Improvement of Passive Time Reversal Communications Using Spatial Diversity Equalization

Passive time reversal approach can implement spatial and temporal focusing at a receiver array using measured channel impulse response and it is a useful method for one-way underwater acoustic communications. The spatial and temporal focusing can mitigate channel fading, reduce dispersion and increase signal strength. While intersymbol interference (ISI) can be reduced significantly using passive time reversal processing, there always is residual ISI. In this paper, we propose a method to reduce residual ISI using spatial diversity equalization. Spatial diversity equalization is the combination of single channel equalization and adaptive multichannel combining in spatial diversity channel. Coefficients of spatial diversity equalizer are adjusted based on the recursive least squares (RLS) algorithm. Results demonstrate that the performance of passive time reversal communications combined with spatial diversity equalization is superior to that of passive time reversal alone and that of passive time reversal communications combined with single channel equalization.