A Review and Analysis of Localization Techniques in Underwater Wireless Sensor Networks

In recent years,there has been a rapid growth in Underwater Wireless Sensor Networks(UWSNs).The focus of research in this area is now on solving the problems associated with large-scale UWSN.One of the major issues in such a network is the localization of underwater nodes.Localization is required for tracking objects and detecting the target.It is also considered tagging of data where sensed contents are not found of any use without localization.This is useless for application until the position of sensed content is confirmed.This article’s major goal is to review and analyze underwater node localization to solve the localization issues in UWSN.The present paper describes various existing localization schemes and broadly categorizes these schemes as Centralized and Distributed localization schemes underwater.Also,a detailed subdivision of these localization schemes is given.Further,these localization schemes are compared from different perspectives.The detailed analysis of these schemes in terms of certain performance metrics has been discussed in this paper.At the end,the paper addresses several future directions for potential research in improving localization problems of UWSN.

Dynamic Coverage with Wireless Sensor and Actor Networks in Underwater Environment

This paper studies the problem of dynamic coverage with wireless sensor and actor networks(WSANs) in underwater environment.Different from most existing works,the WSANs consist of two kinds of nodes,i.e.,sensor nodes(SNs) which cannot move autonomously and actor nodes(ANs) which can move autonomously according to the performance requirement.The problem of how to coordinate two kinds of nodes to facilitate dynamic coverage in underwater environment is challenging due to their heterogeneous capabilities.To reduce redundancy of communication links and improve connectivity between ANs and SNs in underwater WSANs,a min-weighted rigid graph based topology optimization scheme is first developed,such that the underwater communication energy consumption can be saved.With the optimized topology,a dynamic coverage strategy is proposed to improve the coverage among SNs and ANs for underwater WSAN where underwater fluid motions are considered.Furthermore,it is proved that the network coverage area is connected by using the min-weighted rigid graph.Finally,simulation results are presented to show the effectiveness of the main results.

Capacity Research in Cluster-Based Underwater Wireless Sensor Networks Based on Stochastic Geometry

Underwater wireless sensor networks(UWSNs) have attracted wide attention in recent years.The capacity research on it is still in the initial stage,lacking adequate performance evaluation for network construction.This paper will focus on this subject by theoretical analysis and simulation,aiming to provide some insights for the actual UWSNs construction.According to the structure features of cluster-based UWSNs and the propagation characteristics of underwater acoustic signal,with the combination of signal to interference plus noise ratio,we define some capacity performance metrics,such as outage probability and transmission capacity.Based on the theory of stochastic geometry,a network capacity analytical model used in the cluster-based UWSNs is presented.The simulation results verify the validity of the theoretical analysis,and the cause of error between theoretical and simulation results has also been clearly explained.

A New Method to Improve Performance of Cooperative Underwater Acoustic Wireless Sensor Networks via Frequency Controlled Transmission Based on Length of Data Links

In this paper a new method to improve performance of cooperative underwater acoustic (UWA) sensor networks will be introduced. The method is based on controlling and optimizing carrier frequencies which are used in data links between network nods. In UWA channels Pathloss and noise power spectrum density (psd) are related to carrier frequency. Therefore, unlike radio communications, in UWA Communications signal to noise ratio (SNR) is related to frequency besides propagation link length. In such channels an optimum frequency in whole frequency band and link lengths cannot be found. In Cooperative transmission, transmitter sends one copy of transmitted data packets to relay node. Then relay depending on cooperation scheme, amplifies or decodes each data packet and retransmit it to destination. Receiver uses and combines both received signals to estimate transmitted data. This paper wants to propose a new method to decrease network power consumptions by controlling and sub-optimizing transmission frequency based on link length. For this purpose, underwater channel parameters is simulated and analyzed in 1km to 10km lengths (midrange channel). Then link lengths sub categorized and in each category, optimum frequency is computed. With these sub optimum frequencies, sensors and base station can adaptively control their carrier frequencies based on link length and decrease network’s power consumptions. Finally Different Cooperative transmission schemes “Decode and Forward (DF)” and “Amplify and Forward (AF)”, are simulated in UWA wireless Sensor network with and without the new method. In receiver maximum ratio combiner (MRC) is used to combining received signals and making data estimations. Simulations show that the new method, called AFC cooperative UWA communication, can improve performance of underwater acoustic wireless sensor networks up to 40.14%.

Hierarchical self-localization of underwater wireless sensor network nodes

The follow-up application of underwater wireless sensor network is influenced by accuracy of self-localization of nodes. The self-localization of nodes is discussed in this paper. First of all, nodes of underwater wireless sensor network are classified into several levels according to the accuracy of position of nodes and the levels are from the first to the fifth in accordance with accuracy of nodes from high to low respectively. Secondly, the level of anchor nodes can be known by those unknown nodes from the information given by the anchor nodes themselves, At the same time the unknown nodes are able to be located in the area controlled by the first level of anchor nodes that are as the aggregation. Then the positioning algorithm is designed correspondingly in accordance with the accuracy level of nodes. Finally, the positioning algorithm is simulated and analyzed. The result shows that the unknown nodes can be located effectively by hierarchical control.

Cooperative Nodes Localization for Three-Dimensional Underwater Wireless Sensor Network Based on Weighted Centroid Localization Algorithm

The underwater wireless sensor network(UWSN) has the features of mobility by drifting,less beacon nodes,longer time for localization and more energy consumption than the terrestrial sensor networks,which makes it more difficult to locate the nodes in marine environment.Aiming at the characteristics of UWSN,a kind of cooperative range-free localization method based on weighted centroid localization(WCL) algorithm for three-dimensional UWSN is proposed.The algorithm assigns the cooperative weights for the beacon nodes according to the received acoustic signal strength,and uses the located unknown nodes as the new beacon nodes to locate the other unknown nodes,so a fast localization can be achieved for the whole sensor networks.Simulation results indicate this method has higher localization accuracy than the centroid localization algorithm,and it needs less beacon nodes and achieves higher rate of effective localization.

A synchronous duty-cycled reservation based MAC protocol for underwater wireless sensor networks

To design an energy-efficient Medium Access Control(MAC)protocol for the Underwater Wireless Sensor Networks(UWSNs)is an urgent research issue since depleted batteries cannot be recharged or replaced in the underwater environment.Moreover,the underwater acoustic channels are affected by hindrances such as long propagation delay and limited bandwidth,which appear in the design of the MAC protocol for the UWSNs.The available MAC protocols for the terrestrial wireless sensor networks exhibit low performance in energy efficiency,throughput and reliability in the UWSNs,and cannot be used in the UWSNs directly because of their unique characteristics.This paper proposes a synchronous duty-cycled reservation-based MAC protocol named Ordered Contention MAC(OCMAC)protocol.The basic mechanism of this protocol is to schedule data transmission by transmitters through the scheduling of Ready To Send(RTS)frames.The protocol eliminates the possible collision during data transmission and improves communication efficiency.The paper analyzes the performance in energy efficiency,throughput and reliability of the protocol by modeling the queuing behavior of OCMAC with a Markov Chain process.Furthermore,the analytical model is validated through a simulation study.The analysis results demonstrated that while providing good throughput and reliability,OCMAC can achieve energy saving.

A Void Avoidance Scheme for Grid-Based Multipath Routing in Underwater Wireless Sensor Networks

This work proposes a geographic routing protocol for UWSNs based on the construction of a 3D virtual grid structure, called Void-Avoidance Grid-based Multipath Position-based Routing (VA-GMPR). It consists of two main components, the multipath routing scheme and the grid-based void avoidance (GVA) mechanism for handling routing holes. The multipath routing scheme adopts node-disjoint routes from the source to the sink in order to enhance network reliability and load balancing. While the GVA mechanism handles the problem of holes in 3D virtual grid structure based on three techniques: Hole bypass, path diversion, and path backtracking. The performance evaluation of the VA-GMPR protocol was compared to a recently proposed grid-based routing protocol for UWSNs, called Energy-efficient Multipath Geographic Grid-based Routing (EMGGR). The results showed that the VA-GMPR protocol outperformed the EMGGR protocol in terms of packet delivery ratio, and end-to end-delay. However, the results also showed that the VA-GMPR protocol exhibited higher energy consumption compared to EMGGR.

A Comparative Assessment of Floating and Submerged Sensor Network Deployments for Monitoring Underwater Sediment Transport Processes

Wireless Sensor Networks (WSNs) are a pioneering technology in many environmental monitoring applications owing to their ability to be deployed for long periods of time in locations that cannot be reached manually. One such use-case is the monitoring of underwater sediment transport, a process that plays a significant role in coastal erosion. Previous examples of WSNs deployed for this purpose have been in the form of underwater sensor networks (UWSNs), which have a number of shortcomings from both a practical and technical viewpoint. As such, this paper provides a comparative assessment of UWSNs and an alternative deployment approach of floating echo- sounding sensor networks for the purpose of monitoring underwater sediment transport.

Study of Wireless Sensor Network Based on Optical Communication:Research Challenges and Current Results

With the rapid developments of commercial demands,a majority of ad­vanced researches have been investigated for the applications of underwa­ter wireless sensor(WSN)networks.Recently optical communication has been considered for underwater wireless sensor network.An experimental set-up for testing optical communication underwater has been provided and designed in present papers to maximize the energy coupled from these displacements to the transduction mechanism that converts the mechanical energy into electrical.The true case has been considered by measuring dif­fuse attenuation coefficients in different seas.One stand out potential opti­cal communication method,Visible Light Communication(VLC)has been talked and several communication methods are compared from many points of view,for example attenuation in salt water.The evaluation of modula­tion techniques for underwater wireless optical communications has been displayed,and further how the data collection and storage with an under­water WSN is introduced.In this paper current researches for an(UWSN)based on optical communication are studied,in particular the potential VLC method and comparisons of VLC with other optical communication approaches.Underwater challenges would be analyzed by comparing a sort of communication methods,applied in underwater.Future work will be de­veloped at last.

基于改进正余弦优化算法的UWSN节能路由

针对水下无线传感器网络节点更换困难、能量有限的特点,提出了一种基于改进正余弦算法的节能路由。在簇的形成过程中,利用改进的正弦余弦优化算法来选举簇头,综合能量、节点密度、通信距离三方面因素并讨论相应权重,为簇头选择设计了更加合理的适应度函数。簇内单跳传输,簇间传输时则采用多跳传输,通过限制深度、能量及转发区域选择合适的下一跳,将采集的信息传递给水面。经网络仿真验证,在相同条件下,该算法较传统LEACH算法和KACO、DUCISCA算法,将正常工作时间延长了69.10%、24.78%、14.94%,能够有效均衡网络能耗,延长网络寿命,提高数据传输率。

考虑锚节点位置不确定的水下目标定位算法研究

考虑时钟异步和声波分层效应的影响,该文研究了当测量过程受到未知噪声干扰,且锚节点位置不确定时水下目标节点的定位问题。首先构造了水下节点间飞行时间模型,设计了一种交互式异步通信协议,建立了最小化定位误差的优化目标函数。然后提出了一种基于深度强化学习的水下目标定位算法,并采用层归一化来改进深度神经网络,进一步提高模型的泛化能力。最后,仿真和实验结果验证所提方法的有效性。

Mutual-information based weighted fusion for target tracking in underwater wireless sensor networks

Underwater wireless sensor networks(UWSNs)can provide a promising solution to underwater target tracking.Due to limited energy and bandwidth resources,only a small number of nodes are selected to track a target at each interval.Because all measurements are fused together to provide information in a fusion center,fusion weights of all selected nodes may affect the performance of target tracking.As far as we know,almost all existing tracking schemes neglect this problem.We study a weighted fusion scheme for target tracking in UWSNs.First,because the mutual information(MI)between a node’s measurement and the target state can quantify target information provided by the node,it is calculated to determine proper fusion weights.Second,we design a novel multi-sensor weighted particle filter(MSWPF)using fusion weights determined by MI.Third,we present a local node selection scheme based on posterior Cramer-Rao lower bound(PCRLB)to improve tracking efficiency.Finally,simulation results are presented to verify the performance improvement of our scheme with proper fusion weights.

基于REPBR跳数效用转发的改进路由算法

针对基于压力的水下无线传感器网络路由协议数据包传输路径距离过长、能量消耗不均衡等问题,提出一种基于REPBR跳数效用转发的改进路由算法。采用一种效用函数策略即加入剩余能量、节点间的跳数和链路质量3种因子解决能量消耗不均衡的问题,引入最小跳数算法获取节点到sink节点的跳数值,在数据包转发阶段综合比较路由效益选择最佳转发节点。仿真结果表明,改进后算法相比REPBR、EEDBR、DBR有较小的网络时延,提升了数据包的转发效率,提高了网络性能。

基于循环收敛的UWSN时间同步方法

提出了一种适用于水下传感器网络(UWSN,Underwater Wireless Sensor Networks)的时间同步方法。在设计过程中,对同步能耗、同步精度和同步效率进行了综合考虑;在实现中,对水声网络时间同步过程的主要误差因素进行了补偿,然后采用一种循环收敛的方法使所有节点时间戳收敛到一定误差范围内,减小了节点间同步误差在水声对等网络中多跳引起的累计效应。最后的仿真与实验结果表明,该同步方法达到了较高的时间同步精度和收敛速度。

基于表面均匀配置的UWSNs覆盖控制方法研究

本文针对湿地水流较为平缓的特点,提出一种适用于湿地水环境监测、基于表面均匀配置的三维水下无线传感器网络覆盖控制方法。初始配置时,将传感器节点均匀等间距地分布于监测水域的表面,并按照分布式算法将各个节点下降至合适的深度,以实现对水下三维空间最大程度的覆盖。仿真结果表明,在不同的网络规模下,本方法在最大化由覆盖度和平均距离加权而成的综合指标这一覆盖控制方法的优化目标上,均优于二维随机法、一维随机法,以及深度随机法。

能耗均衡与节能的自适应水下路由协议

针对水下传感器网络中节点能耗不均衡和能量有限的问题,提出一种能耗均衡与节能的自适应水下路由协议ECBES(energy consumption balanced and energy saving adaptive underwater routing protocol)。构建双区非均匀分层拓扑。基于能耗均衡因子,利用拓扑和节点剩余能量计算节点转发优先级,实现自适应转发节点选择,均衡网络能耗。与此同时,通过候选转发区域各分区域中节点参与转发数据包的比例确定次优候选转发区域,将次优候选转发区域作为初始策略,利用策略迭代思想确定最优候选转发区域,保证投递率的同时减少不同网络规模中重复数据包的转发,降低网络的整体能耗。仿真结果表明,ECBES相比VBF、ES-VBF和ALRP,在不同节点数量下,节点死亡率均最低,在保证数据包投递率的同时,能耗最少。

UWSNs中基于压缩感知的移动数据收集方案

由于水下无线传感器网络(UWSNs)工作环境的特殊性,降低节点能耗和保证数据收集的实时性是至关重要的问题。提出一种基于压缩感知(CS)的移动数据收集方案。以DEBUC协议和CS理论为基础,簇内节点依据设计的稀疏测量矩阵决定是否参与压缩采样,并将获得的测量值传输至簇头。通过AUV的移动来收集各个簇头上的数据到数据中心,该问题被建模为带有邻域的旅行商问题,并提出了近似算法进行求解。在数据中心处利用CS重构算法进行数据重构。仿真实验结果表明:相比于已有的水下移动数据收集算法,该方案在保证数据收集可靠性的同时,降低了数据收集延时,延长了网络寿命。

基于Hopfield神经网络的UWSNs移动信标路径规划

结合水声信道传播损耗模型,将所有节点中位置重要、邻居节点多的节点选为虚拟信标节点,使信标节点到各个虚拟信标节点位置向周围广播,完全覆盖整个网络。提出筛选策略,最小化虚拟信标节点的数量。把所有虚拟信标节点的路径规划看作旅行商问题(TSP),通过Hopfield神经网络将虚拟节点连接起来,使路径总长度最小。为解决Hopfield神经网络的随机性,使其适用于数量较大的TSP,在结束条件部分引入交叉算子Position-based Crossover的思想,提出交叉策略,减少规划的路径总长度。仿真实验证明:该策略能解决水下无线传感器网络(UWSNs)移动信标节点的路径规划问题,且能有效减少路径总长度。

水下无线传感器网络自适应锥体矢量路由协议

水声传感器网络(Underwater Acoustic Wireless Sensor Networks,UWSNs)由于复杂的水下环境,面临着投递率低、传播延迟高和节点能耗大等挑战。为解决这些问题,文章提出了一种自适应锥体矢量路由协议(Adaptive Cone Vector Routing Protocol,ACVRP),根据节点密度自适应调整锥体区域大小和方向,减少冗余通信和网络能耗,并根据节点的剩余能量和节点在锥体区域中的位置确定节点转发优先级,以提高投递率、减少传输跳数。仿真实验结果显示,与VBF、AHH-VBF和AHHC-VBF相比,ACVRP在包投递率、能效和端到端延迟方面均表现更佳。