# Wireless Remote Control for Underwater Vehicles
## 4 Scenario Description and Simulation Setup
### Optical Modem Simulator  
The performance of the BlueComm 200 optical modem was mapped in the form of lookup tables (LUTs), as presented in [70], by considering a raw bit rate of 5 Mbps and the use of a forward error correction (FEC) mechanism with 80% efficiency (as declared from the manufacturer); hence, the actual data rate was 4 Mbps. Although the modem performs best in a deep, dark water environment, where oil and gas pipelines are typically deployed, in our simulations, we considered the performance of the modem when used in the presence of external lighting sources, such as the light needed for recording video streams, that introduced an important source of noise to the receiver, however, without saturating the photomultiplier. A similar effect was found when the BlueComm 200 optical modem was used during the night in shallow water, where it was observed that the moon, stars, and port lighting may reduce the maximum range of the optical communication to 1/3. The maximum range of the optical communication also depends on how the attenuation coefficient changes along the water column: in this work, we used the values of the attenuation coefficient depicted in Figure 5a and measured during the ALOMEX'15 research cruise offshore the coast of Morocco (latitude 30\({}^{\circ}\)42.520\({}^{\prime}\) N and longitude 10\({}^{\circ}\)18.680\({}^{\prime}\) W). The ALOMEX'15 cruise was organized  
Figure 4: Multimodal remote control for ROV: the red fixed node represents the control station, while the yellow nodes represent the medium-frequency (MF) relays used to extend the control range. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Description** \\ \hline Optical attenuation coefficient & 0.02–0.5 depending on the sea depth \\ Optical light noise conditions & Low light noise caused by external artificial sources. \\ Optical wavelength and data rate & 470 nm, 4 Mbps \\ Optical MAC & TDMA (90\% HROV, 10\% control station) \\ Optical range & from 25 m to 75 m, depending on depth and alignment \\ MF data rate, carrier frequency, bandwidth & 4 kbps, 24 kHz and 12 kHz \\ HF data rate, carrier frequency, bandwidth & 30 kbps, 150 kHz and 60 kHz \\ HF MAC & CSMA \\ MF MAC & CSMA \\ General acoustic parameters & \(s=1\), \(w=1\) m/s, \(g=1.75\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Simulation parameters. by the NATO STO Centre of Marine Research and Experimentation (CMRE), and its dataset was first presented in [18]. The last parameter that affects the optical range is the alignment between the transmitter and receiver. Indeed, the beam pattern of the BlueComm modem is hemispherical and not omnidirectional: this means that the maximum range and the receiving area also depend on the orientation of the two modems. In Figure 5, different cases are analyzed, keeping the position of the control station fixed at a depth of 60.5 m with the modem aligned to the x-axis and with three different setups of the modem installed in the underwater vehicle. First, in Figure 5b, we can observe the receiving area when the modem is installed in the back of the vehicle, that is assumed to be oriented along the x-axis, pointing directly to the modem in the control station. This leads to a symmetric receiving area and maximum range of 75 m; however, in this case, the vehicle can only be controlled by keeping fixed orientation, thus limiting vehicle maneuver. Two possible solutions can overcome this problem: one involves the installation of several modems on the same vehicle, obtaining omnidirectional coverage at the price of a more expensive deployment [24], and the other requires installation of the modem either in the top or in the bottom of the vehicle, hence orienting the modem along the z-axis. In Figure 5c,d we can observe how the receiving area and the maximum range are reduced to 50 m when the modem is installed in the top and in the bottom of the vehicle, respectively.