# Recent Progress on Underwater Wireless Communication Methods and Applications
## 2 Main Methods of Underwater Wireless Communication
### Alternative Underwater Communication Technologies  
In addition to the aforementioned communication methods, several novel approaches are emerging for underwater communication systems. One such innovative method is underwater electric field communication, which leverages the unique properties of electric fields for signal transmission. This approach demonstrates significant potential, particularly in complex underwater environments where traditional methods may face substantial challenges. Traditional underwater communication methods, including acoustic, optical, and RF communication, each offer distinct advantages while being subject to specific limitations. Acoustic communication, although effective for long-distance transmission, suffers from high latency, multipath propagation, and Doppler shifts. Optical communication enables high-speed data transfer in clear water conditions but is highly sensitive to water quality and particulate matter. RF communication, due to the high attenuation of high-frequency signals in water, is predominantly restricted to short-range applications [78]. These limitations underscore the need for a diverse portfolio of communication strategies to address the unique demands of various underwater scenarios. Electric field communication draws inspiration from the biological mechanisms of weakly electric fish, such as the electric eel. These organisms emit electric fields and sense changes in their environment for communication and navigation. This biological principle has been adapted for data transmission among underwater robots, offering advantages such as low power consumption, compact size, and strong adaptability to complex underwater conditions. It ensures stable communication even in murky waters [79]. Figure 3 shows the basic experimental design of underwater electric field communication system. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Category** & **Acoustic** & **Optic** & **RF** \\ \hline Main influencing factors & Depth & Turbidity/Flow & Salinity \\ \hline Application environment & Shallow water/Deep water & Clean water (harbor/deep sea) & Fresh water/Sea water (fresh water is better) [74] \\ \hline Main defects & High latency and high signal-to-noise ratio & Greatly affected by water quality and turbulence & High attenuation over short distances \\ \hline Advantages & Long range & High speed & Cross media transmission \\ \hline Transmitting range & Few kilometers & Within 100 m & Within 10 m \\ \hline Data rate (short range) & 500 m–50 Kbps [75] & 0.6 m–8 Gbps [64] & 2 m–1 Mbps [76] \\ \hline Data rate (long range) & 3.8 km–600 bps [77] & 100 m–600 Mbps [63] & 10 m–50 Kbps [76] \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparison of Underwater Communication Methods. One notable example of an underwater electric field communication system is the Bio-inspired Electrocommunication System (BECS) and its upgraded version [78], BECS-II. The initial BECS achieved a communication speed of 1.2 kbps over a 3-meter range, making it suitable for small robot swarms BECS-II [79], however, employs a dual-frequency design, achieving a speed of 20 kbps in high-frequency mode and extending the range to 20 m in low-frequency mode. This significant improvement in speed and distance allows it to meet the demands of multitasking applications. Another innovative approach involves a triboelectric nanogenerator (TENG)-based electric field communication system, which generates electric field signals via Maxwell's displacement current [13]. This system has demonstrated robust anti-interference capabilities and stable signal transmission over a 100-meter-long water pipe. TENGs represent a novel mechanism for underwater communication through the generation of displacement current signals, which can be modulated and detected over conductive media. Their key advantage lies in self-powered operation, making them suitable for long-duration, maintenance-free deployment in remote environments. However, practical limitations currently constrain their widespread use.