We would also like to express our thanks to the Head of the Department of Electrical &. In this dissertation, we provide a comprehensive survey of the state-of-the-art of UWOC research in three aspects of channel characterization, channel modulation and coding techniques, and practical implementation of UWOC. The existence of the blue light transmission "window" in water provides a foundation for the development of future UWOC.
In 1977, the researcher at Lawrence Livermore Laboratory of University of California proposed a one-way optical communication system from land to submarine [18]. The UWOC system's transmitter used blue-green laser source to generate light pulses. In point-to-point LOS configuration, the receiver detects the light beam in the direction of the transmitter.
Overview of Established Underwater Networks
However, the effectiveness of RF decreases drastically under water; as the frequency of an underwater RF wave increases, its absorption increases dramatically. This means that the frequency of the RF waves underwater must be orders of magnitude less than the frequency of RF waves from waves on land [9]. Furthermore, underwater RF communication necessitates large antennas due to the long wavelengths required as a by-product of low frequency [22].
UOWC also enables high data rates that can be used for streaming video and transferring large amounts of data, as the carrier signal frequency is higher with UOWC than with RF or acoustic.
Non-Technical Consideration 1.3.1: Overview
Safety
There is a need to provide commercial divers with a more effective means of communication while underwater because hand signals often lack the range and throughput required by their work environment. These casualties could be reduced through the use of a UOWC system, which would provide a more comprehensive means of communication for divers. In addition, underwater working conditions could be improved in terms of safety and efficiency with the introduction of the UOWC system.
For example, there are still no workable means of communication to help divers mitigate the uncertainty associated with underwater waste management [25].
Regulation
Another study oversaw the temporary implantation of a UOWC system that used lasers to aid diver communication in a reef blasting public works project [25]. In this regard, a UOWC system using LEDs may show promise as a possible improvement for underwater working conditions. In this regard, the current regulation of the UOWC may previously unattainable opportunities in underwater communication.
As should be clear, while currently less restrictive, the UOWC is subject to some of the same standards and expectations such as the United Nations Convention on the Bottom of the Sea (UNCLOS), Safety of Life at Sea (SOLAS) , the International Convention on Standards of Training, Certification and Watchkeeping (STCW), and the context in which the use of marine technology and equipment is permissible [31].
Industrial and Academic Motivations
Security and Defense
The general of these companies is to protect the marine environment, including preservation of ecosystems, non-interference wildlife and ensuring ethical procedures [31][32]. In each of these, the superior defense capabilities provided by the use of light-based instead of existing radio-frequency and microwave-based systems are evident: higher bandwidth, thus higher network throughput, improved security and increased precision thanks to the high beam directivity and a better resolution due to the shorter wavelengths.
Underwater Research Expeditions
Advances in optical components and an improved laser diode technology increased industrial interest, and thus academic research, for new optical solutions to be included on the available equipment to tackle old problems. The successful implementation of more efficient underwater optical imaging and advances in the overall communication system are also likely to be beneficial in marine ecology, as well as resulting in a better understanding of the Earth's ocean floor. The aforementioned devices (ROV, AUV) can perform tasks at a depth inaccessible to divers due to the associated risks and carry out advanced projects.
Other Underwater Activities
Objectives of the Thesis
Thesis Organization
Theory of the Thesis
Overview
Optical Links
This link can be used when there is an obstacle in the way blocking a LoS link. In this system, a transmitter emits a cone of light, defined by internal and external angles and, in the upward direction, using the water surface to reflect light back down and around obstacles, as seen in Figure 2.3 [35]. Although this technique may be more robust because it does not require a LoS link, the transmitted light has more attenuation compared to a LoS link.
This is because the light travels a greater distance, so more light is scattered due to reflection from the ocean's surface, which is not a flat surface. Finally, although it abandons a LoS link, the effective area to which the signal can transmit is limited by and , which means that this technique requires the same amount of precision as the LoS and modulating retroreflector link. However, it has still been shown to outperform as a LoS link; Carlo simulation demonstrated a reflective link capable of 20MHz bandwidth at a distance of 20m in clear conditions, which is a significant reduction in channel bandwidth compared to the LoS simulation [37].
Signal Modulation
Factors that Affect Underwater Optical Wireless System
Optical Properties of Seawater
- Ocean water types
- Absorption
- Scattering
- Optimum transmission wavelength
- Apparent optical properties
- Fraunhofer line
- Bioluminescence
The transmission wavelength that minimizes the propagation loss factor for a communication link depends on the different types of water and is the sum of absorption a and scattering b. For simplicity and given the intrinsic variability of seawater species, the usual modeling approach is based on chlorophyll concentration. The results demonstrate the main influence that chlorophyll concentration has in the wavelengths of interest for UOCS.
The high variation of the chlorophyll concentration in the seawater is shown in the plots in Figure 2.4. As expected in Section 2.1.2, Morel in 1991 [52] modeled the dependence of the scattering coefficient, , as a function of the chlorophyll concentration. As one would expect, the value of the scattering coefficient equation (2.5) increases as the wavelength increases.
The optimal transmission wavelength is based on an estimate of the global concentration of chlorophyll-a at sea level and with more details in . This section focuses on selecting the transmission wavelength that is least absorbed by the medium, which is a key parameter in any FSO. An analysis of how the values of the optical coefficients discussed so far change with wavelength and chlorophyll-a concentration is presented in Figure 2.11.
In seawater characterized by a very low concentration of chlorophyll-a, the total attenuation coefficient c is mainly a consequence of the absorption contribution. For increasing the concentration of chlorophyll-a, the relative weight of the scattering part becomes dominant in the final value, although its tendency is shaped by the absorption curve. As predicted above, the solar background represents one of the main performance limitations of UOCS.
A numerical example of the radiation generated by a type of marine organism, the dinoflagellate that emits approximately , is of the order [47].
System Design
- System Description
- System Analysis
- Underwater Link Design
- The BER Calculation
The sounds from each photodetector are equalized so that the resulting photocurrents cancel each other out. Thus, the multi-user interference (MUI) is mitigated by removing the sounds coming from all the photodiodes. After push-pull photodetection, original information data is restored by sending the signal through a low-pass filter and threshold detector.
The receiving power of the underwater optical system is given by the following formula [75]:. and are the optical efficiency of the transmitter and the optical efficiency of the receiver, respectively. 36 is the tilt angle of the transmitter. is the beam divergence angle of the transmitter. is attenuation coefficient being is optical source wavelength. The value of depends on the chlorophyll concentration, wavelength, and small as well as large water-soluble particles in water.
For a particular transmission wavelength, the value of the attenuation coefficient varies for different types of water. Thermal noise, short noise and PIIN have been taken into account to calculate BER. The thermal noise is independent of the photocurrents of the photodiodes, but it depends on the noise temperature of the receiver and the load resistance of the receiver.
Result and Discussion
- BER vs. Link Distance for Pure Sea Water
- BER vs. Link Distance for Clear Ocean Water
- BER vs. Link Distance for Coastal Ocean Water
- Comparison of BER vs. Link Distance for Different Types of Water Channels
The connection distance for clear sea water when the simultaneous users are 45, the transmitted power is 30 dBm, the beam divergence angle and the inclination angle are. The connection distance for clear ocean water when the simultaneous users are 45, the transmitted power is 30 dBm, the beam divergence angle and the inclination angle are. The connection distance for the coastal ocean water when the simultaneous users are 45, the transmitted power is 30 dBm, the beam divergence angle and the inclination angle are.
Link distance when simultaneous users is 45, transmitted power is 30dBm, beam divergence angle and inclination angle are. BER for is achieved at 13m, 9.5m and 6.7m in clean seawater, clear seawater and coastal seawater respectively.
Conclusion and Future Works
Conclusion
Future Scopes of the Work
Karp, "The Role of Blue/Green Laser Systems in Strategic Submarine Communications," IEEE Transactions on Communication, vol. Cui, “Prospects and challenges of wireless communication for underwater sensor networks,” Wireless Communications and Mobile Computing , vol. Ooi, “2.3 Gbit/s underwater wireless optical communication using a directly modulated 520 nm laser diode,” Optics Express, vol.
MacKintosh, "Regulating Scientific Diving and Underwater Archaeology: Legal and Historical Considerations," International Journal of Nautical Archaeology, vol. Lloret, "A wireless group-based underwater sensor network for monitoring the sustainability of marine fish farms", Telecommunication Systems: Modelling, Analysis, Design and Management, vol. Liu, "Autonomous Vessel Technology, Safety, and Ocean Impacts", The Future of Ocean Governance and Capacity Development, pp.
Weilgart, "Keeping the Noise Down: Approaches to Mitigation and Regulation of Human-Made Ocean Noise," The Future of Ocean Governance and Capacity, p. Gates, "Toward a Modular, Low-Power, Low-Cost, High-Speed Underwater Optical Wireless Communication Transmitter," UC San Diego Electronic Theses and Dissertations, 2019. Jasman, "Monte Carlo simulation for underwater optical wireless communications nd International Workshop on Optical Wireless Communications (IWOW), pp.
Modeling the inherent optical properties of the ocean based on the detailed composition of the planktonic community”. Bio-optical properties of gelbstof in the Arabian Sea at the onset of the southwest monsoon”.
