A robust adaptive nonlinear asymptotic regulating control law is designed for dynamically positioned vessels exposed to unknown time-varying external disturbances incorporating Fuzzy Logic Systems (FLSs), projection operators, and the “robustifying” term into the vectorial backstepping technique. The FLSs approximate the vessel unknown dynamics and the update laws based on the online projection operators update the fuzzy weight vectors. The robustifying term handles the external disturbances and the fuzzy approximation errors. The designed Dynamic Positioning (DP) control law achieves asymptotic regulation of the vessel's position and heading and makes the other signals in the DP closed-loop control system of vessels be uniformly ultimately bounded. Simulations based on the Marine System Simulator toolbox validate the designed DP control law.

The Global Positioning System (GPS) long-baseline set up has been widely employed to generate high-accuracy positioning, timing and atmospheric information. Bernese GPS software adopts two appropriate strategies for long-baseline Integer Ambiguity Resolution (IAR): Quasi Ionosphere-Free (QIF) and Wide-lane/Narrow-lane (WN). With the goal of reasonably shortening the time required for long-baseline IAR, we propose the Precise Point Positioning (PPP) method for estimating, on a per receiver basis, the Zenith Tropospheric Delays (ZTDs) and the Slant Ionospheric Delays (SIDs) from zero-differenced, uncombined GPS observables. We then reformulate these PPP-derived ZTDs and SIDs into two types of atmospheric constraints with proper uncertainties that could be readily assimilated into the process of IAR with the QIF. Our numerical tests based on five independent long-baselines (>1,000 kilometres) suggest that the empirical precision of PPP-derived ZTDs (SIDs) is always better than 2 (10) centimetres. The modified QIF would be able to correctly resolve at least 98% and 88% of the wide- and narrow-lane ambiguities for all the long-baselines relying on the very simple integer rounding method. However, under the same condition, the WN can only get the correct integers of 76·6% wide-lane ambiguities and 55·2% narrow-lane ones.

The Navigation with Indian Constellation (NavIC)/Indian Regional Navigation Satellite System (IRNSS) is an emerging satellite navigation system that provides an independent navigation system for positioning and timing services in India and up to 1,500 km from its borderline. The dual frequency NavIC system uses the L5 frequency and S-band for navigation. These navigation signals are extremely weak and susceptible to interference when they are received on Earth's surface. Moreover, the performance of these bands may be degraded by other band or out-of-band communication systems, which can become the major threat to the performance of a NavIC receiver. The main focus of this paper is to detect real-time interference of Wi-Fi signals in the S-band of the NavIC receiver. The results are prepared with respect to the Power Spectral Density (PSD), execution of acquisition stage and the detection of Wi-Fi interference with two sample hypothesis testing methods including the Kolmogorov-Smirnov (KS)-test, the t-test and the Variance (var)-test. A performance analysis of the p-value is used to measure the evidence of interference existence for hypothesis testing, decision hypothesis and probability of detection are evaluated for each hypothesis method. The results show the severity of the Wi-Fi signal as a potential source of interference for future NavIC applications.

In this paper, a novel Predictive Variable Structure Filter (PVSF) and its adaptive deformation (APVSF) are presented for attitude synchronisation during Satellite Formation Flying (SFF). The PVSF is proposed based on the variable structure control concept and applied to any nonlinear system with model errors. The model errors in the PVSF need not satisfy the assumption of Gaussian white noise; therefore, it has advantages in dealing with various kinds of uncertainties, parameter variations or noises. Then, the APVSF is also presented to adjust the smoothing boundary layer of PVSF by minimising the Mean-Square Error (MSE). Simulations are performed to demonstrate the accuracy, robustness, and stability of the proposed methodologies for the attitude synchronisation estimation of the SFF system.

Visual–Inertial Navigation Systems (VINS) plays an important role in many navigation applications. In order to improve the performance of VINS, a new visual/inertial integrated navigation method, named Sliding-Window Factor Graph optimised algorithm with Dynamic prior information (DSWFG), is proposed. To bound computational complexity, the algorithm limits the scale of data operations through sliding windows, and constructs the states to be optimised in the window with factor graph; at the same time, the prior information for sliding windows is set dynamically to maintain interframe constraints and ensure the accuracy of the state estimation after optimisation. First, the dynamic model of vehicle and the observation equation of VINS are introduced. Next, as a contrast, an Invariant Extended Kalman Filter (InEKF) is constructed. Then, the DSWFG algorithm is described in detail. Finally, based on the test data, the comparison experiments of Extended Kalman Filter (EKF), InEKF and DSWFG algorithms in different motion scenes are presented. The results show that the new method can achieve superior accuracy and stability in almost all motion scenes.

This paper offers a designed Integrated Navigation System that will permit vessels to transit safely through the Suez Canal avoiding collision and grounding in all weather environments instead of being directed to anchor, thus keeping the Canal open at all times for ship transits. The Suez Canal Integrated Navigation System (SCINS) includes Differential Global Positioning System (DGPS), Suez Canal LORAN-C system, and Vessel Traffic Management System (VTMS). The combination of DGPS and LORAN-C systems would provide real-time DGPS corrections that could be used to calibrate the Loran fix; this can be achieved by means of portable integrated DGPS/LORAN-C sets installed aboard the vessels. The addition of VTMS provides significant capability for preserving system accuracy during periods of GPS outages. Due to the interface between LORAN-C and VTMS systems, the SCINS will be able to solve the problem of targets that cannot be tracked by VTMS radars in the shadow areas behind the new bridges along the Canal. The SCINS automates position fixing in real-time, offers a designed algorithm to return the ship to the middle of the Canal and computes the cross-track error (XTE) and the ship squat. Kalman Filter design and system level performance predictions for the SCINS are briefly described. Simulation results show that the SCINS offers superior performance and better position accuracy than current integrated systems.

If a radar transmitter and receiver are mounted together in the nose of an aircraft and flown at speed V over flat ground towards a vertical reflector (Fig. 1), then the received signal at the reflector differs in frequency from the transmitted signal by + V/λ (the doppler frequency), where λ is the wavelength of the transmitter. The reflected signal back to the aircraft undergoes a further increase of frequency + V/λ, thus the received signal at the aircraft differs from the transmitted frequency by + 2V/λ. This difference in frequency, referred to as the doppler shift, is proportional to the speed of the aircraft.

Ionospheric scintillation effects degrade satellite-based radio communication/navigation links and influence the performance of Global Navigation Satellite Systems (GNSS). An adaptive wavelet-based decomposition technique, Synchrosqueezing Transform (SST), with a Detrended Fluctuation Analysis (DFA) algorithm has been implemented for time-frequency representation of GNSS multi-component signals and mitigation of scintillation effects. Synthetic In-phase (I) and Quadra-phase (Q) samples were collected from the Cornell Scintillation Model (CSM) and the CSM amplitude scintillation signal was processed with SST-DFA for the detection of noisy scintillation components and mitigation of ionospheric scintillation effects. Also, performance of the SST-DFA algorithm was tested for real-time GNSS ionospheric scintillation data collected from a GNSS Software Navigation Receiver (GSNRx) located at a low-latitude station in Rio de Janeiro, Brazil. The de-noising performance of the SST-DFA algorithm was further evaluated and compared with a low-pass Butterworth filter during different ionospheric scintillation time periods. The experimental results clearly demonstrated that the proposed method is reliable for mitigation of ionospheric scintillation noise both in time and frequency scales.

This paper describes a method to determine global navigation satellite systems (GNSS) satellite orbits and clocks for advanced receiver autonomous integrity monitoring (ARAIM). The orbit and clock estimates will be used as a reference truth to monitor signal-in-space integrity parameters of the ARAIM integrity support message (ISM). Unlike publicly available orbit and clock products, which aim to maximise estimation accuracy, a straightforward and transparent approach is employed to facilitate integrity evaluation. The proposed monitor is comprised of a worldwide network of sparsely distributed reference stations and will employ parametric satellite orbit models. Two separate analyses, covariance analysis and model fidelity evaluation, are carried out to assess the impact of measurement errors and orbit model uncertainty on the estimated orbits and clocks, respectively. The results indicate that a standard deviation of 30 cm can be achieved for the estimated orbit/clock error, which is adequate for ISM validation.

The International Maritime Organisation (IMO), in its Sub-Committee for the Safety of Navigation, has recommended the acceptance of GPS as a component of the World-Wide Radionavigation System. However, the Sub-Committee highlighted that GPS accuracy is not sufficient for harbour entrances and approaches and that it does not provide instantaneous integrity to alert users of any malfunction. The Sub-Committee considered that DGPS could improve both the accuracy and the integrity of GPS. In practice, the use of differential corrections to GPS signals allows elimination of most of the errors of GPS and improves the integrity of the service significantly. While GPS does not provide instantaneous integrity, the use of DGPS reference stations, which continuously monitor the signals of the visible satellites, enables the timely warning (under 15 seconds) of any malfunction or failure. However, the recent discontinuation of Selective Availability (SA), which led to an improvement in stand-alone GPS accuracy, has changed some of the premises that justified differential services. This paper presents the needs of mariners in terms of radio positioning, with the aim of evaluating the ability of unaugmented GPS and DGPS to comply with marine navigation requirements. The impact of the removal of SA on DGPS and its benefits for mariners will also be discussed in order to show that DGPS is still adequate and useful for mariners.

Global Navigation Satellite Systems (GNSSs) are easily influenced by the external environment. Signals may be lost or become abnormal thereby causing outliers. The filter gain of the standard Kalman filter of a loosely coupled GNSS/inertial navigation system cannot change with the outliers of the GNSS, causing large deviations in the filtering results. In this paper, a method based on a χ2-test and a dynamically adjusting filter gain method are proposed to detect and separately to suppress GNSS observation outliers in integrated navigation. An indicator of an innovation vector is constructed, and a χ2-test is performed for this indicator. If it fails the test, the corresponding observation value is considered as an outlier. A scale factor is constructed according to this outlier, which is then used to lower the filter gain dynamically to decrease the influence of outliers. The simulation results demonstrate that the observation outlier processing method does not affect the normal values under normal circumstances; it can also discriminate between single and continuous outliers without errors or omissions. The impact time of outliers is greatly reduced, and the system performance is improved by more than 90%. Experimental results indicate that the proposed methods are effective in suppressing GNSS observation outliers in integrated navigation.

On any surface which fulfils the required continuity conditions, the shortest path between two points on the surface is along the are of a geodesic curve. On the surface of a sphere the geodesic curves are the great circles and the shortest path between any two points on this surface is along the arc of a great circle, but on the surface of an ellipsoid of revolution, the geodesic curves are not so easily defined except that the equator of this ellipsoid is a circle and its meridians are ellipses.

The accuracy that can be achieved by a single GPS receiver in stand-alone mode is around 10 metres with SA switched off; this is not adequate for most hydrographic studies. This study aims to improve this level of accuracy using a single geodetic receiver in stand-alone mode by applying a phase smoothing algorithm. The algorithm described in this study requires that the measurements be started from a known point for initialisation. The test site selected for the study is Halic bay, Istanbul. After GPS data were collected on a geodetic point for initialisation, the receiver was moved to a hydrographic vessel and trial measurements were performed along several survey profiles. The position of the vessel was calculated at every epoch using the carrier phase smoothing algorithm. In order to analyse the accuracy of the results, a second receiver collected data on another known point on the seashore during the whole session. The position of the vessel was accurately determined using a kinematic positioning method considering the data collected by both receivers. The results produced show that an accuracy of less than a metre can be achieved using the approach considered in this study.

BeiDou satellites transmit triple-frequency signals, which bring substantial benefits to carrier phase Ambiguity Resolution (AR). The traditional geometry-free model Three-Carrier Ambiguity Resolution (TCAR) method looks for a suitable combination of carrier phase and code-range observables by searching and comparing in the integer range, which limits the AR success probability. By analysing the error characteristics of the BeiDou triple-frequency observables, we introduce a new procedure to select the optimal combination of carrier phase and code observables to resolve the resolution of Extra-Wide-Lane (EWL) and Wide-Lane (WL) ambiguity. We also investigate a geometry-free and ionosphere-eliminated method for AR of the Medium-Lane (ML) and Narrow-Lane (NL) observables. In order to evaluate the performance of the improved TCAR method, real BeiDou triple-frequency observation data for different baseline cases were collected and processed epoch-by-epoch. The results show that the improved geometry-free TCAR method increases the single epoch AR success probability by up to 90% for short baseline and 80% for long baseline. The A perfect (100%) AR success probability can also be effortlessly achieved by averaging the float ambiguities over just tens of epochs.

Tight integration of inertial sensors and stereo visual odometry to bridge Global Navigation Satellite System (GNSS) signal outages in challenging environments has drawn increasing attention. However, the details of how feature pixel coordinates from visual odometry can be directly used to limit the quick drift of inertial sensors in a tight integration implementation have rarely been provided in previous works. For instance, a key challenge in tight integration of inertial and stereo visual datasets is how to correct inertial sensor errors using the pixel measurements from visual odometry, however this has not been clearly demonstrated in existing literature. As a result, this would also affect the proper implementation of the integration algorithms and their performance assessment. This work develops and implements the tight integration of an Inertial Measurement Unit (IMU) and stereo cameras in a local-level frame. The results of the integrated solutions are also provided and analysed. Land vehicle testing results show that not only the position accuracy is improved, but also better azimuth and velocity estimation can be achieved, when compared to stand-alone INS or stereo visual odometry solutions.

The Chinese Area Positioning System (CAPS) is a regional satellite navigation system; its space segment consists of some Geostationary Earth Orbit (GEO) satellites and 2∼3 Inclined Geo-Synchronous Orbit (IGSO) satellites. Only a few satellites are needed to provide good area coverage and hence it is an ideal space segment for a regional navigation system. A time transfer mode is used to transmit navigation signals, so no high-precision atomic clocks are required onboard the satellites; all of the transferred navigation signals are generated by the same atomic clock at the master control station on the ground. By using virtual clock technology, the time of emission of signals from the ground control station is transformed to the time of transfer of signals at the phase centre of the satellite antenna; thus the impact of ephemeris errors of satellite on positioning accuracy is greatly decreased, enabling the CAPS to have the capability of wide area augmentation. A novel technology of orbit determination, called Paired Observation Combination for Both Stations (POCBS), proposed by the National Time Service Centre, is used in CAPS. The generation and measurement of ranging signals for the orbit survey are carried out in the ground station and the instrument errors are corrected in real-time. The determination of the clock offset is completely independent of the determination of satellite orbit, so the error of the clock offset has no impact on orbit determination. Therefore, a very high precision of satellite orbits, better than 4·2 cm (1 drms) can be obtained by the stations under regional distribution.

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.

In this study, a method is presented to maintain real-time positioning at the decimetre-level accuracy during breaks in reception of the measurement corrections from multiple reference stations. The method is implemented at the rover by estimating prediction coefficients of the corrections during normal RTK positioning, and uses these coefficients to predict the corrections when reception of the corrections is temporarily lost. The paper focuses on one segment of this method, the on-the-fly prediction of orbital corrections. Frequently, only a few minutes of data representing short orbit ‘arcs’ are available to the user before losing radio transmission. Thus, it would be hard for the rover to predict the satellite positions using equations of motion. An alternative method is proposed. In this method, GPS orbital corrections are predicted as a time series and are added to the initial positions computed from the broadcast ephemeris to compute relatively accurate satellite positions. Different prediction approaches were investigated. Results show that the double exponential smoothing method and Winters' method can be successfully applied. The latter, however, has a better performance. The impact of the data length used for estimation of the prediction coefficients and the selection of seasonal lengths in Winters' method were investigated and some values were recommended. In general, the method can give orbital correction estimation accuracy of less than 5 cm after 15 minutes of prediction. This will result in a positioning accuracy better than 5 cm.

The issues in this paper are a continuation of those presented previously by the authors in The Journal. In this paper we discuss the changes in maritime navigation and their consequences. We show the changes taking place in the ship's navigation process and in development of Maritime Navigation Safety and Efficiency System (MNSES). The relations between these two processes are examined. As the result, a probable scope of the competencies required by future navigators is proposed.

The European Geostationary Navigation Overlay Service (EGNOS) system is being developed in Europe to provide Global Positioning System (GPS) and GLONASS regional augmentation services to aviation, maritime and land users. The EGNOS system, as any other Wide Area Augmentation System (WAAS), relies on the broadcast of differential correction and integrity information in the pseudo-range domain, which are then used to provide a solution in the position domain. EGNOS is a major element of the European Satellite Navigation Program, which is jointly being implemented by the Commission of the European Union, the European Space Agency (ESA) and Eurocontrol (the European Organisation for the Safety of Air Navigation). It is also the first European step to the GALILEO system.

As part of the EGNOS validation activities, flight trials have been organised by ESA and the EGNOS Industrial Consortium at various locations in Europe during Spring 2005. To demonstrate the system capability in a challenging mountainous environment, tests have been conducted at Lugano airport in the Swiss Alps. Due to the difficult topography of the airport and its surroundings, the use of conventional ground based navigation aids present some limitations. For the trials, a new Satellite Based Augmentation System (SBAS) procedure has been designed to take advantage of the system flexibility. In particular, a reduction of the approach glide path angle has been achieved, potentially allowing more aircraft types to fly the approach than today. This article presents the operational benefits that could be obtained with the new test procedure. The very impressive EGNOS performance is also described in details, showing that it can support Approach Procedure with Vertical guidance (APV) operations even in a very challenging environment.