Underwater acoustic channel model and variations due to changes in node and buoy positions

The underwater acoustic channel (UAC) is known to offer poor communication channel and very limited transmission bandwidth. The channel is highly frequency selective and the channel response changes over time due to variations in channel conditions. Designing a system to deal with the frequency and time selective channel in UAC, therefore, becomes very challenging. Attempts were made to solve this problem by modeling the underwater acoustic channel, using a coded orthogonal frequency division multiplexing (OFDM) system. A detailed explanation of the channel model is provided, which was used for the performance evaluation of the proposed system. Consideration was given, not only to the channel variation due to the positional changes of the node and buoy, but also to the shadowing effects caused by the surrounding objects near the transmitters. A low-density parity check (LDPC) coded OFDM (COFDM) system was designed to deal with the negative effects of deep sub-band fading problems in OFDM systems. The design is simulated over a realistic (lognormal fading) channel, which shows a robust performance of our designed system in comparison with the un-coded communication system.