PPM space-time block coding vs. spatial multiplexing for shallow water acoustic links

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. Concerning this issue, we propose a Pulse Position Modulation-based (PPM) MIMO architecture and compare the performance of SM versus space-time block coding by resorting to the trace-orthogonal principle. The results coming from shallow water experiments in a reservoir are detailed.