International standards require the use of a weighted least-squares approach to onboard Receiver Autonomous Integrity Monitoring (RAIM). However, the protection levels developed to determine if the conditions exist to perform a measurement check (i.e. failure detection) are not specified. Various methods for the computation of protection levels exist. However, they are essentially approximations to the complex problem of computing the worst-case missed detection probability under a weighted system. In this paper, a novel approach to determine this probability at the worst-case measurement bias is presented. The missed detection probabilities are then iteratively solved against the integrity risk requirement in order to derive an optimal protection level for the operation. It is shown that the new method improves availability by more than 30% compared to the baseline weighted RAIM algorithm.

A version of this paper was first presented at the US Institute of Navigation (ION) GNSS 2009 Conference in Savannah, Georgia.

Over the recent decades, there have been a number of trends that have driven the desire to improve the ability to position and navigate in all environments. While GPS has been the driving factor behind most of these trends, there are limitations to GPS that have become more evident over time as the World has increasingly come to rely on location. These limitations are mostly due to the low transmission power of GPS satellites, where navigation signals broadcast from space are comparatively weak, especially by the time they have travelled to receivers on the ground. This makes the signals particularly vulnerable to fading in difficult environments such as built-up urban areas. The low signal-to-noise ratio (SNR) also means that the signals are susceptible to jamming, both hostile and accidental.

This motivates the need for non-GPS (or, more generally, non-GNSS) navigation technologies, for example, terrestrial based alternatives to GNSS such as eLoran. But, there is also significant interest in the exploitation of other non-navigation signals for positioning and navigation purposes. These so-called ‘Signals of Opportunity’ (SoOP) do not generally require any alterations to existing communications transmission infrastructure and often use alternative multi-carrier modulation techniques to those methods used by most GNSS services. The major challenge of using a SoOP for location purposes is that the transmitter network infrastructure has not generally been designed with positioning as a requirement.

An ongoing project, at the Institute of Engineering Surveying and Space Geodesy (IESSG) of the University of Nottingham, is directed towards an investigation of the potential of the Digital Audio Broadcast (DAB) signal for positioning purposes. A prototype Software Defined Radio (SDR) DAB positioning receiver has been developed and has now been tested. This paper presents a detailed review of the structure of the DAB signals and explains how these signals can be used as the basis of a positioning system. In addition the development of the prototype SDR receiver and the initial results are presented and discussed.

The latest attempts at improving small scale autonomously guided Uninhabited Aerial Vehicles (UAVs) have concentrated around the increase of range and speed. One of these ways is to incorporate dynamic slope soaring manoeuvres as part of the flight path. This is in contrast to most conventional path-planning algorithms where waypoint guidance is merged with terrain avoidance or contour following capability. Additionally, current trajectory optimization techniques are iterative and so have a considerable computational load. The proposed algorithm is based on Dubin's curves, and is therefore optimal by definition. Being non-iterative, it is comparatively a more efficient algorithm. Hence, a key advantage of the proposed technique is that the desired trajectory is generated quickly in real time with minimum computational load while satisfying the spatial constraints of dynamic slope soaring.

Carrier phase measurements are used to provide high-accuracy estimates of position. For safety-of-life navigation applications such as precision approach and landing, integrity plays a critical role. Carrier phase-based Receiver Autonomous Integrity Monitoring (CRAIM) has been investigated for many years (Pervan et al, 1998; Feng et al, 2007). Assuming that the carrier phase error has a Gaussian distribution, conventional CRAIM algorithms were directly derived from the Pseudorange-based RAIM (PRAIM). However, the actual carrier phase error does not exactly follow the Gaussian distribution, hence the performance of the conventional CRAIM algorithm is not optimal.

To approach this problem, this paper proposes a new CRAIM algorithm that uses Gaussian sum filters. A Gaussian sum filter can deal with any non-Gaussian error distribution and accurately present the posterior distributions of states. In this paper, a new method of making a Gaussian mixture model, which follows the true error distribution, is introduced. Additionally an integrity monitoring algorithm, using a Gaussian sum filter, is described in detail. The simulation results show that the proposed algorithm can have about 18% smaller Minimum Detectable Bias (MDB) and generates about 20% lower protection levels than those of the conventional CRAIM algorithm. In other words, by considering a non-Gaussian carrier phase error distribution, the new algorithm can improve the accuracy and the availability.

In our present age, radio communication and navigational aids are taken without comment throughout the aviation industry. However, all developments must start somewhere and it is the intention of this paper to look into the earliest days of “wireless” and its gradual application to aviation.

The first step was, as far as I can ascertain, in October 1866 when Mahlon Loomis flew a kite from a mountain top in Virginia, USA. He had fitted a copper mesh to the kite and connected this to a copper wire. Between the wire and earth he connected a galvanometer which, he noted, deflected from static electricity. On flying an identical kite at a similar height some fourteen miles away, if the copper wire were earthed, the deflection on the galvanometer changed. However, if the kite wires were of different length, this effect was not observed. For this, in 1872, he was issued with a US Patent 129971 for “wireless telegraphy” but, as far as we know, apart from a few fading freehand notes, (See Figure 1) no details of his apparatus survive, so it must remain a matter of conjecture what was actually achieved.

The aim of the paper is to inform design staffs on potential Remotely Piloted Air Systems (RPAS) improvements to afford greater utility on the battlespace. The scope of the paper covers Air Warfare Centre experiences working with several NATO Class II RPAS. Using an ‘assurance framework’ that examines integrity of the aircraft, the operational environment and crew competency, the paper identifies what changes need to be made if the utility of RPAS in this category is to be enhanced.

We develop a new frequency-domain dynamic response method to model integrated Inertial Navigation System (INS) and Global Positioning System (GPS) architectures and provide an accurate impulse-response-based INS-only navigation solution when GPS signals are denied (GPS outages). The input to such a dynamic system is the INS-only solution and the output is the INS/GPS integration solution; both are used to derive the transfer function of the dynamic system using Least Squares Frequency Transform (LSFT). The discrete Inverse Least Squares Frequency Transform (ILSFT) of the transfer function is applied to estimate the impulse response of the INS/GPS system in the time domain. It is shown that the long-term motion dynamics of a DQI-100 IMU/Trimble BD950 integrated system are recovered by 72%, 42%, 75%, and 40% for north and east velocities, and north and east positions respectively, when compared with the INS-only solution (prediction mode of the INS/GPS filter). A comparison between our impulse response model and the current state-of-the-art time-domain feed-forward neural network shows that the proposed frequency-dependent INS/GPS response model is superior to the neural network model by about 26% for 2D velocities and positions during GPS outages.

With the existing GPS, the replenishment of GLONASS and the launching of Galileo there will be three satellite navigation systems in the future, with a total of more than 80 satellites. So it can be expected that the performance of the global navigation satellite system (GNSS) will be greatly improved, especially in urban environments. This paper studies the potential benefits of GPS/GLONASS/Galileo integration in an urban canyon – Hong Kong. The navigation performances of four choices (GPS alone, GPS+GLONASS, GPS+Galileo and GPS+GLONASS+Galileo) are evaluated in terms of availability, coverage, and continuity based on simulation. The results show that there are significant improvements in availability, coverage and continuity, by using GPS+GLONASS+Galileo compared with the other choices. But the performance is still not good enough for most navigation applications in urban environments.

In this paper, a novel ship domain model termed quaternion ship domain (QSD) is proposed. Unlike other ship domains, the proposed QSD is more dependable and more flexible for navigators to use to make decisions. The main characteristics are that: the domain size is determined by the quaternion including four radii, i.e. fore, aft, starboard and port, which sufficiently take factors affecting the domain (i.e. ship manoeuvring capability, speeds and courses, etc.) into account; and that the domain shape is modelled by another parameter which makes the QSD more flexible since the ship boundary could not only be linear or nonlinear, but also be thin or fat. In order to reasonably relate the proposed QSD to practical applications, i.e. collision risk assessment, collision avoidance and trajectory planning, etc., a fuzzy QSD (FQSD) has been developed by using fuzzy sets. As a result, fuzzy boundaries rather than crisp ones in the FQSD are more practical and more convenient for navigators to understand and judge since uncertainty and fuzzy information have been merged into the FQSD. Furthermore, concepts of longitudinal and lateral risk based on the FQSD have been introduced to estimate the spatial collision risk (SCR) for the ships encountered. Finally, several computer simulations have been conducted on various encounter situations and comparative studies with other ship domains have been comprehensively analyzed. Simulation results demonstrate that the proposed QSD is more effective and more flexible than other ship domains, and that the intelligent SCR based on the FQSD are reasonable and dependable.

Two distinct methods have been proposed and used to derive the required performance for CAT-II and III precision approaches: the “ILS (Instrument Landing System) Look-Alike Method” and the “Autoland Method”. The former is based on the concept of matching the performance of the ILS at the Navigation System Error (NSE) level through linearization of current specifications at a given height. The latter is based on the need to protect the safety of a landing operation using the current specification for the probability to land in a given landing box. Fundamentally, both methods assume the same safety targets and type of distribution, and are independent of specific navigation architectures. Therefore, they should deliver the same performance requirements. However, the requirements from the two methods for CAT-III approach are different. This paper reviews the two methods in detail, highlighting the key differences, and proposes ways to reconcile the methods and the requirements.

Time-domain simulation of ship manoeuvring has been utilized in risk analysis to assess the effect of changes to the ship-lane, development in traffic volume and the associated risk. The process of ship manoeuvring in a wider socio-technical context consists of the technical systems, operational procedures, the human operators and support functions. Automated manoeuvring simulations without human operators in the simulation loop have often been preferred in simulation studies due to the low time required for simulations. Automatic control has represented the human element with little effort devoted to explain the relationship between the guidance and control algorithms and the human operator which they replace. This paper describes the development and application of a model for the human element for autonomous time-domain manoeuvring simulations. The method is applicable in the time-domain, modular and found to be capable of reproducing observed manoeuvre patterns, but limited to represent the intended behaviour.

Statistics and information from the maritime industry show that the continuous advances in the safety of navigation do not reduce the occurrence of shipping casualties. This controversial fact leads the authors to analyse the applicability of the risk homeostasis theory to maritime transportation. With the aim of investigating this matter 2,584 ship incidents, which took place during the years 2005 and 2006, have been recorded and examined. The same variables which the Paris MOU usually employs to identify substandard ships (flag, classification society, age, type and size) have been used in this research to establish their level of safety in an effort to determine the relationship between that level and the occurrence of maritime incidents in the world cargo carrying fleet with appropriate statistical methods.

This paper pertains to the reduction of the effects of measurement errors in rate gyros used for tracking, recording, or monitoring the position of persons walking indoors. In such applications, bias drift and other gyro errors can degrade accuracy within minutes. To overcome this problem we developed the Heuristic Drift Elimination (HDE) method, that effectively corrects bias drift and other slow-changing errors. HDE works by making assumptions about walking in structured, indoor environments. The paper explains the heuristic assumptions and the HDE method, and shows experimental results. In typical applications, HDE maintains near-zero heading errors in walks of unlimited duration.

This paper proposes a novel mechanism for the initial alignment of low-cost INS aided by GPS. For low-cost INS, the initial alignment is still a challenging issue because of the high noises from low-cost inertial sensors. In this paper, a two-stage Kalman Filtering mechanism is proposed for the initial alignment of low-cost INS. The first stage is designed for the coarse alignment. To solve the problems encountered by the general coarse alignment approach, an INS error dynamic accounting for unknown initial heading error is developed, and the corresponding observation equation, taking into account the unknown heading error, is also developed. The second stage is designed for the fine alignment, where the classical INS error dynamics based on small attitude error is used. Experimental results indicate that the proposed alignment approach can complete the initial alignment more quickly and more accurately compared with the conventional approach.

This paper deals with the problem of determining the baseline vector between two GPS receivers in single frequency (L1) using the basic principles of interferometric Differential GPS, therefore using the interferometric relations between the two receivers and the satellites visible to both receivers. As a preliminary step, ambiguity identification was solved using the results provided by the Kalman filter; these results were optimized by evaluating the Dilution Of Precision indexes for satellites in view of the receivers. Results achieved by applying this first procedure to data collected are discussed. To increase the accuracy of the results, a new, computationally fast algorithm for carrier phase ambiguity resolution on data collected from static and dynamics acquisitions was developed, implemented and tested. The new algorithm permitted an increase of accuracy of about two orders of magnitude with respect to results given by filtered Double Difference in the resolution of baseline vector.

This paper examines the evidence to support the view that the inability of seamen to determine accurate longitude at sea in sailing ships was a major factor in the loss of ships and crews that was effectively solved by the introduction of the marine chronometer. It concludes that this was not the case and that a more compelling factor for the safety of ships was the introduction of mechanical propulsion systems.

The objective of this paper is to explore a hybrid Global Navigation Satellite System (GNSS) architecture that efficiently meets the stringent needs of safety of life systems. An architecture is proposed that allocates error bounding and alerting functionality between the space, ground and user segments based on refining the assumptions of the leading-order fault free error sources expected in the near future from developing GNSS technologies. By revisiting the first principles used to derive standard RAIM fault detection, a modified detection algorithm is developed to more accurately accommodate these new fault-free error distributions while supporting timely user alerts. The results of the analysis and simulation indicate that this optimized receiver algorithm and associated architecture can provide significant development and operational benefit for navigation users requiring high levels of integrity.