Experiential assessment of iteratively residual interference elimination in the passive phase conjugation for acoustic underwater communications

• Proposing an iteratively ISI cancelation algorithm Based on PPC.
• Theoretically discussion of PPC and verifying its received SNR saturation.
• Coarse channel estimation using PPC block output.
• Clarifying the performance improvement by Simulations and practical tests.

Underwater acoustic communications have found a growing interest because of its variety usages both in military and commercial applications. But, for ocean environment, the channel has an extended time varying multipath due to acoustic propagation. These phenomena cause pulse spreading and time varying inter-symbol interference (ISI). To overcome the interference caused by this harsh environment, equalizers with Passive Phase Conjugation (PPC) have been widely used in coherent communications. In this paper, we have proposed a combined scheme of PPC followed by an iteratively ISI cancelation algorithm to remove the residual ISI remained at the output of the PPC processor. By using a coarse estimation of the channel along with the ISI alleviated PPC output symbols; we can eliminate residual ISI from the received data signal. We have conducted extensive simulations and some experimental tests at the coastal environment of the Persian Gulf to investigate the performance of the proposed scheme. The advantages of the proposed combined scheme are using the channel probe signal for both frame synchronization and coarse estimation of the channel impulse response to using it in the iteratively ISI cancellation and the PPC processing block. The results showed the effectiveness of the combined method.