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Global Navigation Satellite Systems (GNSS), today the primary source for position, navigation and time (PNT) information in the maritime domain, are vulnerable to unintentional and intentional interference, e.g. jamming and spoofing. A backup system is needed to overcome this threat and to enable new applications with an increased need for resilient PNT information. Diversity of signals is a promising approach to overcome the dependence on GNSS signals which have in common to be very weak at sea level and located in only few frequency bands. Terrestrial radionavigation systems, which typically operate in lower frequency bands and most often with higher transmitting power, are differently affected by signal distortions or interferences. As a complement to GNSS they can support continuous availability of PNT information even if the accuracy is lower compared to GNSS. While they were state of the art for decades, terrestrial radionavigation systems lost importance with the increasing availability of GNSS receivers. As a consequence, these services were discontinued in parts of the world. Today no world-wide available terrestrial radionavigation system exists. In 2008 Oltmann and Hoppe proposed an efficient way to get back a terrestrial radionavigation system as a backup to GNSS by using already existing maritime radio infrastructure for the transmission of ranging signals in addition to the legacy signal. The system is called ranging mode (R-Mode). Promising candidates were maritime radio beacons and land-based stations of the Automatic Identification System (AIS). Both have in common their good distribution of stations along the coastline near the main maritime traffic routes. First feasibility studies towards R-Mode were conducted by Johnson and Swaszek within the framework of the European ACCSEAS project in 2014. Based on these studies, ranging measurements with modified radio beacons were performed in the Netherlands in 2015 and in Germany in the following years. In 2015 Qing et.al reported about successful tests using AIS base stations for positioning in the Xinghai sea region of Dalian. In 2020 Johnson et.al demonstrated that R-Mode, implemented on three medium frequency DGNSS transmitter sites, can be used for positioning in a limited area on land. Missing so far are R-Mode trials of maritime long-range signals from maritime radio beacons and the R-Mode implementation that follows the new Very High Frequency (VHF) Data Exchange System (VDES) Guideline of the IALA for transmissions in the maritime VHF band. The presentation gives an overview about the achievements of the EU co-financed project R-Mode Baltic which has been conducted by 12 partners from national maritime administrations, industry and research institutions under the leadership of the German Aerospace Center in the time from 2017 to 2021. It reports about the R-Mode requirements on a terrestrial navigation system as backup to GNSS for port approaches and coastal navigation. It shows that the maritime radio infrastructure of the Southern Baltic Sea fulfils the precondition for a successful implementation of a combined MF and VDES R-Mode system. This is based on a coverage prediction and accuracy estimation study of the GRAD Department of Trinity House. During the project eight MF maritime radio beacons and four VDES base stations with R-Mode capabilities were installed in the R-Mode Baltic testbed. The results of first maritime positioning tests in the testbed show that R-Mode is a good candidate for a backup system for maritime applications. A cost-benefit analysis based on the experiences and developments of the project shows that the costs for an R-Mode system depend on the level of time synchronization accuracy. Each maritime administration has to decide if they want to support the mariner for a certain time until he reaches a safe state after detection of GNSS problems, this is called contingency system, or that R-Mode is always available as a true backup system.

The R-Mode terrestrial navigation system evaluates the phase of two carriers next to a modulated signal, from which a range can be derived to allow positioning using different stations. To improve the accuracy of ranging, we propose in this paper to replace the currently used Minimum Shift Keying (MSK) modulation with Gaussian Minimum Shift Keying (GMSK). By applying a Gaussian pulse shape for the bit transition to that of the MSK a higher spectral efficiency is achieved. If the data rate is kept constant, this reduces the energy of the modulated signal within the bandwidth of the phase estimator. This increases the accuracy of the added carrier estimate and achieves our goal of improved distance-estimation accuracy. In this paper, we compare the estimates for an R-Mode signal with MSK and two different GMSK modulations. The increased accuracy is verified using software and hardware in-the-loop simulations.

Due to the worldwide recognition of increased jamming and spoofing events, which threaten the usability of global navigation satellite systems (GNSS), positioning systems using signals of opportunity are gaining importance as backup systems. Especially for maritime usage, a terrestrial system called Ranging-Mode (R-Mode) is under development. Among other signals, it utilizes the maritime medium frequency broadcasts of the differential GNSS (DGNSS) service. Currently, the estimation of phase in a time continuous medium frequency signal is used to determine the distance between transmitter and receiver. Here, the delay of a transmitter on the signal phase is of great interest, since it directly affects the performance of the R-Mode system. In this paper, the influence of a medium frequency power amplifier is characterized as part of the transmitter chain. The aim is to give the operators of DGNSS stations the possibility to characterize their station themselves when the R-Mode system is operational. Therefore, widely used measuring instruments are utilized, rather than using well-known cost-intensive techniques like phase delay measurements. A simple setup with different evaluation methods that fit this requirement is presented. Furthermore, it is capable of measuring the absolute time delay. The presented workflow was tested on an amplifier with output power of 100 W at the transmitter station near Koblenz, Germany.

Inland navigation and shipping is an important pillar of the European Transport System. To support the skipper during safety-critical operations, precise Position, Navigation and Time (PNT) data are required. This work discusses the role of PNT information for enabling inland waterways navigation assistance functions, such as bridge collision warning, mooring aiding or automatic guidance. A Real-Time Kinematic (RTK) technique is developed to provide integrity information alongside reliable and cm-level accurate PNT data. Besides, the transmission of Global Navigation Satellite Systems (GNSS) correction data is investigated. Since Global System for Mobile (GSM) does not currently meet the availability and stability communication requirements along inland waterways, using the Automatic Identification System (AIS) for data transmission is explored. The proposed navigation solution and the communication developments were analysed in real time on challenging GNSS signal-degraded scenarios on the authorized inland waterway testbed. Despite the further developments required on the AIS communication infrastructure, it is shown that our system architecture can nearly meet the integrity and accuracy requirements for driver assistance functions on inland waterways.

Global Navigation Satellite Systems (GNSS), today the primary mean for Position, Navigation and Timing (PNT) information on-board of a vessel, are highly vulnerable to unintentional and intentional interference like jamming or spoofing. Therefore, maritime community seeks for an alternative system to compensate this thread and follow the vision of the eNavigation strategy of International Maritime Organization (IMO), a safe navigation of vessels from berth to berth. The only alternative terrestrial backup for GNSS is the enhanced LOng-RAnge Navigation (eLORAN). However, that system will probably never reach global coverage because a substantial part of LORAN stations was shutdown in the years 2010 to 2015. There are only certain regions where it is still usable as well as Chayka, the Russian system. Today, in case of a temporal loss of GNSS no system can provide absolute positioning in areas with increased necessity for reliable navigation data provision on a global scale. One candidate for a terrestrial backup system is R(anging)-Mode which utilizes existing maritime radio infrastructure for the broadcast of modified signals, which allow distance estimation to the transmitter. First feasibility studies were done in the North Sea, in China and in South Korea. The Baltic Sea is due to the high number of vessels along the shipping routes and its sensitive marine ecosystem a suitable region for the implementation and testing of R-Mode firstly as a terrestrial backup system to GNSS. It will supplement navigation information in order to reduce the risk of collisions and groundings. New marine applications that require a continuous provision of position information will be made possible at sea, in coastal areas and in harbours. A consortium of 12 research institutions, administrations and industry of Germany, Poland, Sweden and Norway is currently engaged to setup the first R-Mode testbed, which utilizes IALA (International Association of Marine Aids to Navigation and Lighthouse Authorities) beacons and Automatic Identification System (AIS) land stations for the broadcast of R-Mode enabled signals. This will be organized in the southern Part of the Baltic Sea until 2020 funded by EU within the scope of R-Mode Baltic Project. Beside this main goal of the Project (back-up to GNSS) further research and development activities will be conducted. This comprises the selection of most suitable way of R-Mode service implementation on IALA beacon and AIS signals without disruption of the legacy service. Further the selection of best algorithms for positioning either with only one type of R-Mode signals or with both is part of the research activities. In addition a concept development and test installation for the time synchronization of a transnational network of R-Mode stations which is currently maintained by independent national maritime administrations as well as the development of first prototypes of R-Mode receiver capable to cope with modified IALA beacons and/or AIS signals as well as R-Mode base station hardware for R-Mode signal generation is planned. Finally, with R-Mode enabled PNT data processing and Pilot Plug Unit the first two R-Mode applications will be made available. All this activities will be done in close contact with the maritime administrations, IALA, and maritime users. It is anticipated, that R-Mode will be a terrestrial backup system that can fulfil their need for robust and reliable PNT data for safe navigation at sea. Beside a general description of the project first results of a common coverage prediction for the IALA beacon and AIS communication channels for the Baltic Sea region will be estimated and presented. Latter shows that especially the relevant Baltic Sea region with its narrow passages of coastlines in the North (Denmark, Norway and Sweden) and in the South (Germany, Poland) is already well equipped with a dense network of IALA beacons and AIS stations in the vicinity of vessel routes. In case of positive Project results, upgrading all of them to R-Mode service level these would allow positioning in the entire region. Furthermore, the output of the requirement phase study on the R-Mode system and its components is presented. This was done starting from relevant documents of IMO and IALA requirements for a terrestrial backup system were extracted and next further broken down for specific components of the R-Mode system. This shall give guidance throughout the project when selecting appropriate algorithms, methods and technical solutions.

Inland shipping is an important pillar of the European transport system; however the challenges of inland navigation due to dense traffic, increasing ship dimension, reduced maneuver space and visibility are multifaceted and increasing. About 20 to 30 collisions per year, partially caused by carelessness, demonstrate the necessity of driving assistance systems for inland waterway applications. The project LAESSI (Guiding and assistance systems to improve safety of navigation on inland waterways) is developing efficient navigation assistance functions for inland waterway transport which aim the reduction of risk of collisions by supporting the skipper in its task. Therefore, nautical information like position, height, velocity and heading has to be determined. One focus in this contribution is a bridge collision warning system, which provides a timely alert to the skipper, whenever the vessel, particularly the wheelhouse or radar mast, will not safely pass the bridge. A feasibility study has identified Global Navigation Satellite System (GNSS) technologies as basis for the reliable height determination for such a bridge collision warning system. This approach requires information about the vertical clearance of the bridge superstructure as well as precise height information in the same height reference system at least 300 m before the vessel will pass the bridge. The high accuracy level of less than 10 cm in the vertical position necessitates the Real Time Kinematic (RTK) as suitable GNSS processing method. RTK is a phase-based differential GNSS technique and uses additional observations from permanent reference stations to mitigate or eliminate effects like tropospheric and ionospheric delays or satellite clocks and orbit errors. As bridge collision warning system is a safely critical application, this means that beside the provision of accurate height information also an integrity monitoring for the complete RTK procedure has to be introduced. The shore-based architecture is designed in such a way that correction data, based on a permanent GNSS reference station network, will be checked for their integrity before they are broadcasted (Pre-Broadcast Monitoring) to the processing computer on the vessel. Furthermore, several station dependent effects like signal interferences, signal losses or multipath effects, caused due to obstacles near the inland waterways, impact the GNSS signals, which hamper or falsify the ambiguity fixing and finally the position results. To prevent the provision of faulty results a further integrity monitoring for the shipborne architecture has to be applied. This shipborne integrity monitoring utilizes on the one hand a number of internal statistical parameters from the RTK algorithm like the conventional used fixed ratio value and on the other hand additional information from other sensors or observations. The contribution will present the derived requirements for accuracy, integrity and time to alert for different inland waterway assistance functions. Furthermore an overview about the system architecture and a communication concept based on VHF Data Exchange System (VDES) communication channels will be given. The main focus, however, is an RTK-algorithm which not only estimates position, velocity and heading, but also provides integrity information. This concept considers in a first realization internal statistical parameters from the RTK adjustment, other observations (e.g. Doppler shift) and physical information (e.g. baseline length of two GNSS antennas). A first measurement campaign was done in July 2016 in Koblenz/Germany on the river Moselle. This test area is characterized by three bridges in a relatively short distance of only 300 m which make the provision of reliable and precise RTK position data rather challenging. The preliminary analyses based on three hours GPS and GLONASS observations showed a high rate (> 85%) of evaluated position and height results, which fulfilled the required cm-level accuracies. The first implementation of the internal integrity check could detect and eliminate faulty results. The results have shown that beside a good height performance also fast provision of the heights after the vessel sailed through the bridges is recognizable. This position data between the bridges allows a provision of information to the skipper to check or adjust the wheelhouse or radar mast height before the next bridge will be passed. In the next implementation the rate of turn and acceleration data from an Inertial Measurement Unit (IMU) will be tightly coupled with the raw GNSS observations. Thereby additional information will be available to evaluate the position, height, velocity and heading results and increase the integrity validation. Furthermore it can be expected that the ambiguities after a complete signal interruption can be fixed faster.

Position, Navigation, and Timing (PNT) is part of the critical infrastructure necessary for the safety and efficiency of vessel movements, especially in congested areas such as the North Sea. Global Navigation Satellite Systems (GNSS), especially the U.S. Global Positioning System (GPS), have become the primary PNT sources for maritime operations. The GNSS position is used both for vessel navigation and as the position and timing source for other systems such as Automatic Identification System (AIS). Unfortunately, GNSS is vulnerable to jamming and interference, intentional or not, which can lead to the loss of positioning information or, even worse, to incorrect positioning information. The user requirement is for dependable PNT information at all times. One potential source of resilient PNT services is Ranging Mode (R-Mode), an alternative PNT concept related to Signals of OPportunity (SoOP) PNT, which uses signals independent of GNSS. In 2013 the German Federal Waterways and Shipping Administration contracted for a feasibility study of R-Mode using medium frequency (MF) Differential GNSS (DGNSS) and very high frequency (VHF) AIS signals as well as those signals in combination and in combination with eLoran. At ION GNSS+ 2014 some of the authors presented the results from that feasibility study and showed the projected performance using the signals individually and in combination. In most of the shipping lanes on the North Sea it appeared that 10m or better performance could be achieved. Following up on that work, prototypes of a transmitter and receiver for MF-DGNSS R-Mode have been developed. The transmitter was installed in IJmuiden (Netherlands) and the receiver deployed along the Dutch coast to the south of the transmitter for initial on-air testing of the R-Mode concept; both were synchronized to UTC via GPS. While positioning is not possible with only one R-Mode transmitter, the combination of a synchronized transmitter and receiver pair allows for useful testing of the R-Mode concept. Specifically, the receiver could estimate a true range (rather than a pseudorange); hence, the stability of the range with environmental variations (e.g. weather, day/night skywave effects, etc.) can be studied. To further study skywave effects, the R-Mode modulator was relocated to a more powerful transmitter at Heligoland (Germany) and the receiver moved to a location near the Kiel Canal (Germany). A second receiver was installed at a similar distance from the transmitter to enable simultaneous comparison of two different propagation paths. Later a third receiver was added in order to provide three paths of different lengths. The original R-Mode feasibility study also examined the number of stations that it would be possible to receive in the North Sea area to ensure there were sufficient stations for positioning. However, it did not look at the converse question; how would a large number of R-Mode signals impact legacy users. As part of the prototype development, very limited experiments were performed to assess the impact of the new signals on legacy DGNSS receivers. Specifically, during the on-air testing mentioned above, a commercial DGNSS receiver was able to accurately demodulate and decode the on-air transmissions from the single prototype R-Mode transmitter; the impact of multiple signals was not examined. A new study, funded by the General Lighthouse Authorities of the UK and Ireland, has just been initiated to analyze how legacy equipment would respond to multiple R-Mode signals at different frequencies, both in-band and out-of-band. This paper presents details of the prototype transmitter and receiver and includes statistical analyses of the range estimates recorded to date and the impact of skywave interference at night using data from the German test sites. Additionally, this paper includes preliminary results of the R-Mode signal interference study.

The IMO e-Navigation concept supports the developed of resilient positioning, navigation and timing (PNT) information. The need for resilient PNT well documented and it is recognised that the use of a number of technically dissimilar systems are required to ensure resilient PNT is achieved. Global Navigation Satellite Systems (GNSS) are expected to remain the primary means of navigation at sea; however additional supporting and complementary systems are required to give resilient PNT. One candidate system which could provide alternative positioning and timing information is called R-mode, or ranging mode. This is the name given to the provision of a new ranging signal to marine radio beacon 300 kHz transmissions and AIS base stations transmissions, from which the mariner could then potentially calculate their position, independently to GNSS. The concept of such a system was developed under the ACCSEAS project, which considered a number of potential e-Navigation solutions, resilient PNT being one. The ACCSEAS project has been introduced and discussed at ION conferences; however, this paper will focus on R-mode. This paper will report on the aims and objectives of R-Mode, the results of the feasibility study that was produced by the ACCSEAS project, review the development of the concept to date and report on the development and test of a prototype marine beacon broadcast and receiver. It will review the performance of the prototype system and then consider the proposed way forward, both from a local perspective, but also from the wider international perspective for the use of such a system world-wide. The latter will consider the development path, international standardisation activities and the questions which need to be addressed. The paper will describe the current developments for R-mode in both the marine beacon and AIS variants, raising awareness and seeking support for further investigation and development of this potentially important approach to support resilient PNT across the maritime sector.

Virtualization has gained great popularity in recent years with application virtualization being the latest trend. Application virtualization offers several benefits for application management, especially for larger and dynamic deployment scenarios. In this paper, we initially introduce the common application virtualization principles before we evaluate the security of Microsoft App-V and VMware ThinApp application virtualization environments with respect to external security threats. We compare different user account privileges and levels of sandboxing for virtualized applications. Furtherwmore, we identify the major security risks as well as trade-offs with ease of use that result from the virtualization of applications.

Περιέχει το πλήρες κείμενο eSciDoc is the open-source e-Research framework jointly developed by the German Max Planck Society and FIZ Karlsruhe. It consists of a generic set of basic services (“eSciDoc Infrastructure”) and various applications built on top of this infrastructure (“eSciDoc Solutions”). This paper focuses on the eSciDoc Infrastructure, highlights the differences to the underlying Fedora repository, and demonstrates its powerful und application-centric programming model. Further on, we discuss challenges for e-Research Infrastructures and how we addressed them with the eSciDoc Infrastructure.