Design of a Propagation-Delay-Tolerant MAC Protocol for Underwater Acoustic Sensor Networks

Underwater acoustic sensor networks (UASNs) can be employed in a vast range of applications, retrieving accurate and up-to-date information from underneath the ocean's surface. Although widely used by terrestrial sensor networks, radio frequencies (RFs) do not propagate well underwater. Therefore, acoustic channels are employed as an alternative to support long-distance and low-power communication in underwater sensor networks even though acoustic signals suffer from long propagation delay and have very limited bandwidth. In this paper, we introduce an adaptive propagation-delay-tolerant collision-avoidance protocol (APCAP) for the media access control (MAC) sublayer of UASN. The protocol includes an improved handshaking mechanism that improves efficiency and throughput in UASN where there is a large propagation delay. The mechanism guarantees nodes that can potentially interfere with a forthcoming transmission are properly informed. It also allows a node to utilize its idle time while waiting for messages to propagate, which is otherwise wasted by most existing MAC protocols. The simulation results indicate that where employed by UASN, APCAP exhibits good performance and outperforms the other MAC protocols examined in this paper.      

面向水下无线传感器网络的介电弹性体能量收集技术研究

水下无线传感器网络为海洋资源勘探、海洋灾害预警、海洋权益维护和海洋安全防御等提供了重要助力。然而,利用传统蓄电池对传感器进行供电的方式,需要定期充电或更换蓄电池,难以保证长时间持续可靠工作,介电弹性体能量收集技术原位供电成为解决这一难题的有效途径。目前,面向水下能量收集的介电弹性体发电机（DEG）存在能量收集性能低的问题,针对该问题,通过构建的 DEG 理论模型,研究不同参数下 DEG 的动态响应和能量收集性能,以探究提高其能量收集性能的方法。结果表明：增大负载电阻或提高 DEG 拉升阶段在其周期中所占时间比可以增强其能量密度。研究结果能够为增强介电弹性体水下能量收集性能提供新途径。     

Lifetime Prolonging Algorithms for Underwater Sensor Networks

1.IntroductionRecent advances in acoustic communication,sensor networks and ad hoc networks have motivatedthe development of UASNs which are generallyformed by a surface station,autonomous underwater ve-hicles(AUVs)and sensor nodes that possess sensing,si…     

无线传感器网络路由协议研究

总结目前已提出的基于地理位置信息的无线传感器网络路由协议存在的问题,着重讨论路由协议中的安全性能,分析GPSR和GEAR存在的能量消耗和安全性能问题,以改进GEAR路由协议。文中将新设计的路由协议的安全性能与GPSR和GEAR进行了比较,结果表明该路由协议不仅可以节省无线传感器节点的能量消耗,而且还可以抵抗一些针对无线传感器网络的特定方式的攻击。     

一种适用于水声通信的Doppler估计算法

在水下声通信中,收发双方相对运动产生的Doppler效应会导致信号的伸缩,引起信噪比的降级,需要采用Doppler补偿措施。在补偿前需要得到Doppler估计。文中提出了一种利用DFT进行Doppler估计的有效算法,该算法通过估计频率偏移来计算Doppler率。仿真结果验证了该算法的有效性。     

Turbo码在水下无线通信中的应用

详细阐述了Turbo码的原理，围绕Turbo码技术具体实现了一个水声通信系统，并用VC对系统进行仿真。仿真的结果及水池中获得的试验数据表明，该方案可使水下无线通信系统的性能得到显著改善。     

网格编码调制在水下无线通信中的应用

详细阐述了网格编码调制(TCM)的原理及其在水下无线通信中的应用。同时用System View对系统进行仿真，仿真结果显示，该方案使水下无线通信系统的性能得到明显改善。     

VBF水下传感器网络路由协议的路径优化与模拟

针对水下传感器网络节点的移动性,以基本VBF(Vector-Based Forwarding Protocol)路由协议为基础,提出了1种适用于水下移动传感器节点的路径优化算法.为了验证此路径优化算法的有效性,分别对基本VBF算法和改进的VBF算法进行了3个模拟实验;从数据包接收成功率和网络负载两方面分析比较了实验模拟结果.比较结果可以看出:文中提出的路径优化的VBF路由协议的数据包成功接收率要优于VBF路由协议,降低了网络负载,并且该优化算法实现简单,不需要增加额外的网络延迟时间.     

多模式自适应水下无线通信网络框架研究

对当前典型的水下无线通信网进行分析,针对水声、光、射频3种通信模式在水下无线通信中的优缺点,提出基于软件无线电技术的多模式自适应水下无线通信网络的概念及其框架结构,并对其中的自适应调制解调方式展开研究.结合MAC层协议,提出一种跨层的自适应调制解调解决方案,即通过收发双方的握手信息携带当前信道状态,由发射方根据握手信息,判断双方通信距离,预计信道未来状态,结合需要传输的数据量,自适应选择合适的通信模式和调制方式,并利用握手信号通知接收方,从而实现在通信网络范围内数据或指令的快速可靠传输.     

水声通信网络的资源分配发展综述

随着陆地资源的枯竭,人类逐渐把目光转向了蓝色海洋。水声通信网络（Underwater Acoustic Communication Network,UACN）能够有效实现水下信息交互,是认识、开发、利用海洋的重要工具,并在推动“智慧海洋”建设中发挥着重要作用。但是,水下节点的发射功率、转发中继、通信信道等通信资源严重受限,这将无法满足UACN长期且有效作业的需求。资源分配技术能够在不提升网络硬件成本的情况下有效改善网络能量效率、抗干扰性等相关性能,在水下信息交互需求激增的背景下具有极高的研究意义与应用价值。因此,如何对有限的网络资源进行合理分配已成为UACN领域的研究热点之一。首先对UACN系统进行了简要介绍,然后研究分析了UACN资源分配技术及意义,并重点指出了其资源分配的发展现状、趋势和面临的挑战。     

An Iterative Equalization and Decoding Approach for Underwater Acoustic Communication

In this paper, we present an iterative approach for recovering information sent over a shallow underwater acoustic (UWA) communication channel. The procedure has three main tasks: estimation of channel model parameters (CMPs), channel equalization, and decoding. These tasks are performed cyclicly until the algorithm converges. Information bits are convolutionally encoded, punctured and permuted, mapped into quaternary phase-shift keying (QPSK) symbols, linearly modulated, and transmitted through a downward-refracting ocean waveguide. Training symbols are prepended to the transmitted sequence for initial estimation of CMPs. Our algorithm processes data from a single receive sensor. Data are received on a vertical array and the performance of the algorithm for each sensor in the array is examined. There is negligible Doppler spread in the received data. However, difference between transmitter and receiver clocks as well as slight motion of the receive array produce a nonnegligible compression of the received signals. Consequently, there is observable Doppler “shift.” Nonuniform resampling of the data produces time series we model as the output of a linear time-invariant system. Resampling and CMP estimation are done iteratively, in conjunction with equalization and decoding. The algorithm successfully processes the data to yield few or no information bit errors.      

Bounding Cube:一种无线传感器网络节点三维定位算法

无线传感器网络经常会部署在三维区域内,但目前大部分节点定位方法仅考虑的是二维应用.针对无线传感器网络节点能量有限特点,提出1种三维节点定位算法bounding cube,研究算法的原理和实现方法,并进行仿真分析.仿真结果表明,在100 m×100 m×100 m的三维空间内随机部署400个节点,当已知节点密度>20%,通信半径分别为r=30 m,r=40 m,r=50 m时,相对定位误差均<40%,当已知节点密度>20%、通信半径>30 m时,一次定位比例可以达到100%.该算法的突出特点是方法简单、计算量小.     

无线传感器网络中基于能量平衡的部署算法

为平衡能量损耗并用网络生存期最大化,提出1种无线传感器网络(WSNs)中基于能量平衡的节点部署算法.此算法基于距离调整网络部署,也就是根据不同位置的节点能耗调整节点的间距.文中提出能耗最低点并不等于生存期最优.仿真证明基于这种部署策略网络的能耗大大降低,网络生存期比均匀部署策略高160%,同时给出调整距离、网络半径、节点传递范围和节点数量之间的参考关系.     

一种针对小多普勒扩展水声信道的OFDM接收算法

在水声正交频分复用（OFDM）通信系统中,水声信道中的多径时延扩展会带来频域选择性衰落,多普勒效应会带来子载波间干扰（ICI）。传统接收算法需要开展复杂的二维（时延/多普勒）信道估计,再进行复杂的信道均衡和符号检测。针对有限多普勒扩展的信道条件下多普勒矩阵元素变化缓慢、ICI干扰范围有限的特点,借鉴多项式拟合思想,提出了一种创新的接收算法。该算法将多普勒矩阵元素近似为多项式函数,迭代进行多项式拟合和数据符号频域均衡。和传统方法相比,该算法无需进行信道多普勒估计,仅需信道的一维（时延）估计即可实现较好的性能。利用Bellhop产生的水声信道仿真结果验证了该算法的可行性。     

高速水声通信中的相位补偿研究

利用相位补偿来解决高速水声通信中的载波恢复问题,并分析了联合相位补偿和信道均衡时的系统性能。研究结果表明：使用相位补偿后,均衡器可以有效地抵抗频率偏移造成的信道相位旋转,跟踪频率偏移能力提高了一个数量级以上。     

海洋环境无线传感器网络监测体系与应用技术研究

针对目前海洋环境监测中急需解决的主要技术问题.对海洋环境无线传感器网络监测的体系结构进行了研究,通过对Crossbow无线传感器网络的拓扑结构和软件架构进行分析与试验.提出其技术优势和有待解决的应 用问题.     

A Variable-Rate Spread-Spectrum System for Underwater Acoustic Communications

A key research area in underwater acoustic (UWA) communication is the development of advanced modulation and detection schemes for improved performance and range-rate product. In this communication, we propose a variable-rate underwater data transmission system based on direct sequence spread spectrum (DSSS) and complementary code keying (CCK), particularly for shallow-water acoustic channels with severe multipath propagation. We provide a suboptimum receiver that consists of a bidirectional decision feedback equalizer (BiDFE) to cancel both postcursor and precursor intersymbol interference (ISI). We also develop iterative signal processing and time-reversal (TR) diversity processing to mitigate the effect of error propagation in BiDFE. We present performance analysis on bit error rate (BER) for different data rates. Our works show that this new variable-data-rate DSSS-CCK is a suitable candidate for UWA communications over varying channel conditions and distance.      

Precoding Based Channel Prediction for Underwater Acoustic OFDM

The life duration of underwater cooperative network has been the hot topic in recent years. And the problem of node energy consuming is the key technology to maintain the energy balance among all nodes. To ensure energy efficiency of some special nodes and obtain a longer lifetime of the underwater cooperative network, this paper focuses on adopting precoding strategy to preprocess the signal at the transmitter and simplify the receiver structure. Meanwhile, it takes into account the presence of Doppler shifts and long feedback transmission delay in an underwater acoustic communication system. Precoding technique is applied based on channel prediction to realize energy saving and improve system performance. Different precoding methods are compared. Simulated results and experimental results show that the proposed scheme has a better performance, and it can provide a simple receiver and realize energy saving for some special nodes in a cooperative communication.