A Single-Carrier Turbo-Coded System for Underwater Communications

In the last several years, the Swedish Defence Research Agency (FOI, Stockholm, Sweden) has been engaged in developing a system for underwater (UW) acoustic communications for both point-to-point (P2P) and network applications. The basis of the system is a single-carrier (SC) scheme with recursive equalization on the receiver side. In this paper, we will give a motivation for our choice of SC by discussing some aspects of modulation and coding for UW communication systems from an information-theoretic point of view. The system is able to take advantage of the diversity offered by the multipath and/or by multiple receivers. Due to the great variations in the UW channel, reliable prediction of communication performance in terms of achievable range and data rate is nontrivial. This has motivated the development of a simulation tool called COMLAB, based on combining the communication system with hybrid ray-trace plane-wave time-domain modeling of sound propagation. The simulation tool is designed to account for environmental effects with significant influence on communication performance, including surface and bottom reflections, transmission loss, ambient noise, and ray-path-dependent Doppler shifts caused by moving source, receivers, or surface waves. Short descriptions of the communication system and the simulation tool are given. A comparison of the predicted performance with experiments made at the UAN´11 trials in the Trondheim fjord (Norway) is presented.