Underwater Communication Channel Research Articles

Communication-Efficient and Collision-Free Motion Planning of Underwater Vehicles via Integral Reinforcement Learning.

Motion planning of underwater vehicles is regarded as a promising technique to make up the flexibility deficiency of underwater sensor networks (USNs). Nonetheless, the unique characteristics of underwater channel and environment make it challenging to achieve the above mission. This article is concerned with a communication-efficient and collision-free motion planning issue for underwater vehicles in fading channel and obstacle environment. We first develop a model-based integral reinforcement learning (IRL) estimator to predict the stochastic signal-to-noise ratio (SNR). With the estimated SNR, an integrated optimization problem for the codesign of communication efficiency and motion planning is constructed, in which the underwater vehicle dynamics, communication capacity, collision avoidance, and position control are all considered. In order to tackle this problem, a model-free IRL algorithm is designed to drive underwater vehicles to the desired position points while maximizing the communication capacity and avoiding the collision. It is worth mentioning that, the proposed motion planning solution in this article considers a realistic underwater communication channel, as well as a realistic dynamic model for underwater vehicles. Finally, simulation and experimental results are demonstrated to verify the effectiveness of the proposed approach.

Modeling and oblique transmission characteristics of an underwater wireless optical communication channel based on ocean depth layering.

Underwater wireless optical communication is widely considered in the field of underwater communication due to its high bandwidth and low latency. In a real transmission link, the temperature and salinity of seawater, chlorophyll concentration, and bubble density vary with ocean depth. Therefore, the depth of the optical transmitter in seawater and the tilt angle of the beam will exhibit different beam transmission characteristics. In this paper, an underwater oblique-range layered channel model considering the combined effects of dynamic turbulence, absorption, and scattering is developed based on real data of seawater at different depths measured by the Global Ocean Observing Buoy Argo and the Woods Hole Oceanographic Institution BCO-DMO. The effects of transmission distance, transmitter tilt angle, and transmitter depth on the oblique-range transmission characteristics of the beam in seawater are discussed. The simulation results show that, at the same transmission distance, the beam centroid displacement increases with an increase in transmitter depth only when the transmitter is located above the interior of the thermocline. When the transmitter is located below the interior of the thermocline, the influence of the transmitter tilt angle on the beam centroid displacement decreases. This indicates that at different depths within the interior of the thermocline, the optical beam transmission characteristics exhibit significant variations.

A Transmission-Reliable Topology Control Framework Based on Deep Reinforcement Learning for UWSNs

This paper focuses on the topology optimization problem to decrease transmission delay and prolong network lifetime on the premise of reliable transmission in Underwater Wireless Sensor Networks (UWSNs). This is extremely challenging owing to dynamic ocean current movement, harsh underwater communication channel and increasingly demanding application requirements. With the development of software defined network architectures, the centralized topology control (TC) strategy with a global perspective in UWSNs is expected to become a more effective way to tackle the above challenges compared with the existing distributed and heuristic TC strategies involving local network state information. Therefore, we first transform the topology optimization problem of UWSNs into an integer nonlinear programming (INLP) model and design a centralized TC framework to solve the INLP model. In this framework a TC center is built to periodically generate the network topology for UWSNs according to the current network state information. Further, an efficient topology generation algorithm based on deep reinforcement learning (TGA-DRL) is proposed in the TC center. In TGA-DRL, to reduce computing overhead and improve operational efficiency, we formulate an action-space narrowed Markov decision process suitable for network topology generation and solve it with the aid of the rainbow algorithm which is a deep reinforcement learning model. Finally, the performance of our centralized TC framework is verified in terms of the node out-degree, algorithm convergence and optimization effect.

Enhanced Quantum Key Distribution Algorithm for Underwater Optical Wireless Sensor Network

The research aims to develop an attack-free underwater optical communication channel at a distance of 50 meters. In this work, we have emphasized the importance of Quantum Key Distribution (QKD) in Naval and many other applications. An in-detail study of the Benette Brassard QKD protocol proposed in 1984 [BB84] is done with its implementation. Then as the next step, we analyzed the drawbacks of BB84 and the necessity of QKD in Underwater Optical Wireless Sensor Networks [UO-WSN]. As a solution, to identified problems, we have proposed the Enhanced BB84 protocol (EBB84) with considerations of its usage in the UO-WSN. The results showed that the EBB84 algorithm is best suitable algorithm for the underwater environment.

Modelling of an Efficient Electromagnetic Method for Underwater Wireless Communication

This paper investigates the characteristics of brief-term variety in wireless communications in the underwater environment. Nowadays, they are extensively used in experimental research related to underwater communication networks and channel estimations for an efficient link. From the first perspective, the main research exploration enquiry depends upon increasing the distance and frequency range. In this research work, an electric current method focusing on RF wave propagation is chosen. This technique in the seawater is produced by a couple of electrodes sensed by two receipt electrodes. The method can be an option as the waves show less effective refraction and reflection effecting in deep and shallow water.

Statistical channel modeling of intensity fluctuations in a turbulent underwater wireless optical communication system

Subject of study. The statistical modeling of received intensity fluctuations due to temperature-induced turbulence and the random presence of air bubbles in an underwater wireless optical communication channel is presented. Aim of study. Temperature-induced turbulence and air bubbles induce severe intensity fluctuations in the received optical signal, which degrade the underwater wireless optical communication link performance. Method. Therefore, to characterize the turbulent water channel, an experimental setup has been designed in the laboratory that considers uniform and gradient-based temperature variations along with variable-sized bubble populations. To estimate the effect of these random variations in the water channel, a statistical approach has been followed, which characterizes the nature of the recorded observations. Main results. It is observed that the behavior of random irradiance fluctuations due to uniform and gradient-based temperature variations in the underwater wireless optical communication link follows a single-lobe Gaussian distribution. Moreover, with the incorporation of air bubbles, the received irradiance fluctuations no longer follow a single-lobe Gaussian distribution but follow a multi-lobe Gaussian distribution, i.e., the Gaussian mixture model, which is the weighted sum of the Gaussian distribution. The accuracy of the proposed underwater wireless optical communication link models is verified by conducting the goodness of fit test; the observed confidence interval of 95% authenticates the proposed model. Also, the performance of the Gaussian-mixture-model-based underwater wireless optical communication link has been evaluated in terms of bit error rate, and the acceptable bit error rate levels between 1014 and 1010 have been observed. The proposed underwater wireless optical communication with Gaussian mixture model completely depicts thermally uniform, gradient-based nonuniform, and variable air bubble populations in the ocean. Practical significance. The Gaussian mixture model can further be utilized by the researchers to estimate numerous performance parameters of the turbulent underwater wireless optical communication links using advanced modulation schemes and diversity techniques and paves a valuable way to address the future aspects of research in this area.

Reliable Data Transmission in Underwater Wireless Sensor Networks Using a Cluster-Based Routing Protocol Endorsed by Member Nodes

Considering Underwater Wireless Sensor Networks (UWSNs) have limited power resources (low bandwidth, long propagation delays, and non-rechargeable batteries), it is critical that they develop solutions to reduce power usage. Clustering is one solution because it not only saves energy consumption but also improves scalability and data integrity. The design of UWSNs is vital to the development of clustering algorithms. The limited energy of sensor nodes, narrow transmission bandwidth, and unpredictable topology of mobile Underwater Acoustic Wireless Sensor Networks (UAWSNs) make it challenging to build an effective and dependable underwater communication network. Despite its success in data dependability, the acoustic underwater communication channel consumes the greatest energy at a node. Recharging and replacing a submerged node’s battery could be prohibitively expensive. We propose a network architecture called Member Nodes Supported Cluster-Based Routing Protocol (MNS-CBRP) to achieve consistent information transfer speeds by using the network’s member nodes. As a result, we use clusters, which are produced by dividing the network’s space into many minute circular sections. Following that, a Cluster Head (CH) node is chosen for each circle. Despite the fact that the source nodes are randomly spread, all of the cluster heads are linked to the circle’s focal point. It is the responsibility of the MNS-CBRP source nodes to communicate the discovered information to the CH. The discovered data will then be sent to the CH that follows it, and so on, until all data packets have been transferred to the surface sinks. We tested our techniques thoroughly using QualNet Simulator to determine their viability.

An analytical framework for low-power underwater backscatter communications

Acoustic underwater backscatter enables ultra-low-power communication with applications in ocean exploration, monitoring, navigation, and aquaculture. Unlike traditional communication systems, acoustic backscatter does not require active signal generation. Instead, it communicates data by modulating existing acoustic signals, requiring few microwatts of power for operation. Backscatter communication enables ultra-low power sensors by switching between absorbing and reflecting acoustic waves transmitted from a central station. The energy burden is shifted to the transmitting station, and the acoustic power supplied by the station can power the sensor, allowing for battery-free operation. Initial demonstrations of underwater backscatter communication were encouraging; however, the theoretical and practical limits are still unknown. In this work, we develop a multiphysics analytical framework for the communication and power link budget of underwater backscatter. The framework calculates practical communication and power-up range, transmitter power budget, and signal-to-noise ratio, accounting for transducers’ characteristics and the underwater communication channel. The analytical predictions are validated for practical transducers using high-fidelity piezo-acoustic finite element simulations and experimental measurements. The framework will guide future backscatter systems design, identifying practical operation ranges and optimal frequencies for data transmission and batteryless operation.

Effect of bioluminescence on the performance of an underwater optical wireless communication channel

The performance of an underwater wireless optical communication channel (UWOC) is affected by the ambient noise in the water medium. However, no major studies have estimated the spectral bioluminescence upwelling radiance (BLu) numerically with the inputs of measured bioluminescence potential (BP) in oceanic conditions. This study presents a numerical model to estimate the BLu in open ocean and coastal waters and to investigate the UWOC channel performance in terms of the bit error rate (BER) in presence of bioluminescence using Monte Carlo numerical technique. The simulation results suggested that the BER performance degrades in the presence of bioluminescence and can be improved with a narrower receiver FOV. Further, the impact of bioluminescence on the BER performance of the UWOC system at different operational depths is investigated under typical system specifications (APD/PMT, FOV, and receiver aperture). The simulation results showed that BER at different operational depths is more sensitive in open ocean waters than in coastal turbid water with the bioluminescence signal. The results demonstrate that the PMT improves the UWOC channel performance better than the APD. Besides, these results revealed that the BP stimulation at multiple depths deteriorates the BER performance heavily in comparison to the BP stimulation at single depth in the real sea environment. The results presented in this study provide valuable insights and information for accurate design and development of the UWOC system for the enhanced bioluminescence background noise conditions.

Performance Comparison of Different Rotated QAM Based DMT Schemes in Underwater Optical Wireless Communication

In the paper, different rotated QAM-based DMT schemes are proposed and experimentally demonstrated. To overcome the severe high-frequency fading in the underwater optical wireless communication (UOWC) channel, a deviation correction-based maximum likelihood detection (DC-MLD) is introduced into the rotated-QAM scheme. It can improve the precision of the de-rotated process and achieve a better performance than the MLD. Besides, other rotated-QAM schemes using machine learning, including k-means clustering, support vector machine (SVM), and logistic regression (LR), are investigated. These schemes do not need channel state information to achieve the de-rotated process. Meanwhile, the training overhead and execution time of SVM and LR are compared. The experimental results show that, after 5-m air and 4.2-m water channel, compared with the 16QAM DMT, the rotated-16QAM DMT can improve more than 2.5dB received optical power (ROP) sensitivity at the bit error rate (BER) of 1e-3 under the data rate of 3 Gb/s. Meanwhile, the proposed rotated-16QAM scheme with DC-MLD can save more 0.8dB ROP than that with MLD at BER of 2e-4. Besides, it has better performance than the rotated-16QAM DMT with k-means, LR, and SVM.

Deep reinforcement learning-based adaptive modulation for OFDM underwater acoustic communication system

Due to the time-varying and space-varying characteristics of the underwater acoustic channel, the communication process may be seriously disturbed. Thus, the underwater acoustic communication system is facing the challenges of alleviating interference and improving communication quality and communication efficiency through adaptive modulation. In order to select the optimal modulation mode adaptively and maximize the system throughput ensuring that the bit error rate (BER) meets the transmission requirements, this paper introduces deep reinforcement learning (DRL) into orthogonal frequency division multiplexing acoustic communication system. The adaptive modulation is mapped into a Markov decision process with unknown state transition probability. Thereby, the underwater communication channel environment is regarded as the state of DRL, and the modulation mode is regarded as action. The system returns channel state information (CSI) and signal–noise ratio in every time slot through the feedback link. Because the Deep Q-Network optimizes in the changing state space of each time slot, it is suitable for a variety of different CSI. Finally, simulations in different underwater environments (SWellEx-96) show that the proposed adaptive modulation scheme can obtain lower BER and improve the system throughput effectively.

The principle of organizing an underwater radio communication channel using spherical antennas

The principle of operation of spherical antennas, which were used in experiments on the transmission of a short-wave radio signal in the marine environment, is theoretically described. A solution of a spherically symmetric electrodynamic problem based on the experimentally found potential component of the magnetic field is proposed. The characteristics of a potential wave process in an electrically conductive medium are determined. The law of transformation of an electromagnetic wave at the "conductor-dielectric" interface has been established. Keywords: generalized electrodynamics, longitudinal electromagnetic waves, potential magnetic field.

HW/SW Platform for Measurement and Evaluation of Ultrasonic Underwater Communications.

The purpose of this work is to present a flexible system that supports the study of wideband underwater acoustic communications (UAC). It has been developed both to measure channels and to test transmission techniques under realistic conditions in the ultrasonic band. This platform consists of a hardware (HW) part that includes multiple hydrophones, projectors, analog front-ends, acquisition boards, and computers, and a software (SW) part for the generation, reception, and management of acoustic sounding signals and noise. UAC channels are among the most hostile ones and exhibit an important attenuation and distortion, essentially due to both multipath propagation, which results in a very long channel impulse response, and time-varying behavior, which produces a notable Doppler spread. To cope with this challenging medium, sophisticated transmission techniques must be employed. In this sense, adequate signal processing algorithms have been designed aiming not only at the analysis and characterization of underwater communication channels but also at the evaluation of diverse modulation, detection, and coding schemes, from Orthogonal Frequency Division Multiplexing (OFDM) to single-carrier digital modulations with a single-input multiple-output (SIMO) configuration that takes advantage of diversity techniques. Wideband sounding signals, to be injected into the sea from the transmitter side, are created with patterns that allow multiple tests on a batch. With offline processing of the captured data at the receiver side, different trials can be carried out in a very flexible manner. The different aspects of the platform are described in detail: the HW equipment used, the SW interface to control acquisition boards, and the signal processing algorithms to estimate the UAC channel response. The platform allows the analysis and design of new proposals for underwater communications systems that improve the performance of the current ones.

Improvement of a Monte-Carlo-simulation-based turbulence-induced attenuation model for an underwater wireless optical communications channel.

The light propagating in an underwater wireless optical communications (UWOC) channel suffers absorption and scattering effects jointly caused by particles and turbulence. By using Monte Carlo simulation (MCS), most of the research involving UWOC channel modeling has sufficiently considered the attenuation caused by particles while ignoring or erroneously considering the absorption and scattering effects induced by turbulence, which will result in an underestimation of attenuation. Motivated by this, we use a MCS method to construct a more complete and more reasonable channel model, which makes up for the deficiencies of previous studies and provides a general analysis framework for the absorption and scattering effects brought by the two factors of particles and turbulence. We further study the path loss, channel impulse response (CIR), and probability density function (PDF) of the light intensity under different communication scenarios. Results show that, compared to the situation involving only particle effects, the addition of consideration of turbulence effects increases the path loss by more than 5 dB, reduces the CIR amplitude to less than one-third, and makes the light intensity PDF become more dispersed. Our research can provide certain theoretical guidance for UWOC system design and performance evaluation.

An Alternative Experimental Method for Determination of Light Beam Attenuation Coefficient in Underwater Wireless Optical Communication

In wireless optical communication systems, the transmission of optical signals via the channel (air or water) is affected by absorption and scattering. These reduce the signal strength (attenuation) and transmission distance of the signals. In pure water, the blue-green region of the visible light gives low attenuation. Some models have been developed to characterize the underwater optical channel such as Beer Lambert’s law, Radiative Transfer equation and Monte Carlo model. In underwater optical communication, optical power meters are an invaluable tool in the determination of attenuation coefficients. However, optical power meters for underwater optical communication are very expensive. There is a need to be able to determine the attenuation in the underwater optical communication channel at a low cost, especially in the absence of underwater optical power meters. In this paper, we present an alternative low-cost experimental method of obtaining the approximate attenuation coefficient of the visible light beam in underwater optical wireless communication without the use of optical power meters. A wireless visible light communication system was set up experimentally for underwater measurements involving an oscilloscope as the only measuring device. The system uses sub-carrier frequency modulation; a white light-emitting diode array for the transmitter, and a solar panel at the receiver front end. A theoretical transmission model was developed from the experimental setup based on the line of sight method in an unbounded medium, Beer Lambert’s law, and the received sub-carrier signals; in order to provide an alternative method of determining approximately the attenuation coefficient of the underwater medium. Experiments were performed in air, clear water and in saline water. The attenuation in the air was used as a reference upon which attenuation in the clear water and the saline water was based. The saline water has a salt concentration of 6.7 g/100 mL by weight and a total dissolved solid of 86.2 ppt. The trend of the measured received sub-carrier signals showed deviation from the developed theoretical model, and the model was therefore adjusted to conform to the experimental results. From the adjusted model, the attenuation coefficient of 0.0007379 cm-1 and 0.02447 cm-1 were obtained for clear water and the saline water respectively. The method is simple, straightforward, easy to set up in a laboratory, low cost and can be applied to visible light of any wavelength.

Medium Access Control layer protocol design based on stochastic network calculus for underwater wireless communication in open‐ocean fish farming

SummaryThe usage of the underwater communication channel and medium access control (MAC) layer protocol architecture is the most problematic aspect of a seawater wireless communication network. The underwater acoustic wireless communication is a highly appealing choice for information transfer in the communication medium. However, calculating the deferral rate for transmitting real‐time traffic is a challenging task in the underwater environment. Therefore, it introduces the research challenges related to underwater communication, especially throughput and transmission deferral. This research work investigates an MAC protocol U‐TDMA with multi‐hop worst‐case delay analysis for different flow and relays. This research intended to compare the execution of the U‐TDMA protocol with stochastic network calculus (SNC) and without SNC. The U‐TDMA‐wireless protocol establishes the connection and forwards the fish‐mandated information to the mobile sink with the help of upper layers. Also, it improves interface efficiency by taking account of the lengthy delay time of the underwater acoustic channel and addressing difficulties connected to the terminal.

Reliable Data Transmission Scheme for Perception Layer of Internet of Underwater Things (IoUT)

Internet of Underwater things (IoUT) is growing into one of the most important research interests since the last few decades. The primary objective of IoUT is to develop a worldwide network of smart underwater-interconnected objects. It has wide-ranging aquatic applications, including surveillance, pollution reduction, monitoring offshore oil and gas pipelines, disaster prevention, and navigation assistance, making it as important as a terrestrial communication system. The underwater communication channel poses unique acoustic communication challenges that suffer from long propagation delay, low bandwidth, multipath, and fading. IoUT significantly differs from the conventional Internet of Things (IoT) due to disparate environmental conditions under the ocean that require re-designing the underwater communication channel model. In addition to the challenges mentioned above, end-to-end delay and efficient energy utilization are also of great concern. Therefore, in this research paper, diverse attributes of underwater acoustic communication, including the speed of sound, transmission loss, absorption, and ambient noise, are analyzed to design a channel model for underwater communication. These environmental conditions also make underwater acoustic channels highly variable, so efficient resources, including bandwidth and power, are required. Adaptive modulation is proposed to make the communications system efficient by considering the distance between nodes and the signal-to-noise ratio as channel state information. The proposed channel model critically analyzed the CSI factors, results show efficient bandwidth utilization and appropriate power consumption for the well-suited route. The proposed research also aims to reduce end-to-end propagation delay by considering vertical angle-based shortest path (efficient route) in the Multilevel rotating priority MRP-routing algorithm.

Errorless Underwater Channel Selection Scheme Using Forward Error Rectification and Modulation

Acoustic and optical communication are the best options for data transmission in underwater communication. This paper presents the simulation model of an underwater wireless optical communication channel using the Errorless Channel Selection Using Forward Error Rectification and Modulation Progression (ECFM). The suitable modulation methods are used to encode and transfer the packets properly, the data is encoded in differential phase shift key mode at the phase of the light wave carrier. In addition, to send and receive data, an error rectification method is developed in the transport layer, which improves network speed. In addition, we create connections by observing the impact of the refractive index of the optical channel and the reflections formed on the surface of the water. As well as the distance the data travels, throughput, packet delivery ratio, energy consumed, and delay are calculated and discussed using a network simulator. We also look at the losses caused by the operation of the channels running on the network and its location points.

Analysis of the Underwater Wireless Optical Communication Channel Based on a Comprehensive Multiparameter Model

A comprehensive multiparameter model is proposed for underwater wireless optical communication (UWOC) channels to integrate the effects of absorption, scattering, and dynamic turbulence. The simulation accuracy is further improved by the combined use of the subharmonic method and the strict sampling constraint method by comparing the phase structure function with the theoretical value. The average light intensity and scintillation index are analyzed using the channel parameters of absorption, scattering, turbulence, flow velocity, and transmission distance. Under weak or medium turbulence, the bit error rate (BER) performance can be effectively improved by increasing the transmitting light power. The power penalty of a 50 m UWOC channel is 5.8 dBm from pure seawater to ocean water and 1.0 dBm from weak turbulence to medium turbulence, with the BER threshold of 10−6.

Estimation of underwater acoustic channel parameters for Erdek/Turkey region

Due to their chaotic nature, underwater communication channels contain many adverse factors affecting the communication link quality and its performance. These adverse effects directly affect the data transfer between the source and the receiver. Absorption loss, which is one of these adverse factors, depends on depth, temperature, salinity, pH, and speed of sound, as well as frequency, and it has direct impact on the bandwidth used by the system and the distance required for reliable communication. In this study, the effects of variation of temperature, salinity, depth, and sound velocity on the channel bandwidth, channel capacity, and transmission power of the channels formed in the underwater environment in Erdek/Turkey were examined. Within the scope of the study, estimations of the bandwidth, capacity and transmission power parameters were conducted by using temperature, salinity, and sound velocity data relative to the depth recorded between July 2018 and December 2018. Cylindrical, spherical, and practical propagation models are used to compute the propagation loss. In contrast to the studies performed in the literature regarding absorption loss calculations, instead of using only the frequency-dependent approach, realistic models were created by including the effect of changes in the underwater environment in the channel estimation calculations using measurement data. Simplified absorption loss parameters for absorption loss calculations are proposed in the study. It was observed that the channel estimated within the scope of the study are compatible with the outputs obtained from the analysis.