Experimental Evaluation of the Impact of Jamming on Maritime Navigation

Kurzfassung

Resilient provision of Position Navigation and Timing (PNT) data is one of the key enablers of the e-Navigation strategy of the International Maritime Organization (IMO). Currently Global Navigation Satellite Systems (GNSS) are the primary source for the determination of absolute position, velocity and time (PVT) for merchant vessel navigation. On a ship bridge a number of systems like Electronic Chart and Information Systems (ECDIS), automatic track control systems and the Automatic Identification System (AIS) are relying on that PVT provision. Nevertheless it is well known that GNSS performance can strongly degrade due to space weather events, jamming and spoofing. Especially the availability and usage of low cost jammers, so called personal privacy devices (PPD) lead to the question on how the navigation equipment onboard a vessel would perform on the presence of a PPD jammer. In the past the General Lighthouse Authorities (GLA) had conducted jamming sea trials, focusing mainly on the question, how resilient PNT provision can be assured by using a backup radio navigation system like e-LORAN. However, the potential of novel GNSS receiver technologies, which are supposed to lead to higher resilience against jamming, as well as the opportunities of multi-sensor fusion for real-time provision of PNT data on board the vessel so far have not been systematically investigated and a careful evaluation is needed in order to evaluate their performance during real maritime jamming measurement campaign. In order to address the aforementioned issues the German Aerospace Center (DLR) in cooperation with the German Federal Network Agency has allocated a civil maritime GNSS jamming testbed in the Baltic Sea. The test area is located approximately 6 nm north of the Darß peninsula with the first jamming measurement campaign in the area conducted in November 2015. The goal of the first measurement campaign was to evaluate the impact of a commercial PPD jammer on the position accuracy and the availability of the position fix of standard GPS/GNSS receivers. For that measurement campaign a PPD Jammer was mounted on the monkey deck of the tugboat AARON (length 26m, beam 8m). During the campaign the AARON was anchoring in the center of the Jamming test area, keeping a fixed position and orientation (heading). Due to some waves (wave height: 1-2m) the roll and pitch angle of the vessel was varying significantly. The applied PPD Jammer was sweeping a cw signal around the GPS L1 frequency covering a bandwidth of 17 MHz. Therefore this device was affecting both GPS L1 and Galileo E1 signal tracking, but not GLONASS L1. This enabled us the usage of GLONASS for the calculation of a highly precise PPP reference trajectory in post processing even in the direct vicinity of the Jammer. The measurement equipment was installed on the multipurpose research and diving vessel BALTIC TAUCHER II (length 29 m, beam 7 m), which was navigating around the tugboat AARON with a max. speed of 8 knots and a distance to the jammer varying from ~50m to 4000m. The vessel was equipped with three separate dual frequency GNSS antennas and receivers (Javad Delta), FOG and MEMS IMUs, gyrocompass, Doppler Velocity Log (DVL) and echo sounder. All relevant sensor measurements were provided either directly via Ethernet or via serial to Ethernet adapter to a Box PC where the measurements were processed in real-time and in parallel stored in a SQlite3 database along with corresponding time stamps. The described setup enables a record and replay functionality for further processing of the original sensor data. The system consists of a highly modular hardware platform and a Real-Time software Framework (RTF) implemented in ANSI-C++. Results: The GPS L1 based single point positioning results using the pseudorange measurements of the three GNSS receivers/antennas show large differences in both accuracy and availability. As all the three receivers were completely identical with the same firmware versions and were identically configured, the only difference is in the mounting of three corresponding antennas to be distributed throughout the vessel. Therefore the mounting environment of the antenna seems to have a relatively large impact on the position performance in the presence of a jamming signal, especially, when the jammer is located in a comparable altitude like the antennas themselves. The largest horizontal position errors in the presence pf a jamming signal were found to be ~250m. In a second step the performance of a state-of-the-art Receiver Autonomous Integrity Monitoring (RAIM) approach in the presence of a jamming signal was evaluated for all three antennas. While the availability of position results, which were declared as ‘safe’ by the RAIM algorithm, is obviously reduced, no large horizontal position errors (HPE) (>10m) were found. Moreover, the calculated horizontal protection level (HPL) was reported to be always larger than the actual HPE for the whole time period evaluated here. The preliminary results confirm that the navigator can mostly avoid getting an erroneous position fix without a warning by applying properly designed RAIM approaches. Further improvements both in accuracy and the availability of the solution are expected due to complementary behavior of spatially distributed antennas and corresponding extension of the RAIM-like methods. Finally, the performance of the corresponding integrated navigation solutions supported by inertial sensors and Doppler Velocity Log (DVL) and corresponding extensions for multiple-antenna setup should be evaluated.