Polarized OFDM-Based Pulse Position Modulation for High-Speed Wireless Optical Underwater Communications

An underwater wireless optical communication link can provide high-speed data transfer for robotics applications in deep waters. However, optical links are limited in terms of coverage range because of the high attenuation of light in water caused by absorption and scattering effects. In this work, a new optical transceiver architecture is proposed to solve this coverage problem via a novel Orthogonal Frequency Division Multiplexing (OFDM)-based Polarized Pulse Position Modulation (in short, P-OFDM-PPM) with time-frequency spreading. The optical polarization diversity and multiplexing are utilized at the optical transmitter to improve the system’s robustness and the transmission data rate. This new scheme is able to boost the range coverage by several folds as verified via simulations using realistic models of optical channel propagation. The proposed architecture can be integrated into existing underwater robots to enable next-generation range-extended and high-speed optical links for oceanic explorations.

I. Introduction

Applications of underwater robots include natural resource detection, scientific ocean exploration, environmental monitoring, and tactical surveillance, to name a few. Large scientific data file transfer and multimedia data streaming are expected for underwater robots during exploration tasks. In recent years, tremendous progress has been made in the field of Underwater Optical Wireless Communication (UOWC), bringing advantages in terms of a wide bandwidth—in the scale of hundreds of MHz—and a short transmission latency—in the scale of several ns. Nevertheless, the major bottleneck of UOWC is the high attenuation of the optical signal due to absorption or scattering caused by particles. The noise current at the receiver also introduces interference to received signals [1], [2].