# Wireless Remote Control for Underwater Vehicles
## 2 Underwater Communication Technologies
### Radio Frequency and Magneto-Inductive Communications  
Also, electromagnetic radio frequency and magneto-inductive communications can be used underwater. Compared with acoustic and optical waves, RF waves can perform a relatively smooth transition through the air-water interface [85]. This benefit can be used to achieve cross-boundary communication: for instance, the authors in [19] used this concept to pilot an ROV deployed up to 45 cm below the water surface. Another advantage is that RF and MI are almost unaffected by water turbulence, turbidity, misalignment between transmitters and receivers, multipath, and acoustic and solar noise, that are the main causes of poor performance for either optical or acoustic modems when used in practical scenarios. For these reasons, when in range, RF and MI can provide a much more stable link than optical and acoustic communications, with less disruptions; thus, in our opinion, they should be preferred to the other media whenever the bit rate and the range required by the application can be supported. However, their communication range is usually limited to no more than a few meters. Inductive modems [86; 87; 88], for instance, are often deployed in mooring systems [89; 90], as they enable communication over jacketed mooring lines and can be used to retrieve data from instruments such as Conductivity, Temperature, and Pressure sondes (CTDs) and Acoustic Doppler Current Profilers (ADCPs) by substituting physical connectors and the need for dedicated cables for communication. These modems generate a low-frequency signal that travels in the mooring line and can only substitute mechanical connectors for low-rate communications (up to 5 kbps). Also RF modems [5; 91] can be used to replace the mechanical connector of cables in very short ranges, but they provide broadband communications (up to 100 s of Mbps) and thus can support high-rate-demanding applications, such as real-time control and high-quality video streaming. For example, Hydromea uses an RF connector in the umbilical cable of the EXRAY ROV [24], where the vehicle's tether can be disconnected to perform an autonomous mission before being reconnected again. Also, in this case, the \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Manufacturer and Model** & **Max Range** & **Bit Rate** \\ \hline \multirow{5}{*}{**Variant**} & FUDAN modem [76] & 34.5 m & 2.70 Gbps \\ \cline{2-4}  & Oceanit ultra [78] & 100 m & 1 Gbps \\ \cline{2-4}  & USTC modem [77] & 100 m & 500 Mbps \\ \cline{2-4}  & Sonardyne BlueComm 5000 [75] & 7 m & 500 Mbps \\ \cline{2-4}  & SA Photonics Neptune [80] & 200 m & 200 Mbps customized, with beam steering capabilities \\ \cline{2-4}  & MC100 [74] & 10 m & 95 Mbps \\ \cline{2-4}  & JAMSTEC modem [79] & 50 m & 20 Mbps \\ \hline \multirow{5}{*}{**Variant**} & Sant’Anna OptoCOMM [8] & 10 m & 10 Mbps \\ \cline{2-4}  & Sonardyne BlueComm 100 [7] & 15 m & 5 Mbps \\ \cline{2-4}  & CoSa optical [5] & 20 m & 2 Mbps \\ \cline{2-4}  & ENEA PoC [81] & 1 m & 2 Mbps \\ \cline{2-4}  & IST Medusa Optical Modem [84] & 10 m & [20, 200] kbps \\ \cline{2-4}  & Aquatee AQUADodem Op1 [9] & 1 m & 80 kbps \\ \hline \multirow{5}{*}{**Variant**} & Penguin Automated Systems [82] & [10, 300] m & \{1.5, 100\} Mbps custom \\ \cline{2-4}  & Sonardyne BlueComm 200 [7] & 120 m & 10 Mbps \\ \cline{1-1} \cline{2-4}  & Sonardyne BlueComm 200 UV [7] & 75 m & 10 Mbps \\ \cline{1-1} \cline{2-4}  & MIT AquaOptical modem [72] & 50 m & 4 Mbps \\ \cline{1-1} \cline{2-4}  & Ifremer optical modem [73] & 60 m & 3 Mbps \\ \cline{1-1} \cline{2-4}  & Hydromea Luma 500 ER [25] & 50 m & 500 kbps \\ \hline \hline \end{tabular}
\end{table} 
Table 2: List of performance figures for representative optical modems. communication range is in the order of few centimeters. WiSub supplies the Maelstrom connector [92], able to support both power and data transfer via RF. Communication based on a microwave link has a rate of 100 Mbps up to a distance of 5 cm between the connectors. Similar devices are sold also by Blue Logic [93].