Application of time reversal technique in shallow water environment

Underwater acoustic communications in shallow water environment is a challenging problem
due to the intersymbol interference caused by time-varying dispersive multipath channel.
The paper describes this effect and the passive time reversal technique and its spatial and
temporal focal properties to reduce channel fading and intersymbol interference which causes
severe distortions of received communication signals. Recently time reversal technique is a
method introduced to the underwater acoustic communication. In a significant multipath environment
the time reversal process offers unique opportunity for solving the multipath problem
and recovering the original signal at the focus. Communication systems can be divided into incoherent
or coherent modulation. In this article coherent underwater acoustic communication
method was presented by using passive phase conjugation and 16QAM (quadrature amplitude
modulation) as a modulation method. Presented results confirm the utility of the passive phase
conjugation in shallow water environment to underwater communications.