# Recent Progress on Underwater Wireless Communication Methods and Applications
## 2 Main Methods of Underwater Wireless Communication
### Underwater RF Communication  
Underwater RF communication has lately surfaced as a captivating substitute for conventional underwater acoustic communication systems, mainly attributed to its capacity to facilitate higher data transmission rates. In contrast to the low bandwidth and high latency that usually restrict underwater acoustic waves, RF communication distinguishes itself by its ability to support considerably faster data rates. This makes it extremely appropriate for high-bandwidth applications such as real-time video streaming, large-scale sensor networks, and remote monitoring of underwater environments. RF communication transmits information via electromagnetic waves that can propagate through water. While the propagation of electromagnetic waves shares similarities with the way radio waves propagate in the air, there are notable differences in range and performance due to the inherent properties of water. Among the many advantages of RF communication in underwater settings, its capacity for high data rates stands out. RF signals can transmit large amounts of data at a much faster speed than underwater acoustic signals. This is essential for applications that need quick transmission of high-resolution data, like underwater imaging, sonar data, and environmental monitoring. What's more, RF communication is especially effective in shallow water. In such scenarios, signal attenuation is not as serious as long distance communication [51]. So, it can ensure better signal clarity and faster data transfer over short to medium distances. Also, RF communication systems have an edge in hardware configuration. The antennas needed for RF communication at higher frequencies are usually smaller than those for acoustic communication. This brings more flexibility in system design, which is highly valued for mobile underwater devices such as Autonomous Underwater Vehicles (AUVs) [11]. To better understand how RF communication compares with other underwater communication techniques in key performance metrics, Table 3 summarizes several typical communication modalities. As shown in the table, each method exhibits trade-offs between data rate, range, and hardware complexity, which must be carefully considered for specific underwater applications. Undoubtedly, underwater RF communication has its limitations, mainly attributable to seawater's high conductivity, which in turn causes speedy signal attenuation. Compared to acoustic signals, RF signals experience far greater attenuation when travelling through water, especially in high-frequency bands, thus posing challenges for long-distance transmission. The significant loss of RF signal strength during underwater propagation confines RF communication to relatively shallow settings. For example, in seawater, the range of RF signals is often just a few meters, whereas acoustic communication can cover hundreds or even thousands of meters. What's more, low-frequency RF communication demands large, cumbersome antennas. This creates difficulties for miniaturization and integration into compact underwater systems, as cited in [52; 53]. In addition to attenuation, complex environmental factors like salinity, temperature fluctuations, and turbulence further undermine RF communication performance. These factors bring about changes in RF signal propagation, making it arduous to sustain stable links in dynamic underwater conditions. Simultaneously, multipath propagation effects, where RF signals reflect off the seafloor or underwater objects, can trigger signal interference and distortion. This results in heightened error rates and less reliable communication [53; 54]. To surmount these limitations, numerous optimization strategies have been proposed for underwater RF communication. A critical research focus involves developing more precise channel models capable of accounting for the frequency-selective attenuation and the dynamic nature of the underwater environment.