The Evaluation of Probe Signals for Impulse Response Measurements in Shallow Water Environment

Understanding the characteristics of channel propagation plays an important role in designing communication systems. Underwater acoustic channel modeling is commonly done by the direct measurement result from a specific location and time. This paper presents an evaluation of channel impulse response (CIR) and power delay profile (PDP) measurements in shallow water environment using three types of probe signals, i.e., pseudonoise (PN)-sequence, exponentially sine swept (ESS), and amplitude-modulated ESS (AM-ESS). The measurements have been carried out in a laboratory-scale towing tank. The ESS signal has been found to produce CIR and PDP that are close to those of the ray tracing model. The multipath pattern of CIR obtained from ESS signal shows an 80% similarity; it was closer to the ray tracing model compared with other results, made using PN-sequence and AM-ESS signals. The estimated value of rms delay spread obtained by the ray tracing model is 1.023 ms and that obtained by the ESS signal is 1.502 ms. Meanwhile, the values obtained by the PN-sequence and AM-ESS signals are 0.769 and 1.410 ms, respectively. In the frequency domain, the spaced-frequency correlation function, obtained using the PN-sequence and ESS signals, is more similar to the ray tracing model compared with the AM-ESS signal.