Phase estimation of single tones next to modulated signals in the medium frequency R-mode system

Position, navigation, and timing information are critical to today’s infrastructures; as a result, the possibility of estimating ranges is being explored in more and more radio systems. One way to achieve this is to extend the modulation with time-synchronised aiding carriers and to estimate their phase at the receiver side. In this paper, we present two ways to minimise the negative influence of the modulation on the phase estimation. We show that the classical maximum likelihood estimator is still an efficient estimator for our problem, using a medium-frequency R-Mode signal as an example, and is therefore used in receiver designs. We then describe two possible ways to precondition the signal to increase the accuracy for short observations. As a first approach, we describe how window functions can positively change the signal-to-noise ratio for our estimation. As a second approach, we show the use of a narrowband bandpass filter. Finally, we show that these approaches, applied to real measurements, improve the variance of the estimate by up to two orders of magnitude

Direct Position Estimation for VDES R-Mode

As maritime traffic strongly relies on Global Navigation Satellite Systems (GNSS) such as GPS or Galileo, there are efforts to mitigate the risks that come with this reliance. One such effort is the development of VDES R-Mode, which aims to provide a terrestrial contingency system to GNSS that is based on the VHF Data Exchange System (VDES). Terrestrial VDES provides a bandwidth of 100 kHz. To make best use of the available bandwidth, VDES R-Mode can use a signal that is optimized for a high effective bandwidth. This signal however, has a very regular structure that leads to ambiguities that degrade the ranging performance at lower SNRs. We found that this drawback can be mitigated by evaluating the signals of multiple base stations jointly in a direct position estimation approach. To assess the improvement, we applied the Ziv-Zakai Bound and performed simulations. We found that using the direct position estimation approach can significantly lower the SNR at which it is still possible to resolve the ambiguities caused by the regular signal structure

VDES R-Mode Performance Analysis and Experimental Results

Global Navigation Satellite Systems (GNSS) have become an essential part of maritime navigation, in particular to improve situational awareness and vessel traffic management. The dependence on GNSS creates vulnerability for maritime shipping. Driven by this vulnerability, the desire for a backup system for maritime navigation has been emerging. The VHF Data Exchange System (VDES) standard provides communication capabilities for maritime applications. VDES is currently being revised. As part of this revision, VDES will be extended by ranging and navigation functionalities, called R-Mode, as an alternative for maritime navigation. In this paper, we address system design aspects and evaluate the positioning performance of VDES R-Mode. We derive estimation theory bounds on the accuracy of VDES R-Mode distance and velocity. In a case study, we discuss and evaluate the benefit of satellite links to complement VDES R-Mode positioning. Furthermore, we introduce a Kalman filter for position and velocity tracking, which we apply to experimental data. We describe an experiment we conducted at Lake Ammer, southwest of Munich, and evaluate the VDES R-Mode positioning performance for this setup. Our experimental results show that VDES R-Mode is capable of achieving a 95th-percentile horizontal position error of 22?m. Thus, VDES R-Mode is a promising approach for a maritime backup system that can meet the IALA accuracy requirements

On the Positioning Performance of VDES R-Mode

Ships nowadays greatly rely on Global Navigation Satellite Systems (GNSSs) in order to deter- mine their position. Since GNSS outages or jamming events do occur, there are efforts to reduce the dependency on GNSS for maritime navigation. One such effort is called R-Mode (Ranging Mode), and focuses on complementing maritime communication systems by a ranging compo- nent to enable a vessel to determine its position. One of the systems to be extended by R-Mode is the VHF Data Exchange System (VDES). The VDES communication system is currently in standardization and offers 100 kHz of bandwidth in the maritime VHF band. It utilizes sin- gle carrier modulation with pi/4-QPSK. The proposed R-Mode extension works by sending a precisely timed known data sequence, so that time of arrival estimation allows determination of the range. Using software defined radios (SDR), we implemented a test setup for VDES R-Mode with three base stations on land and one receiver located on a vessel. Using this setup, we performed the first VDES R-Mode positioning trials on the Lake Ammer in Germany. By determining the time of the arrival as well as the Doppler shift of the received signals we tracked the vessels position with an Unscented Kalman Filter. The positioning accuracy performance ranged to up to 22 m under favourable conditions. Crucial was the consideration of the Doppler measurements to enhance tracking performance considerably

Autonomous Waypoint Sailing with an Alternative PNT System: Practical Experience with VDES R-Mode

Due to reliance of ships on Global Navigation Satellite Systems (GNSS), there is a need for a contingency system that can provide positioning information to ships in case of GNSS being unavailable. One such contingency system called VDES R-Mode is planned to be built on top of the VHF Data Exchange System (VDES). To test the imple- mentation of VDES R-Mode, we used an autonomous unmanned surface vehicle (USV). The USV is equipped with a controller that allows autonomous navigation along predefined waypoints. This controller requires an ex- ternal position source; usually a GNSS receiver. We replaced this GNSS receiver with a receiver for VDES R- Mode. This setup was tested on the Weßlinger See. Three VDES base stations on the shore of the lake provided ranging signals. The same predefined route was navigated once with GNSS as a position source, and once with VDES R-Mode as a position source. In both cases, a GNSS receiver was also used to record the actual route of the USV

Designing a Ranging Signal for use with VDE R-Mode

As GNSS signals are not always reliable and subject to jamming and spoofing, it is desired to have alternative means of maritime navigation. One approach for that is to equip communication systems on the shore with the option to transmit ranging signals (R-Mode), which vessels can use to determine their position. The VHF Data Exchange System (VDES), which is currently in standardization, can be utilized for this R-Mode application. For that purpose, a ranging signal has to be chosen that will provide good time of arrival estimates. By using the Cramér-Rao-Bound (CRB) and the Ziv-Zakai Bound (ZZB), we investigate different options of the ranging signal. We find that optimising for high bandwidth is desirable at high Signal to Noise Ratios (SNR), while optimising for low autocorrelation sidelobes is desirable at low SNRs. By utilizing a combination of both options, we are able to find a suitable ranging signal for any given SNR

Positioning Performance of VDES R-Mode

Global navigation satellite systems (GNSSs) have become an essential part of maritime navigation, in particular for collision avoidance and vessel traffic management. The dependence on GNSSs creates vulnerability for maritime shipping. Driven by this vulnerability, the desire for a backup system for maritime navigation has been emerging. The VHF data exchange system (VDES) standard provides communication capabilities for maritime applications. VDES is currently being revised at the ITU-R Working Party 5B and foreseen to be finalized as early as 2022. As part of this revision, VDES will be extended by ranging and navigation functionalities, called R-Mode, as backup for maritime navigation. In this paper we evaluate the positioning performance of VDES R-Mode. For VDES R-mode performance evaluation, we derive estimation theory bounds for the distance and velocity estimation and introduce a Kalman filter which we use for position and velocity tracking. For validation of the positioning performance of VDES R-mode, we describe an experiment we conducted at Lake Ammer, southwest of Munich. Results obtained from this experiment show that VDES R-Mode achieves a positioning accuracy of 10 m, therefore providing an appropriate backup solution for maritime navigation

Correction Data Transmission by VDE Considering AIS Reception on Inland Waterways

Colocation techniques for AIS and VD