# The Ocean-Going Autonomous Ship--Challenges and Threats
## 2 Navigational Equipment and Related Challenges
### Navigation Threats  
It is expected that the GNSS receiver will be the primary source of position information for the autonomous ship. It is a very reliable and accurate positioning system, however, the problem of threats to its correct operation is currently being raised. Many parts of today's critical infrastructures rely on uninterrupted access to GNSS positioning, navigation and timing services, but, at the same time, threats to denial of GNSS services are increasing. Radio frequency interference can be unintentionally emitted by commercial high power transmitters, ultra-wideband radar, television, very-high frequency (VHF), mobile satellite services and personal electronic devices. Moreover, malicious intentional interference is produced by jammers, whose rapid spreading is becoming a severe threat to GNSS. [PERSON] et al. proposed in 2016 the 6 groups of threats for GNSS work (see Figure 3). Some of them are common to all users (GNSS segment errors or atmosphere influence). Others, for example multipath, seem unlikely on the high seas. This kind of threat is mainly taken into account in very accurate measurements like hydrographic surveys of a harbor's waters, etc. although the signal reflection from large vessel's structures cannot be neglected. However, the most common threat is currently an intentional jamming interference and false signals sent intentionally with the intention of misleading the receiver. This type of threat was formerly considered as very unlikely, but there is a lot of evidence that this has become a very serious threat. This kind of attack against ships is not  
Figure 2: Proposed navigation data network scheme for the high sea passage of autonomous vessel. evidenced as strongly as against aerial drones, although it is obvious that this problem may be serious everywhere [22]. The example has been presented in [23] and is related to the Red Sea, Black Sea and the North-East area of the Mediterranean, where multiple GPS disruptions incidents has been reported in 2018 by several vessels operating in the listed areas. It is assumed that the reasons for these situations can be related to the armed conflict in Syria, but also the actions against the participants of North Atlantic Treaty Organization (NATO) exercises or travels of government officials may be engaged here. But we are not able to exclude that kind of events from the group of potential causes of GPS disruptions, because the unmanned vessels in many cases are design to operate in high risk areas of all types, including tensions or even armed conflicts between states. Another case has been raised in [24] where the GPS jamming attacks from the North Korea are presented as the main reason of the eLoran system implementation around the territory of South Korea. At the beginning of the 21 st century, jamming was considered the most common threat. The accuracy and availability of the receiver's position solution during the interference were analyzed, for example, in the STRIKE3 project [25]. This investigation shows that as the interference power increases, the receiver performance continues to degrade and finally loses the position fix. These results are partially different for mass-market and professional-grade receivers. It can be seen that the mass-market receivers prioritizes the availability of the position solution over its accuracy, in contrary to professional-grade ones. The satellite frequency band is expected to become increasingly congested as the same band is exploited not only for navigation and communication, but for different services also, such as remote sensing, surveillance, or weather forecast. A larger number of users sharing the same frequency band means increased risk of interference. However, interference is not always unintentional, but could also be caused by signals deliberately transmitted with the purpose of disrupting receiver operations. This is associated with satellite navigation, but in many cases jammers generate noise in very wide spectrum, wider than the GNSS spectrum.