Implementation of multiuser detection strategies for coherentunderwater acoustic communication

This paper presents multiple access interference cancellation techniques based on joint implementation of spatial-beamforming and multiuser detection strategies for coherent underwater acoustic communication network. Performances of adaptive multiuser detection strategies based on weighted parallel, successive, and recursive successive interference cancellation techniques are compared using experimental sea-trial data. Results show that the receiver structure adopting weighted recursive successive interference cancellation (RSIC) exhibits robustness in extracting useful data for weak users in the presence of co-channel interference from strong users. In addition, this type of structure simultaneously suppresses the summed interference effects contributed by weaker users toward the strongest user. The RSIC structure is therefore a potential candidate for multiple access interference suppression in coherent shallow water acoustic communication systems     

Adaptive equalization techniques for acoustic telemetry channels

A tutorial review of adaptive equalization techniques for combating intersymbol interference in high-speed digital communications over time-dispersive channels is given. Various equalizer structures and the associated adaptive algorithms, including both fractionally spaced and symbol-spaced equalizers, are presented. Also considered is the application of adaptive equalization techniques to underwater acoustic telemetry channels     

Signal detection for communications in the underwater acousticenvironment

Signal detection is a critical stage in the implementation of any effective communications system. The underwater acoustic environment, particularly in the presence of underwater vehicles, presents significant challenges to reliable detection without excessive false alarms. While there is often sufficient signal-to-noise ratio with respect to stationary broad-band background noise to permit reliable operation, the presence of strong event-like interference signals such as narrow-band signals and impulsive broad-band signals complicates the detection problem significantly. Frequency-hopped signals interleaved with quiescent bands are proposed as the basis of a robust detection system. These signals also make robust detection possible in a multi-access communications system. Two new detection algorithms that exploit the particular structure of these frequency-hopped signals are developed and their performance is analyzed. This analysis uses a modification of the doubly noncentral F-distribution that has not been used previously for such analysis. This distribution makes possible the direct calculation of probabilities of detection and false-alarm under interference and signal scenarios that cannot be analyzed using the better known noncentral F-distribution. With this analysis, the two developed detectors are shown to offer superior performance to that of either the CFAR detector or the binary data sequence detector. Experimental data confirms the theoretically derived results     

Multichannel processing of broad-band multiuser communicationsignals in shallow water acoustic channels

High-throughout multiple-access communication networks are being considered for use in underwater acoustic channels. Bandwidth limitations of underwater acoustic channels require receivers to process broad-band communications signals in the presence of several active users. To deal with the resulting multiple-access interference in addition to high intersymbol interference, the spatial variability of ocean multipath is exploited in a multichannel multiuser receiver. Two configurations of such a receiver, a centralized and a decentralized one, are presented in fully adaptive modes of operations. While greatly reducing intersymbol and multiple-access interference, spatial diversity implies high increase in adaptive multiuser receiver complexity. To reduce the complexity of the optimal multichannel combiner, spatial structure of multipath is exploited. The complexity of resulting adaptive decentralized multichannel multiuser receiver is reduced at almost no cost in performance. Comparison of proposed multichannel receivers in an experimental shallow water channel demonstrates superior performance of spatial signal combining. The use of multiple input channels is shown to provide high level of tolerance for the near-far effect in both centralized and decentralized receivers. Decentralized receiver with reduced-complexity combining is found to satisfy the performance/complexity trade-off required for practical receiver realization in shallow water networks     

水声信道高速率数据传输技术

本文介绍近年来水声信道高速率数所传输技术的一些研究进展，并结合本所研究的水声数据遥测，数字语音通讯和视频图像传输实验样机，讨论了具有抗多途干扰的声传输系统在调制信号设计及信号处理上所采用的关键技术。     

一种基于双通道的水下图像增强卷积神经网络

近年来各国对于海洋生物的保护意识日益强烈,用来监测海洋生物生存状态的水下机器人装备的研发是保护海洋生物资源的关键。水下相机是这类机器人在水下进行海洋生物监测时的光学感知设备。然而水下环境复杂,拍摄到的图像模糊不清,为解决水下图像模糊等问题,提出了一种基于双通道的水下图像增强卷积神经网络。在网络的编码器中采用双通道结构,其中一个通道采用了密集连接和高效通道注意力机制,提取水下图像的细节特征,另一个通道采用多尺度结构,提取原始图像的多尺度语义特征。接着,在网络中引入残差注意力模块和自适应特征融合模块,进一步优化了特征。最后将优化后的特征输入解码器重建出增强后的水下图像。试验表明：提出的网络算法在UIQM指标和Entropy指标上分别为3.005 6和7.654 7,较第二名的算法分别高出0.097 5和0.123 2。     

基于水声环境空间中多模态深度融合模型的目标识别方法研究

随着对水下目标特性研究的深入和声学探测技术的发展,基于单模态的阵列式信息融合或基于空间信息的分布式信息融合的水下目标识别方法研究已有一定成果,但针对复杂海况导致单一物理场或单一融合层次的系统识别性能提高有限等方面影响的水下目标识别方法研究还有所不足,因此,开展基于多模态深度融合模型的水下目标识别方法研究可利用模态互补,共享信息而提升识别率。文中在国内外研究基础上,深入研究了基于到达时差法和多模态方法组合的检测方法,初步形成了基于水声环境空间中多模态深度融合模型的识别框架,开展了海洋中典型自然与人为事件的信号分析与特征提取,并在此基础上,设计新型基于海底基站的被动识别系统。该系统同步记录和由位置等组成的时间序列标记声、磁和压数据,可实现高精度、高分辨率的识别。本研究可满足未来海洋观测对高性能水下目标探测、定位和跟踪系统的迫切需要,为海洋安全监管、海洋突发事件应急响应等领域提供新的技术手段和科学参考。     

Adaptive detection for shallow-water acoustic telemetry withcochannel interference

Adaptive decision feedback equalization (DFE) has recently been used to enable high-rate data transmission through shallow-water acoustic channels. This adaptive receiver successfully tracks and suppresses intersymbol interference due to a dispersive multipath channel. However, acoustic modems which are used for network applications must also contend with interference due to cochannel signals from proximal modems. In this work, we propose and evaluate a multiuser receiver with cochannel interference suppression. The advantages of this multiuser receiver in the presence of strong cochannel interference are shown by a performance comparison to a bank of the single-user DFEs described above. Conclusions are supported in part by the demodulation of experimental data for two simultaneous cochannel signals and by a steady-state performance analysis     

Adaptive sliding mode control of autonomous underwater vehicles inthe dive plane

The problem of controlling an autonomous underwater vehicle (AUV) in a diving maneuver is addressed. Having a simple controller which performs satisfactorily in the presence of dynamical uncertainties calls for a design using the sliding mode approach, based on a dominant linear model and bounds on the nonlinear perturbations of the dynamics. Nonadaptive and adaptive techniques are considered, leading to the design of robust controllers that can adjust to changing dynamics and operating conditions. The problem of using the observed state in the control design is addressed, leading to a sliding mode control system based on input-output signals in terms of drive-phase command and depth measurement. Numerical simulations using a full set of nonlinear equations of motion show the effectiveness of the proposed techniques     

时变水声信道中基于BEM的迭代信道估计技术

水声信道的多径时延扩展和时变特性对信道估计和均衡技术的研究带来了很大的挑战,同时也决定了水声信道是一种时频双扩展信道,提出一种水声OFDM通信系统中基于软信息的迭代信道估计技术,利用基于复指数基扩展模型(CE-BEM)进行信道估计。OFDM系统本身可以消除由于多径引起的符号间干扰(ISI)。基于导频的BEM信道估计,可以实现对时变信道的估计,结合基于软信息迭代的迭代均衡模块,将每次迭代生成的符号软判决信息作为辅助导频用于信道估计。同时,为了防止由于信道时变引起的信道子载波间干扰(ICI)对导频符号的影响,采用基于保护间隔的导频插入法插入导频。仿真结果显示基于BEM的软信息迭代信道估计性能较非迭代信道估计时明显提升。     

浅海海底管线检测艇操纵性和运动仿真研究

研究了用于维护和检修中国渤海海域输油管道的浅海管道检测艇的操纵性和运动仿真,提出了浅海海底管道检测艇的水动力学方程。为了更好地了解在配置上与一般潜器不同的浅海海底管线检测艇的动力学性能,通过水动力系数分析,研究了浅海海底管线检测艇的操纵性。最后根据运动方程建立了仿真系统,并通过仿真试验结果验证了仿真试验平台的可行性和可靠性。     

基于光学技术的水下气泡探测实验研究

热液/冷泉溢出含有硫化氢、甲烷、二氧化碳等化学成分的气泡。实验室模拟海底热液/冷泉资源溢出气泡环境搭建了实验平台,以甲烷气体为实验气体,在黑暗环境下用高速光电探测器对气泡后向散射光进行接收,用拉曼光谱仪实现甲烷气体气泡后向散射光的拉曼检测,并与计算拉曼光谱比较。由结果可知激光拉曼光谱可以探测到气泡后向散射光,并识别气泡中含有的气体成分。通过探测气泡成分,从而判定这些气泡是否来自海底热液/冷泉等甲烷资源溢出。这样的探测方式,探测准确率高,缓解探测深度,同时避免探测设备直接与海底资源直接接触而造成的寿命缩减,为将来的海洋探测与实际应用打下了良好的基础。     

浅海管线检测维修潜水器控制系统自航模试验

浅海海底管线检测维修潜水器是具有复杂动力特性和作业方式的特种载人潜水器，其作业需配备姿态及航行自动控制系统。为了保证其自动控制系统研制成功，研制了1：8缩尺的自航模作为平台，将实际控制系统方案遵循相似性准则改造为自航模控制系统，包括校正与补偿回路、指令分配器、姿态控制回路、航行控制回路。在海洋工程水池模拟风浪流等海洋环境，进行各种情况下的控制试验，对实现的控制律加以验证和改进，这些改进又按照相似性准则反映到实际控制系统方案的修正中。控制系统的设计方案由此得到全面验证和改善。     

水下机器人视频图像高效压缩方法研究

水下视频图像压缩一直是有限带宽水声信道实时传输海量视频数据的关键技术之一。本文首先介绍了目前水下机器人和水下视频图像压缩研究存在的主要问题,并综合分析了目前几种高效视频压缩方法的特点并探讨了进一步研究的方向。此外,根据水下视频的成像特点,提出了高效的全局与局部运动混合补偿方案和基于小波变换的预处理方法。初步实验结果表明：本文提出的预处理方法可以有效去除视频图像中存在的大量视觉冗余和空间冗余,提出的混合运动补偿方案可以获得很高的压缩编码效率;但必须进一步研究快速、有效的全局运动估计方法。     

海底管线检修潜水器垂直面控制及自航模试验

论述了纵倾控制律设计及自航模试验。首先选择一系列深度,对同一深度采用频域校正法单独设计控制律,使之对不同的速度和漂角具有足够的稳态精度和抗干扰性,这些控制律被集成统一为纵倾控制器,并根据潜深变化进行切换,对于其它深度采用同样的方法设计。控制器首先通过计算机仿真,然后进行自航模试验验证。设计的纵倾控制系统同时在其他试验项目中(水下管线跟踪和动力定位)发挥了重要的作用。     

A behavior-based approach to adaptive feature detection andfollowing with autonomous underwater vehicles

This paper presents a technique for adaptively tracking bathymetric contours using an autonomous underwater vehicle (AUV) equipped with a single altimeter sonar. An adaptive feature mapping behavior is developed to address the problem of how to locate and track features of unknown extent in an environment where a priori information is unavailable. This behavior is implemented as part of the layered control architecture used by the AUV Odyssey II. The new adaptive feature mapping behavior builds on previous work in layered control by incorporating planning and mapping capabilities that allow the vehicle to alter its trajectory online in response to sensor data in order to track contour features. New waypoints are selected by evaluating the expected utility of visiting a given location balanced against the expected cost of traveling to a particular cell. The technique is developed assuming sensor input in the form of a single, narrow-beam altimeter sensor attached to a non-holonomic, dynamically controlled survey-class AUV such as the Odyssey II. Simulations of the Charles River basin which have been constructed from real bathymetry data are used as test missions. The 7-m contour line of a prominent trench in the river serves as the target feature. The adaptive contour following behavior tracks the contour despite navigation error and environmental disturbances, supplying the capability of autonomously detecting and following distinctive bathymetric features using a point sensor. This behavior provides a foundation for future research in tracking of dynamic features in the water-column and for concurrent mapping and localization over natural terrain using a point sensor     

Simulation analysis and experimental study of defect detection underwater by ACFM probe

This article studies the application of the alternating current field measurement (ACFM) method in defect detection for underwater structures. Numerical model of the ACFM system is built for structure surface defect detection in seawater environment. Finite element simulation is performed to investigate rules and characteristics of the electromagnetic signal distribution in the defected area. In respect of the simulation results, underwater artificial crack detection experiments are designed and conducted for the ACFM system. The experiment results show that the ACFM system can detect cracks in underwater structures and the detection accuracy is higher than 85%. This can meet the engineering requirement of underwater structure defect detection. The results in this article can be applied to establish technical foundation for the optimization and development of ACFM based underwater structure defects detection system.     

一种新型水下声学浮标在目标探测中的应用

针对海上目标探测问题, 将矢量水听器和Argo浮标相结合, 可构建一种具有水中目标探测能力的新型水下声学浮标平台。该浮标平台可多次上浮和下潜, 具有在位时间长、隐蔽性能高、成本低等特点, 单台水下声学浮标即可实现海上目标探测, 利用多台水下声学浮标可快速形成大面积区域覆盖能力。为进一步验证水下声学浮标对海上目标探测性能, 2019年8月在南海海区开展了多台水下声学浮标海上试验, 数据处理结果表明: 南海夏季典型声速剖面下, 水下声学浮标对船长42m航速8.4kn的水面航船目标最远探测距离可达13.8km, 目标估计方位均方根误差最优可达5°, 在水面航船距离最近的1.9km处, 目标估计方位标准差可达2°。     

Adaptive optimal control of an autonomous underwater vehicle in the dive plane using dorsal fins

In this paper, adaptive control of low speed bio-robotic autonomous underwater vehicles (BAUVs) in the dive plane using dorsal fins is considered. It is assumed that the model parameters are completely unknown and only the depth of the vehicle is measured for feedback. Two dorsal fins are mounted in the horizontal plane on either side of the BAUV. The normal force produced by the fins, when cambered, is used for the maneuvering. The BAUV model considered here is non-minimum phase. An indirect adaptive control system is designed for the depth control using the dorsal fins. The control system consists of a gradient based identifier for online parameter estimation, an observer for state estimation, and an optimal controller. Simulation results are presented which show that the adaptive control system accomplishes precise depth control of the BAUV using dorsal fins in spite of large uncertainties in the system parameters.