Multipath effects on high-frequency coherent acoustic communications in shallow water

Abstract

Shallow-water acoustic communication channel, referred to as a multipath-limited channel, produces inter-symbol interference that poses a significant obstacle to reliable communication. Accordingly, signal-to-multipath ratio (SMR), rather than signal-to-noise ratio (SNR), becomes an important factor affecting communication performance. However, it is difficult to estimate SMR from measured communication data, especially at higher frequency (>10 kHz) because many arrivals scattered from rough ocean boundaries produce a significant intrapath time spreading, which acts as random noise in communication. In this paper, the energy fraction of the channel impulse response existing in one symbol duration is proposed as a parameter for estimating the quality of shallow-water communication channels. This parameter is compared with the bit-error-rate performance for data acquired in shallow water off the south coast of Korea, where the water depth is 45m and the bottom consists of sandy clay sediment. The results imply that the energy fraction in one symbol duration may be used as a parameter for describing shallow-water communication channels and applied to the quick decision of a symbol or bit rate in a shallow-water field for reliable underwater communication. © 2013 The Japan Society of Applied Physics.