Capacity Estimation of the Very Short-Range Electromagnetic Underwater Channel Based on Measurements

The significant attenuation experienced by electromagneticwaves in sea water is the main reason why acousticwaves are generally preferred in underwater communication. Nevertheless, acoustic waves have various drawbacks. For example,they are negatively affected by factors such as mechanicalnoise, slow propagation speed, and, particularly, low bandwidth,which leads to digital links at a lower bit rate. However, in short-rangelinks, these problems can be overcome by reconsideringthe use of electric current communications. For instance, datacollected by remote-control vehicles in offshore oil and gas andrenewable energy plants can be transmitted at distances ofeven 1 m or less. This study uses previous frequency responsemeasurements taken in deep water to explore the capacity ofa short-range electromagnetic underwater channel. Because ofwater movement, the nonstatic position of the vehicle whenthe transmission occurs means that the channel is regarded asrandomly time-variant. A statistical model is proposed and theergodic capacity is calculated for a 7 MHz bandwidth channel atdistances ranging from 0.5 m to 5 m as well as for differentvalues of transmitter power. The results of this study reflectcapacity values of tens of kbps at distances of approximately5 m to several Mbps at distances of less than 1.5 m.