Synchronization, Identification, and Signal Detection for Underwater Photon-Counting Communications With Input-Dependent Shot Noise

TL;DR

This work tackles asynchronous grant-free underwater photon-counting optical wireless communication under signal-dependent Poisson shot noise. It introduces a group-based synchronization approach with Bayesian delay updates and a detection window to align frames, followed by a nonlinear iterative MUD that identifies interfering symbols and refines delays on a slot-by-slot basis using MAP detection. The method jointly performs activity detection, delay verification, and MUI suppression, achieving BER comparable to perfect synchronization and converging within five iterations, while reducing complexity via grouping. The results demonstrate practical viability for dense, asynchronous underwater networks and highlight the framework’s robustness to SDSN, channel fading, and CSI imperfections.

Abstract

Photon counting (PhC) is an effective detection technology for underwater optical wireless communication (OWC) systems. The presence of signal-dependent Poisson shot noise and asynchronous multi-user interference (MUI) complicates the processing of received data signals, hindering the effective signal detection of PhC OWC systems. This paper proposes a novel iterative signal detection method in grant-free, multi-user, underwater PhC OWC systems with signal-dependent Poisson shot noise. We first introduce a new synchronization algorithm with a unique frame structure design.The algorithm performs active user identification and transmission delay estimation. Specifically, the estimation is performed first on a user group basis and then at the individual user level with reduced complexity and latency.We also develop a nonlinear iterative multi-user detection (MUD) algorithm that utilizes a detection window for each user to identify interfering symbols and estimate MUI on a slot-by-slot basis, followed by maximum \textit{a-posteriori} probability detection of user signals.Simulations demonstrate that our scheme achieves bit error rates comparable to scenarios with transmission delays known and signal detection perfectly synchronized.

Figures (20)

• Figure 1: Illustration of grant-free, multi-user, underwater PhC OWC systems.
• Figure 2: The system architecture and modules of the considered grant-free, multi-user, underwater PhC OWC systems.
• Figure 3: An illustration of the proposed signal frame structure for the grant-free uncoordinated transmission system.
• Figure 4: Flowchart of the proposed delay estimation and user activity estimation.
• Figure 5: An example of the detection window for user 3 at the receiver of the considered, grant-free, multiuser, underwater PhC OWC system.