High-Performance Time-Code Diversity Scheme for Shore-to-Sea Maritime Visible-Light Communication

Abstract

This paper presents a novel shore-to-sea maritime data transmission system based on time-code diversity, using visible light in maritime environments to overcome the limitations of conventional maritime wireless communications. The proposed system is primarily comprised of existing LED-based lighthouses and maritime transceivers (marine beacons, buoys, etc.), and thus is considered cost-effective in terms of implementation. We first analyze maritime visible-light communications on the basis of the unique properties of a maritime environment, i.e. sea states (wave height, wind speed, etc.), plus atmospheric turbulence, using the Pierson-Moskowitz (PM) and JONSWAP (JS) spectrum models. It is found that the JS model outperforms the PM model, and that the coverage distance depends on the LED power and sea states. To combat maritime fading conditions that significantly degrade performance and coverage distance, we propose a time-code diversity (TCD) scheme in which the delayed versions of the original data are retransmitted using orthogonal Walsh codes. This TCD scheme is found to be superior, in that it offers three orders of magnitude in terms of BER performance, compared to a conventional (non-TCD) transmission scheme. The proposed scheme is robust and efficient in overcoming the effect of impairments present in maritime environments with a BER of approximately 10 -5 and a data rate of 100 Kbps at a distance of 1 km.

Improving modulation bandwidth and optical power of GaN‐based blue LED by hollow‐runway active area

“…The curves shown in Figure B reveal the relationship between response frequency and current just as in References ; that is to say, the minimum current injection density increases as the current increases, so the response frequency increases. Figure B exhibits that the response frequency of CA‐LEDs is higher than that of a single LED, and, in contrast, HRCA‐LEDs have considerable superiority in response frequency.…”

“…In this Letter, we demonstrate GaN‐based VLC LED with hollow‐runway active area, hollow‐runway current‐confined aperture structure, and ITO/graphene composite conductive layer which has an extremely high optical power (~48.65 mW) and an extremely f −3 dB (~89.2 MHz) at 50 mA. Compared with other VLC device in References , it makes the f −3 dB and optical power to the more optimization extent, which makes VLC possible to enter the Light Fidelity (LiFi) era. We also demonstrate an integrated LiFi device with a communication module using our LEDs and a lighting module consisting of rectangle LEDs.…”

“…Liao et al reported a green GaN‐based LED with an aperture diameter of 75 μm with a 3‐dB modulation bandwidth ( f ‐3dB ) of 463 MHz and an optical power of 1.6 mW at 50 mA . However, its optical power was so little that they can only be used for plastic optical fiber (POF) communications . VLC is not only for data transmission communication but also for lighting.…”

“…VLC is not only for data transmission communication but also for lighting. The frequency of the previously described LED was very high and its optical power too small to make a photoreceiver work, which limited its use in VLC beyond POFs communication …”

“…6 However, its optical power was so little that they can only be used for plastic optical fiber (POF) communications. 7,8 VLC is not only for data transmission communication but also for lighting. The frequency of the previously described LED was very high and its optical power too small to make a photoreceiver work, which limited its use in VLC beyond POFs communication.…”