# The Ocean-Going Autonomous Ship--Challenges and Threats
## 3 Overview of the Potential Solutions to Navigational Threats
Another potential future development area is the rules of cooperation between Autonomous or Unmanned Surface Vessels (ASV/USVs) in the swarm, not only in terms of the accomplishment of their tasks but also in terms of collision avoidance. Positioning technology is the next promising field for current and future research. Autonomous vessels are strongly dependent on GNSS-based services. While on a manned vessel, terrestrial navigation or even celestial navigation, still taught in the marine academies and required by the International Convention on Standards of Training, Certification and Watchkeeping (STCW), can be considered as the back-up to GPS, there is no such an option developed for the unmanned units. Therefore, many people have raised the need for a land-based radio-navigation system. Enhanced Loran (eLoran) is operational in some areas of UK, USA and the Korea [41; 42; 43]. This high-power terrestrial radio-navigation system, utilizing 100 kHz signals, can be the complementary positioning, navigation, and timing service, providing an alternative to GNSS. The authors of [24] report the lower position accuracy compared to the GNSS and propose the solution for its improvement. An analogous solution to eLoran is considered to be applied in AIS and DGPS (Differential GPS) systems as R-mode (Ranging mode). The concept is currently being tested in the Baltic Sea, within the multinational project called 'R Mode Baltic' under the Interreg Baltic Sea Region Program, planned for the years 2017-2020. Positioning in the tested system is based on the range estimation from the signals transmitted by modified IALA beacons and AIS base stations, which makes it in fact an Earth-based radio-navigation system [44]. The consistency of positioning in case of short absence of satellite positioning system input can be provided by inertial sensors or inertial measurement units (IMU). The interesting case of a hybrid navigation system (GNSS augmented by IMU and Doppler velocity log), evaluated in a real maritime GNSS jamming scenario, is presented in [45]. A simple and cost-effective solution to the jamming problem has been proposed in [46]. The author suggests using at least three independent receiving devices grouped in a way that they cover the entire upper hemisphere, although each of them calculates its position based on the chosen portion of the total number of available satellites. In this way it is possible to detect the fact of jamming and the direction of the jamming signal. The position is calculated based on the sufficient number of satellites' signal, even after the exclusion of the part affected by jamming. The author claims that this solution can be dedicated rather for civilian and not-high-end users, although it can be an interesting approach for autonomous vessel testing platforms. Navigators tend to concentrate on the vessel position and movement parameter-related systems. But it must be emphasized that the communication systems are essential for autonomous vessel control and supervision. The measurements are taken in a location remote from the place where the reads are done, and in case of lower autonomy levels, where the decisions are made. Surely there is a huge potential for the development of communication technologies with a global coverage.