SignalEx: linking environmental acoustics with the signaling schemes

Although work on digital underwater acoustic communications dates back to the early 70s, the mid-/late-1990s have seen a strong renewed interest. The signaling schemes include a variety of noncoherent and coherent schemes including MFSK, DPSK, and QAM and a variety of manufacturers provide such modems `off-the-shelf´. Meanwhile, the R&D community has demonstrated the impressive potential of the modems as the key connector in undersea networks. While the signaling schemes have become much more sophisticated, the role of the ocean environment on their performance remains poorly understood. As a corollary, predictive models of modem performance are not readily available. The SignalEx tests are designed to address specifically these issues, drawing upon the significant navy experience with acoustic propagation models originally developed largely for ASW applications. A variety of different test sites have been selected with the goal of understanding better how modems respond to multipath and variability induced by a changing ocean. This paper summarizes the lessons learned from SignalEx tests conducted on the Loma Shelf near San Diego and on the New England Shelf near Long Island