Time-domain modelling of turbo-coded underwater communication

A technique for prediction of the performance of underwater acoustic communication by simulations is presented. The simulation technique, implemented in a software called COMLAB, is composed of three main modules for, respectively, describing the underwater environment, numerical modeling of the communication channel and the communication signal processing. The environment is modelled as a water layer above a fluid or solid seabed, admitting full 3D variations of the bathymetry and media parameters for realistic modelling of sites near a shoreline and inside harbour basins or archipelagos. The communication channel is represented by time-domain hybrid ray-trace/plane wave modelling of underwater sound propagation, accounting for effects with significant influence on communication performance, in particular transmission loss, bottom and surface interactions, ambient noise, reverberation, and ray path dependent doppler shifts caused by moving source, receivers or surface waves. The signal processing algrithms handle a SIMO (Single Input Multiple Output) communication channel, i.e. a single transmitter and a receiver array. The algorithms employ error-corrective encoding by adding redundancy into the message bitstream and iterative channel estimation, equalization and SISO (Soft Input Soft Output) decoding formulated in likelihood ratios for the bit values. For a given communiaction scenario the complete communication chain comprised of encoding - signal emission -sound propagation - signal reception - decoding is simulated and the incurred bit error rate (BER) is computed. The bit error rate, interpretable as the probability of communication error, then provides an estimate of the communication performance. Simulations of point-to-point communication scenarios from the UAN10 field trials at Pianosa in the Mediterranean in September 2010 are presented, and compared with experimental results.