Interference Awareness and Characterization for GNSS Maritime Applications
E. Pérez Marcos, S. Caizzone, A. Konovaltsev, M. Cuntz, W. Elmarissi, K. Yinusa, M. Meurer, German Aerospace Center (DLR), Germany
Global Navigation Satellite System (GNSS) has become the main technology to provide position and timing services in the world. This increasing dependency on GNSS across many application fields has raised concerns about the vulnerability of the same. The GNSS signals travel long distances from the satellites and are emitted with relatively low power (constraint mainly by the solar panels capabilities), therefore the GNSS signals are very weak when they arrive at the receiver. Thus the signals can be easily blocked by interfering radio transmissions. These radio frequency interferences are usually of unintentional nature, but they can also be deliberately produced. Unintentional and deliberate interference signals constitute a challenging problem in many Safety of Life applications and in Liability Critical applications.
The maritime domain surely offers such scenarios, an application field where the GNSS technology has been widely adopted and trusted yet, only recently, its reliability is being put into question . This relationship between GNSS dependency and increasing concern is confirmed by the International Maritime Organization (IMO), that addresses the topic as part of its e-Navigation plan .
Whereas in other domains, such as aeronautics, researches about radio frequency interference (RFI) signals in the operation environment are available , not the same can be said about the maritime domain. Some events have been reported in some harbors , but the information is far from offering a complete picture. In order to provide some more insight into the topic, the Institute of Communications and Navigation of the German Aerospace Center (DLR) is conducting a worldwide maritime RFI measurement campaign. The measurement campaign is developed under the framework of a national program for Next-Generation Maritime Technologies.
The main objective of the measurement campaign is to detect, observe and record radio frequency interference events in the GPS and Galileo Open Services frequency bands. Therefore signals in L1/E1 and L5/E5a frequency bands are the objective of the measurement campaign. Both L1 and L5 bands are strictly regulated. The International Telecommunication Union (ITU) declares the radio navigation services within the L1 band as primary user, whereas in the L5 band, the radio navigation services are not a primary user, thus they shall coexist with other systems. Therefore any non-intended signal detected in the L1 band is, by definition, an interfering signal, independently of its impact in the corresponding receiver performance. However for the L5 band, having to share the spectrum with other services, the definition is not so straightforward.
A vessel from the company Hapag-Lloyd, specifically a large container ship, serves as mobile measurement platform. The vessel travels in a route from Europe to Asia, covering very different regions and docking in several countries. On-board two independent systems run in parallel. One is a DLR’s developed multi-channel, multi-band RFI data recorder, whose function is to detect and record time snapshots of interference signals. The other system is a DLR’s developed prototype GNSS multi-antenna navigation receiver. Both systems are simultaneously fed by a seven elements conformal antenna array. The antenna array has been shaped to increase the received energy from signals impinging with low elevation angles, in order to gain maximum information from signals of all possible receiving directions.
This paper will contain a brief description of the measurement systems, including antenna, subsystems and detection methodologies used (more system details can be found in ), pertinent interference results of the recorded data are going to be presented, together with the newest data obtained in the second part of the project.
The collected data is evaluated in post-processing, with the aim of characterizing and cataloging the detected interferences. This task will be accomplished by concurrently using data from the recorded RFI snapshots and the real time GNSS receiver prototype, in order to assess the impact of the recorded interference on the received GNSS signal. Also the real time GNSS positioning information is used, when available, to geographically situate the recorded event. Also the quality of the on-board obtained position solution will be assessed, either under interferences or any other detected disturbances.
The work will therefore show a map of interference events along the route of the vessel, i.e. along a worldwide route, with emphasis on the interference characterization and the effects on the GNSS receiver positioning quality.
Though not claiming to be an exhaustive analysis of all possible interference events in the maritime domain, the presented work will however show a first worldwide analysis, a general view including strong and weak signal, and it will highlight the most frequently occurring ones.
 “The impact of new signals on precise marine navigation - initial results from an experiment in Harwich harbour.”, A. Parkins, A. Grant, and P. Cross, pp. 1–14, 2008.
 “GPS Jamming and the Impact on Maritime Navigation”, A. Grant, P. Williams, N. Ward, and S. Basker, J. Navig., vol. 62, no. 2, pp. 173–187, 2009.
 “Development of an e-Navigation strategy implementation plan.”, IMO Sub-Committee on Safety of Navigation, 2011. And also “MSC 85/26/Add.1 Annex 20”.
 “Assessment of Radio Frequency Interference Relevant to the GNSS (RTCA/DO-235A)”, RTCA, Inc., 2002.
 “System challenge - The hunt for RFI - Unjamming a Coast Harbor”, J. R. Clynch, A. A. Parker, R. W. Adler, and W. R. Vincent, GPS World, pp. 16–22, 2003.
 “Interference Detection and Characterization with an Array based GNSS Receiver using Conformal Antennas in Maritime Environments”, Andriy Konovaltsev, Emilio Pérez Marcos, et al., presented at ION GNSS+ 2017.