# O2O: An Underwater VLC Approach in Baltic and North Sea
## 1 Introduction
Due to this, hybrid communication scenarios are widely introduced for multiple underwater applications [11; 12]. In our previous work [8], we investigated and compared the two different system models as non-ocean-to-ocean (O2) scenarios such as UVLC/RF and UVLC/FSO for the purpose of underwater exploration and observation of marine lives.The main causes of signal fading underwater are the optical signal absorption, scattering, color division organic materials (CDOM), and strong turbulence due to suspended particles and random phenomena of water currents. The suspended particles exist in the channel, contribute turbulence, and the physical properties of water such as temperature, pressure, and salinity lead to the refraction index, leads to the scintillation index [2]. The sum of the total optical absorption and scattering contributes the signal attenuation, while the randomness of water molecules is responsible for turbulence. In order to characterize the optical signal fading within a strong turbulence channel, the Gamma-Gamma (GG) distribution fading model is proposed as in [3; 8; 14]. Besides, the proposed fading model is a unified framework for the existing VLC channel model under weak turbulence conditions, including log-normal distribution [15] and Weibull distribution [16] models as special cases. Later in this study, a unified probability distribution function (PDF) and cumulative distribution function (CDF) are derived for the VLC link over GG-distribution fading to obtain the BER and outage performance of the proposed system. Motivated by this study and summarizing the above mentioned facts, we are investigating the average bit error rate (ABER) and outage probability performance of the proposed system model. This work has presented the performance of a UVLC link in ocean-to-ocean meeting environments within the framework of highly critical channel conditions. However, to the best of our knowledge, there is no performance evaluation investigated within the isolated Baltic-North oceans in the existing literature. Besides, heterodyne detection, and intensity modulation/direct detection (IM/DD) techniques are also considered for signal modulation within the strong turbulence channel conditions. Heterodyne detection is an information signal extraction methodology for encoded modulation phase, frequency, or both of the electromagnetic radiation in the wavelength band of the optical signal. Additionally, in the literature, it has been proposed as an alternative detection approach which is more conveniently deployable for turbulence environmental effects [17; 18]. and intensity modulation/direct detection (IM/DD) techniques are also considered for signal modulation within the strong turbulence channel conditions. Therefore, throughout this study, we investigate the performance based on the experimental data that has been taken during the whole year 1996s. Due to the unavailability of current practical data in North-Baltic oceans, we are using the data available in [PERSON] et al. [1]. As a benchmark, our investigated system model and performances are applicable for the current scenarios of mingled waters all around the world. Throughout this study, the following contributions are summarized as follows:  
* The system model is developed to support the human underwater exploration activities, especially for coastal securities and goods transportation within EU based North and Baltic water reservoirs;
* The performance of the proposed system subjects to the generalized GG distribution fading is analyzed within the mingled Baltic-Northern Ocean trait for the first time to the best of the authors' knowledge. Additionally, the performance of the system is analyzed based on the experimental data in both of the oceans as in [1];
* We investigate the UVLC system performance under strong channel conditions in the Baltic-North ocean for the direct connectivity and real-time monitoring of floating vehicles, observation of the marine life, etc.