Abstract: Relevant characteristics of the underwater channel used for acoustic communications are briefly described. There is a trade-off between achievable transmission range and data throughput. Transmission range of several kilometers with carrier frequency of 50kHz and several tens of kilometers with frequency less than 10 kHz might be possible using only 75 watts of acoustic power. Also, we investigated the required acoustic power for certain transmission ranges at given signal-to-noise ratio (SNR) values and the effect of wind speed. A shallow water channel model is proposed to study signal attenuation and arriving angles of the multipath. As the signal time delay increases, the arriving angle of the reflected signals becomes larger, allowing us to limit the number of multipath signals using a directional receiver. We will see that using directional receiver is better suited for a channel with a small range-to-depth ratio (RDR) and that equalization methods are better suited for a channel with a large RDR. Finally hardware complexity for designing shallow water acoustic communication systems is studied using a currently available digital signal processing (DSP) technology.