所有结果:(9,355)

1

Reliability-Aware Cooperative Routing with Adaptive Amplification for Underwater Acoustic Wireless Sensor Networks
The protocols in underwater acoustic wireless sensor networks (UAWSNs) that address reliability in packets forwarding usually consider the connectivity of the routing paths up to one- or two-hops. Since senor nodes are connected with one another using other nodes in their neighborhood, such protocols have compromised reliability. It is because these protocols do not guarantee the presence of neighbors beyond the selected one- or two-hops for connectivity and path establishment. This is further worsened by the harshness and unpredictability of the underwater scenario. In addition, establishment of the routing paths usually requires the nodes' undersea geographical locations, which is infeasible because currents in water cause the nodes to move from one position to another. To overcome these challenges, this paper presents two routing schemes for UAWSNs: reliability-aware routing (RAR) and reliability-aware cooperative routing with adaptive amplification (RACAA). RAR considers complete path connectivity to advance packets to sea surface. This overcomes packets loss when connectivity is not established and forwarder nodes are not available for data routing. For all the established paths, the probability of successfully transmitting data packets is calculated. This avoids the adverse channel effects. However, sea channel is unpredictable and fluctuating and its properties may change after its computation and prior to information transmission. Therefore, cooperative routing is introduced to RAR with adaptive power control of relays, which makes the RACAA protocol. In RACAA, a relay node increases its transmit power than normal when the error in the data; it receives from the sender, is more than 50% before transferring it further to destination. This further increases the reliability when such packets are forwarded. Unlike the conventional approach, the proposed protocols are independent of knowing the geographical locations of nodes in establishing the routes, which is computationally challenging due to nodes' movements with ocean currents and tides. Simulation results exhibit that RAR and RACAA outperform the counterpart scheme in delivering packets to the water surface.

提交时间：2020年03月25日

2

On Spatial Smoothing for DOA Estimation of 2D Coherently Distributed Sources with Double Parallel Linear Arrays
Considering coherently-distributed (CD) sources are correlated with each other, a two-dimensional (2D) coherent CD source model is proposed according to the characteristics of an underwater acoustic channel. Under the assumption of small angular spreads, rotational invariance relationships within and between subarrays of double parallel linear arrays are derived. As the covariance matrix of spatial smoothing obtained from receive vectors expressed by rotational invariance relationships is proven to be full rank, decoherence of the 2D coherent CD source is proposed by spatial smoothing of the double parallel linear arrays. A propagator method base on spatial smoothing (SS-PM) and estimation of signal parameters via rotational invariance techniques (ESPRIT) base on spatial smoothing (SS-ESPRIT) method established by covariance matrix of spatial smoothing are proposed. The proposed methods do not require peak-searching, angles matching and information of deterministic angular signal distribution function. Simulations are conducted to verify the effectiveness of the proposed methods.

提交时间：2020年03月25日

3

Underwater sound production varies within not between species in sympatric newts
Sound production is a widespread phenomenon among animals. Effective sound use for mate or species recognition requires some acoustic differentiation at an individual or species level. Several species of caudate amphibians produce underwater sounds, but information about intra-and interspecific variation in their acoustic production is missing. We examined individual, sex, and species variation in underwater sound production in adults of two sympatric newt taxa, Ichthyosaura alpestris and Lissotriton vulgaris. Individual newts produced simple low-(peak frequency = 7-8 kHz) and mid-high frequency (14-17 kHz) clicks, which greatly overlap between sexes and species. Individual differences explained about 40-50% of total variation in sound parameters. These results provide foundations for further studies on the mechanisms and eco-evolutionary consequences of underwater acoustics in newts.

提交时间：2020年03月25日

4

On wave propagation and attenuation properties of underwater acoustic screens consisting of periodically perforated rubber layers with metal plates
The underwater acoustic screens made of periodically perforated rubber layers with metal plates are often used to enhance reflections and reduce transmissions of sound in water, under high hydrostatic pressure. Previous studies have tended to focus on the acoustic response of finite-thickness structures of the screens, rather than on the wave propagation properties of the corresponding infinite crystal structures. In this work, a numerical method, which combines finite element method and the layer-iteration technique, is developed to study the complex band structure of the infinite crystals and the acoustic response of the finite-thickness structures for the screens. Numerical results for the screens with elastic and viscoelastic rubber materials are presented for analyzing the features of propagation modes, band gaps, and attenuation of the waves in the screens. Reflection, transmission and absorption spectra of the screens are compared with the corresponding complex band structure of the infinite crystals in detail for providing a comprehensive understanding of the wave propagation and attenuation properties of the screens. (C) 2018 Elsevier Ltd. All rights reserved.

提交时间：2020年03月25日

5

Resource allocation for relay-aided underwater acoustic sensor networks with energy harvesting
Underwater acoustic sensor networks play a significant role in ocean observation, pollution monitoring and underwater remote control. Different from conventional sensor networks, transmission efficiency and lifetime for nodes in underwater acoustic sensor networks is vital since it is difficult to change batteries of buoy relays and underwater sensors. In this paper, two resource allocation algorithms for energy harvesting time and transmit power allocation in underwater acoustic sensor networks with single and multiple wireless energy harvesting buoy nodes are proposed to maximize the sum rate and energy efficiency. Both of the circuit power consumption and transmission power consumption are considered as the power consumption of the system. We first propose an optimal algorithm to allocate the time of energy harvesting slot for sum rate maximization. From the derivation, we show that the sum rate of the network grows as the transmission power increases. However, when the transmission power is extremely large, the energy efficiency of the network starts to decrease. Thus a joint algorithm with energy harvesting time and transmit power allocation is further provided for energy efficiency maximization. Simulation results validate the sum rate improvement under our proposed sum rate maximization algorithm and energy efficiency improvement under the proposed energy efficiency maximization algorithm. (C) 2019 Elsevier B.V. All rights reserved.

提交时间：2020年03月25日

6

Asynchronous Localization for UASNs: An Unscented Transform-Based Method
This letter is concerned with an asynchronous localization issue for underwater acoustic sensor networks (UASNs), subject to asynchronous clocks and stratification effects in physical channels. A novel unscented transform-based localization algorithm is proposed to estimate the positions of sensor nodes. Instead of linearizing the measurement equations, the proposed algorithm employs the unscented transform to compute the Jacobian matrix to reduce the linearization errors. Particularly, the ray-tracing approach is adopted to model the stratification effect. Moreover, the convergence analysis and Cramer-Rao lower bound for the algorithm are also provided. Simulation results show that the proposed algorithm can effectively improve the estimation accuracy as compared with the existing works.

提交时间：2020年03月25日

7

Target tracking based on improved cubature particle filter in UWSNs
In this study, an improved cubature particle filter based on the artificial bee colony (ABC) algorithm is proposed and applied to target tracking via underwater wireless sensor networks (UWSNs). In the proposed method, the square root cubature Kalman filter is used to generate the proposal distribution and the ABC algorithm is employed to optimise the particles before resampling, which makes the particles move toward the high likelihood region and maintain the diversity of the particles. Moreover, linear minimum variance criterion is utilised to fuse local estimates together in distributed fusion architectures of UWSNs. The simulation results show that the proposed method outperforms other classical algorithms in tracking accuracy.

提交时间：2020年03月25日

8

Study on the integrated calculation method of fluid-structure interaction vibration, acoustic radiation, and propagation from an elastic spherical shell in ocean acoustic environments
A modeling method based on the wave superposition method is studied in this paper. Different underwater acoustic propagation models are used in the near and far field. Taking the acoustic radiation field calculation of an elastic spherical shell as an example, the near and far field can be analyzed as a unified system, using this method. Many studies use FEM/BEM (finite element method/boundary element method) to calculate acoustic radiation fields of elastic structures, but only a few of these methods can be applied when considering finite ocean depth, seafloor reflection loss, and sound velocity profile. In this study, the Green function is calculated differently in the near and far field to significantly simplify calculations. The virtual source method is used to calculate the acoustic radiation field in the near field and source strength, while the normal mode method is used in the far field. The results are compared with those obtained using the COMSOL finite element software, which showed that this method was both computationally efficient and accurate. Based on numerical examples, the influence of sea surface, seafloor, and sound velocity on the acoustic radiation field of elastic structures in an ocean acoustic environment is quantitatively analyzed.

提交时间：2020年03月25日

9

A PDMS-based broadband acoustic impedance matched material for underwater applications
Having a material that is matched in acoustic impedance with the surrounding medium is a considerable asset for many underwater acoustic applications. In this work, impedance matching is achieved by dispersing small, deeply subwavelength sized particles in a soft matrix, and the appropriate concentration is determined with the help of Coherent Potential Approximation and Waterman & Truell models. We show experimentally the validity of the models using mixtures of Polydimethylsiloxane (PDMS) and TiO2 particles. The optimized composite material has the same longitudinal acoustic impedance as water and therefore the acoustic reflection coefficient is essentially zero over a wide range of frequencies (0.5-6 MHz). PDMS-based materials can be cured in a mold to achieve desired sample shape, which makes them very easy to handle and to use. Various applications can be envisioned, such the use of impedance-matched PDMS in the design and fabrication of acoustically transparent cells for samples, perfectly matched layers for ultrasonic experiments, or superabsorbing metamaterials for water-borne acoustic waves.

提交时间：2020年03月25日

10

Acoustic Absorption Characteristics of New Underwater Omnidirectional Absorber
We investigate a new underwater omnidirectional absorber with acoustic black hole effect to realize a broadband omnidirectional acoustic wave absorption. Based on multiple scattering theory, a two-dimensional axisymmetric model of underwater omnidirectional absorber comprised of an acoustic gradient refractive index structure and a hollow core is developed, and the mechanisms of omnidirectional absorption and dissipation of acoustic waves are studied. The numerical results indicate that the omnidirectional absorber developed here can achieve the omnidirectional absorption of incident acoustic waves in a broadband frequency and can effectively reduce the backscattering of acoustic waves. It potentially provides a new notion for underwater acoustic coating design.

提交时间：2020年03月25日