Constellation-constrained capacities for parametric underwater communication

In this paper, constellations-constrained capacities of a parametric underwater communication system, which employs robust modulation for quadrature-amplitude-modulation, are analysed. A parametric underwater communication (PUC) system uses nonlinear effects in the underwater channel for data transmission. For performance analysis from the information theoretical point of view, a nonlinear channel model for PUC is derived from the physical modelling. On this basis, robust modulation is discussed and a time-discrete equivalent lowpass channel model is derived. According to this, appropriate constellations are introduced and the corresponding achievable transmission rates are determined. To evaluate the overall performance loss, the maximum achievable transmission rate of the system, which is the channel capacity of the considered equivalent lowpass channel, is calculated numerically. For this purpose, the nonlinear channel is transformed to a linear channel with adapted constraints. The results give valuable insights in the performance of a PUC system from the information theoretical point of view and support the system design.