Underwater Optical Wireless Communication
Underwater wireless information transfer is of great interest to the military, industry, and the scientific community, as it plays an important role in tactical surveillance, pollution monitoring, oil control and maintenance, offshore explorations, climate change monitoring, and oceanography research. In order to facilitate all these activities, there is an increase in the number of unmanned vehicles or devices deployed underwater, which require high bandwidth and high capacity for information
... ransfer underwater. Although tremendous progress has been made in the field of acoustic communication underwater, however, it is limited by bandwidth. All this has led to the proliferation of underwater optical wireless communication (UOWC), as it provides higher data rates than the traditional acoustic communication systems with significantly lower power consumption and simpler computational complexities for short-range wireless links. UOWC has many potential applications ranging from deep oceans to coastal waters. However, the biggest challenge for underwater wireless communication originates from the fundamental characteristics of ocean or sea water; addressing these challenges requires a thorough understanding of complex physio-chemical biological systems. In this paper, the main focus is to understand the feasibility and the reliability of high data rate underwater optical links due to various propagation phenomena that impact the performance of the system. This paper provides an exhaustive overview of recent advances in UOWC. Channel characterization, modulation schemes, coding techniques, and various sources of noise which are specific to UOWC are discussed. This paper not only provides exhaustive research in underwater optical communication but also aims to provide the development of new ideas that would help in the growth of future underwater communication. A hybrid approach to an acousto-optic communication system is presented that complements the existing acoustic system, resulting in high data rates, low latency, and an energy-efficient system. INDEX TERMS Underwater optical wireless, optical beam propagation, visible light, radio frequency, acoustic communication, hybrid optical-acoustic system, modulation and coding. 1518 2169-3536 2016 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. VOLUME 4, 2016 1520 VOLUME 4, 2016 H. Kaushal, G. Kaddoum: UOWC establishing communication paths between terrestrial and underwater bodies. They are used for long distances propagation and are successfully deployed for communication with naval submarines. The first ELF project was developed in 1968 for communication between deeply submerged submarines. In this project, an alerting system was used to call the submarine to the surface for high bandwidth communication using terrestrial radio links  . It has been reported in  that RF frequencies in MHz range are capable of propagating in sea water up to distance of 100 m by using dipole radiation with high transmission powers in the order of 100 W. However, it requires sophisticated antennas design and high transmission power. FIGURE 1. Underwater RF system design architecture (a) Buoyant RF communication system (b) Direct RF communication System. For RF system design which involves a communication link between underwater and terrestrial transceiver, any frequency range from MHz to GHz works effectively. Such communication systems are called buoyant RF communication system as shown in Fig. 1 (a) and they are not truly underwater communication. Other design configuration involves direct RF communication link between two transceivers submerged underwater or one FIGURE 2. RF attenuation in sea water .