## 2 Wireless Communication for Maritime Applications
### Communication to On-Shore Base Station  
In a remote ocean monitoring application, data may have to be sent to an onshore base station for collection, processing, and decision making. The data from many sensor nodes may have been collected by a coordinator, or each of the sensor nodes may send the data directly to the base station, depending on the application. In any of the cases, a long-range wireless communication method is required, of which there are several available for use, each with its pros and cons. Common long-range wireless communication methods are highlighted in Table 2. As expected, those that rely on terrestrial infrastructures, such as LTE and GSM, provide the lowest ranges. Additionally, depending on the amount of data to be transferred, these can become expensive. Using a radio link in the VHF frequency range can deliver data at a long distance, but the data rate is very limited, and the transmission antennas' size can be cumbersome and even restrictive in some applications, especially considering that line of sight is restricted by the earth's curvature at long distances, thus requiring high communication towers that may be too expensive or difficult to build [22]. Long-range Wi-Fi consists of the use of the standard Wi-Fi protocol but relies on directive antennas, amplifiers, and more sensitive receivers to increase the achievable range and create a point-to-point connection. Satellite communication is also possible. Digital amateur radio communication is a feasible alternative for a low rate and small data package exchange. An Automatic Packet Reporting System (APRS) is a two-way packet communication protocol for real-time communication, using low-Earth orbit or geostationary satellites to interconnect local networks. It is mainly used for location reporting, weather station telemetry, text messages, and danger reports. With a data rate of 1200 bps and a frequency around the 2 m amateur band, it is a reliable and low-power data transfer solution for long-range applications. Global coverage is assured by the many amateur radio transponders sent to space aboard satellites, such as the International Space Station and recently the Es'hail 2, the first geostationary satellite with an integrated amateur radio transponder. The main disadvantages of this choice are the large equipment required, mainly the antenna, which may limit its deployment to fixed structures such as offshore wind turbines or oil platforms, the low data rate, and the requirement of an amateur radio license to be operated. The Iridium satellite network consists of 66 satellites that orbit 780 km above the Earth and provide worldwide coverage [23]. In order to communicate through the iridium network, transceivers such as Iridium Core 9523 [24] and Iridium 9602 [25] can be used. Unfortunately, the cost of this implementation can also be high, but it is the only available solution for remote applications. An alternative to Iridium, called the Starlink, is currently being deployed. It is planned to consist of over 42,000 satellites at an orbit of 550 km. As of January 2022, more than 1900 Starlink satellites have been launched, with download speeds around 100 Mbps and latencies as low as 20 ms [26]. From the analysis of the technologies presented here and in Table 2, it is possible to conclude that when the coordinator that needs to transfer data is near the shore, LTE or long-range Wi-Fi can be used, as they allow high data rates, although for shorter ranges, as seen in [29; 30]. GSM can also be employed in that scenario, but only if the required data rate is low [31]. For truly remote devices, VHF is a possible solution for low-data-rate applications, despite the possible technical difficulties caused by the size of the required antennas. Consequently, satellite-based communications such as the Iridium network [32] and eventually Starlink appear to be the best available solutions, despite the high costs involved.