Ricerc@Sapienza

In underwater acoustic networks (UWANs) with bidirectional communication links, channel state information (CSI) plays an important role since having a good channel knowledge allows system performance enhancements. Two communicating nodes can use the information obtained by their respective channel estimation in order to adjust the transmission parameters to the channel characteristics. However forward channel estimation is generally different from the backward one. In this paper we investigate the acoustic channel reciprocity in a shallow water communication.

Acoustic communications in underwater environment are considerably influenced by the physical characteristics of the medium. This is even more true in the polar regions where the presence of icebergs and icy water layers represent an additional dependence to the signal propagation. Considering a MIMO scenario, we investigate how the channels spatial correlation is conditioned in the case of both frozen and fluid water surface. More, we evaluate the impact of the medium changes on the signal delay spread.

Underwater acoustic communications performance are severely limited by the high number of reflections especially in shallow water environment so producing large delay spread on the signal during the propagation. Multiple-input-multiple-output (MIMO) solutions combined with spatial multiplexing (SM) techniques have been investigated in order to increase the communication rate despite the bandwidth-limited channel.

The achievement of an optimal trade-off between reliability and rate has always been one of the most challenging issues in underwater acoustic links. In this context, the implementation of suitable transmission techniques on Multiple-Input Multiple-Output (MIMO) architectures results to be an efficient solution to improve the communication performance. Following this direction, we investigate a space-time block coding scheme for MIMO-PPM (Pulse Position Modulation) systems that is able to provide a satisfactory compromise between rate and reliability.