Underwater localization using stochastic proximity embedding and multi-dimensional scaling

Localization for underwater acoustic sensor networks is an active research topic where a large number of techniques have been proposed recently. This paper addresses one of the open research issues, the impact of underwater sound speed variation on the localization accuracy. In this paper, modified versions of stochastic proximity embedding and multi-dimensional scaling localization algorithms customized for underwater application are proposed. The algorithms are found to provide good performance in underwater scenario as they take into account refractive ray bending of acoustic waves. Detailed study of the algorithm performance has been done and the results are reported. Cramer Rao Lower Bound for the problem is also derived.     

基于两级变参数滤波时延校正的声源定向

在人机交互、视频会议、军事国防等众多领域中,基于麦克风阵列的声源定位系统已经受到了人们的广泛关注。在空间噪声和混响的环境中,时延估计往往会出现很大的偏差,而声源角度的计算又依赖于时延估计的准确性。因此,本文在双阵元模型下提出了一种用于声源定向的时延校正算法,该算法采用一个权值系数可变的两级滤波器对GCC-PHAT-ργ估计出的时延点进行校正,有效地让偏差较大的时延点回归到正确的时延群当中,从而避免了错误时延值对进一步角度定向的影响。实验结果表明,本文提出的算法在不删除时延异常点的前提下,在误差均值和均方根误差等方面都表现出了很好的性能,而且对每组数据进行角度定向的时间都很短。理论分析与实验结果表明该方法不仅有效的提高了角度估计的估计精度,而且当说话人以正常走路的速度移动时,该算法可对说话人的方向进行及时的跟踪。      

Localization under anchor node uncertainty for underwater acoustic sensor networks

This paper deals with the problem of sensor node localization in the presence of uncertainty in anchor node location. Aqueous environments are prone to adverse effects of underwater currents. This adversity causes non‐negligible mobility to the anchor nodes deployed under water. Localization in the presence of uncertainty in the anchor node location is quite challenging. Also, the authors consider the ray‐bending property of underwater medium due to depth dependent sound speed, to furnish the accurate position estimate of the target node. Standard ray equations are used to model the path followed by acoustic rays in water. Maximum likelihood estimation is proposed to estimate the location of target node with uncertainty in anchor node positions and is compared with the scheme with exact knowledge of anchor node positions, and the results are reported. Monte Carlo simulation is used to assess the performance of the proposed method. Also, the Cramer‐Rao lower bound with uncertainty in anchor nodes is derived and described. Simulation results of the proposed algorithm outperform the existing algorithm with known anchor location by up to 49.4%, and hence, accuracy is improved in the proposed method.     

水下传感器网络时间同步技术综述

 时间同步是传感器节点协同工作的基础.水下传感器网络由于采用水声通信方式,具有不同于陆地无线传感器网络的特点,为时间同步算法研究带来了新的挑战.论文首先说明同步问题与同步算法的形式化定义,然后讨论水下传感器网络不同于陆地传感器网络的特点,并指出相关特点对于同步问题的影响;接着综述陆地传感器网络同步算法的研究进展,分析相关算法用于水下环境的不足;进而介绍水下传感器网络同步算法的研究进展,并通过仿真实验完成了相关算法的性能对比;最后总结水下传感器网络时间同步的关键问题,指出进一步的研究方向.     

The challenges of building mobile underwater wireless networks for aquatic applications

The large-scale mobile underwater wireless sensor network (UWSN) is a novel networking paradigm to explore aqueous environments. However, the characteristics of mobile UWSNs, such as low communication bandwidth, large propagation delay, floating node mobility, and high error probability, are significantly different from ground-based wireless sensor networks. The novel networking paradigm poses interdisciplinary challenges that will require new technological solutions. In particular, in this article we adopt a top-down approach to explore the research challenges in mobile UWSN design. Along the layered protocol stack, we proceed roughly from the top application layer to the bottom physical layer. At each layer, a set of new design intricacies is studied. The conclusion is that building scalable mobile UWSNs is a challenge that must be answered by interdisciplinary efforts of acoustic communications, signal processing, and mobile acoustic network protocol design.     

Energy‐efficient design of 3D UWSNs leveraging compressive sensing and principal component analysis: A communication techniques perspective

The design of energy‐efficient underwater wireless sensor networks (UWSNs) poses many challenges due to the intrinsic properties of propagation medium and limited battery power of sensor nodes. This paper proposes the concept of optimal clustering for three‐dimensional (3D) UWSNs leveraging compressive sensing (CS) and principal component analysis (PCA) technique of data compression. Optimal clustering reduces the energy consumption by selecting the optimal number of clusters whereas CS and PCA compression techniques reduce the energy consumption by considering a lesser number of samples and reduce the data redundancy at cluster heads (CHs) level, respectively. Moreover, three communication techniques like acoustic, electromagnetic (EM), and free‐space optical (FSO) wave are considered for communication in 3D UWSNs. We compared the energy efficiency for all three communication techniques by examining the three base station (BS) positions at the center, at the corner, and at the lateral midpoint of the 3D sensing area. Moreover, performance parameters (network lifetime, throughput, packet drop rate, and latency) are also evaluated for 3D UWSNs. It is observed that PCA outperforms the CS technique. The proposed technique is suitable for long‐term and densely deployed 3D UWSNs, in which saving energy is of crucial importance.     

Enhancing the spectral efficiency and energy efficiency of underwater channel communication by optimal cooperative spectrum sensing using hybrid optimization

Underwater wireless sensor networks (UWSNs) contain quite a lot of components such as vehicles and sensors that are deployed in a specific acoustic area to perform collaborative monitoring and data collection errands. These networks are adopted interactively between diverse nodes and ground‐based stations. Currently, UWSNs face problems and challenges that pertain to limited bandwidth, media access control, high propagation delay, 3D topology, spectrum sensing, resource utilization, routing, and power constraints. This proposal deals with the intelligent spectrum sensing in underwater cognitive sonar communication networks (CSCN). Here, the improved performance of spectrum sensing in underwater communication is attained by optimizing the cooperative spectrum sensing and data transmission. The parameters of system like subchannel allocation and transmission power is optimized by a new hybrid meta‐heuristic algorithm by integrating the concepts of deer hunting optimization algorithm (DHOA) and lion algorithm (LA) termed as lion‐enabled DHOA (L‐DHOA). The main intention of optimizing these parameters is to maximize the spectrum efficiency (SE) and energy efficiency (EE) of the underwater channel communication system. From the analysis, with respect to convergence rate, minimum detection probability, and local sensing time, it is proved that the novel hybrid optimization algorithm keeps a great role in making the trade‐off between the SE and EE in underwater channel modeling.     

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.     

基于射线模型的浅海水声传播仿真研究

浅海是我国船只活动的主要区域,在计划海上实验、设计最优声纳系统和预测海上声纳性能时,水声模型被广泛地应用于预报声学环境。用射线模型为浅海声场建模,由于射线理论有足够的准确性,可以用来获得声波在空间传播的重要信息,在一定的条件下,射线声学的数学运算也比较简捷。在此结合仿真结果,证明了由射线理论给出的声线图可以给声场以直观、形象的理解,其建立的水声信道模型在工程应用上具有重要意义。     

适用于水平迭代声线的声速剖面B-样条构建

使用声线法研究水声传播的问题中,特别是分层声速环境下,如何计算合理的本地声速及声速的一阶导数是一个关键问题。文章使用B-样条从有限的声速样点内插得到满足连续性、有限导数存在等要求的声速剖面以及声速的一阶导数。文中完整介绍了构造声速剖面的方法,进一步还介绍了如何通过调整控制点位置,以及本文提出的参数生成因子来改善内插曲线的平滑度、起伏、样点的拟合程度的过程。通过实例验证这个方法构造的声速曲线能够满足实际计算的需要。     

Compensation of sound speed deviations in 3-D B-mode ultrasound for intraoperative determination of the anterior pelvic plane

An accurate determination of the pelvic orientation is inevitable for the correct cup prosthesis placement of navigated total hip arthroplasties. Conventionally, this step is accomplished by percutaneous palpation of anatomic landmarks. Sterility issues and an increased landmark localization error for obese patients lead to the application of B-mode ultrasound imaging in the field of computer-assisted orthopedic surgery. Many approaches have been proposed in the literature to replace the percutaneous digitization by 3-D B-mode ultrasound imaging. However, the correct depth localization of the pelvic landmarks could be significantly affected by the acoustic properties of the penetrated tissues. Imprecise depth estimation could lead to a miscalculation of the pelvic orientation and subsequently to a misalignment of the acetabular cup implant. But so far, no solution has been presented, which compensates for acoustic property differences for correct depth estimation. In this paper, we present a novel approach to determine pelvic orientation from ultrasound images by applying a hierarchical registration scheme based on patch statistical shape models to compensate for differences in speed of sound. The method was validated based on plastic bones and a cadaveric specimen.     

MRP: A Localization-Free Multi-Layered Routing Protocol for Underwater Wireless Sensor Networks

Underwater Wireless Sensor Networks (UWSNs) have distinctive characteristics due to the use of acoustic signals as its physical medium for communications, including high propagation delay, limited bandwidth and high error rates. Hence, designing communication protocols, particularly, an efficient routing protocol for UWSNs is a challenging issue. Routing protocols can take advantage of the localization of sensor nodes. However, the localization itself is not impeccable in UWSNs. In this paper, we therefore propose a localization-free routing protocol named MRP (multi-layered routing protocol) for UWSNs. MRP utilizes super nodes in order to eliminate the need of localization. MRP works in two phases: Layering phase and Data forwarding phase. During layering phase, different layers are formed around the super nodes. In data forwarding phase, data packets are forwarded based on these layers. Through simulation study using NS-2 simulator, we proved that MRP contributes significant performance improvements against representative routing protocols.     

RPCP‐MAC: Receiver preambling with channel polling MAC protocol for underwater wireless sensor networks

To design a reliable and energy efficient medium access control (MAC) protocol for underwater wireless sensor networks (UWSNs) is an active research area due to its variety of applications. There are many issues associated with underwater acoustic channels including long and variable propagation delay, attenuation, and limited bandwidth which pose significant challenges in the design of MAC protocol. The available sender‐initiated asynchronous preamble‐based MAC protocols for UWSNs are not reliable and energy‐efficient. This is due to the problems caused by transmission of preambles for longer duration and collision of preambles from hidden nodes in sender‐initiated preamble‐based MAC protocols. To resolve these issues, the paper proposed an asynchronous receiver‐initiated preamble‐based MAC protocol named Receiver Preambling with Channel Polling MAC (RPCP‐MAC) protocol for shallow underwater monitoring applications with high data rates. The protocol is proposed to resolve data packet collision and support reliability in an energy‐efficient way without using any transmission schedule. The proposed protocol is based on the following mechanisms. Firstly, receiver preambling mechanism is adopted to reduce idle listening. Secondly, channel polling mechanism is used to determine missing data frame during its sleeping period and to minimize the active time of node and reduces energy wastage. Finally, a back‐off mechanism is applied to resolve collision when preambles are received simultaneously. In addition, performance analysis through Markov chain together with its validation with simulation‐based studies is reported in the paper. Both the analytical and simulation results have demonstrated the reliability achievable with RPCP‐MAC while providing good energy efficiency.     

DFR: an efficient directional flooding‐based routing protocol in underwater sensor networks

Unlike terrestrial sensor networks, underwater sensor networks (UWSNs) have salient features such as a long propagation delay, narrow bandwidth, and high packet loss over links. Hence, path setup‐based routing protocols proposed for terrestrial sensor networks are not applicable because a large latency of the path establishment is observed, and packet delivery is not reliable in UWSNs. Even though routing protocols such as VBF (vector based forwarding) and HHVBF (hop‐by‐hop VBF) were introduced for UWSNs, their performance in terms of reliability deteriorates at high packet loss. In this paper, we therefore propose a directional flooding‐based routing protocol, called DFR, in order to achieve reliable packet delivery. DFR performs a so‐called controlled flooding, where DFR changes the number of nodes which participate in forwarding a packet according to their link quality. When a forwarding node has poor link quality to its neighbor nodes geographically advancing toward the sink, DFR allows more nodes to participate in forwarding the packet. Otherwise, a few nodes are enough to forward the packet reliably. In addition, we identify two types of void problems which can occur during the controlled flooding and introduce their corresponding solutions. Our simulation study using ns‐2 simulator proves that DFR is more suitable for UWSNs, especially when links are prone to packet loss. Copyright © 2011 John Wiley & Sons, Ltd.     

Acoustic Tomography

High-resolution measurements of the density field in the ocean are prohibitively expensive if traditional ship-borne instruments are used. Tomography uses acoustic remote sensing to infer ocean structure, and avoids many of the limitations of direct measurements. Sound pulses follow distinct trajectories through the water from source to receiver, and the travel time for a given pulse is a known functional of the sound speed field. This functional can be inverted to recover an estimate of the sound speed field through which it passed. The inversion is accomplished with either detenninistic linear matrix inversion or stochastic optimal estimation, and the sound speed field estimate returned can be converted to an estimate of density. A numerical simulation of the pilot tomography experiment is presented to demonstrate that tomography can be effective in reproducing significant ocean features.     

Disturbance torque estimation in a sensorless DC drive

The estimation of the disturbance torque in a sensorless DC motor drive is carried out by extending the classical observer theory. Three estimation schemes are formulated according to the representation of the disturbance torque and the processing of the observer states. In addition to the disturbance torque, all the schemes deliver an estimation of the motor speed. Steady-state accuracy and dynamics of the schemes are first determined in nominal conditions, identifying the scheme with the best performance. The effects of variations in the motor parameters are then analyzed, with the finding that a proper modeling of the motor makes the steady-state estimation of the disturbance torque insensitive to any variation. As a test, the schemes are applied to a sensorless DC motor drive for both compensating for the disturbance torque and closing the speed loop. The responses obtained with the best-performance scheme are reported     

采用单水听器的匀速圆弧运动直升机三维参数估计算法

针对空中匀速圆弧运动目标激发的水下声信号,该文采用单水听器解决该动目标3维运动参数的估计问题。首先以直升机离散线谱为声源特征,在空气-水介质中建立声源线谱特征在匀速圆弧运动下3维多普勒传播模型。然后根据多普勒频移曲线、声源运动模型以及声线传播几何关系,选取3个时间观测点计算目标多普勒频移,推导了单水听器估计空中匀速圆弧运动声源的3维参数估计算法。最后,通过仿真单水听器所接收的水声信号,验证了该算法估计匀速圆弧运动声源飞行参数的有效性和精度。     

体育馆短线阵列扬声器系统EASE仿真

高校体育馆实质上是一种多功能大厅。为满足其多功能的声学要求,采用短线阵列扬声器系统来提升体育馆内声音质量,并采用声学设计软件EASE对体育馆声学环境进行建模,调整和预测线阵列扬声器布置方案,并对设计方案进行声学特性分析,从而得出最优化电声系统布置方案,为指导厅堂扩声工程施工提供相应的技术数据。     

An adaptive target tracking method for 3D underwater wireless sensor networks

Today, underwater target tracking using underwater wireless sensor networks (UWSNs) is an essential part in many military and non-military applications. Most of moving target tracking studies in UWSNs are considered in two-dimensional space. However, most practical applications require to be implemented in three-dimensional space. In this paper an adaptive method based on Kalman filter for moving target tracking in three dimensional space using UWSNs is proposed. Since, energy protection is a vital task in UWSNs; the proposed method reduces the energy consumption of the entire network by a sleep/wake plan. In this plan only 60% of the closer nodes along the path of the moving target will be waked up using a sink activation message and participate in the tracking, while the other nodes remain in sleep state. At each stage of tracking, the location of the target is estimated using a 3D underwater target tracking algorithm with the trilateration method. Subsequently, the estimations and target tracking results are inserted into the Kalman filter as measuring model to produce the final result. Performance evaluation and simulations results indicated that the proposed method improves the average location error by 45%, average estimated velocity by 86%, and average energy consumption by 33% in comparison to the trilateration method. However, computation time is increased as a result of improving tracking accuracy; and tracking accuracy is lost about 20% due to saving energy. It was shown that the proposed method has been able to adaptively achieve a trade-off between tracking accuracy and energy consumption based on real-time user requirements. Such adaption can be controlled trough the sink node based on real-time requirements.     

全相位FFT在合成孔径水声通信运动补偿中的应用

该文针对浅海远程水声信道提出合成孔径技术与直接序列扩频相结合的通信方案,并重点分析了影响通信质量的多普勒效应问题,提出了一种有效的多普勒估计和补偿算法。该补偿算法采用重采样与全相位快速傅里叶变换(AP-FFT)处理技术,实现了频率和相位的高精度估计,同时消除多普勒造成的时间模糊。该文利用声学工具箱对声信道进行了建模,对合成孔径通信系统进行了仿真验证。结果表明,该文所提出的多普勒补偿算法有效地抵抗了收发节点以较高航速相对运动时所产生的多普勒效应,实现了多虚拟子阵发射信号的相干叠加,减少了运动造成的合成孔径处理空间增益损失,显著改善了通信质量。