# Underwater Communications for Video Surveillance Systems at 2.4 GHz
## 2 Related Work  
In order to implement an underwater ad hoc wireless network for video transmission, it is important to know the minimum bandwidth for video transmission. In the related literature, we can find some proposals where video is sent over wireless technologies such as IEEE 802.11n Standard [17]. In addition, knowing the best way of compressing and processing video is also important [18; 19]. On the one hand, there are some works where authors analyze underwater wireless communications. On the other hand, there are very few papers about underwater communications based on EM waves. However, it is easy find to several proposals about underwater acoustic communication. This section provides a concise and precise description of the experimental results and their interpretation as well as their conclusions. [PERSON] et al. [20] investigated the possibility of designing and implementing a marine wireless sensor network based on RF EM communications. The authors developed a small scale wireless sensor network (WSN) to collect data from the seabed and monitor the effects of underwater coastal erosion. Their proposal was based on a multi-hop WSN with a fixed topology of 30 nodes. Ad hoc On-Demand Distance Vector Routing (AODV) was used as routing protocol. The system used low frequency in order to achieve a 40 m transmission radius. However, the data transfer rate is only 100 bps. The authors concluded that this network needed to implement some failure tolerance mechanism to maintain a certain confidence level before a manual intervention. They also explained that when a node failed, the network suffered a worse convergence time, although the performance remained in acceptable level due to the features of the AODV protocol. A RF system was presented in [21] by [PERSON] et al. as a possible solution to transmit information with higher transmission data rates in underwater environments. The transmitter used tank tests with a direct digital synthesizer (DDS) and a PIC microcontroller in charge of processing the information. The DDS worked between 0.5 MHz to 25 MHz. As the results showed, in sea water, RF signals at frequencies up to 5 MHz can be transmitted over a distance of 90 m. However, the results for a bigger salt concentration showed that the attenuation increased with distance, with a rapid attenuation for low distances and a more gradual progression for longer distances. [PERSON] and [PERSON] presented in [22] electric current method based on a pair of copper plate electrodes used as antennae for implementing a digital underwater communication system with high data rates and short range. The experiment was carried out in a fiber glass aquarium with sea water and seabed sand. The experimental results showed that this system is able of transmitting data with higher bit rates over short ranges compared to the acoustic methods. [PERSON] et al. presented in [23] some recent investigations that demonstrated it is possible to use EM waves up to the MHz frequency range to implement wireless links in seawater. The results showed that EM wave propagation in sea water is highly affected by parameters such as permittivity and conductivity. The authors also showed that the EM wave propagation presented high attenuation in the near field. However, the transmission in the far field region can allow transmissions over longer distances and applications such as compressed video, radar or data telemetry could use this system. [PERSON] et al. [24] investigated underwater wireless links in a shallow water environment from two points of view, i.e., experimental and theoretical. Authors described a model useful to describe the shallow water environment from an EM point of view. From these analyses, authors defined the maximum distance coverable with a node transmitting with a specific power. The tests were performed with an electric dipole in a homogeneous and a stratified dielectric. The results showed that lateral wave propagation can be used for wireless communication in shallow water environment.