1,548 research outputs found
Orbital Angular Momentum-based Space Division Multiplexing for High-capacity Underwater Optical Communications
To increase system capacity of underwater optical communications, we employ
the spatial domain to simultaneously transmit multiple orthogonal spatial
beams, each carrying an independent data channel. In this paper, we multiplex
and transmit four green orbital angular momentum (OAM) beams through a single
aperture. Moreover, we investigate the degrading effects of
scattering/turbidity, water current, and thermal gradient-induced turbulence,
and we find that thermal gradients cause the most distortions and turbidity
causes the most loss. We show systems results using two different data
generation techniques, one at 1064 nm for 10-Gbit/s/beam and one at 520 nm for
1-Gbit/s/beam, we use both techniques since present data-modulation
technologies are faster for infrared (IR) than for green. For the higher-rate
link, data is modulated in the IR, and OAM imprinting is performed in the green
using a specially-designed metasurface phase mask. For the lower rates, a green
laser diode is directly modulated. Finally, we show that inter-channel
crosstalk induced by thermal gradients can be mitigated using multi-channel
equalisation processing.Comment: 26 pages, 5 figure
Scattering regimes for underwater optical wireless communications using Monte Carlo simulation
Optical wireless communications has shown tremendous potential for underwater applications as it can provide higher bandwidth and better security compared to acoustic technologies. In this paper, an investigation on scattering regimes for underwater links using Monte Carlo simulation has been presented.While the focus of this paper is on diffuse links, the simulation results of collimated links is also provided for comparison purpose. Three types of water namely clear, coastal and turbid water are being used in the simulation. It is shown that the effect of scattering on the path loss cannot be accurately modeled by the existing channel model; ie. Beers-Lambert (BL) law. It has been shown that the distance at which the unscattered light drops to zero can be used to estimate the transition point for the scattering regimes in case of diffuse links. The transition point for diffuse links in coastal water and turbid water can be estimated to be around 22 m and 4 m respectively. Further analysis on the scattering order probability at different scattering regimes illustrates how scattering is affected by beam size, water turbidity and distance. From the frequency response plot, it is estimated that the bandwidth of several order of GHz can be achieved when the links are operating in the minimal scattering region and will reduce to several hundreds of MHz when the link is operating in multiple scattering region
Cellular Underwater Wireless Optical CDMA Network: Potentials and Challenges
Underwater wireless optical communications is an emerging solution to the
expanding demand for broadband links in oceans and seas. In this paper, a
cellular underwater wireless optical code division multiple-access (UW-OCDMA)
network is proposed to provide broadband links for commercial and military
applications. The optical orthogonal codes (OOC) are employed as signature
codes of underwater mobile users. Fundamental key aspects of the network such
as its backhaul architecture, its potential applications and its design
challenges are presented. In particular, the proposed network is used as
infrastructure of centralized, decentralized and relay-assisted underwater
sensor networks for high-speed real-time monitoring. Furthermore, a promising
underwater localization and positioning scheme based on this cellular network
is presented. Finally, probable design challenges such as cell edge coverage,
blockage avoidance, power control and increasing the network capacity are
addressed.Comment: 11 pages, 10 figure
Underwater Optical Wireless Communication Systems: A Concise Review
Underwater optical wireless communications (UOWC) have gained a considerable interest during the last years as an alternative means for broadband inexpensive submarine communications. UOWC present numerous similarities compared to free space optical (FSO) communications or laser satellite links mainly due to the fact that they employ optical wavelengths to transfer secure information between dedicated pointâtoâpoint links. By using suitable wavelengths, high data rates can be attained. Some recent works showed that broadband links can be achieved over moderate ranges. Transmissions of several Mbps have been realized in laboratory experiments by employing a simulated aquatic medium with scattering characteristics similar to oceanic waters. It was also demonstrated that UOWC networks are feasible to operate at high data rates for medium distances up to a hundred meters. However, it is not currently available as an industrial product and mainly testâbed measurements in water test tanks have been reported so far. Therefore, extensive research is expected in the near future, which is necessary in order to further reveal the âhiddenâ abilities of optical spectrum to transfer broadband signals at higher distances. The present work summarizes the recent advances in channel modeling and system analysis and design in the area of UOWC
A Review on Feasible and Reliable Underwater Wireless Optical Communication System for Achieving High Data Rate and Longer Transmission Distance
Underwater Wireless Optical Communication (UWOC) offers significant research prospective with major challenges in the design and implementation. UWOC is capable of providing high rate of data transmission across large distances. This paper attempts to focus on the intricacies of practical implementations and open research issues of UWOC systems. Critical advances and progresses made in the field, modelling techniques and link design challenges are summarised. The purpose of this review is to give suggestions towards feasible and reliable UWOC design with improved performance. Finally the major points are summarized so that it will assist the future research in UWOC
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