# Wireless Remote Control for Underwater Vehicles
## 2 Underwater Communication Technologies
### Optical Communications
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Manufacturer and Model** & **Max Range** & **Bit Rate** \\ \hline Rutgers MIMO modem [62] & 10 s of m & [100, 250] kbps \\ \hline Northeastern SEANet prototype [65] & 10 s of m & [41, 250] kbps \\ \hline BaltRobotics Prototype [66] & [100, 200] m & [1, 115] kbps \\ \hline MIT Prototype [59] & 200 m & 100 kbps \\ \hline FAU Hermes modem prototype [64] & 150 m & 87.7 kbps \\ \hline EvoLogics S2C M HS [29] & 300 m & \begin{tabular}{c} {2, 62.5 kbps raw bit rate with no coding, \\ [1.2, 35] kbps net data rate with coding \\ \end{tabular} \\ \hline Marecomms ROAM Prototype [67] & \
\begin{tabular}{c} 0.6 km \\ 1 km expected \\ \end{tabular} &
\begin{tabular}{c} 26.7 kbps actual throughput in shallow water \\ 50 kbps expected in the new version \\ \end{tabular} \\ \hline AHOI modem [56] & 200 m & 200 bps \\ \hline Waterlinked M64 [57] & 200 m & 64 bps \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont_. ambient light environments [9]. In the MR class, we can find Sonardyne BlueComm 200 [7], equipped with a very sensitive receiver based on a photomultiplier. This modem achieves a hemispherical transmission rate of 10 Mbps up to a distance of 100 m, but only in deep, dark waters. The same modem would perform poorly in the presence of light noise due to saturation of the receiver: for this reason, Sonardyne designed an ultraviolet version of this modem, able to achieve a maximum range of 75 m even in the presence of some ambient light. Still, from our experience, both models are unable to establish a communication link when deployed a few centimeters above the sea surface during daytime. Similar issues have been experienced with Hydromea Luma 500 ER [25], able to cover, in good conditions, more than 50 m with a bit rate of 500 kbps (beam pattern 120\({}^{\circ}\)); the Ifremer optical modem [73], that can communicate at a similar range with a bit rate of 3 Mbps; and the early-stage version of the ENEA proof of concept (PoC) prototype [81]. Also, the AquaOptical modem developed by MIT [72] can perform MR communications in low solar noise conditions by reaching a maximum range of 50 m with a rate of 4 Mbps. The beam patterns of both the Ifremer and MIT modems are 100\({}^{\circ}\), while the ENEA optical modem is omnidirectional. Customized LED-based MR optical modems are developed by Penguin ASI [82; 83]; the maximum performance of their system is in the order of 100 s of Mbps at hundreds of meters but comes at the price of very bulky and expensive modems that are only suitable for extremely specialized applications, such as deployment in heavy-size working-class ROVs or similar vehicles. Models designed for SR communications, instead, typically overcome the ambient light noise issue by employing a noise-compensating mechanism to avoid receiver saturation, at the price of lower bit rate and range. This mechanism typically consists of measuring the average noise at the receiver and of injecting a signal with equal intensity but opposite sign at the receiver unit. BlueComm 100 [7], for instance, can be used in all water conditions, including shallow water in daytime to transmit at a rate of 5 Mbps in SR at a maximum distance of 15 m. Its beam pattern is 120\({}^{\circ}\). Similarly, the Sant'Anna OptoCOMM modem [8] can establish a 10-meter communication link at a speed of 10 Mbps, when both the receiver and transmitter are deployed just half a meter below the sea surface. They use optical lenses to reduce the beam aperture angle to 20\({}^{\circ}\) and to reduce the receiver field of view to 70\({}^{\circ}\) to limit sunlight noise. Also, ENEA developed a solar light noise-cancellation mechanism for their new version of the optical modem: preliminary results declared by ENEA proved that their new prototype can now communicate in high ambient light conditions, at the price of a reduced bit rate. Another commercial off-the-shelf optical modem for SR is the AQUAmodem Op1 [9], which achieves 80 kbps at 1 m, with a beam pattern of 34\({}^{\circ}\).