An Improved Passive Phase Conjugation Array Communication Algorithm.

The time-varying, dispersive, multipath underwater acoustic channel is a challenging environment for reliable coherent communications. A method proposed recently to cope with intersymbol interference (ISI) is Passive-Phase-Conjugation (PPC) cascaded with Decision-Feedback Equalization (DFE). Based on the theory of signal propagation in a waveguide, PPC can mitigate channel fading and improve the signal-to-noise ratio (SNR) by using a receiver array. At the same time the residual ISI will be removed by DFE. This method will lead to explosive divergence when the channel is changed by a large amount, because PPC estimates channels inaccurately. An improved algorithm is introduced in this paper to estimate the channel during all the communication process; as a result, the change of the channel can be found in time and the PPC could use more accurate channel estimated. Using simulated and at-sea data, we demonstrate that this algorithm can improve the stability of original algorithm in changed channels. [ABSTRACT FROM AUTHOR]