Shore-to-Sea Maritime Visible Light Communication

Abstract

A new wireless technology known as visible light communication (VLC) came into limelight with the advent of light emitting diodes (LEDs). VLC is a communication method using LEDs, where blinking of an LED is used for communication and illumination simultaneously. LED communication offers innovative wireless technologies in terms of communication speed, flexibility, usability and security. Unseen by the human eye, this variation is used to carry high-speed data, thereby creating wireless communication network using existing light resources in order to achieve low-cost communication. Currently the widespread use of LEDs in maritime applications presents a multitude of opportunities for visible light based maritime communications. Conventional maritime wireless communications rely predominantly on radio frequency (RF), which suffer from high cost with low transmission speed and scarce operation spectrum. To overcome these limitations in maritime communications, VLC can be considered an alternate technology in maritime environments. This thesis provides a detailed analysis of VLC under various atmospheric and sea conditions, which will eventually lead to significant improvement in communication range as well as link performance in maritime environments, thus leading to a low-cost, high-speed wireless link in the shore-to-sea maritime VLC (MVLC) system.

In the first study, for providing an efficient VLC link for maritime environments, it is important to analyze the effects of transmission under sea states (spectrum of sea waves due to blowing wind, atmospheric turbulence, etc.). Computer simulations are conducted based on the Pierson-Moskowitz (PM) and JONSWAP (JS) spectrum models with various sea states for analysis. The transmission system presented for shore-to-sea communication considers unique properties of maritime environments where wave height, wind speed, etc. exist.

Secondly, the thesis presents a MVLC scheme using color clustered multiple-input and multiple-output (MIMO) for satisfying International Association of Lighthouse Authorities (IALA) requirements for maritime buoyage system. Selection combining is performed at the receiver, producing diversity effect within that color cluster. The simulation results show the maritime link quality analyzed in terms of coverage distance and bit error rate (BER) performance provides an efficient MVLC and also offers sufficient illumination from high power LEDs. The next study is a novel time-code diversity (TCD) scheme using the delayed versions of the original signal and orthogonal Walsh codes for MVLC system. The proposed TCD scheme has an advantage of simplicity to achieve a reasonable diversity gain resulting in a significant performance improvement, compared with related schemes such as adaptive optics and forward error correction for maritime environments.

In the later part of the thesis, a multi-hop decode-and-forward (DF) relay based VLC system is proposed to provide an efficient maritime link covering a longer distance with adequate performance in maritime environments. The performance of the proposed multi-hop VLC system over maritime channels with DF relay is further improved using receiver diversity with combining techniques.

The quality of a VLC link in the troposphere is strongly influenced by weather conditions such as fog, rain and snow. Thus, the final study in the thesis work focuses on analyzing the link quality of MVLC system under foggy conditions. Investigation of communication link under fog condition is important for a MVLC system, as it causes severe loss of signals as compared to signal fading phenomenon. Computer simulations were conducted considering fog condition to analyze MVLC system in terms of BER and coverage distance.