Efficient encoding and decoding schemes for wireless underwater communication systems

With the deepening exploration of ocean, underwater wireless communication technology has become the key to restrict its development. Aiming at the requirement of high speed and long distance underwater wireless communication, an underwater bidirectional link communication system for marine commercial was designed. The laser LD and LED dual emission light sources were adopted at the transmitting end, the system design scheme of dual emission light sources was proposed, and the feasibility of the scheme by designing the corresponding drive circuits was verified. At the receiving end, 5 mm large-area APD and high-sensitivity PMT dual receiving detector were used to receive optical signals, which were suitable for long-distance and high-speed communication. The information processing part of the system was completed by FPGA, and information interaction was carried out with PC through network communication. Finally, the whole system was designed and commercialized. The underwater simulation experiment shows that the communication rate of the system can reach 60 Mbps when the communication distance is 5 m and the bit error rate is 10−7. The communication rate of the system can reach 10 Mbps when the communication distance is 60 m and the bit error rate is 10−7.

In traditional underwater communication systems, acoustic waves are commonly used. However, acoustic underwater systems have low bandwidth, which is not enough for modern wireless sensors and underwater vehicles. The use of radio waves also does not provide the desired combination of transmission speed and range. All this has led to the development of optical wireless underwater communication, as it potentially provides a higher data rate than traditional acoustic underwater communication systems with significantly lower energy consumption. One of the main difficulties in designing underwater optical wireless systems is the complexity of modeling the physical and chemical characteristics of ocean water. The purpose of this survey is to generalize the available models of underwater optical communication links taking into account the various propagation effects that affect the range and speed of the system.

In scientific, military, and industrial sectors, the development of robust and efficient submarine wireless communication links is of enormous interest. Underwater wireless communications can be carried out through acoustic, radio frequency (RF), and optical waves. Underwater optical communication is not a new idea, but it has recently been considered because seawater exhibits a window of reduced absorption both in the visible spectrum and long-wavelength UV light (UV-A). Compared to its bandwidth limited acoustic counterpart, underwater optical wireless communications (UOWCs) can support higher data rates at low latency levels. Underwater wireless communication networks are important in ocean exploration, military tactical operations, environmental and water pollution monitoring. Anyway, given the rapid development of UOWC technology, documents are still needed showing the state of the art and the progress made by the most current research. This paper aims to examine current technologies, and those potentially available soon, for Underwater Optical Wireless Communication and to propose a new perspective using UV-A radiation.

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.

Because of the requirements of marine resources exploration and underwater cooperative operation, the underwater operation of common detection and communication equipment is difficult and unreliable. Therefore, it is urgent to establish an accurate underwater target detection and multi-node communication integrated system. An integrated method of underwater electric field detection and communication based on P4 code-modulated OFDM signal is proposed in response to the above requirements. The working principle, system structure, and signal processing of underwater electric field detection and electric field communication are similar. This article uses detection signal P4 code to modulate the phase of OFDM communication signal, thus realizing the integration of Underwater Detection and Communication System (IUDCS). The simulation results show that IUDCS can meet the detection range and velocity characteristics of underwater dynamic targets. The simulation results also meet the requirements for communication error rate and symbol error rate, thereby verifying the performance of underwater electric field IUDCS. This method is necessary for the realization of IUDCS in terms of reducing platform size, reducing power consumption, and enhancing concealment. Moreover, it shows good application prospects in underwater robot cluster operations.

Underwater communication is a critical and challenging issue, on account of the complex underwater environment. This study introduces an underwater wireless communication approach via Maxwell’s displacement current generated by a triboelectric nanogenerator. Underwater electric field can be generated through a wire connected to a triboelectric nanogenerator, while current signal can be inducted in an underwater receiver certain distance away. The received current signals are basically immune to disturbances from salinity, turbidity and submerged obstacles. Even after passing through a 100 m long spiral water pipe, the electric signals are not distorted in waveform. By modulating and demodulating the current signals generated by a sound driven triboelectric nanogenerator, texts and images can be transmitted in a water tank at 16 bits/s. An underwater lighting system is operated by the triboelectric nanogenerator-based voice-activated controller wirelessly. This triboelectric nanogenerator-based approach can form the basis for an alternative wireless communication in complex underwater environments.

Underwater wireless communications (UWCs) play a major role in both civilian and military applications. The features of the underwater transmission media are big challenges towards the design of efficient and robust UWCs. Many types of propagation waves have been investigated for UWCs such as acoustic, electromagnetic, optical and magnetic induction. Underwater acoustic communications have long transmission range, but with limited data rate and high-power consumption. Meanwhile, electromagnetic and optical UWCs can achieve high data rate but with difficulties in establishing reliable communication links due to their short communication distances and alignment problem respectively. Recently, magnetic induction has been introduced as a new physical layer for UWCs providing unique features such as high data rate and low propagation delay, but it still suffers from high propagation losses especially in sea water. In this paper, the performance of these different UWCs paradigms are explored and compared in terms of energy efficiency and total system throughput under different scenarios. Then, a hybrid UWC network based on an interoperability among these different technologies is suggested.

Underwater wireless optical communication (UWOC) has been regarded as one of the promising solutions to underwater wireless communication systems due to its advantages of high bandwidth, fast transmission and good confidentiality. In UWOC systems, after emitting from light source, photons will be scattered with random deviated angles before propagating to the receiver plane. Hence, the light beam suffers a spatial angle spread at the receiver side. In order to improve the system performance with an appropriate receiver design, it is of significance to figure out the angle of arrival (AOA) distribution of the received light beam. In addition, the UWOC channel is susceptible to other effects such as absorption, turbulence and bubbles, especially when it is exposed to the complex ocean environment. Therefore, analyzing the impacts of these factors on AOA distribution is also essential to evaluate UWOC system performance. The existing studies of AOA distribution only considered single scattering component, which is not practical for turbid water. Furthermore, there are few studies focusing on multi-source scenarios. In this paper, we first present a simple expression for AOA distribution with single light source, taking both single and multiple scattering components into account. Then we extend the work to multi-source scenarios and derive the corresponding closed-form expression of AOA distribution. Compared to the traditional single scattering case, numerical results show that the proposed AOA distribution can fit well with Monte Carlo simulation results with various water types, link distances, and the characteristics of actual light sources.

Design and deployment of IoT based underwater wireless communication system using electronic sensors and materials

There is a speedy development withinside the place of broadband wi-fi communications as the global call for in elevating for large bandwidth and extra mobility. The speedy increase withinside the previous few a long time withinside the WAN's and LAN's is particularly because of growing improvement in excessive potential and occasional loss optical fiber. But, the main downside in optical fiber cable communique is that optical fiber receives broken in a long-haul installation. Thus, underwater communication has paved the way for overcoming this disadvantagefor programs of underwater statement and sea monitoring, the importance of underwater wi-fi optical communication has expanded. Attenuation and fading of light propagation, as well as impairment in the performance of underwater wireless optical communications, are caused by elements such as underwater absorption, scattering, and turbulence (UWOC). UWOC is a short-range wireless communication system that allows for greater data throughput than classic acoustic communication systems while using less power and posing fewer computing problems. The main challenge for underwater wireless communication, on the other hand, is from the fundamental properties of ocean or sea water. Understanding the feasibility and minimising the BER, as well as boosting the reliability of high data rate underwater communication lines, is the main topic of this paper. This study's purpose is to conduct underwater optical communication research while also producing new ideas to aid in the development of future underwater communication systems.

Underwater laser communication has been developed in the field of deep-sea exploration, also become a highlight of modern communication technology research. It has the edges of hidden, safe, non-contact and rapid mobility. By now, most data exchange and transmission between underwater sensors and devices are achieved by RS-232 serial ports communication. But it is not able to meet the demands of present underwater communication due to the limitations of transmitting rate and distance. For the first version of our laser system the signals flowing through the RS-232 ports had not been modulated. Therefore, the bit error rate of our previous work was adversely high. In this paper, we progress our system by introducing in a novel signal modulating module, which mainly consists of FPGAs and PPM method. Considering with the effect of absorption and scattering [1], a series of experiments are performed in this paper: unmodulated and modulated underwater laser communication experiments under different visibility water. By comparing the bit error rate results, we suggest that the whole underwater laser communication system is compact, efficient and reliable. Finally, we based on multiple of visibility, the theoretical communication distance of the system can be estimated.

Guest Editorial

In this paper, a Universal Underwater Software Defined Modem (UniSDM) architecture is proposed that may operate in different modes (acoustic, magnetic induction, optical and RF), in order to utilize the advantages of each mode and accordingly satisfy the requirements of many latest use cases in underwater communication systems. A detailed description of the novel UniSDM architecture is presented first. The novelty of this architecture is its flexibility, i.e., allowing the designers to produce a device that may include any type of modes operating seamlessly and jointly by exchanging data, control and synchronization. Many challenges, including high system costs and coordination between different modes, are addressed in the paper. Moreover, numerical evaluation is conducted to assess the performance of the proposed UniSDM architecture. Finally, the performance evaluation shows that the utilization of the UniSDM allows to decrease the transmission latency and improve the energy efficiency, while maintaining high reliability and robustness in underwater communication systems.

Ocean turbulence is an important factor affecting the development of underwater wireless optical communication (UWOC). To improve the error characteristics of the underwater optical communication system, we propose a differential detection-based multi-receiver-multi-transmitter (MIMO) underwater laser communication transmission method. Additionally, we derive the expressions for calculating the average BER of the MIMO underwater wireless optical communication system with differential detection and non-differential detection in the case that the two transmitted beams are completely uncorrelated. The error characteristics of the MIMO system are simulated and analyzed from the perspective of ocean turbulence intensity and link distance. The simulation results show that the differential detection method has a lower average BER compared to the non-differential detection method in the case of moderate-to-strong ocean turbulence. In addition, the differential detection methods do not have the error floor effect, and non-differential detection methods have the error floor effect. The more the turbulence intensity affects the average BER of the MIMO UWOC system with the increase of the communication link distance, the more obvious is the effect of the turbulence intensity on the average BER of the MIMO UWOC system. Accordingly, the simulation analysis shows that the differential detection method is more suitable for the construction of communication links under long-distance and medium-strong turbulence.

Underwater acoustic channels are affecting by many factors like time varying multipath propagation, Doppler spread, and salinity, which can greatly limit the quality of data rate and transmission distance. Underwater optical communication represents a crucial technology that supporting higher data rate, secure links and low latency. In his paper the use of 64- Quadrature Amplitude Modulation (64-QAM) in underwater optical communication systems is investigated. The system is designed to offer higher data rate than those of acoustic communication system. The proposed design achieve data rate of 10 Gbps over a challenging transmission distance of 50 km. In our study, a simulation technique is used to evaluate the performance of the proposed design in the underwater conditions, focusing on factors such as Bit Error Rate (BER), constellation diagram and Quality factor (Q-factor). The achieved BER is of about 10-10 with a minimum signal to noise ratio (SNR) of about 30dB. This paper provides valuable results for the design of next-generation underwater communication systems for applications such as pollution monitoring, oil control and oceanography research.