# Wireless Remote Control for Underwater Vehicles
## 1 Introduction
For example, two nodes may communicate with each other via acoustics when they are more than 50 m apart and with optical modems when their distance is less than 50 m. Additionally, an RF modem can be employed to support high-rate communications when the distance between the nodes is less than 5 m and the optical channel cannot be used due to poor channel conditions (e.g., high turbidity or ambient light noise). Also, the concept of designing a wireless hybrid ROV/AUV has already been addressed in the literature. In [13], the Woods Hole Oceanographic Institute (WHOI) presented an untethered ROV for intervention applications that make use of optical and acoustic modems to allow an ROV pilot to carry out the intended mission. In [14], we proved via simulation the possibility to exploit an underwater multimodal acoustic and optical link to pilot an inspection-class hybrid ROV/AUV, and in [15], we presented how the control range of the vehicle performing an AUV mission can be extended through a multihop acoustic network. Following the same concept, some offshore companies are currently developing commercial hybrid ROVs that can be piloted wirelessly for simple semiautonomous inspection operations [16, 17]. Both our system and the WHOI untethered ROV perform best in deep water, where optical signals can reach longer distances and acoustic links are less affected by multipath [18]. On the contrary, in [19], the authors presented a wireless remote-controlled ROV for very shallow water operations: specifically, they proved through a tank test that, if the ROV is deployed in fresh water at a depth of less than 45 cm, it can be controlled through an RF wireless link in the 420-450 MHz band. In [20], the authors investigated the acoustic networking of an AUV with Autonomous Surface Vehicles (ASVs) to accomplish a common mission. After introducing the vehicle control architecture, the authors described the acoustic communication and ranging capabilities of each node and finally showed some experimental results obtained with two vehicles in the Douro river in Portugal. Recently, in [21], the authors designed an RF and acoustic wireless remote control for a BlueROV [22] vehicle. The used RF link permits a transmission rate of 1.9 kbps and a maximum range of 5 m in sea water [4]. In late 2019, the authors in [23] presented a smart buoy used as a relay for controlling and retrieving data from underwater vehicles. The buoy employs a hybrid surface RF and free-space optical link to communicate with the shore station and an underwater optical link to communicate with the underwater vehicle. The simulation model used in this paper is quite simplistic, as it does not consider solar light noise in the underwater optical link. Hydromea has recently developed an underwater drone [24] that can be piloted through a tethered system until it reaches a high-risk area, where it unplugs the cable to avoid any possibility to get entangled. From that point on, it can be controlled through a wireless optical link: indeed, both the cable connector and the drone are equipped with the LUMA optical modem [25]. This paper extends the results presented in [14, 15], first by updating the review of available communication technologies, basing the remote control design and simulation results on field measurements and realistic models, and then by using realistic simulated application layers to best emulate the behavior of the vehicle and the control station. The structure of the paper is as follows. In Section 2, we review the state-of-the-art of underwater communication technologies, paying particular attention to experimental results and selecting the most suitable underwater modems to be employed for wireless remote control. In Section 3, we analyze the data-rate requirements of an ROV control system, considering each type of traffic that needs to be transmitted. In the same section, we also define different working modes based on the level of autonomy required by the vehicle mission.