Chlorophyll concentration-based CSK constellation point design for underwater SLIPT with priority on communication performance

Simultaneous light wave information and power transfer (SLIPT) plays an important role in constructing a flexible underwater network system to achieve both underwater visible light communication (UVLC) and underwater power transfer. In this paper, color shift keying (CSK) is considered as a modulation method of underwater SLIPT (USLIPT). Also, optimized CSK (OCSK) constellation points are presented for USLIPT using time splitting receiver. This paper considers the constellation design to maximize the minimum distance between the constellation points while mitigating total received current constraint for communication performance optimization. In this study, the attenuation coefficient in the underwater channel is derived from the chlorophyll concentration and the wavelength of each color, and the proposed constellation points are optimized for this underwater channel. In this paper, the average bit-error rate and harvested energy are analyzed and evaluated for the OCSK, and the performances are compared with USLIPT with an on-off keying (OOK) using time splitting receiver. The results show that the error rates of OCSK and OOK are less than 1$0^{-6}$ for the water quality of pure sea, and that of OCSK is less than that of OOK for the water quality of clear ocean when the distance between the transmitter and receiver, the full width transmitter beam divergence angle and the receiver aperture diameter are 50 m, 6 degrees and 0.05 m, respectively. Furthermore, in this pure sea condition, the harvest energy of OCSK was found to be slightly greater than that of OOK for the same DC bias current value at the transmitter.