The Feasibility of R-Mode to Meet Resilient PNT Requirements for e-Navigation

Position, Navigation, and Timing (PNT) is part of the critical infrastructure necessary for the safety and efficient of vessel movements, especially in congested areas such as the North Sea. GNSS (primarily GPS and GLONASS) has become the primary PNT source for maritime operations. The GNSS position is used both for vessel navigation and as the position source for AIS. Unfortunately, GNSS is vulnerable to jamming and interference – not intentional and unintentional. This 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, even under GNSS jamming conditions. One potential source of resilient PNT services is Ranging Mode (R-Mode) using signals independent of GNSS. The German Federal Waterways and Shipping Administration has contracted for a feasibility study of R-mode using MF-DGNSS and VHF AIS signals as well as those signals in combination and in combination with eLoran. The first part of the study focused on the feasibility of using MF-DGNSS signals for ranging and timing. It examined the state of the art, identified potential solution methods, and, after examining Pros and Cons of the various options, selected a few options for further study. Part 2 examined the proposed solutions in depth and identified the modifications required for both the reference stations (transmitters) and user equipment (beacon receivers). Part 3 and 4 of the study repeated Parts 1 and 2, but using AIS signals rather than MF. Part 4 of the study examined the possibility of combining MF and AIS R-mode or combining MF R-Mode and eLoran. This paper presents the results of this study including recommended R-Mode implementations and bounds on the positioning performance using the various R-Mode methods. Included are predictions of DGNSS and AIS R-Mode coverage and the resulting HDOP using existing and preposed DGNSS and AUS sites with specific detail in the area of the planned test bed in the North Sea

Preliminary Analysis of Skywave Effects on MF DGNSS R-Mode Signals During Daytime and Nighttime

Accurate positioning, navigation, and timing (PNT) performance are prerequisites for several technologies today. In a marine environment, it is difficult to visually identify one's position accurately, leading to safety concerns. Currently, PNT information is provided mainly from Global Navigation Satellite Systems (GNSS); however, it is vulnerable to radio frequency interference, spoofing, and ionospheric anomaly. Therefore, research on a backup system is needed. Ranging Mode (R-Mode), a terrestrial integrated navigation system, is being investigated for use in a marine environment. R-Mode is a positioning technology that integrates terrestrial signals of opportunity such as medium frequency (MF) differential GNSS (DGNSS), very high frequency (VHF) automatic identification system (AIS), and enhanced long-range navigation (eLoran) signals. Previous studies in Europe show that signals in the MF band differ greatly in accuracy between daytime and nighttime. This difference is primarily caused by skywave. In this study, the MF DGNSS R-Mode signal transmitted from Chungju, Korea was received in Daesan and Daejeon, Korea. The skywave effect during daytime and nighttime was compared and investigated. In addition, the continuous wave intensity of the R-Mode signal was increased during the nighttime to compare its effect on the measurement accuracy

Control of position sensor input to Ecdis on high speed craft

Project thesis submitted in part fulfilment of the requirements for the degree of Master of Science in Position and Navigation Technology at The University of NottinghamBy 2018 all larger ships are to be equipped with Electronic Chart Display and Information System (ECDIS). The paradigm shift from paper charts to electronic charts has been a technological leap for mariners, and the Integrated Navigation Systems (INS) are getting more and more complex. This leads to new challenges for the navigators of today. Global Navigation Satellite Systems (GNSS) such as GPS are the primary position sensor input for ECDIS, and it has since its early beginning in the middle of the 1990s been very reliable. National and worldwide statistics show that there has been a slight increase in navigational accidents since the introduction of ECDIS, but the reasons for this is not clear. In the literature review it is laid down that position sensors have its potential fault, and GNSS and its augmentation systems is described to better understand its advantageous and limitations. Control of ECDIS with position control methods are explored, and divided into two methods of control: Visual- and Conventional methods. Through field work, simulator tests and interviews the findings are clear. The navigators of today rely too much upon their primary position sensor which normally is a GNSS such as GPS. A questionnaire reveals that the navigators have insufficient deeper system knowledge of the navigation aids in use. This can lead to a potentially serious accident with loss of lives and large environmental damage. To achieve safe navigation it is important to continuously conduct control of primary position sensor input to ECDIS with a secondary position sensor by visual- and/or conventional control methods. The advantages and limitations with the different methods of control are discussed. Position sensors such as GNSS can fail, and navigators of today and tomorrow need to monitor the position sensor input to ECDIS with other means than GNSS

Exhaustive Search-based Model for Hybrid Sensor Network

A new model for a cluster of hybrid sensors network with multi sub-clusters is proposed. The model is in particular relevant to the early warning system in a large scale monitoring system in, for example, a nuclear power plant. It mainly addresses to a safety critical system which requires real-time processes with high accuracy. The mathematical model is based on the extended conventional search algorithm with certain interactions among the nearest neighborhood of sensors. It is argued that the model could realize a highly accurate decision support system with less number of parameters. A case of one dimensional interaction function is discussed, and a simple algorithm for the model is also given.Comment: 6 pages, Proceeding of the International Conference on Intelligent & Advanced Systems 2012 pp. 557-56

Simulation of Medium-Frequency R-Mode Signal Strength

Assuming failure in the global navigation satellite systems due to radio frequency interference and ionospheric anomaly, an R-Mode system, a terrestrial integrated navigation system, is being actively studied for domestic deployment in South Korea. In this study, parameters for an approximate calculation of the received signal strength were obtained and applied to develop a performance simulation tool for a medium-frequency R-Mode system. As a case study, the signal strength from the Yeongju transmitter was simulated using the proposed parameters.Comment: Submitted to ICCE-Asia 202

Strategically Positioned Inhibitory Synapses of Axo-axonic Cells Potently Control Principal Neuron Spiking in the Basolateral Amygdala.

Axo-axonic cells (AACs) in cortical regions selectively innervate the axon initial segments (AISs) of principal cells (PCs), where the action potentials are generated. These GABAergic interneurons can alter the activity of PCs, but how the efficacy of spike control correlates with the number of output synapses remains unclear. Moreover, the relationship between the spatial distribution of GABAergic synapses and the action potential initiation site along the AISs is not well defined. Using paired recordings obtained in the mouse basolateral amygdala, we found that AACs powerfully inhibited or delayed the timing of PC spiking by 30 ms, if AAC output preceded PC spiking with no more than 80 ms. By correlating the number of synapses and the probability of spiking, we revealed that larger numbers of presynaptic AAC boutons giving rise to larger postsynaptic responses provided more effective inhibition of PC spiking. At least 10-12 AAC synapses, which could originate from 2-3 AACs on average, were necessary to veto the PC firing under our recording conditions. Furthermore, we determined that the threshold for the action potential generation along PC axons is the lowest between 20 and 40 mum from soma, which axonal segment received the highest density of GABAergic inputs. Single AACs preferentially innervated this narrow portion of the AIS where action potentials were generated with the highest likelihood, regardless of the number of synapses forming a given connection. Our results uncovered a fine organization of AAC innervation maximizing their inhibitory efficacy by strategically positioning synapses along the AISs

A Taxonomy Framework for Maritime Cybersecurity: A Demonstration Using the Automatic Identification System

The maritime transportation system is increasingly a target of cyber attacks. This paper describes a taxonomy that supports the creation of adversarial cyber models, risk mitigation, and resiliency plans as applied to the maritime industry, using the Automatic Identification System as a specific illustration of the approach. This method has already been applied to the aviation sector; retooling it for a maritime example demonstrates its broad applicability to the transportation sector, in general