Evaluation of Wifi data transmission algorithms for short distance underwater communication

Abstract

Underwater communication becomes more and more important because the number of UUVs (unmanned underwater vehicles) and ROVs (remotely operated vehicles) used in underwater applications rises. These robots collect data from exploration and or inspection tasks and need to transfer them to be processed or evaluated.There are several methods of wireless underwater data transfer. Communication with acoustic waves is the most widespread. Another method uses LEDs for optical communication. Electromagnetic waves are rarely used due to their poor propagation under water.This paper examines the possibilities of underwater data transmission for short distances with a high bandwidth. The approach is chosen because acoustic communication has a very low bandwidth and optical methods are heavily dependent on the environmental conditions (turbidity etc.).Acoustic methods have a very long range compared to other transmission methods, but the bandwidth is not sufficient to quickly transfer larger amounts of data. Furthermore, the corresponding latency is too large for realtime communication. Acoustic transmission methods are mostly used to send indirect commands to an AUV (autonomous underwater vehicle).Communication with optical signals is a suitable approach for short to medium distances. Depending on the water quality and ambient light, the light signals are attenuated relatively strong over the distance. In addition, direct visual contact between receiver and transmitter is necessary.Data transmission with electromagnetic waves offers a shorter latency time, faster data transmission and widely used standards compared to the other methods. After the use of analog transmission standards, information technology raised the need for a wireless data transfer. As a result, standards such as IEEE 802.11 are now commonly used around the globe.Especially when using IEEE 802.11 as a protocol, a variety of existing devices can be used. It saves costs by utilizing commercial of the shelf products and simplifies their use. In addition, the standardized procedures are very well documented, and the documentation is usually freely available. Many described application examples enable the implementation of new tasks. However, the propagation conditions of electromagnetic waves in water are comparable to those of light. Electromagnetic waves in the micrometer range are absorbed after only a few centimeters. Communication over long distances is simply not possible with this approach.A reasonable scenario for the radio transmission described here is the fast data backup when operating an AUV. For example, the AUV uses a camera and a sonar to collect data on autonomous missions. At the end of a mission, this data is transmitted to a docking station underwater. As a result, the time-consuming and energy-intensive emerge and submerge of the vehicle for a data transfer can be avoided.Numerical calculations will not give a general statement about the range of electromagnetic waves in fresh water. The main reason is that the material constants of water depend on many highly fluctuating parameters. Unlike air, temperature, salinity, chemical composition, and pressure have a significantly greater influence on electrical conductivity and permittivity, which significantly describe the propagation of electromagnetic waves in water. Although all parameters can be determined with the corresponding sensors, using them for a range model is complicated.In this paper, we present a setup for several commercial WIFI components for underwater data transmission. All tests will compare the range of the transmission as well as the bandwidth and as a result we will give recommendations about the most suitable setup for short range underwater WIFI.The measured results show that the range and possible data rate allows the application of WIFI in an underwater docking station for the data transmission of big datasets.