Integer ambiguity validation is pivotal in precise positioning with Global Navigation Satellite Systems (GNSS). Recent research has shown traditionally used ambiguity validation methods can be classified as members of the Integer Aperture (IA) estimators, and by the virtue of the IA estimation, a user controllable IA fail-rate is preferred. However, an appropriately chosen fail-rate is essential for ambiguity validation. In this paper, the upper bound and the lower bound for the IA fail-rate, which are extremely useful even at the designing stage of a GNSS positioning system, have been analysed, and numerical results imply that a meaningful IA fail-rate should be within this range.

The average inter-station distances in most established network Real Time Kinematic (RTK) systems are constrained to around 50 km. A sparse network RTK system with an average inter-station distance of up to 300 km would have many appealing advantages over a conventional one, including a significant reduction in the development and maintenance costs. The first part of this paper introduces the key approaches for sparse network RTK positioning technology. These include long-range reference baseline ambiguity resolution and real-time kinematic ambiguity resolution for the rover receivers. The proposed method for long-range kinematic ambiguity resolution can overcome the network weaknesses through three procedures: application of the interpolated corrections from the sparse network only to wide-lane combination; searching the ambiguities of wide-lane combination; and searching L1 ambiguities with wide-lane combination and ionosphere-free observables. To test these techniques, a network including ten reference stations was created from the Ordnance Survey's Network (OS NetTM) that covers the whole territory of the United Kingdom (UK). The average baseline length of this sparse network is about 300 km. To assess the positioning performance, nine rover stations situated inside and outside the network were also selected from the OS Net™. Finally, the accuracy of interpolated corrections, the positioning accuracy and the initialization time required for precise positioning were estimated and analysed. From the observed performance of each rover receiver, and the accuracy of interpolated network corrections, it can be concluded that it is feasible to use a sparse reference station network with an average inter-station distance up to 300 km for achieving similar performance to traditional network RTK positioning. The proposed approach can provide more cost-efficient use of network RTK (NRTK) positioning for engineering and environmental applications that are currently being delivered by traditional network RTK positioning technology.

This paper presents a new Electronic Travel Aid (ETA) ‘Acoustic Prototype’ which is especially suited to facilitate the navigation of visually impaired users. The device consists of a set of 3-Dimensional Complementary Metal Oxide Semiconductor (3-D CMOS) image sensors based on the three-dimensional integration and Complementary Metal-Oxide Semiconductor (CMOS) processing techniques implemented into a pair of glasses, stereo headphones as well as a Field-Programmable Gate Array (FPGA) used as processing unit. The device is intended to be used as a complementary device to navigation through both open known and unknown environments. The FPGA and the 3D-CMOS image sensor electronics control object detection. Distance measurement is achieved by using chip-integrated technology based on the Multiple Short Time Integration method. The processed information of the object distance is presented to the user via acoustic sounds through stereophonic headphones. The user interprets the information as an acoustic image of the surrounding environment. The Acoustic Prototype transforms the surface of the objects of the real environment into acoustical sounds. The method used is similar to a bat's acoustic orientation. Having good hearing ability, with few weeks training the users are able to perceive not only the presence of an object but also the object form (that is, if the object is round, if it has corners, if it is a car or a box, if it is a cardboard object or if it is an iron or cement object, a tree, a person, a static or moving object). The information is continuously delivered to the user in a few nanoseconds until the device is shut down, helping the end user to perceive the information in real time.

The aviation community has very stringent navigation integrity requirements that apply to a variety of manned and Unmanned Aerial Vehicle (UAV) operational tasks. This paper presents the results of the research activities carried out by the Italian Air Force Flight Test Centre (CSV-RSV) in collaboration with the Nottingham Geospatial Institute (NGI) and Cranfield University (CU) in the area of Avionics-Based Integrity Augmentation (ABIA) for mission- and safety-critical Global Navigation Satellite System (GNSS) applications. Based on these activities, suitable models were developed to describe the main causes of GNSS signal outage and degradation in flight, namely: antenna obscuration, multipath, fading due to adverse geometry and Doppler shift. Adopting these models in association with suitable integrity thresholds and guidance algorithms, the ABIA system delivers integrity caution (predictive) and warning (reactive) flags, as well as steering information to the pilot and electronic commands to the aircraft/UAV flight control system. These features allow real-time avoidance of safety-critical flight conditions and fast recovery of the required navigation performance in case of GNSS data losses. This paper presents the key ABIA concepts, architecture and mathematical models. A successive paper will address the ABIA integrity thresholds criteria and detailed results of a TORNADO simulation case-study.

Evidence for the existence of risk compensation behaviour in the operation of vessels is shown in the paper The Risk Homeostasis Theory (Baniela and Ríos, 2010). In that analysis, it is concluded that the people engaged in the commercial affairs of ships tend to exchange the level of safety standard of vessels for a more profitable and riskier activity, which makes the rate of shipping accidents fluctuate within certain limits. Since the different levels of power and motivation of those involved in the risk-taking process were not considered in that research, it is the aim of this paper to analyse, on the one hand, how the pressure of the shipping market influences the risk behaviour of shipping business decision-makers and to show, on the other hand, how this influence makes them alter their target level of risk and introduce risks related to low operating cost strategies on vessels. This behavioural adaptation to the shipping market demand has led the human element to be regarded as a factor of risk in the activity of commercial vessels. In this context, the increasing incidence of human errors has arisen as a consequence of practices and manning policies established by the managers of shipping companies.

The Precise Point Positioning (PPP) concept enables centimetre-level positioning accuracy by employing one Global Navigation Satellite System (GNSS) receiver. The main advantage of PPP over conventional Real Time Kinematic (cRTK) methods is that a local reference network infrastructure is not required. Only a global reference network with approximately 50 stations is needed because reference GNSS data is required for generating precise error correction products for PPP. However, the current implementation of PPP is not suitable for some applications due to the long time period (i.e. convergence time of up to 60 minutes) required to obtain an accurate position solution. This paper presents a new method to reduce the time required for initial integer ambiguity resolution and to improve position accuracy. It is based on combining GPS and GLONASS measurements to calculate the float ambiguity positioning solution initially, followed by the resolution of GPS integer ambiguities.

The results show that using the GPS/GLONASS float solution can, on average, reduce the time to initial GPS ambiguity resolution by approximately 5% compared to using the GPS float solution alone. In addition, average vertical and horizontal positioning errors at the initial ambiguity resolution epoch can be reduced by approximately 17% and 4%, respectively.

Single-frequency Precise Point Positioning (PPP) using a Global Navigation Satellite System (GNSS) has been attracting increasing interest in recent years due to its low cost and large number of users. Currently, the single-frequency PPP technique is mainly implemented using GPS observations. In order to improve the positioning accuracy and reduce the convergence time, we propose the combined GPS/GLONASS Single-Frequency (GGSF) PPP approach. The approach is based on the GRoup And PHase Ionospheric Correction (GRAPHIC) to remove the ionospheric effect. The performance of the GGSF PPP was tested using both static and kinematic datasets as well as different types of precise satellite orbit and clock correction data, and compared with GPS-only and GLONASS-only PPP solutions. The results show that the GGSF PPP accuracy degrades by a few centimetres using rapid/ultra-rapid products compared with final products. For the static GGSF PPP, the position filter typically converges at 71, 33 and 59 minutes in the East, North and Up directions, respectively. The corresponding positioning accuracies are 0·057, 0·028 and 0·121 m in the East, North and Up directions. Both positioning accuracy and convergence time have been improved by approximately 30% in comparison to the results from GPS-only or GLONASS-only single-frequency PPP. A kinematic GGSF PPP test was conducted and the results illustrate even more significant benefits of increased accuracy and reliability of PPP solutions by integrating GPS and GLONASS signals.

Map matching is an important algorithm for any location-based service, especially in navigation and tracking systems and services. Identifying the relevant road segments accurately and efficiently, given positioning data, is the first and most important step in any map matching algorithm. This paper proposes a new approach to searching for road candidates by clustering and then searching road segments through a constructed hierarchical clustering tree, rather than using indexing techniques to query segments within a fixed search window. A binary tree is created based on the hierarchical clustering tree and adaptive searches are conducted to identify candidate road segments given GPS positions. The approach was validated using road maps with different scales and various scenarios in which moving vehicles were located. Both theoretical analysis and experimental results confirm that the proposed approach can efficiently find candidate road segments for map matching.

This paper presents the design and implementation of a Chip Scale Atomic Clock (CSAC) driven dual-channel Digitally Configurable Receiver (DCR) for Global Navigation Satellite Systems (GNSS). The receiver is intended to be used for research applications such as; multipath mitigation, scintillation assessment, advanced satellite clock and spatial frame transformation modelling, Precise Point Positioning (PPP) as well as rapid development and assessment of novel circuits and systems for GNSS receivers. A novel sub-Nyquist sampling (subsampling) receiver architecture incorporating dual-band microstrip RF filters is employed in order to minimize the complexity of the multi-frequency Radio Frequency (RF) front-end. Moreover, the digital receiver incorporates a novel and complexity-reduced Fast Fourier Transform (FFT) core for signal acquisition as well as COordinate Rotation DIgital Computer (CORDIC) cores for the code/carrier discriminators in order to minimize the resource allocation on the FPGA. The receiver also provides easy access to enable adjustment of its internal parameters such as; RF gain, position update rate, tracking channel correlator spacing and code/carrier loop noise bandwidth. Correlator outputs, code/carrier error, Carrier-to-Noise Ratio (C/N0), navigation and RINEX data are provided to the end-user in real-time. This paper collectively highlights and reports on the implementation, test and validation of the novel techniques, elements and approaches in both the RF and digital part of the DCR that comprise the multi-constellation receiver.

This paper will demonstrate that the Master Pilot Exchange (MPX) is a document of debatable value in pilotage waters. The MPX exists in many formats which are designed to reflect local navigational challenges and port requirements. A generic form exists which can aid the design of local MPX forms. Both the generic and port MPX forms may require the recording of information that has a neutral outcome on the planned act of pilotage. Analysis of significant incidents suggests that investigation recommendations are not consistently reflected in MPX forms and there is a gap between what should be recorded and reality.

When a collision occurs between two ships on the high seas, very likely one may need to determine who should be liable for the collision and the apportionment of liability between them. However, it is not unusual to see a collision between an anchored vessel and another vessel underway. When determining apportionment of liability between them, it seems that there is a presumption of fault against the vessel underway. To counteract such a presumption, the author discusses some issues in respect of collisions between a vessel at anchor and others underway under the International Regulations for Preventing Collisions at Sea, 1972 (COLREGs) by examining the obligations of anchored vessels to avoid a collision at sea.