Estimation of the Angle of Arrival of AIS Signals with an SDR-based Solution

Kurzfassung

With the growing maritime traffic, monitoring vessels accurately is becoming essential. Introduced in 1998, Automatic Identification System (AIS) messages, broadcasted by vessels on the two frequencies 161.975 MHz and 162.025 MHz, are supposed to support this task. However, these messages can be easily falsified, intentionally or not. Therefore, false information, for example, about a position can be broadcasted.

The aim of this work is to develop a solution that detects modified AIS messages based on the Direction of Arrival (DoA) estimation. Therefore, a KrakenSoftware Defined Radio (SDR) is chosen to build an antenna array in order to perform DoA estimations with algorithms such as Multiple Signal Classification (MUSIC). Then, the estimated DoA is compared to the bearing, obtained from the data transmitted by the vessels. In case of a mismatch, the AIS message is considered to be falsified. First, a GNU Radio pipeline is developed to decode and register AIS messages. Then three different arrays, each composed of 5 antennas, are used with the KrakenSDR and the GNU Radio pipeline: an Uniform Linear Array (ULA), a pentagon array and a cross array. These recorded AIS messages are later used in MUSIC to estimate the DoA. The arrays were first tested on the site of Deutsches Zentrum für Luft- und Raumfahrt (DLR) and later tested with two measurement campaigns that both took place in Altwarp. The final results of the two measurement campaigns present the ULA as the best performing configuration, followed by the cross array and then the pentagon array. However, the results still show errors that are too significant to validate the performance of the KrakenSDR setup. To improve its performance, other antennas, such as VHF maritime antennas, could be used.