UNDERWATER ACOUSTIC CHANNEL MEASURING

Abstract

In this paper, the measuring method of delay profile characteristic of underwater acoustic channel in the shallow water using the auto-correlation characteristic of PN (Pseudo-Noise) sequence is described. For measuring the underwater acoustic channel characteristic, two PN sequences are used as a transmitted data of I-channel and Q-channel of QPSK symbol and QPSK symbol is transmitted with symbol rate of 5kHz and carrier frequency of 25kHz. In the receiver, the received signal is sampled at 200 kHz and stored in the memory. The channel delay profile is computed via the correlation of received data and transmitted QPSK symbol sequences over one period of PN sequence used as a transmitted symbol. The authors acquire the channel data for 675m and 1429m propagation distances from source to sink, and analyze the delay profile of each channel cases. For 675m distance case, the delay profile spans about 30ms and there are3 paths, having relatively high energy, within 1ms delay time difference. For 1429m distance case, the delay profile spans about 2ms and there are 3 paths. Based on the observations of delay profiles, several guidelines are suggested for the design and implementation of underwater transmission systems.