This paper charts the history of Global Satellite Navigation Systems (GNSS) from the earliest days of the ‘Space Race’ in the 1960s and 1970s to the latest plans for modernisation of existing systems and the development of new systems yet to be deployed or become operational. The paper is based on lectures and presentations given by the author to postgraduate students at The University of Nottingham, students on the RAF General Duties Aero-Systems Course at the Air Warfare Centre, RAF Cranwell and to a number of RIN, RAeS and IEE Branches and to local aviation groups.

Shoe mounted Inertial Measurement Units (IMU) are often used for indoor pedestrian navigation systems. The presence of a zero velocity condition during the stance phase enables Zero Velocity Updates (ZUPT) to be applied regularly every time the user takes a step. Most of the velocity and attitude errors can be estimated using ZUPTs. However, good heading estimation for such a system remains a challenge. This is due to the poor observability of heading error for a low cost Micro-Electro-Mechanical (MEMS) IMU, even with the use of ZUPTs in a Kalman filter. In this paper, the same approach is adopted where a MEMS IMU is mounted on a shoe, but with additional constraints applied. The three constraints proposed herein are used to generate measurement updates for a Kalman filter, known as ‘Heading Update’, ‘Zero Integrated Heading Rate Update’ and ‘Height Update’.

The first constraint involves restricting heading drift in a typical building where the user is walking. Due to the fact that typical buildings are rectangular in shape, an assumption is made that most walking in this environment is constrained to only follow one of the four main headings of the building. A second constraint is further used to restrict heading drift during a non-walking situation. This is carried out because the first constraint cannot be applied when the user is stationary. Finally, the third constraint is applied to limit the error growth in height. An assumption is made that the height changes in indoor buildings are only caused when the user walks up and down a staircase. Several trials were shown to demonstrate the effectiveness of integrating these constraints for indoor pedestrian navigation. The results show that an average return position error of 4·62 meters is obtained for an average distance of 1557 meters using only a low cost MEMS IMU.

Galileo is a global civil navigation satellite system developed in Europe as an alternative to the GPS controlled by the US Department of Defense and GLONASS controlled by Russian Space Forces. It is scheduled to be operative in 2013 and it will have 30 satellites orbiting on three inclined planes with respect to the equatorial plane at an altitude of about 24 000 km. The aim of this work is the study of the pseudorange error of the GIOVE satellites. To achieve this goal, the specifications defined in Giove A-B Navigation Signal in Space Interface Control Document (ICD) are used to develop a suitable software tool in MATLAB® environment. The tool is able to compute GIOVE A and GIOVE B position from the broadcast ephemerides, to calculate the pseudorange error and to process it. From the known receiver position and the computed satellite coordinates, the geometric range is obtained and compared with the pseudorange measurement, in order to obtain the pseudorange error.

The determination of the correct integer number of carrier cycles (integer ambiguity) is the key to high accuracy positioning with carrier phase measurements from Global Navigation Satellite Systems (GNSS). There are a number of current methods for resolving ambiguities including the Least-squares AMBiguity Decorrelation Adjustment (LAMBDA) method, which is a combination of least-squares and a transformation to reduce the search space. The current techniques to determine the level of confidence (integrity) of the resolved ambiguities (i.e. ambiguity validation), usually involve the construction of test statistics, characterisation of their distribution and definition of thresholds. Example tests applied include ratio, F-distribution, t-distribution and Chi-square distribution. However, the assumptions that underpin these tests have weaknesses. These include the application of a fixed threshold for all scenarios, and therefore, not always able to provide an acceptable integrity level in the computed ambiguities. A relatively recent technique referred to as Integer Aperture (IA) based on the ratio test with a large number of simulated samples of float ambiguities requires significant computational resources. This precludes the application of IA in real time.

This paper proposes and demonstrates the power of an integrity monitoring technique that is applied at the ambiguity resolution and positioning stages. The technique has the important benefit of facilitating early detection of any potential threat to the position solution, originating in the ambiguity space, while at the same time giving overall protection in the position domain based on the required navigation performance. The proposed method uses the conventional test statistic for ratio testing together with a doubly non-central F distribution to compute the level of confidence (integrity) of the ambiguities. Specifically, this is determined as a function of geometry and the ambiguity residuals from least squares based ambiguity resolution algorithms including LAMBDA. A numerical method is implemented to compute the level of confidence in real time.

The results for Precise Point Positioning (PPP) with simulated and real data demonstrate the power and efficiency of the proposed method in monitoring both the integrity of the ambiguity computation and position solution processes. Furthermore, due to the fact that the method only requires information from least squares based ambiguity resolution algorithms, it is easily transferable to conventional Real Time Kinematic (RTK) positioning.

Recent developments in GPS positioning show that a user with a standalone GPS receiver can obtain positioning accuracy comparable to that of carrier-phase-based differential positioning. Such technique is commonly known as Precise Point Positioning (PPP). A significant challenge of PPP, however, is that about 30 minutes or more is required to achieve centimetre to decimetre-level accuracy. This relatively long convergence time is a result of the un-modelled GPS residual errors. A major residual error component, which affects the convergence of PPP solution, is higher-order Ionospheric Delay (IONO). In this paper, we rigorously model the second-order IONO, which represents the bulk of higher-order IONO, for PPP applications. Firstly, raw GPS measurements from a global cluster of International GNSS Service (IGS) stations are corrected for the effect of second-order IONO. The corrected data sets are then used as input to the Bernese GPS software to estimate the precise orbit, satellite clock corrections, and Global Ionospheric Maps (GIMs). It is shown that the effect of second-order IONO on GPS satellite orbit ranges from 1·5 to 24·7 mm in radial, 2·7 to 18·6 mm in along-track, and 3·2 to 15·9 mm in cross-track directions, respectively. GPS satellite clock corrections, on the other hand, showed a difference of up to 0·067 ns. GIMs showed a difference up to 4·28 Total Electron Content Units (TECU) in the absolute sense and an improvement of about 11% in the Root Mean Square (RMS). The estimated precise orbit clock corrections have been used in all of our PPP trials. NRCan's GPSPace software was modified to accept the second-order ionospheric corrections. To examine the effect of the second-order IONO on the PPP solution, new data sets from several IGS stations were processed using the modified GPSPace software. It is shown that accounting for the second-order IONO improved the PPP solution convergence time by about 15% and improved the accuracy estimation by 3 mm.

The next generation Global Navigation Satellite Systems (GNSS), such as Galileo and Global Positioning System (GPS) modernization, will use signals with equal code and bit periods, resulting in a potential bit sign transition in each primary code period of the received signal segments. A bit sign transition occurring within an integration period usually causes a splitting of the Cross Ambiguity Function (CAF) main peak into two smaller side lobes along the Doppler shift axis in the search space and it may lead to an incorrect Doppler shift estimate, which results in a serious performance degradation of the acquisition system. This paper proposes a novel two steps based bit sign transition cancellation method which can overcome the bit sign transition problem and remove or mitigate the CAF peak splitting impairments. The performance of the proposed technique has been comprehensively evaluated with Monte Carlo simulations in terms of detection and false alarm probabilities, which are presented by Receiver Operating Characteristic (ROC) and Signal-to-Noise-Ratio (SNR) curves. The test results show that the proposed acquisition technique can provide improved performance in comparison with the state-of-the-art acquisition approaches.

The Istanbul Strait is one of the most congested waterways in the world and is difficult to navigate due to its ‘S-shaped’ geographic structure (Akten, 2004). Much of the local marine traffic affects navigation safety. Results of Yurtoren and Inoue (2004)'s study, which investigated navigational risks in the Istanbul Strait in terms of manoeuvring difficulties and accident statistics, indicates the necessity of effective and applicable local traffic management in the southern entrance of the Strait. In this study, Marine Traffic Fast Time Simulation (MTFTS) studies are used and an attempt is made to improve navigation safety by proposing Local Traffic Separation Schemes (LTSS).

To improve the geolocation performance of an Unexploded Ordnance (UXO) survey platform, a geodetic Global Positioning System (GPS) receiver was combined with two tactical-grade Inertial Measurement Units (IMUs) and mounted on two types of detection systems. Analysis of data collected for typical trajectories focused on the dual-IMU/GPS pre/post processing using optimal nonlinear estimation together with a Wave Correlation Filter (WCF) and end-matching. Each trajectory of the platforms was estimated by the Extended Kalman Filter (EKF) and the Unscented Kalman Filter (UKF). The WCF was then applied to the two solutions of the platform trajectories derived from each IMU in order to extract the common components in the frequency domain, assuming that uncorrelated components are errors. The remaining bias and trends of the estimated position results were further removed by end-matching IMU solutions and GPS update points. The results of these methods were applied to our field test data to show that the WCF and end-matching can improve position accuracy from 4% to 14% with respect to the Unscented Kalman Smoother (UKS) solution alone.

In a car navigation system the conventional information used to guide drivers in selecting their driving routes typically considers only one criterion, usually the Shortest Distance Path (SDP). However, drivers may apply multiple criteria to decide their driving routes. In this paper, possible route selection criteria together with a Multi Objective Path Optimisation (MOPO) model and algorithms for solving the MOPO problem are proposed. Three types of decision criteria were used to present the characteristics of the proposed model. They relate to the cumulative SDP, passed intersections (Least Node Path – LNP) and number of turns (Minimum Turn Path – MTP). A two-step technique which incorporates shortest path algorithms for solving the MOPO problem was tested. To demonstrate the advantage that the MOPO model provides drivers to assist in route selection, several empirical studies were conducted using two real road networks with different roadway types. With the aid of a Geographic Information System (GIS), drivers can easily and quickly obtain the optimal paths of the MOPO problem, despite the fact that these paths are highly complex and difficult to solve manually.

When a ship is moored by a single anchor at the anchorage, its combined motions (i.e. yaw, sway, surge, etc.) are usually induced by external forces. Previous studies have gained some insights into the forces on anchor chains, but the motions for Capesize vessels still need to be further investigated. The length of anchor chain required for safe anchoring also needs to be carefully calculated rather than determined solely by the experience and judgement of Captains. The relationship between the length of chain and water depth, wind force, current velocity and the trim (draught difference forward/aft) requires further study. Our new methods consider all necessary factors which may exert significant influence on ships, including not only the water depth at the anchoring location but also the particulars of the ships, its equipment and the environmental conditions. Here, a numerical simulation model to describe the behaviour of an anchored Capesize ship is presented, with the comparison of results between simulations and real time model tests carried out. A discussion highlights the important features of the methods which provide mariners with theoretical solutions.

Satellite Navigation Systems (SNS) provide Position, Velocity and Time (PVT) services. The SNS is required to maintain its own System Time with high accuracy. To set up the precise System Time, each system component should maintain its own time within a specified limit. In the SNS, the onboard Space Vehicle (SV) time generator is one of the components and it should be set and maintained with few nanoseconds accuracy. To achieve accurate time setting with minimum difference between the ground and onboard SV systems, the onboard time setting should be highly predictable and accurate. This paper proposes an approach to initialize/set the onboard SV Time. The paper also discusses the concept of synchronization of SV Time with System Time with an overall accuracy better than 1 nsec. The proposed technique requires minimum setting time and synchronization steps and there is no need to predict accurate uplink propagation delay and command execution time.

Aided Inertial Navigation Systems (INS) systems are commonly implemented in land vehicles for a variety of applications. Several methods have been reported in the literature for evaluating aided INS performance. Yet, the INS error-state-model dependency on time and trajectory implies that no closed-form solutions exist for such evaluation. In this paper, we derive analytical solutions to evaluate the fusion performance. We show that the derived analytical solutions manage to predict the error covariance behavior of the full aided INS error model. These solutions bring insight into the effect of the various parameters involved in the fusion of the INS and an aiding sensor.