Design and Analysis of Co-operative Acoustic and Optical Hybrid Communication for Underwater Communication

Underwater communication is an emerging field of research currently, which is an important aspect in predicting the climatic conditions accurately. Underwater communication is disadvantageous when compared with aerial communication because water is basically non transparent and blurred to electromagnetic radiations excluding visible region. In the visible region, factors such as suspended sediments and the presence of aquatic life affects the penetration of light. It may penetrate only upto a few hundreds of metres in clear water and in turbid waters, penetration is even less. Underwater communication is also affected by Intersymbol Interference (ISI) due to multipath fading. Currently, a booming and mature technology called acoustic technology is employed for underwater communication systems. Acoustic systems are proficient for long distance communication. But acoustic communication has limitations. They have very low data rates for monitoring applications and due to velocity of sound in water, it has a huge latency which means a significant time delay. To cope up with the limitations of acoustic communication, we use optical communication whose wavelength lies in the visible region. Optical communication is known for high data rate and low latency. Many accidents take place under water such as the plane crash, ship sinking. It is a tedious job to find the lost debris. Hence an underwater optical link is developed which could identify the lost debris. In this project, a hybrid model comprising of acoustic as well as the optical link is proposed. The comparison between acoustic and optical technique is studied and simulated using MATLAB simulation and the responses were plotted. The simulated results can be used in various applications including climate monitoring, military services.

     

Three-dimensional image generation and processing in underwateracoustic vision

Underwater exploration is becoming more and more important for many applications involving physical, biological, geological, archaeological, and industrial issues. This paper aims at surveying the up-to-date advances in acoustic acquisition systems and data processing techniques, especially focusing on three-dimensional (3-D) short-range imaging for scene reconstruction and understanding. In fact, the advent of smarter and more efficient imaging systems has allowed the generation of good quality high-resolution images and the related design of proper techniques for underwater scene understanding. The term acoustic vision is introduced to generally describe all data processing (especially image processing) methods devoted to the interpretation of a scene. Since acoustics is also used for medical applications, a short overview of the related systems for biomedical acoustic image for motion is provided. The final goal of the paper is to establish the state of-the art of the techniques and algorithms for acoustic image generation and processing, providing technical details and results for the most promising techniques, and pointing out the potential capabilities of this technology for underwater scene understanding     

Underwater acoustic sensor networks: research challenges

Underwater sensor nodes will find applications in oceanographic data collection, pollution monitoring, offshore exploration, disaster prevention, assisted navigation and tactical surveillance applications. Moreover, unmanned or autonomous underwater vehicles (UUVs, AUVs), equipped with sensors, will enable the exploration of natural undersea resources and gathering of scientific data in collaborative monitoring missions. Underwater acoustic networking is the enabling technology for these applications. Underwater networks consist of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area.In this paper, several fundamental key aspects of underwater acoustic communications are investigated. Different architectures for two-dimensional and three-dimensional underwater sensor networks are discussed, and the characteristics of the underwater channel are detailed. The main challenges for the development of efficient networking solutions posed by the underwater environment are detailed and a cross-layer approach to the integration of all communication functionalities is suggested. Furthermore, open research issues are discussed and possible solution approaches are outlined.     

Synchronization techniques for underwater acoustic communications

Underwater acoustic channel is a challenging medium for communication due to the presence of significant multipath, high noise, frequency-dependent propagation loss, and high and non-uniform Doppler spread. Doppler shift is non-negligible in underwater communication due to the low velocity of underwater signals. Synchronization and Doppler estimation are important requirements for achieving good performance in this channel. Synchronization algorithms that give good performance in radio communication do not work well in underwater communication. Hence, this area has received a lot of attention from researchers. This paper surveys important works in the area. The techniques proposed in the literature for frame synchronization, frequency and phase synchronization, and timing synchronization in single carrier communications are reviewed here. The synchronization techniques proposed for OFDM, MIMO OFDM, and spread spectrum communication are also surveyed. Doppler estimation methods proposed in the literature are also reviewed. It is found that most of the recent works in underwater acoustic communication focus on OFDM synchronization. Deep learning-based methods proposed in the literature are also reviewed. Key open problems and areas that require future research attention in the field of synchronization and Doppler estimation in underwater communications are highlighted in this paper. The area needing most attention of underwater communication researchers was found to be MIMO OFDM due to the difficulty in synchronization in such systems while used in underwater communication. Reducing the computational complexity of the algorithms used is also important for future work. Schemes that work with Doppler due to relative velocity over 10 m/s also need to be developed.     

水下近场探测与成像的光学调制技术研究

基于光学调制的水下探测与成像技术是目前最先进的水下光电探测技术之一。本文结合国外最新的理论研究成果、实验装置与实验结果对水下近场探测与成像的光学调制技术进行了进一步的探索。论证了光学调制技术作为水下探测方面的最新技术,其相对于众多成熟技术的优势与在该领域的发展潜力,并对水下环境特征、基于频域的水下探测技术以及应用于水下近场成像的时变强度调制技术进行了分析与讨论。     

The past, present, and the future of underwater acoustic signalprocessing

This is a collection of articles written by members of the Underwater Acoustic Signal Processing (UASP) Technical Committee. The first article, by D. W. Tufts, deals with the history of UASP prior to 1980. In this period, initial mathematical models were developed and the first experimental investigations of underwater acoustic propagation were performed. It was also recognized during this time that there are many similarities between radar and sonar signal processing. The article by J.P. Ianniello deals with research in passive and active sonar from 1980 to the present. Work in this period included experimental verification of algorithms that had been developed in the 1960s and 1970s (e.g. for adaptive beamforming), as well as the development of new approaches, which include acoustic propagation modeling in the design of signal processing algorithms. Such processing is referred to as matched field processing. A common task in passive sonar systems is to estimate the difference in times at which different sensors receive the same signal. Time-delay estimation is a first stage that feeds into subsequent processing blocks. I. Lourtie provides a concise review of work in this field. The article by J.C. Preisig deals with underwater acoustic communications. The underwater channel has several features that make reliable communication a challenging problem. Nevertheless, progress is being made by combining results from ocean acoustic modeling, communication theory, and signal processing. The final article, by J.M.F. Moura, deals with the future of signal processing in the ocean. In addition to considering advances in detection and localization, he deals with new applications such as acoustic tomography, physical oceanography, and synthetic aperture sonar     

水声通信网的研究进展及其应用

随着现代"网络中心战"理论的完善,现代立体化信息战争已从传统的空天地战场延伸至海面以下战场。水声通信技术是构建水下通信网络的有效手段,是构建立体化战争、立体化作战平台的必要技术。首先分析了水下通信与水声网络的特点和发展现状。其次,结合美国海军在水声通信网络的实验研究成果,以及国内在该领域内取得的研究进展情况,展望了水声通信网络在现代海军建设中的应用前景。     

Low-Power Based Coherent Acoustic Modem for Emerging Underwater Acoustic Sensor Networks

Smart, small, inexpensive sensor nodes are used to construct underwater acoustic sensor networks. In addition, with the recent increase in the importance of underwater applications, the need for underwater communication has become more important. Hence, an acoustic modem capable of effective underwater communications has become more necessary for the sensor nodes to obtain underwater data. To develop an acoustic modem for effective underwater communications, some limitations must be overcome, such as the very short transmission range of radio waves, limited power supply, and high cost of commercial acoustic modems. Recently, low-power, low-cost acoustic modems have been developed. However, the data rates of these modems are so slow that sensor nodes cannot perform energy-efficient protocols. The objective of this work is to develop an acoustic modem capable of supporting high data rates. We introduce a coherent acoustic modem that uses waterproof ultrasonic sensors to process acoustic waves. The proposed modem is based on a low-power, low-cost, short-range concept, and it also supports a high data rate for energy-efficient MAC and routing protocols. Underwater experiments are conducted to evaluate the performance improvements of our modem. Experimental results show that our modem has the best performance among all recently developed low-power modems and that it is preferable to develop a coherent modem able to perform effective underwater communications.     

A Framework for Testing of Wireless Underwater Robots

Underwater applications of wireless robots are foreseen to hold a market potential. The standardization process will drive the development of the necessary technology so that devices can work cooperatively. Specific testing procedures have to be developed in order to verify that a device meets requirements. In this paper, a general framework for testing of underwater wireless robot communications is described. The methodology for conformance and interoperability tests is addressed by considering wireless robots as terminals in an underwater acoustic network.     

Anomaly Detection in UASN Localization Based on Time Series Analysis and Fuzzy Logic

Mobile Networks and Applications - Underwater acoustic sensor network (UASN) offers a promising solution for exploring underwater resources remotely. For getting a better understanding of sensed...     

水下无线通信技术发展研究

水下无线通信是水下通信技术的重要分支,是进行水下监测、水下开发和开展水下军事斗争的关键支撑。为了争夺水下资源和增强水下作战能力,水下无线通信已成为世界大国竞相发展的重要通信技术之一。文章首先介绍了水下无线电磁波通信、水声通信等水下无线通信的发展现状,接着对水下光通信、引力波通信、中微子通信、水下量子通信等水下无线通信的发展进行了展望,最后分析了水下无线通信技术发展面临的问题。     

基于NS-3的声电协同网络实现及路由性能分析

水下无线通信主要依靠水声通信的方式进行信息传输。但水声链路本身具有高时延和高误码率等不足,为水下应用提供低时延的通信服务是一项具有挑战性的工作。声电协同网(CRAN)旨在充分利用水面无线电链路弥补水声网络(UAN)的性能局限,提升网络的整体性能。其中,CRAN中的路由协议需要构建声、电混合路径,是声电协同网络研究中的关键问题。该文首先在网络模拟器3(NS-3)中设计并实现了声电浮标节点与CRAN协议栈,搭建了CRAN的仿真平台。随后探讨了以无线自组网按需平面距离向量路由协议(AODV)为代表的被动式路由在CRAN中的应用。该文发现,AODV协议使用的距离向量准则在CRAN中能够更多地选择高速的无线电链路进行数据转发,有效地降低了网络传输时延。最后,通过仿真对AODV与其他协议的性能进行了对比、分析。结果表明,CRAN在投递率、传输时延、网络吞吐量、能效和路由响应速度方面对比水声通信网有较大提升。同时,以AODV为代表的被动路由协议,相比于以优化链路状态路由协议(OLSR)为代表的主动路由协议更适用于CRAN。     

Underwater acoustic sensor networks: Target size detection and performance analysis

Underwater acoustic sensor network consists of a variable number of sensors and vehicles that are deployed to perform collaborative monitoring tasks over a given area. Scalability concern suggests a hierarchical organization of underwater sensor networks with the lowest level in the hierarchy being a cluster. In this paper, we show that an ultra-wide band (UWB) channel can be used for underwater channel modeling and propose a maximum-likelihood (ML) estimation algorithm for underwater target size detection using collaborative signal processing within a cluster in underwater acoustic sensor networks. Theoretical analysis demonstrates that our underwater sensor network can tremendously reduce the variance of target size estimation. We show that our ML estimator is unbiased and the variance of parameter estimation matches the Cramer–Rao lower bound. Simulations further validate these theoretical results.     

Shallow water acoustic networks

Underwater acoustic networks are generally formed by acoustically connected ocean bottom sensor nodes, autonomous underwater vehicles (AUVs), and surface stations that serve as gateways and provide radio communication links to on-shore stations. The quality of service of such networks is limited by the low bandwidth of acoustic transmission channels, high latency resulting from the slow propagation of sound, and elevated noise levels in some environments. The long-term goal in the design of underwater acoustic networks is to provide for a self-configuring network of distributed nodes with network links that automatically adapt to the environment through selection of the optimum system parameters. This article considers several aspects in the design of shallow water acoustic networks that maximize throughput and reliability while minimizing power consumption     

Doppler Effect in the Acoustic Ultra Low Frequency Band for Wireless Underwater Networks

It is well known that communication is affected by the change in frequency of a signal for an observer that is moving relative to the source. As a result of the motion of either the source or the observer, successive waves are emitted from a position that may get closer or further to the observer. This phenomenon, known as Doppler effect, also affects underwater acoustic waves used for communications between Autonomous Underwater Vehicles (AUVs), Underwater Sensors (USs) and remote operators. There have been few studies on the impact of Doppler shift in underwater communications. Assuming underwater communications using acoustic waves, in this paper we study the Doppler effect in relation to the half-power bandwidth and distance in the Ultra Low Frequency (ULF) band (i.e., from 0.3 to 3 kHz). We investigate two specific issues. Firstly, the maximum shift that can be expected on underwater links in the ULF band. Secondly, the maximum frequency drift, and associated patterns, that can happen during the reception of data frames. Numeric simulations are conducted. The analysis is based on scenarios that show the existence of significant Doppler effect. More specifically, we show that Doppler effect, under narrow half-power bandwidth, is significant with respect to the half-power bandwidth in the ULF band, for long distance communications. Furthermore, we show that Doppler effect patterns are not necessarily linear.     

水下偏振清晰成像方法综述

水下成像环境复杂多变,在水下视觉的研究中会遇到许多典型的问题:在复杂的光学环境中,水下成像质量急剧下降,传统成像方法中常用的诸如颜色、亮度等特征衰减严重,难以有效地提高水下成像的质量。偏振成像可以对水下散射进行有效抑制,在水下成像环境中,分析目标信息光、后向散射光和前向散射光相应的偏振特性,针对性地解决不同分量对图像的影响进而实现图像质量的提高。基于水下成像物理模型、偏振成像原理详细阐述了水下偏振成像原理,着重论述了几种经典的水下偏振成像方法,总结了当前基于偏振特性的水下成像技术,并对其实际效果进行评价分析,依据现有的水下偏振成像技术的优缺点和实际成像效果对水下偏振成像技术的未来发展进行总结展望。     

强海洋湍流水下光通信系统误码率研究

水下无线光通信（underwater wireless optical communication,UWOC）系统具有宽带宽、低衰减、低延时时间、高安全、高速率等优点,可满足水下数据、图像、传感器网络、视频通信的高速需求,受到了广泛研究。然而,除了水下的吸收、散射效应外,湍流效应也会使光信号衰减和衰落,限制了UWOC系统的通信质量和传输距离。探讨了外差式差分移相键控（differential phase shift keying,DPSK）调制对误码率（bit error rate,BER）的提升能力。假定强海洋湍流信道为Gamma-Gamma分布,利用改进的Rytov方法,得出了UWOC系统采用平面波和球面波传输时的闪烁系数表达式。借助于Whittaker M函数推导了DPSK调制的UWOC系统采用这两种光波传输时BER的解析式,并利用数值结果验证了解析结果的正确性。应用解析公式,仿真分析了DPSK调制的UWOC系统采用两种光波在三种重要的海洋湍流因素和通信距离下的BER,并对比分析了DPSK调制与OOK调制的BER。仿真结果表明,UWOC系统采用DPSK调制和球面波传输,在较小的均方温度耗散率、较小的温度和盐度波动对海洋湍流贡献的比值、较大的湍流动能耗散率的海洋中及通过较短的通信距离传输可以得到更优的BER。      

水下超视距三角形距离能量相关三维成像(特邀)

水下超视距三角形距离能量相关三维成像是一种新型的快速非扫描三维成像技术,可填补水下摄像机（空间分辨率高但作用距离近、无三维信息）与水下声呐（作用距离远但空间分辨率低）间的技术空白。介绍了水下距离能量相关三维成像国内外研究进展,并重点介绍中国科学院半导体研究所在水下成像方面开展的三角形距离能量相关三维成像的研究工作,提出了一种融合多脉冲延时积分的三角形距离能量相关三维成像,梳理了多脉冲延时积分景深调节技术下的典型时域工作参数,研制的水下激光选通三维成像系统绿瞳、凤眼和龙睛可实现探测距离大于4.8 AL的超视距百万像素三维成像,已用于渔网等微小目标探测、海洋生物原位探测、水下光学详查等应用中。     

基于空时处理的水声扩频通信

由于海洋干扰严重,水声通信十分困难。扩频通信技术具有良好的抗干扰性能,能够保证在复杂的海洋环境中进行可靠的通信,常被用于水声通信中。水声信道是典型的相干多径信道。沿不同路径到达的信号具有不同的传播时延和到达角,因此接收信号具有时空特性。即接收信号具有时延扩展和角度扩展。多径信号的相干叠加导致接收信号中存在严重的符号间干扰。为了充分利用水声信号的时空聚类特性,该文设计了一个空时处理器,分别对沿每条路径到达的信号进行滤波。结合时空簇的多样性,可以有效提高通信系统的可靠性。提出了一种基于空时聚类处理的水声扩频通信方案。并在仿真和实验中对该通信方案进行了比较和分析,以验证其性能优势。     

利用水下平行光管测量水下相机成像分辨率

水下光学成像是重要的水下探测方式。现有水下相机成像检测方法受到水体本身以及测量方法的影响,难以准确进行成像分辨率检测。提出了基于水下平行光管的水下相机成像分辨率检测技术,通过在水中产生平行光束,直接对水下相机成像分辨率进行检测。通过仿真得出：水下平行光管在水中可见光和空气中单波长的调制传递函数(Modulation Transfer Function, MTF)基本一致。利用这一结论,提出了水下平行光管空气中装调检测的方法。针对实验室所研制的一款水下相机开展实验测试,其在水中可见光与空气中635 m光源照明条件下的分辨率相同。实验结果表明,所提出的基于水下平行光管的水下相机成像分辨率检测方法可有效消除水体对分辨率测量的影响,实现水下相机成像分辨率的准确测量。