Underwater Wireless Communication Research Articles

Recent Advances, Future Trends, Applications and Challenges of Internet of Underwater Things (IoUT): A Comprehensive Review

Oceans cover more than 70% of the Earth’s surface. For various reasons, almost 95% of these areas remain unexplored. Underwater wireless communication (UWC) has widespread applications, including real-time aquatic data collection, naval surveillance, natural disaster prevention, archaeological expeditions, oil and gas exploration, shipwreck exploration, maritime security, and the monitoring of aquatic species and water contamination. The promising concept of the Internet of Underwater Things (IoUT) is having a great influence in several areas, for example, in small research facilities and average-sized harbors, as well as in huge unexplored areas of ocean. The IoUT has emerged as an innovative technology with the potential to develop a smart ocean. The IoUT framework integrates different underwater communication techniques such as optical, magnetic induction, and acoustic signals. It is capable of revolutionizing industrial projects, scientific research, and business. The key enabler technology for the IoUT is the underwater wireless sensor network (UWSN); however, at present, this is characterized by limitations in reliability, long propagation delays, high energy consumption, a dynamic topology, and limited bandwidth. This study examines the literature to identify potential challenges and risks, as well as mitigating solutions, associated with the IoUT. Our findings reveal that the key contributing elements to the challenges facing the IoUT are underwater communications, energy storage, latency, mobility, a lack of standardization, transmission media, transmission range, and energy constraints. Furthermore, we discuss several IoUT applications while highlighting potential future research directions.

Обзор ключевых особенностей при построении подводной оптической беспроводной связи

Increased interest in the researches of the underwater environment of the oceans is required for the study of flora and fauna, the ocean floor, the search for minerals, monitoring existing oil rigs and other objects in the ocean, collecting the necessary information. All this cannot be done without high-quality and reliable communication in underwater oceanic conditions. Known methods of organizing underwater wireless communication considered communication systems using acoustic, radio frequency and optical waves. Foreign and Russian researchers note that underwater acoustic and radio frequency wireless communication is characterized by a low speed of information transmission and high latency, but at the same time, it allows you to transmit information over long distances. The need for high-speed information transmission has contributed to the development of underwater optical wireless communication. It allows you to organize communication at a high speed of information transmission with low latency over short distances. An increase in the communication range may provided with the help of network technology for building such communication systems. Purpose: the purpose is to review the scientific works of foreign researchers in the analysis of theoretical and experimental research in the field of underwater optical wireless communication. Results: It is shown, that underwater optical wireless communication maybe organized directly between the surface station and optical nodes, or using network technology to build a network to organize a multi-level communication system from the surface station to the optical nodes using optical access points and/or optical base stations. The analysis showed that when organizing underwater optical wireless communication, the main influence on the quality and reliability of communication is directly exerted by the underwater oceanic environment. Practical relevance: of the work lies in the systematization of scientific works of foreign researchers on the problems of underwater optical wireless communication and use as a basis for future applied research.

Underwater short distance magnetic communication based on coupling coils in sealed metal bin

With the more and more extensive demand of ocean exploration, the communication system of deep-water operation equipment in the ocean requires higher and higher performance. Due to the absorption of electromagnetic wave by seawater, underwater wireless communication is very difficult. In order to adapt to the complex working environment in the deep sea, it is necessary to adopt the communication system with the characteristics of non-contact, low power consumption, small size, two-way transmission and so on. In this paper, a set of underwater short distance magnetic coupling communication system equipment is developed. Combined with the parameter calculation formula of magnetic coupling coil, the short spiral coil is wound, and the experiment is carried out to simulate the seawater environment. The experimental results show that the system has the advantages of low power consumption, small volume, two-way transmission and good stability.

Analysis and Simulation of BER Performance of Chaotic Underwater Wireless Optical Communication Systems

It is shown that modulation methods based on the phenomenon of dynamic chaos and correlation processing can improve the noise immunity of underwater wireless communication systems. This provides the possibility of signal recovery at negative values of the signal-to-noise

Improving the Performance of Underwater Wireless Optical Communications by Pointing Adjustable Beam Arrays

Considering the limited bandwidth of underwater wireless communications with radio frequency and acoustic waves and the constant increasing need for underwater high-speed data transmission, underwater wireless optical communication (UWOC) has been regarded as an attractive and viable alternative. However, UWOCs suffer from degradation attributed to underwater attenuation, oceanic turbulence, and pointing errors in oceanic channel. Therefore, performance enhancement technique plays a key role in the design and deployment of a UWOC system. In this article, we propose to improve the performance of a UWOC by transmitting with pointing adjustable beam arrays (PABA). In a PABA, we can adjust pointing directions of every single beam by reflectors. To decrease the path loss and turbulence-induced scintillations and weaken the influence of pointing errors in UWOCs, we make the one central beam and several surrounding beams in a PABA point toward the center of a receiver aperture, and make the remaining surrounding beams in a PABA point toward several target points located symmetrically on a ring with an adjustable radius around the center of a receiver aperture. This adjustable radius is set according to the average pointing errors in every specific UWOC link. To estimate the average pointing errors more accurate, we calculate pointing errors in view of both beam wander caused by oceanic turbulence and the misaligned displacements resulted by the changes in the position and attitude of an underwater platform. Finally, we validate the effect of PABA on improving the performance of UWOCs by simulations.

UQRCom

While communication in the air has been a norm with the pervasiveness of WiFi and LTE infrastructure, underwater communication still faces a lot of challenges. Even nowadays, the main communication method for divers in underwater environment is hand gesture. There are multiple issues associated with gesture-based communication including limited amount of information and ambiguity. On the other hand, traditional RF-based wireless communication technologies which have achieved great success in the air can hardly work in underwater environment due to the extremely severe attenuation. In this paper, we propose UQRCom, an underwater wireless communication system designed for divers. We design a UQR code which stems from QR code and address the unique challenges in underwater environment such as color cast, contrast reduction and light interfere. With both real-world experiments and simulation, we show that the proposed system can achieve robust real-time communication in underwater environment. For UQR codes with a size of 19.8 cm x 19.8 cm, the communication distance can be 11.2 m and the achieved data rate (6.9 kbps ~ 13.6 kbps) is high enough for voice communication between divers.

Acoustic Wave Propagation Patterns in the Ocean Column

Temperature and salinity play a role in the speed of sound and the process of sound propagation of acoustic waves in the water. Research on the propagation of sound waves in the ocean is a very interesting topic to do because it has many applications, including in underwater wireless communication systems and maritime security. This study aimed to analyze the propagation of acoustic waves in different water depths. The modeling was carried out with flat wave characteristics, in which the bathymetry characteristics of the seawater were ignored. In this ray path simulation, the frequency of 5.3Hz was used at 3 stations with different seawater depths in the Makassar Strait using temperature and salinity data downloaded from marine.coperniccus.eu data. The movement pattern of the acoustic waves was simulated using the Bellhop method. The ray tracing simulation results showed significant differences at the three locations. This was influenced by several factors, including the condition of the seawater environment, the placement of the transducer, the speed of sound, and the depth. Shallow seawater would show a more complicated ray path than deep seawater. The greater the angle of the half beam used, the greater the distance of the range of each beam of light will be so that the reflection of the resulting beam of light covers each column of seawater. The closer the distance between the resulting ray paths, the smaller the energy lost.

Fast auto-alignment underwater wireless optical communications employing orbital angular momentum modes

Underwater wireless communication plays an increasingly important role in more and more emerging ocean activities. Underwater wireless optical communication is a potential underwater communication technology with the advantages of high communication rate, large information capacity, and high bandwidth, but its ability to resist environmental turbulence is challenged. Different from free space optical communication, in underwater optical communication, turbulence not only directly affects the beam transmission, but also influences the transceiver, causing severe mechanical vibration of the transceivers, thus interfering with the optical communication link. At present, the research on mechanical vibration underwater has not received much attention. Hence, we propose and demonstrate fast auto-alignment underwater wireless optical communications employing orbital angular momentum (OAM) modes. The fast auto-alignment system is used to against the mechanical vibration. Two OAM modes multiplexing transmission link with 4-Gbit/s aggregate capacity is demonstrated in the experiment under four different vibration conditions assisted by the fast auto-alignment system with a response time of 244 Hz. After the fast auto-alignment system, the vibrations under for conditions are all greatly reduced to maintain a stable link. The demonstrations may open up new perspective to robust stable underwater wireless optical communications exploiting spatial modes in practical environment.

Analysis of Impulse Responses Measured in Motion in a Towing Tank

The growing interest in developing autonomous underwater vehicles (AUVs) and creating underwater sensor networks (USNs) has led to a need for communication tools in underwater environments. For obvious reasons, wireless means of communication are the most desirable. However, conducting research in real conditions is troublesome and costly. Moreover, as hydroacoustic propagation conditions change very significantly, even during the day, the assessment of proposed underwater wireless communication methods is very difficult. Therefore, in the literature, there are considered simulators based on real measurements of underwater acoustic (UWA) channels. However, these simulators make an assumption that, during the transmission of elementary signals, the impulse response does not change. In this article, the authors present the results of the measurements realized in a towing tank where the transmitter could move with a precisely set velocity and show that the analyzed channel was non-stationary, even during the time of the transmission of a single chirp signal. The article presents an evaluation method of channel stationarity at the time of the chirp transmission, which should be treated as novelty. There is also an analysis of the impulse responses measured in motion in a towing tank.

Performance analysis and design of quasi-cyclic LDPC codes for underwater magnetic induction communications

Magnetic induction (MI) communication is an effective scheme for underwater wireless communication. In this paper, we aim to design an underwater MI communication system based on Quasi-cyclic LDPC (QC-LDPC) codes. Firstly, for a given QC-LDPC code used in underwater MI communication, we propose a novel algorithm to evaluate its performance, which is named as underwater magnetic induction protograph (UWMIP) extrinsic information transfer algorithm. Furthermore, we present a differential evolution UWMIP (DE-UWMIP) algorithm, which incorporates the differential evolution method and the UWMIP algorithm. By this algorithm, we search the optimized QC-LDPC codes with best distance threshold. Simulation results show that the proposed algorithm is effective and provide a good guidance to design the underwater MI communication system.

Support Vector Machine-Based Soft Decision for Consecutive-Symbol-Expanded 4-Dimensional Constellation in Underwater Visible Light Communication System

Nowadays, underwater visible light communication (UVLC) has become one of the key technologies for high-speed underwater wireless communication. Because of the limited modulation bandwidth and nonlinearity of the optoelectronic devices in the UVLC system, the combination of inter-symbol interference and nonlinear impairment will inevitably degrade the transmission performance. Advanced digital signal processing methods including equalization and decoding are required. In the past few years, Support vector machine (SVM) has been widely investigated in quadrature amplitude modulation (QAM) for soft decision in the decoding process. However, previous works only consider 2-dimensional (2-D) separate symbol, ignoring the correlation between consecutive symbols. In this paper, we propose to use SVM for soft decision with a 4-dimensional (4-D) constellation by concatenating two consecutive symbols. To deal with the increasing computational complexity in the SVM training phase, bit-based binary SVM multi-class strategy and an edge-detection-based data pre-processing method are employed. In this paper, we demonstrate a carrierless amplitude and phase (CAP) 16-QAM UVLC system. Experimental results indicate that the performance is greatly improved when using consecutive-symbol-expanded 4-D constellation with SVM for soft decision.

Efficient Equalization and Carrier Frequency Offset Compensation for Underwater Wireless Communication Systems

Efficient Equalization and Carrier Frequency Offset Compensation for Underwater Wireless Communication Systems

Implementation Adaptive Decision Feedback Equalizer for Time-Reversal Communication in Shallow Water Environment

Underwater wireless communications are growing very fast along with human needs for applications such as defense, state security, underwater control and monitoring systems. Until now, an acoustic signal is a practical way to achieve long distance communication in the ocean. However, the underwater acoustic channel faces many challenges including limited available bandwidth, long delays, time-variability, and Doppler-spread. These challenges can reduce the reliability of the communication system and the achievement of high data-rate becomes a challenge. Adaptive decision feedback equalization is a method to compensate for the distortion of information signals on the underwater acoustic channel. On the other hand, time reversal is an effective method of overcoming intersymbol interference (ISI) problems which is the effect of multipath phenomena in underwater channels. Spatial focusing on time reversal can reduce the co-existing system disturbances and its temporal focusing makes the received power concentrated within a few taps so that the equalizer design work becomes much simpler. The temporal focusing can also increase the transmission rate. This paper shows that the combination of time reversal and adaptive DFE (TR-DFE) has superior performance than TR and DFE itself. By modifying the step-size parameters in the adaptive DFE, the TR-DFE level of convergence and performance can be improved. The geometry-based modeling which is used proves that distance and multipath variation greatly affect the quality of time reversal communication on the underwater acoustic channel.

A Testbed for Investigating the Effect of Salinity and Turbidity in the Red Sea on White-LED-Based Underwater Wireless Communication

Several industrial and scientific underwater applications require high-speed wireless connectivity. Acoustic communications have low data rates and high latency, whereas attenuation in seawater severely limits radio frequency communications. Optical wireless communication is a promising solution, with high transmission rates (up to Gb/s) and little attenuation in water at visible wavelengths. This study explores the feasibility of white-LED-based underwater optical wireless communication (UWOC) by considering Red Sea parameters. High salinity is the most prominent attribute of the Red Sea that can affect underwater communication and requires investigation. Considering this, the received signal intensity fluctuation under increasing water salinity was experimentally investigated. In the same experiment, the impact of growing turbidity was tested, as it is the most influential parameter and tends to block the entire LED-based communication system with little increase. The experimental results show that the signals are affected less by salinity and more by turbidity but are found to be sufficiently strong to be used for communication in the Red Sea. Finally, it was concluded that a white LED is capable of sending data at the maximum possible salinity values of 40 g/L. However, the turbidity can significantly limit the transmission distance to less than 60 cm.

Net 5.75 Gbps/2 m Single-Pixel Blue Mini-LED Based Underwater Wireless Communication System Enabled by Partial Pre-Emphasis and Nonlinear Pre-Distortion

Blue LEDs are cost-effective optical sources suitable for underwater optical wireless communication (UOWC) systems. However, the nonlinearity and the low-pass response of LEDs alongside the limited sensitivity of photodetectors constrain the capacity and reach of UOWC systems. Here we address these issues by means of a combined DSP scheme consisting of partial pre-emphasis and nonlinear pre-distortion. Partial pre-emphasis pre-compensates for the low-pass response of the system while relaxing the power reduction induced by a high peak-to-average power ratio, whereas nonlinear pre-distortion can effectively alleviate the LED nonlinearity with only marginal impact on the signal power. Further, it is found that the signal power and the signal SNR at the receiver can be improved by setting a low current bias for the mini-LED because of less saturated radiative recombination. The effectiveness of this combined DSP scheme and device conditioning approach is experimentally validated and enables the transmission of a net 5.75 Gb/s PAM-8 signal over 2 m of distance underwater, which, to our knowledge, is the highest net data rate achieved for single-pixel LED-based UOWC systems.

Dual-Hop Mixed FSO-VLC Underwater Wireless Communication Link

Underwater optical wireless communications (UOWCs) are promising and potential wireless carriers to envisage underwater phenomenal activities for various applications towards the futuristic 5G and beyond (5GB) wireless systems. The main challenges to deploy underwater applications are the physicochemical properties and strong turbulence channel conditions. In this regard, the end-to-end (E2E) performance analysis of a dual-hop mixed FSO/UVLC system under the intensity modulation/direct detection (IM/DD) technique in consideration of pulse amplitude modulation (PAM) scheme is investigated. Throughout this study, to tackle the issues of moderate-to-strong turbulence channel conditions, this work deploys the Gamma-Gamma (GG) distribution fading model and the links are designed by unifying plane wave models in the corresponding links, respectively. This investigation outperforms higher achievable data rate with minimal delay response and enhance network connectivity in real-time monitoring scenarios as compared with the traditional underwater wireless communication technologies. In more contrast, the probability distribution function (PDF), cumulative distribution function (CDF), and closed-form expression of the system are derived and presented in terms of Meijer-G function as well as Extended Generalized Bivariate Meijer-G Function (EGBMGF). The significant E2E performance metrics are obtained by employing the decode-and-forward (DF) relay protocol in hostile channel conditions. In aggregating this work, we combine the analytical expressions that present an efficient tool to depict the impact of channel parameters on the system. The simulation results are plausible of the system performance metrics as average BER (ABER) and outage probability <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(P_{out})$ </tex-math></inline-formula> in the presence of pointing and without pointing error events. Finally, in this work, we use the Monte-Carlo approach for the best fitting curves and validate the numerical expression yields simulation results.

IR Underwater Wireless Communication: A Review

One of the biggest difficulties in the realm of technology is underwater wireless communication. Due to the increase in the number of vehicles and other equipment being used underwater, which need high bandwidth and consequently large capacity for information transfer, underwater wireless information transfer is of great importance. It was put forth and has gotten the most attention in the past 10 years. Although this field has made successive advancements, there has also been a concurrent constraint, which led to the replacement of acoustics with infrared waves (IR). The light emitting diode that delivers pulsed bursts of IR radiation to the light sending diode inside the second communication module receives the pulsed signal after it has passed through the modulation circuit. A suitable strategy is then chosen for the communication with the least amount of loss and the greatest amount of distance. In this paper, a secure underwater communication method is proposed.

INFRARED WIRELESS UNDERWATER COMMUNICATION SYSTEM

The Wireless communication has been booming in the recent years. However, not much has been done to accomplish communication in water in a wireless manner which can be useful in many scenarios. Most of the communication modes that are existing as of now are either not reliable or are very expensive. IR rays can pass through water and thus be used in case of line of sight for communication purpose in this medium. This IR communication using Keyboard uses two units both controlled by ATmega family microcontroller. Both of the units have IR trans-receivers as communicating agents. Keyboards are needed to be connected on both the ends to enter input to the system. The communication messages get displayed on the LCD connected to the system. The system communicates with confirmation key that is sent back by receiving unit to the sending unit. In this way wireless communication is implemented with great efficiency within a line of sight range of about 3-4 meters under the water with the help of IR wireless underwater Communication project.

New approach for designing an underwater free-space optical communication system

Ocean observation system that involves multiple underwater vehicles and seafloor nodes plays an important role in better learning the ocean, where underwater wireless communication is mandatory for massive data interaction. Optical communication that has wide bandwidth and comprehensive working distance is the preferred method compared to acoustic and other methods. However, the presence of directionality makes the optical method difficult to use especially when the transceiver is equipped on a motive vehicle. In this study, an underwater free-space optical communication method of transmitting information is proposed. Characteristics of underwater optical transmission, as well as the photoelectric signal processing and modulation and demodulation algorithms, are studied and modeled. New approach for realizing underwater free-space optical communication is proposed and simulated. A prototype including a free-space optical transmitter and a receiver is developed; tests in different scenarios were carried out, and the results were observed: (1) by using the minimum number of LEDs, the effect of uniform lighting in space is achieved, and the transmitter coverage reaches 160°. (2) When the power of the transmitter is 10 W and the communication rate is 1 Mbps, the maximum communication distance reaches 13 m.

Lifetime Maximization in Underwater Wireless Communication Networks

The rise in demand for underwater wireless communication networks (UWCN) has been driven by the emergence of new applications including unmanned underwater vehicles, deep-sea exploration, maritime and underwater archaeology research, and diver communications. For various applications, underwater network lifetime must be long, since unlike terrestrial sensor networks, it is a major job to change/recharge node batteries in underwater environments. In this paper, we introduce a solution where critical nodes in a UWCN are periodically recharged by small renewable energy sources. Further, a caching mechanism is introduced to relieve critical nodes of heavy workload when their residual energies run low. By leveraging these two techniques of energy replenishment and content-caching, the network lifetime extension challenge is formulated as an optimization problem. The results indicate that our proposed solution offers up to 45% longer UWCN lifetime compared to existing solutions.