Errorless Underwater Channel Selection Scheme Using Forward Error Rectification and Modulation

The Earth is a water planet, two-thirds of which is covered by water. With the rapid developments in technology, underwater communications has become a fast growing field, with broad applications in commercial and military water based systems. The need for underwater wireless communications exists in applications such as remote control in the off-shore oil industry, pollution monitoring in environmental systems, collection of scientific data from ocean-bottom stations, disaster detection and early warning, national security and defense (intrusion detection and underwater surveillance), as well as new resource discovery. Thus, the research of new underwater wireless communication techniques has played the most important role in the exploration of oceans and other aquatic environments. In contrast with terrestrial wireless radio communications, the communication channels in underwater wireless networks can be seriously affected by the marine environment, by noise, and by limited bandwidth and power resources, and by the harsh underwater ambient conditions. Hence, the underwater communication channel often exhibits severe attenuation, multipath effect, frequency dispersion, and constrained bandwidth and power resources, etc., which turn the underwater communication channel into one of the most complex and harsh wireless channels in nature. When facing these unique conditions in diverse underwater applications, many new challenges, which were not encountered in terrestrial wireless communications, are emerging in underwater acoustic, optical, and RF communications for future underwater wireless networks. Of these challenges, acoustic and optical are the most compelling, and somewhat complementary, owing to the potential for longer range and high bandwidth networked communications in sizeand power-constrained modems and unmanned systems.

Understanding the effect of ocean turbulence on optical beam propagation is critical to the design and performance evaluation of underwater wireless optical communication systems. In this Letter, we propose a unified Weibull-generalized gamma distribution to characterize the laser beam irradiance fluctuations of turbulent underwater thermocline wireless optical channels. The proposed model shows an excellent agreement with the measured data under various experimental emulated channel conditions that cover turbulences induced by temperature, salinity, and air bubbles. To the best of our knowledge, this is the first model that comprehensively describes the statistics of the laser beam irradiance fluctuations in underwater wireless optical channels due to both thermohaline gradient and air bubbles.

Underwater wireless optical sensor networks require high-speed, long-range, and scalable underwater wireless optical communication/ultra-wideband hybrid links to enable real-time data transmission and reliable communication between sensors and surface stations. Such hybrid links can provide seamless connectivity, adaptability to changing underwater environments, and support for various applications including ocean exploration, monitoring, and surveillance. We report an underwater wireless optical communication/ultra-wideband converged transmission link for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m1"><mml:mrow><mml:mn>5</mml:mn><mml:mo>×</mml:mo><mml:mn>1.5</mml:mn></mml:mrow></mml:math> Gb/s underwater wireless optical sensor networks. The directly-modulated lasers are used to modulate and transmit the sensors’ data over underwater wireless optical communication channels towards floating optical base station having radio-access units where multiple ultra-wideband signals are generated employing optical delay line technique. Intensity modulation/direct detection scheme based upon On-off keying modulation is employed in this work. The performance of the sensors is examined taking into account various water bodies and turbulence regimes using metrics of Bit-error rate, Quality factor, and Error-vector magnitude utilizing Gamma-Gamma statistical channel model. The simulation results obtained indicate that forward-error correction target Bit-error rate of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="m2"><mml:mrow><mml:mn>3.8</mml:mn><mml:mo>×</mml:mo><mml:mn>1</mml:mn><mml:msup><mml:mrow><mml:mn>0</mml:mn></mml:mrow><mml:mrow><mml:mo>−</mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math> is successfully achieved for sensors considering different water bodies and turbulence regimes. The proposed system is potentially scalable, accommodating increased sensors, and supporting higher rates while efficiently generating and processing ultra-wideband signals.

Underwater wireless sensor networks are essential for ocean exploration and military use. Acoustic communication is the predominant method due to the unique underwater conditions, though challenges like low bandwidth and multipath effects hinder its effectiveness. Terrestrial communication protocols are not directly applicable underwater, making network security and stable data transmission critical research areas. This paper reviews underwater sensor network communication technologies, architectures, protocol stacks, and security challenges, assessing the suitability of various communication methods and the components of these networks. It also analyzes the main topological structures and the security risks across the physical, data link, network, transport, and application layers. Additionally, the paper investigates positioning and navigation technologies in underwater communications and their future applications. Advancements in underwater optical communication and the development of intelligent underwater networks and the underwater Internet of Things (IoUT) are identified as key future directions.

Underwater acoustic communication is paid more and more attention with the development of marine researches in recent years. Underwater acoustic communication channel is considered to be one of the most complicated channels, it suffers from the less available bandwidth, the more serious multipath effect and the even complex noise. Due to the severe distortion of the received signals, the underwater acoustic communication always experiences a high Bit Error Rate (BER). To solve this problem, Carrier Waveform Inter-Displacement (CWID) modulation was proved to be an effective method to decrease BER in our previous work. The Linear Frequency Modulation (LFM) carrier-waves are used in CWID modulation. The frequency band of LFM carrier-waves has an important effect on the communication performance. The Particle Swarm Optimization (PSO) is introduced to search the optimal frequency band of the LFM carrier-waves in this paper, due to its excellent performance in solving complicated optimization problems. The multiple objective optimization nature of the PSO gives a clear hint to deduce the relationship of upper band and lower band of the LFM carrier-waves. Simulations verify the improved performance and effectiveness of the optimization method.

Distinctive features of underwater communication channel pose significant challenges to effective underwater acoustic communication. Due to bandwidth limitation, orthogonal frequency division multiplexing is widely used for its high spectrum efficiency. However, orthogonal frequency division multiplexing also has its shortcomings, one of which is the relatively high peak-to-average power ratio, which leads to saturation in the power amplifier and consequent distortion of the signal. Clipping is the most commonly used method to address the high peak-to-average power ratio; however, it introduces additional noise resulting in degradation of the system’s performance. This article proposes a compressed sensing technique for mitigation of the clipping noise, which exploits pilot and data tones instead of reserved tones, thus making it distinct from the previous works and improves data rate. Moreover, in contrast with previous works, the channel is also estimated using compressed sensing technique, which provides more accurate channel characteristics for estimating the clipping noise than traditional methods like least square or minimum mean squared error. The better performance of the proposed Iterative compressed sensing algorithm is proved in simulations as well as in a pool experiment using acoustic wave sensors.

Разработана компьютерная модель спутникового канала связи с учетом влияния доплеровского сдвига по частоте и стороннего спутника связи. Компьютерная модель построена в графической среде имитационного моделирования Simulink, которая входит в программный пакет MATLAB. В статье рассматривается имитационная модель спутникового канала связи с использованием сигнала MSK (Minimum Shift Keying). В ходе работы изучены и применены алгоритмы цифровой обработки сигналов при разработке компьютерной модели спутникового канала связи. По заданным параметрам принимаемого сигнала определены основные параметры цифрового демодулятора сигнала MSK, такие как частота повторения бита, частота дискретизации, минимальная разрядность аналого-цифрового преобразователя (АЦП), количество уровней квантования, частота среза цифрового фильтра-дифференциатора. В результате компьютерного моделирования спутникового канала связи было исследовано влияние отстройки по частоте сигнала MSK и уровня мешающего сигнала (стороннего спутника) на помехоустойчивость модема. По результатам моделирования получены графики зависимости вероятности ошибки приема бита от уровня мешающего сигнала и вероятности ошибки от отстройки по частоте. Разработанная компьютерная модель существенно расширяет круг задач, связанных с оперативной оценкой параметров электромагнитной совместимости (ЭМС) и радиоподавления в группировках подвижных РЭС.

Recent years have seen a growing interest in underwater communication and some progress has been made in this area. However, underwater communication is still immature compared with terrestrial communication. A prime reason for this is that the underwater environment is intrinsically not suitable for propagation of electric waves. Instead, ultrasonic waves are mainly used for underwater communication. Since ultrasonic waves cannot provide sufficient communication speed or capacity, they cannot use existing network technologies, which assume use of radio waves. In particular, communication in shallow water is still an uncharted territory. Few communication technologies are employed in environments where people enjoy scuba diving. This paper addresses problems faced by recreational scuba divers. It proposes constructing an ad hoc mesh-shaped network between divers within a group and use ultrasonic waves as transmission media in order to enable the detection of a stray diver. It also proposes a communication protocol in which messages are relayed in multiple hops, and a message collision avoidance method, which is intended to reduce the rate of packet loss caused by message propagation delay. We have implemented the proposed methods in a network simulator, and compared them with an existing communication method that has no message collision avoidance function, in terms of the packet loss rate, the stray driver detection rate, and the rate of the ability to communicate in multiple hops.

Ultrasonic signals can be utilized as a viable communication method to transmit information through gas, liquid, and solid channels or a mixed media consisting of a solid interfaced with liquid and/or gas. Underwater communication channels using sound waves cause many challenges, often unforeseen, due to absorption, scattering, refractions, reverberations, multipaths, doppler shifts, temperature, salinity, and acoustic scintillation. Ultrasonic communication through the air is less prone to the environmental challenges that are often encountered in the underwater communications. Ultrasonic communication in solid channels is also adversely affected by absorption, scattering, refractions, reverberations, beam skewing, dispersion, mode conversation, multipaths, and above all these challenges are compounded by the geometrical structure of solids and type of ultrasonic waves. With solid structures many different ultrasonic wave types can be generated including Longitudinal (Compressional), Shear (Transverse), Surface-Rayleigh, Plate-Lamb (Symmetrical or Extensional Mode and Asymmetric or Flexural Mode), Plate-Love, and Stoneley (Leaky Rayleigh). The type of waves is governed by the frequency and angle of the incident waves on a solid structure where the quality of the signal for communication is limited by the composition and geometrical shape of the solids. For this study we have developed a testbed platform using the ZYNQ SoC (System-on-Chip) FPGA by Xilinx which offers reconfigurability and high-performance computational capability, high speed signal converters, power amplifiers for excitation of transducers, low noise receiving amplifiers and high frequency ultrasonic transducers for transmitting and receiving information. Theoretically, ASK (amplitude shift keying) or any form of digital modulation can be realized with the system using the concept of the software-defined ultrasonic communications (SDUC). In practice, the received signal is very complex, primarily caused by dispersion, reverberation, and multipath effects. We have examined SDUC system using AM (Amplitude Modulation), OOK (on and off keying), BPSK (Binary Phase Shift Keying), QPSK (quadrature phase shift keying), and OFDM (orthogonal frequency-division multiplexing). This system is tested using differently structured solid channels (such as blocks, plates and pipes); and bitrates and bit rate errors are compared using 2.5 MHz ultrasonic transducers. Furthermore, this paper presents an overview of using EMAT for ultrasonic communications in metal channels.

Nowadays, the increasing availability of commercial off-the-shelf underwater acoustic and non-acoustic (e.g., optical and electromagnetic) modems that can be employed for both short-range broadband and long-range low-rate communication, the increasing level of autonomy of underwater vehicles, and the refinement of their underwater navigation systems pave the way for several new applications, such as data muling from underwater sensor networks and the transmission of real-time video streams underwater. In addition, these new developments inspired many companies to start designing hybrid wireless-driven underwater vehicles specifically tailored for off-shore operations and that are able to behave either as remotely operated vehicles (ROVs) or as autonomous underwater vehicles (AUVs), depending on both the type of mission they are required to perform and the limitations imposed by underwater communication channels. In this paper, we evaluate the actual quality of service (QoS) achievable with an underwater wireless-piloted vehicle, addressing the realistic aspects found in the underwater domain, first reviewing the current state-of-the-art of communication technologies and then proposing the list of application streams needed for control of the underwater vehicle, grouping them in different working modes according to the level of autonomy required by the off-shore mission. The proposed system is finally evaluated by employing the DESERT Underwater simulation framework by specifically analyzing the QoS that can be provided to each application stream when using a multimodal underwater communication system specifically designed to support different traffic-based QoSs. Both the analysis and the results show that changes in the underwater environment have a strong impact on the range and on the stability of the communication link.

Recently, underwater wireless sensor network (UWSN) has paved the way for researchers towards a new era of exploring ocean realm targeting envisioned landscape of underwater applications. These applications can be made viable through underwater communication by using acoustic waves, giving rise to several design challenges like limited bandwidth, large and variable propagation delay, frequent connectivity loss, etc. Reliable data delivery in UWSN is always a tempting issue to be addressed, which is jeopardised by link failures and communication void. Under this context, Link failure Avoidance and Void Recovery (LAVR) routing protocol is proposed that uses link quality as forwarding factor, computed using Triangle Metric, to achieve reliability. A void node recovery procedure is proposed to displace the void node to a new depth to increase the packet delivery ratio. Simulations are performed in Aqua-Sim simulator and LAVR outperforms other existing protocols in terms of packet delivery ratio and network lifetime.

This paper discusses the method for extending the range of Magnetic Induction (MI) and its application in underwater networks for the Internet of Underwater Things (IoUT). In underwater communication, this technology would provide a wider frequency band than acoustic systems, shorter propagation delay, and increased conductivity, with the added benefit of underwater wireless power transfer. As a use case, we consider a system that allows energy to be transferred from one circuit to another without cables, as in an aerial environment. In this work, transmit and receive coils for underwater environments are designed and analyzed using ANSYS Maxwell v16.0 software. The results show an improvement in terms of underwater magnetic field propagation. We have conducted underwater experiments by applying a frequency range up to 100 kHz and 12 Volts with varied current, achieving a distance up to 80% greater than in air, as determined by parametric analysis. With an improved bit error rate, a delay of less than 2 microseconds, a packet delivery ratio near 100%, and a packet loss ratio less than 10%, the results show an improvement in magnetic field propagation underwater. This demonstrates that it is possible to conduct future research into other underwater applications by implementing MI for underwater communication.

The complexity and variability of underwater environments makes it difficulate to evaluate the channel characteristics of the underwater laser communication. To overcome this, the paper establishes a laser communication channel model based on Monte Carlo model, simulating and analyzing the distribution and loss properties of a laser beam propagating under realistic marine conditions. The proposed model is validated against benchmark simulations by Cox, achieving excellent agreement with a relative error below 1.1%. From the perspective of scattering orders, the study elucidates the physical mechanisms behind temporal pulse broadening and spatial beam spreading, which are primarily attributed to high order scattering events. A comprehensive analysis of key system parameters are conducted, encompassing number of photons, attenuation coefficient, transmission distance, divergence angle, receiver aperture, and received FOV, to evaluate their influence on the received optical intensity and channel temporal dipersion. Simulation results show that the scattering orders increases with transmission distance and attenuation coefficient, which leads to increased temporal spread and reduced received power. Notably, the received intensity and temporal dipersion are found to be more significantly affected by water quality than that of transmission distance, and the traditional Beer’s law is inapplicable in harbor seawater. The received intensity of clear, costal, and harbor seawater are found to be 2.7, 6.8, and 20.1 times that of pure seawater, and temporal dipersion of clear, costal, and harbor seawater is 1.6, 2.1, and 15.9 times that of pure seawater under certain conditions. Furthermore, increasing the divergence angle leads to more severe temporal dispersion and greater decline in received intensiy. The divergence angles of 0.25 mrad, 2.5 mrad, 5 mrad, and 50 mrad yield temporal dispersion of $0.59 \mathrm{~ns}, 0.61 \mathrm{~ns}$, 0.68 ns, and 0.8 ns, accompanied by received intensity of -32.5 dB, $-35.6 \mathrm{~dB},-40.5 \mathrm{~dB}$, and -57.7 dB. In addition, the receiver aperture and FOV exhit a minor influence on these performance metrics, particularly at narrow divergence angles, where their impact can be considered negligible. Across all transmission distances, the received intensity varies remain within $\mathbf{5 d B}$, and the maximum variation in temporal dispersion is less than 0.1 ns. This work establishes a theoretical framework to support the design and performance evaluation of underwater laser communication systems.

A novel fuzzy trust-based secure routing scheme in flying ad hoc networks

In this paper the development of a channel model for wireless indoor communication, specifically with regard to indoor retransmission of satellite signals and reception by fixed and portable receivers in the L band, is described. The study is confined to the channel model, though it does not include the assessment of particular transmission forms. The theories and approaches used in the model are mainly derived from the field of mobile communication. They are combined to a straightforward chain from large- to small-scale variations yielding information about the several stages of fading. One of the features is the evaluation of the complex field distribution across a local area that can be transformed into a time-varying fading when assuming a moving receiver or a non-stationary environment. © 1998 John Wiley & Sons, Ltd.