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The underwater channel poses numerous challenges for acoustic communication. In practical, these channels are significantly dynamic due to many aspects such as transmitter receiver movement, variable ambient noise, transmission loss, attenuation, time varying sound speed profiles, boundary reflections and scattering. Hence the acoustic waves transmitted in water suffer long propagation delay, fading, multipath, limited bandwidth, and high spatial and temporal variability. In order to construct a realistic acoustic channel model or simulator, knowledge of the channel physics and statistics is required. Channel simulation based entirely on acoustic modeling is highly ambitious, and in practice one requires in situ channel soundings, i.e., measurements of the time varying impulse response, to validate models. Channel characterization by sounding will improves understanding of system performance at sea. Designing a reliable communication system requires knowledge of transmission parameters of the channel, namely multipath delay spread, Doppler spread, coherence time and coherence bandwidth. However, the possibilities of the measurement of transmission characteristics are limited, especially in case of overspread channels. Channel impulse response (CIR) is the basis for computation of transmission characteristics. From the measured CIRs, one separates the multipaths and studies the amplitude and phase variations, and temporal correlation of individual paths. This work is to understand how the channel affects transmission signals to the design of an efficient communication system. The objective of this work is to study the characterization of the statistical characteristics of the multipath channel in which the evolution of the channel temporal impulse response is examined together with the spreading functions. This work presents about the channel characterization from the data measured from south west Bay of Bengal during July 2017 at a range of about 1km and 3km in depth of approximately 20m. Linear Frequency Modulated (LFM) pulse with the center frequency of 11kHz and bandwidth of 4kHz used as a probe signal to estimate the channel impulse response. Experimental data analysis shows the variations between two channels of 1km and 3km range. From the channel impulse response, spreading function and other characterization functions such as multipath intensity profile and Doppler power spectrum are estimated. These characterization functions estimate the delay spread as well as the severity of the fading in the communication channel.
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