs of drivers and passengers, V2X technology will allow local vehicles to communicate with each other and with other road agents and fixed infrastructure. In the US, the National Highway Traffic and Safety Administration (NHTSA) recently commented that connected vehicle technology “can transform the nation’s surface transportation safety, mobility and environmental performance”, with industry experts pre¬dicting the widespread uptake of the technology within 5-6 years. This provides an opportunity for road vehicles to share GNSS information. (As the V2X technology is not under test in this paper, any V2X communication is made using a local Wi-Fi P2P network). This is demonstrated in this paper by directly sharing Network RTK correction information for one receiver (in this case Virtual Reference Station (VRS) corrections) with a second receiver on a separate vehicle. This is done using an NTRIP client running on an Android cellular device at the end-user distributing the VRS corrections from the NTRIP server to both the primary and secondary receivers (in the same locality). Network RTK corrections are not always available, not least because it requires a subscription to a service provider. However, if a GNSS receiver on a road vehicle has access to raw GNSS observations and is capable of calculating its absolute position to a reasonable accuracy (perhaps using an integrated sensor approach), then it has the necessary ingredients to generate its own VRS-like RTK corrections. These VRSs are left like breadcrumbs in the road, ready for any other GNSS receiver in the vicinity to use. Any received VRS correction information will continue to be valid for up to 10 seconds. By utilising the open source RTKLIB GNSS processing software, and the most recent RTCM standard messages (RTCM v3.1) generated through software provided by BKG, one receiver can perform the task of a VRS or a moving base station. The position of the receiver is processed whilst separately recording the raw RINEX information, in order to generate an RTCM stream that simulates that of a Network RTK VRS correction service. Additional information about the source of the correction information is also transmitted, in-cluding the self-assessed quality of the position and hardware used, using the RTCM message types reserved for proprietary information from service providers. Sharing GNSS information between vehicles is shown to significantly increase the availability of ambiguity fixed so-lutions, for both dual and single frequency receivers; and improves the performance of DGNSS receivers. However there needs to be caution, as the use of a single epoch of raw observations from a moving base station is less reliable than traditional static base station Network RTK GNSS positioning. Fixing the integer ambiguity is more likely to be successful (passing the ratio test), but also more likely to be incorrect, and relies heavily on the initial position of the moving base station (i.e. the relative position or baseline may be accurate, but not necessarily the absolute position). Three control solutions are used to assess the performance of the cooperative positioning techniques in real world tests: An RTK GNSS control solution provided by a local static continuously operating reference station (CORS); a Network RTK GNSS solution based on the MAC standard; and an Applanix POS/RS dual frequency GPS inertial navigation system. The processing parameters are adjusted to assess the optimum configuration for successful cooperative positioning (delivering accuracy and reliability), and the limitations of the technique are addressed. It is shown that although the cooperative position may not match the positioning accuracy of the initial moving base station vehicle (<5 centimetre), the solution is valid for sub-decimetre accuracy for up to one minute using dual frequency GPS observations. A cooperative DGNSS solution is accurate to 20 centimetres over the same period

Position Reconstruction of Bubble Formation in Liquid Nitrogen using Piezoelectric Sensors

Cryogenic liquids, particularly liquid xenon and argon, are of interest as detector media for experiments in nuclear and particle physics. Here we present a new detector diagnostic technique using piezoelectric sensors to detect bubbling of the liquid. Bubbling can indicate locations of excess heat dissipation e.g., in immersed electronics. They can also interfere with normal event evolution by scattering of light or by interrupting the drift of ionization charge. In our test apparatus, four sensors are placed in the vacuum space of a double-walled dewar of liquid nitrogen and used to detect and locate a source of bubbling inside the liquid volume. Utilizing the differences in transmitted frequencies through the different media present in the experiment, we find that sound traveling in a direct path from the source to the sensor can be isolated with appropriate filtering. The location of the source is then reconstructed using the time difference of arrivals (TDOA) information. The reconstruction algorithm is shown to have a 95.8% convergence rate and reconstructed positions are self-consistent to an average +/-0.5cm around the mean in x, y, and z. Systematic effects are observed to cause errors in reconstruction when bubbles occur very close to the surfaces of the liquid volume.Comment: 8 pages, 5 figure

A Hansel and Gretel approach to cooperative vehicle positioning

There is little doubt in the benefit gained from cooperative modes of road transport, as agents working together generally perform better. In simple terms, this is the holistic idea that the whole is greater than the sum of its parts, commonly known as synergy. On top of this clear advantage, the complex systems theory of emergence suggests that novel strategies will develop from the as-yet-undefined patterns and structures. It is clear, however, that to facilitate this development certain technological advances need to be achieved. In this case, individual road agents need to accurately identify their location, and communicate easily and safely with other agents. This is a shift away from protective and passive systems toward preventative and active transport safety

A further cost for the sicker sex? Evidence for male-biased parasite-induced vulnerability to predation

Males are typically the sicker sex. Data from multiple taxa indicate that they are more likely to be infected with parasites, and are less ‘tolerant’, or less able to mitigate the fitness costs of a given infection, than females. One cost of infection for many animals is an increased probability of being captured by a predator. A clear, hitherto untested, prediction is therefore that this parasite-induced vulnerability to predation is more pronounced among males than females. We tested this prediction in the sexually size dimorphic guppy, Poecilia reticulata, in which females are typically larger than males. We either sham or experimentally infected guppies with Gyrodactylus turnbulli, elicited their escape response using an established protocol and measured the distance they covered during 60 ms. To discriminate between the effects of body size and those of other inherent sex differences, we size-matched fish across treatment groups. Infection with G. turnbulli reduced the distance covered during the escape response of small adults by 20.1%, whereas that of large fish was unaffected. This result implies that parasite-induced vulnerability to predation is male-biased in the wild: although there was no difference in escape response between our experimentally size-matched groups of males and females, males are significantly smaller across natural guppy populations. These results are consistent with Bateman’s principle for immunity: natural selection for larger body sizes and longevity in females seems to have resulted in the evolution of increased infection tolerance. We discuss the potential implications of male-biased parasite-induced vulnerability for the evolutionary ecology of this host-parasite interaction in natural communities

Sunspot observations on 10 and 11 February 1917: a case study in collating known and previously undocumented records

An extensive investigation of ships’ logs, as part of the ‘Old Weather’ citizen-science project, identified a sunspot observation made from HMS Hilary on 10 February 1917. This sunspot record was accompanied by detailed meteorological records that have enabled a reconstruction of the conditions under which the observation was made (overcast with detached clouds). Although there is no incontrovertible evidence that this was an unaided-eye observation, comparison with an unaided-eye observation recorded on the 11 February 1917 in a local treatise from Hénán province in China confirms that this sunspot group was visible to the unaided eye. White-light photographs from the Dehra Dun Observatory confirm the detailed description of the sunspot group provided by the naval observer. Moreover, comparisons with tabular data published by the Royal Observatory, Greenwich, confirm the statement that this was an unusually large sunspot group. Indeed, on 11 February 1917 the area of the sunspot group was greater than the area of any sunspot group recorded previously at the Royal Observatory, Greenwich. A comparison with a modern unaided-eye observation confirms that it is possible to observe sunspots under meteorological conditions similar to those experienced on-board HMS Hilary