## 3 Types of Underwater Communication Systems
### Underwater Wired Communication
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Types of Systems (\(\lambda\))** & **Signal** & **Pros** & **Cons** & **Range** \\ \hline UWiC (1300–1600 nm) [54] & Electrical, Optical & Reliable, high data rates (optical), secure & Expensive to install, limited range (optical), susceptible to physical & As far as cable length \\  & & & damage & \\ \hline UWOC (380–750 nm) [72] & Optical & High bandwidth, low latency, energy-efficient & Short range, susceptible to absorption and scattering & 10 to 100 m in UWSNs \\ \hline UWRE (1–10 mm) [60], (1 mm–10 km) [73] & Electromagnetic (RF) & Moderate bandwidth, long range, versatile & High power consumption, large antenna, susceptible to attenuation in saltwater & Up to 100 m between 30 Hz and 300 Hz \\ \hline UWAC (15 mm–15 nm) [74] & Acoustic & Long range, low attenuation & Low bandwidth, high latency, susceptible to noise pollution & Up to 100 km in submarines \\ \hline Hybrid UWAC-UWOC & Acoustic and optical & Combines advantages of both & Complex implementation & Refer to UWAC and UWOC \\ \hline UEPC (30-3000 m) [75] & Electric field & Potential for high data rates, inspired by natural communication & Limited range due to attenuation & Approx. 8 m \\ \hline UVLC (430–550 nm) [76] & Visible light (blue/green) & High data rate, low latency, high security, no electromagnetic, potential for high-resolution imaging & Limited by water turbidity and distance & Up to 500 m in pure seawater \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Types of underwater communication systems and their strengths and weaknesses. icantly [54; 55]. Additionally, underwater cables are expected to be inextensible in both length and diameter due to the effects of the Poisson ratio [54; 55]. To further demonstrate the cost and specialised material requirements involved in UWiC communications, types of connectors are introduced. Several types of connectors exist, varying in application and cost, as summarised in Table 3. The connector's mating location is determined by the type of underwater connector in use. For example, dry-mate connectors, shown in Figure 2, are designed for surface connections; they are assembled outside of the water [77]. In contrast, wet-mate electrical connectors, in Figure 3, are designed to be mated and unmated in wet environments, unlike traditional cables that rely on a watertight seal, which can be susceptible to water ingress [63]. There are several variants of wet-mate cables [63]. Rubber-moulded wet-mate connectors utilise a locking sleeve and neoprene or polyurethane over-moulding to create a watertight seal between a female connector end and a glass-reinforced epoxy bulkhead connector [63]. Rigid shell wet-mate connectors, on the other hand, are moulded into a rigid body, providing greater stability, strength, and lockability. The water-locking mechanism involves screwing the two connector halves together and sealing the junction with an O-ring [63]. The water-locking is normally performed underwater, and adequate connector treatment is necessary to ensure proper sealing against water ingress [63]. Connectors must be greased with Molykote 44 Medium before each mating. Adhering to proper procedures using standard greasing products for the application of grease ensures quality mating and secure connectivity, preventing water ingress. Figure 2: Dry-mate connector [63].