Path Loss Measurement of Wideband Signals at sub-GHz Frequencies in a Line-of-Sight Underwater Environment

Intelligent underwater systems comprises of multiple sensors require a high data rate communication scheme for data transmission between sensor nodes and base station. One of the solutions to achieve high data rate is by using a larger signal bandwidth. Nevertheless, propagation characteristics of wide band signal in underwater environments is not fully studied. This paper presents an investigation on the path loss of a wideband signals propagating in underwater environments, through actual measurements. The path loss of wideband signals at sub-GHz frequencies were obtained by measuring the transmission loss against distance while varying the signal bandwidth, inside a tap water-filled water tank using vector network analyzer connected to a pair of optimized wideband underwater antennas. It was found that the slope of the path loss curve decreases when using larger signal bandwidth compared to narrowband signal. For example, using 800 MHz of bandwidth at 600 MHz center frequency marked maximum of 5 dB of losses over 0.5 m distance, compared to maximum 20 dB when using narrowband signals. This result provides an initial validation of the frequency diversity effects obtained from utilization of wide band signal in underwater transmission.