## 3 Examples of Maritime Internet of Things Networks in Applications  
The bibliography contains several examples of wireless sensor networks applied to the ocean where wireless communications are employed. Some notorious examples are briefly highlighted in the following paragraphs, and Table 3 presents a summary of the literature review regarding communication technologies and the intended implementation of the prototype. Water quality monitoring is one application where the MIoT has been significantly employed. Examples of employments of wireless communications for this purpose are found in [4], in which the authors use GSM and the 2.4 GHz ISM band to transfer data from sensors to on-shore data centers. A similar approach was reported in [41], with the use of 3G. \begin{table}
\begin{tabular}{l l l l} \hline \hline \multirow{2}{*}{**Reference**} & \multicolumn{2}{c}{**Communication**} & \multirow{2}{*}{**Implementation**} \\ \cline{2-2} \cline{4-4}  & **Nodes to Coordinator** & & **To Base Station** & \\ \hline
[4] & & GSM/2.4 GHz ISM & Field tests (Italy, Sea) \\ \hline
[5;35] & ZigBee & GPRS & Field tests (Spain, Sea) \\ \hline
[29] & & LR Wi-Fi & Field tests (Indonesia, Sea) \\ \hline
[30] & & LTE & Field tests (Korea, Sea) \\ \hline
[31] & Zigbee & GSM & Field tests (Lithuania, Sea) \\ \hline
[32] & & Iridium & Field tests (China, Sea) \\ \hline
[36] & & Wi-Fi & Field tests (aquaculture tanks) \\ \hline
[37] & ZigBee & CDMA & Field tests (China, Lake) \\ \hline
[38] & Satellite VHF/UHF & Wire & Field tests (Iran, Sea) \\ \hline
[39] & & LoRaWAN, 4G, Wi-Fi, ZigBee & Field tests (India, River) \\ \hline
[40] & & LoRaWAN & Lab tests \\ \hline
[41] & & 3G & Field test (Japan, Lake) \\ \hline
[42] & VLC (visible light communication) & Simulation \\ \hline
[43;44] & & LoRaWAN & Field tests (Korea, Sea) \\ \hline
[45] &
\begin{tabular}{l} IEEE 802.11a/g/n/ac \\ and GPRS/LTE \\ \end{tabular} & IEEE 802.11g & Field tests (Portugal, Ocean) \\ \hline
[46] & ZigBee & 3G & Field tests (Japan, Lake) \\ \hline
[47] & & Wi-Fi/LoRaWAN & Field tests (Korea, Sea) \\ \hline
[48] & & 5G & Field tests (Japan, Sea) \\ \hline
[49] & & IEEE 802.16 (5.8 GHz) & Field tests (Singapore, Sea) \\ \hline
[50] & ZigBee & WiMax & Lab tests (man-made lake) \\ \hline
[51] & & IEEE 802.11n (5.8 GHz) & Field tests (Portugal, Sea) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of the literature review in terms of the communication protocol implemented between nodes and coordinators and towards base stations (when applied) and the implementation of the prototypes. In [39], the authors use a ZigBee-enabled sensor network to monitor water quality in a river. The data generated by the sensors are aggregated in a central node via Zigbee and they are then relayed to a base station via Wi-Fi or 4G. Similar approaches are used in [46] (Zigbee and 3G) and in [47], where Wi-Fi or LoraWAN are used for short-range communication to a gateway which then uses long-range Wi-Fi for long-distance communication to a central station. Finally, in [50], Zigbee is used for short-range communication to a WiMAX gateway that relays the data to the shore. Water quality monitoring is also extremely important in aquaculture, and some examples of wireless sensor networks employed in this field are reported in the bibliography. Due to the shorter ranges involved in this application, direct communication from sensors to a central station is preferred, with Wi-Fi [36] and LoRaWAN [40] being employed. In [38], a marine monitoring network implemented in the Caspian Sea is reported. The network comprises shallow and deep-water measuring devices, coastal monitoring devices, and central data stations. From shallow water to the data stations, data are transferred via a cable. On-shore and deep-water data are transferred via satellite. In [5; 35], the authors detail a coastal oceanographic observation system to monitor the physical environment of the Mar Menor and its interaction with the Mediterranean Sea.