The performance of sparse time-reversal mirrors in the context of underwater communications

Recently, wave focusing using a uniform time-reversal array has been demonstrated in the ocean with very encouraging results. This technique may be used to regenerate a mildly distorted signal at the input of a digital underwater acoustic receiver, hence reducing its equalization requirements at the expense of additional complexity at the transmitter. This work investigates the performance improvements that become possible when sparse and non-uniform arrays are used. Results from the theory of randomly-spaced arrays are extended to a simplified ocean waveguide, revealing that familiar relations between the sensor placement density function and the directional characteristics of the generated acoustic field are still valid in the large-scale. Simulation results confirm the validity of these derivations.