# Wireless Remote Control for Underwater Vehicles
## 1 Introduction  
Remotely operated vehicles (ROVs) are unmanned underwater vessels typically operated through the so-called umbilical cable, composed of an optical fiber for a broadband low-latency communication link and a power line to supply the vehicle, making it possible to manage the system in real time. However, the umbilical cable inherently limits mobility of the ROV due to cable strain and entanglement risks. Wireless ROV control would help avoid such issues by removing the need for a physical cable at the price of an increased need for ROV power autonomy and smaller data rates, a price that can be accepted only for some possible ROV applications (Figure 1). Depending on the tasks they are designed to accomplish, ROVs can be divided into intervention-class ROVs and inspection-class ROVs [1]. The former type of vehicle, also known as work-class ROVs, is mostly used in the oil and gas industry; can weigh from 100 kg (light work-class) up to 5000 kg (heavy duty work-class); and is used for tasks such as cleaning, stabbing, and drilling as well as for carrying and operating heavy tools and sensors, such as 3D scanners for ship-hull inspection operations [2]. The latter, instead, is easier to deploy and can be used for several applications, including archaeology, coastal monitoring, search and rescue, and ship-hull and shipw inspection. Depending on their size, they can weigh from 3 kg (micro-ROVs) up to 120 kg (medium-size ROVs) and are typically equipped with a camera plus other optional small operational tools, such as a small manipulator or an imaging sonar. While the power consumption of intervention-class ROVs is more than 50 kW, the power required by medium-size inspection-class ROVs is less than 6 kW, and micro-ROVs require less than 1.8 kW; thus, both medium- and small-size inspection-class ROVs can be powered by lithium batteries. For some ROV applications, such as under-ice research and high-risk environment missions where the tether could be entangled, the availability of on-board batteries may be advantageous: if an emergency maneuver becomes necessary and the cable needs to be cut, this is easier thanks to its smaller size (as it does not need to carry a power supply) and the ROV can then safely resurface, behaving like an autonomous underwater vehicle (AUV). In this paper, we inspect how the use of a wireless communication system to substitute the umbilical cable would affect the quality of service (QoS) experienced by ROV pilots1 while using a medium-size battery-powered inspection-class ROV during a survey operation. In particular, we start by analyzing the required application data rates for typical services offered by inspection-class ROVs. We identify a number of operational modes which can be chosen as a function of range to support a given set of ROV services, from simple guidance and positioning up to real-time video streaming. Indeed, with the increase of the communication range, there is an exponential decrease in the achievable bit rate. Footnote 1: An ROV pilot technician controls the movement of the vehicle from a ship’s cabin or another indoor location on the surface. Nowadays, it is possible to establish a wireless communication link underwater through radio frequency (RF), optical, or acoustic modems [3]. These three technologies provide different performance and are used for different types of applications. Specifically, underwater RF [4; 5; 6] and optical communications [7; 8; 9] can be used for short-range broadband communication links, while acoustic signals are used for long-range low-rate communications [10; 11; 12]. The best communication performance is obtained when the three technologies are combined together into so-called underwater multimodal networks [3], where the best performing channels in the experienced condition are used  
Figure 1: Comparison between a tethered remotely operated vehicle (ROV) and a wireless ROV control scenario. simultaneously to achieve the desired QoS.