# Marine Internet for Internetworking in Oceans: A Tutorial
## 4 Communication Systems in Oceans
### Maritime Radio System  
The maritime radio system is the most popular and mature communication system developed mainly for maritime transport long time ago. It works in broadcast mode to cover wide water areas at low data rates for many applications, as listed in Table 3. For example, Navigational Telex (Navtex), part of the Global Maritime Distress and Safety System (GMDSS) defined by the International Maritime Organization (IMO), can reach 370 km off shore at 100 bit/s [36]. The very high frequency (VHF) here operates at 156-162.025 MHz with a total 6.025-MHz bandwidth and the channel spacing of 50 kHz and 25 kHz, respectively. Traditionally, it only supports analog voice communication up to about 111 km. It is enhanced by a digital selective calling (DSC) at a rate up to 1.2 kbps, which allows a distress signal to be sent by pressing a single button. Furthermore, high frequency (HF) at 3-30 MHz is also used for very long-distance communication at low rates (e.g., 9.6 kbps) for voice and fax with unstable quality. Some VHF channels are used to develop a VHF data link (VDL) to provide data communication for automatic identification systems (AISs) at a maximum rate of 9.6 kbps. The AIS is an automatic tracking system that identifies and locates vessels for navigation and collision avoidance. Ships equipped with an AIS meeting anywhere can identify and track each other. Consequently, the position information of a ship is continuously transmitted to ensure that its neighbors can know its position [37]. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Deployment Location** & **Objects for Communication** & **Medium** & **Power Source** & **CP** & **DDS** & **ER** \\ \hline Coast and island & BS/AP, tower, observatory & Radio, fiber & Grid, generator, solar/wind energy & ++ & – & ++ \\ \hline Water surface & Vessels, buoys, platforms & Radio & Generators, battery, solar/wind/tide & - & + & + \\ \hline Air and space & Aerial units, HAP, satellite & Radio & Battery, solar energy & + & - & - \\ \hline Underwater & AUV, sensors & Acoustic, fiber & Battery, generator & – & – & – \\ \hline \multicolumn{7}{c}{CP, Communication performance; DDS, Dense deployment in sea; ER, Energy reliability; AUV, Automatic underwater vehicle; Aerial units = [Balloon, drone, helicopter, plane]; BS/AP, Base stations/access point.} \\ \end{tabular}
\end{table} 
Table 2: Conditions for communication in oceans. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**System** & **Bandwidth** & **Speed** & **Distance** & **Typical** & **Frequencies** \\
**Name** & **(kHz)** & **(kbps)** & **(nautical mile)** & **Application** & **(MHz)** \\ \hline \hline NAVTEX & 0.17 & 0.1 & 200–400 & GMDSS & 0.518 (English broadcast), 0.49 \\ \hline HF & 2–3 & 2.4 & 500–1500 & Sea-to-shore & 3–30 \\ \hline VHF/VDL & 200 (8 \(\times\) 25) & 13/9.6 & 30–50 & Voice/AIS & 156-174 \\ \hline VHF-DSC & 0.3 & 1.2 & 20–30 & GMDSS & 155.5–159.5, 160.6–163.5 \\ \hline VDES & 25,50,100 & \(k^{\star}\times 76.8\) & 50 & Data & 156.0125–157.4375, 160.6125–162.0375 \\ \hline \multicolumn{6}{l}{* \(k=1,2,4\), AIS, Automatic Identification Systems; DSC, Digital Selective Calling; GMDSS, Global Maritime Distress Safety System; NAVTEX, Navigation Telex; HF, High Frequency; VHF, Very High Frequency; VDES, VHF Data Enhanced System; VDL, VHF Data Link.} \\ \end{tabular}
\end{table} 
Table 3: Maritime radio and its applications [23; 38]. E-navigation has been defined by IMO to further improve the safety of maritime navigation and operations. To this end, more information has to be exchanged in real-time, such as weather, ice charts, the status of aids to navigation, water level and rapid changes of port status, voyage information, passenger manifest, pre-arrival report, etc. [39]. Due to the popularity of AISs and increasing demands of ship-to-shore and ship-to-ship data exchange, the capacity of the current VDL becomes inadequate.