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Table Of Integrals Series And Products

Seven models for computing underwater radiances and irradiances by numerical solution of the radiative transfer equation are compared. The models are applied to the solution of several problems drawn from optical oceanography. The problems include highly absorbing and highly scattering waters, scattering by molecules and by particulates, stratified water, atmospheric effects, surface-wave effects, bottom effects, and Raman scattering. The models provide consistent output, with errors (resulting from Monte Carlo statistical fluctuations) in computed irradiances that are seldom larger, and are usually smaller, than the experimental errors made in measuring irradiances when using current oceanographic instrumentation. Computed radiances display somewhat larger errors.

Comparison of numerical models for computing underwater light fields

In recent years, underwater visible light communication (UVLC) has become a potential wireless carrier candidate for signal transmission in highly critical, unknown, and acrimonious water mediums such as oceans. Unfortunately, the oceans are the least explored reservoirs in oceanogeographical history. However, natural disasters have aroused significant interest in observing and monitoring oceanic environments for the last couple of decades. Therefore, UVLC has drawn attention as a reliable digital carrier and claims a futuristic optical media in the wireless communication domain. Counterparts of traditional communications, the green, clean, and safe UVLC support high capacity data-rate and bandwidth with minimal delay. Nevertheless, the deployment of UVLC is challenging rather than terrestrial basis communication over long ranges. In addition, UVLC systems have severe signal attenuation and strong turbulence channel conditions. Due to the fact that, this study provides an exhaustive and comprehensive survey of recent advancements in UVLC implementations to cope with the optical signal propagation issues. In this regard, a wide detailed summary and future perspectives of underwater optical signaling towards 5G and beyond (5GB) networks along with the current project schemes, channel impairments, various optical signal modulation techniques, underwater sensor network (UWSN) architectures with energy harvesting approaches, hybrid communication possibilities, and advancements of Internet of underwater things (IoUTs) are concluded in this research. 

https://ieeexplore.ieee.org/ielx7/6287639/9668973/09707771.pdf

Recent Trends in Underwater Visible Light Communication (UVLC) Systems

Underwater visible light communication (UVLC) has been introduced to support emerging high data rate applications such as real-time image and video transmission. Initial works on UVLC build upon the assumption of fixed turbulence strength through the transmission range which can be justified only for horizontal links. In vertical underwater links, the gradient of temperature and salinity changes with depth. This effectively results in ocean stratification where water with different values of salinity and temperature form non-mixing layers. In this paper, we first model the vertical underwater link as a cascaded fading channel where fading coefficients associated with different layers are modeled as independent and non-identical distributed. Based on the cascaded lognormal and Gamma-Gamma distributions respectively for weak and moderate/strong turbulence conditions, we first derive closed-form expressions for the bit error rate (BER) performance of UVLC systems. Then, we analyze the asymptotic BER performance and determine the diversity orders. In addition, we derive closed-form expressions for the average ergodic capacity of underwater cascaded fading channels under consideration. We present simulation results to confirm the analytical findings.

Vertical Underwater Visible Light Communication Links: Channel Modeling and Performance Analysis

In recent years, underwater visible light communication (UVLC) has become a potential wireless carrier candidate for signal transmission in highly critical, unknown, and acrimonious water mediums such as oceans. Unfortunately, the oceans are the least explored reservoirs in oceanogeographical history. However, natural disasters have aroused significant interest in observing and monitoring oceanic environments for the last couple of decades. Therefore, UVLC has drawn attention as a reliable digital carrier and claims a futuristic optical media in the wireless communication domain. Counterparts of traditional communications, the green, clean, and safe UVLC support high capacity data-rate and bandwidth with minimal delay. Nevertheless, the deployment of UVLC is challenging rather than terrestrial basis communication over long ranges. In addition, UVLC systems have severe signal attenuation and strong turbulence channel conditions. Due to the fact that, this study provides an exhaustive and comprehensive survey of recent advancements in UVLC implementations to cope with the optical signal propagation issues. In this regard, a wide detailed summary and future perspectives of underwater optical signaling towards 5G and beyond (5GB) networks along with the current project schemes, channel impairments, various optical signal modulation techniques, underwater sensor network (UWSN) architectures with energy harvesting approaches, hybrid communication possibilities, and advancements of Internet of underwater things (IoUTs) are concluded in this research.

The performance of underwater visible light communication (UVLC) system is severely affected by absorption, scattering and turbulence. In this article, we study the performance of spectral efficient DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) in combination with the transceiver spatial diversity in turbulence channel. Based on the approximation of the weighted sum of lognormal random variables (RVs), we derived a theoretical exact bit error rate (BER) for DCO-OFDM systems with spatial diversity. The simulation results are compared with the analytical prediction, confirming the validity of the analysis. It is shown that spatial diversity can effectively reduce the turbulence-induced channel fading. The obtained results can be useful for designing, predicting, and evaluating the DCO-OFDM UVLC system in a weak oceanic turbulence condition.

/pdf/performance-of-spatial-diversity-dco-ofdm-in-a-weak-1vgl2834fq.pdf

Performance of Spatial Diversity DCO-OFDM in a Weak Turbulence Underwater Visible Light Communication Channel

Ergodic Capacity and Error Performance of Spatial Diversity UWOC Systems over Generalized Gamma Turbulence Channels

In this paper, low-density parity-check (LDPC)-coded carrierless amplitude and phase (CAP) modulation with spatial diversity is proposed to mitigate turbulence-induced fading in an underwater visible-light communication (UVLC) channel. Generalized-gamma (GG) distribution was used to model the fading, as this model is valid for weak- and strong-turbulence regimes. On the basis of the characteristic function (CHF) of GG random variables, we derived an approximated bit-error rate (BER) for the CAP modulation scheme with spatial diversity and equal-gain combining (EGC). Furthermore, we simulated the performance of the CAP system with diversity and LDPC for various turbulence conditions and validated the analysis. Obtained results showed that the combination of LDPC and spatial diversity is effective in mitigating turbulence-induced fading, especially when turbulence strength is strong.

https://www.mdpi.com/1424-8220/20/12/3378/pdf

LDPC-Coded CAP with Spatial Diversity for UVLC Systems over Generalized-Gamma Fading Channel.

For the optoacoustic communication from in-air platforms to submerged apparatus, a method based on speech recognition and variable laser-pulse repetition rates is proposed, which realizes character encoding and transmission for speech. Firstly, the theories and spectrum characteristics of the laser-generated underwater sound are analyzed; and moreover character conversion and encoding for speech as well as the pattern of codes for laser modulation is studied; lastly experiments to verify the system design are carried out. Results show that the optoacoustic system, where laser modulation is controlled by speech-to-character baseband codes, is beneficial to improve flexibility in receiving location for underwater targets as well as real-time performance in information transmission. In the overwater transmitter, a pulse laser is controlled to radiate by speech signals with several repetition rates randomly selected in the range of one to fifty Hz, and then in the underwater receiver laser pulse repetition rate and data can be acquired by the preamble and information codes of the corresponding laser-generated sound. When the energy of the laser pulse is appropriate, real-time transmission for speaker-independent speech can be realized in that way, which solves the problem of underwater bandwidth resource and provides a technical approach for the air-sea communication.

Hongbing Qiu

Papers

Performance of Spatial Diversity DCO-OFDM in a Weak Turbulence Underwater Visible Light Communication Channel

Ergodic Capacity and Error Performance of Spatial Diversity UWOC Systems over Generalized Gamma Turbulence Channels

LDPC-Coded CAP with Spatial Diversity for UVLC Systems over Generalized-Gamma Fading Channel.

Research on the optoacoustic communication system for speech transmission by variable laser-pulse repetition rates