Two issues have recently triggered an increasing interest in the use of multiple different sensors for navigation. Firstly, in all modes of traffic and transportation navigation aids need to function in an environment characterised by increasing levels of traffic density, dense construction and radio frequency congestion. Existing navaids appear to be inadequate to cope with this situation. A second factor is the increasing distrust in the use of satellite navigation as a sole means of navigation since its vulnerability to radio frequency interference makes it a high-risk single point of failure. The aim of this dissertation is to show the potential advantages of integrated navigation in the different modes of traffic and transportation. Multi-modal operational requirements on navigation systems are identified first. Then it is shown how these requirements can be translated into a design using a top-down approach applying the ideas contained in ICAO's concept of Required Navigation Performance (RNP). A general configuration of an integrated navigation system is presented, which is made more specific for different levels of integration. The topdown RNP approach is then applied to integrated navigation system design and it is shown how the selection of a specific level of integration using specific integration tools can meet the operational requirements of the user. This approach is subsequently applied in two case studies, MIAS and Eurofix. In chapter 1 the objective of this dissertation is introduced. Thereafter, chapter 2 introduces multi-modal operational needs on navigation and traffic management systems and discusses ICAO's RNP concept. It is shown that the RNP concept is well suited to translate general multi-modal operational needs into navigation system requirements and constraints. The main shortcoming of the RNP concept is identified - namely that total system performance is only considered for a static point in space, which limits the validity of the current concept. Chapter 3 presents a general sensor fusion model, identifying all necessary elements. This model is discussed in more detail for the fusion of navigation sensors, which is then referred to as integration. The concept of sensor interoperability is discussed and it is shown how supplementary and complementary characteristics of multiple sensors can be exploited through integration. Different Kalman filtering implementations in integrated navigation are reviewed, where the main focus is on the operational application and safety aspects, e.g. for demanding applications such as aircraft approaches. It is also shown under which conditions the redundancy in integrated navigation systems may be used to enhance integrity. Finally, different levels of sensor integration are discussed including benefits and limitations. The general conclusion is that deeper levels of integration yield higher accuracy, but integrity and reliability (i.e. the continuity-of-function) are more easily maintained at reduced levels of integration. Chapter 4 presents the first case study: the integration of MLS and DGNSS in the Multi-mode integrated Approach System (MIAS). The aviation community needs a new approach and landing system to succeed 1LS; but it must have at least a similar accuracy. Safety requirements are preferably to be more stringent to maintain the absolute level of safety, defined by the parameters integrity and continuity-of-service with an increasing level of traffic, The design should require a minimal impact on the infrastructure of the ground equipment and the aircraft to minimise cost. To maintain current accuracy levels, a medium level of integration is selected with MLS performance as a baseline. In order to minimise cost, advantage is taken of existing and proven means - MLS and GNSS - transmitting GNSS corrections taking advantage of the MLS datalink. Accuracy performance is illustrated using flight test results, while integrity and continuity performance is demonstrated using analysis. Chapter 5 presents the second case study: the integration of LORAN-C and DGNSS in Eurofix. The user interest in such a system is to have available a multi-modal navigation aid applicable over a wide area, where usage could range from continental air- and waterways to aircraft approach capability. Differences in accuracy performance result in DGNSS being taken as the baseline, while calibrated LORAN-C is used as a high reliability back-up. In order to minimise cost, advantage is taken of existing and proven means, namely LORAN-C and GNSS, broadcasting GNSS corrections by additional modulation of the LORAN-C signal. Performance is optimised through exploitation of the available infrastructure, which is illustrated using analysis. The conclusion is that a well integrated combination of currently existing navaids may offer an answer to many multi-modal user needs at a minimum required investment, while solving the single-point of failure problems. (Author/publisher)
Abstract