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111.
Estimation of Rapidly Time-Varying Sparse Channels 总被引:2,自引:0,他引:2
The estimation of sparse shallow-water acoustic communication channels and the impact of estimation performance on the equalization of phase coherent communication signals are investigated. Given sufficiently wide transmission bandwidth, the impulse response of the shallow-water acoustic channel is often sparse as the multipath arrivals become resolvable. In the presence of significant surface waves, the multipath arrivals associated with surface scattering fluctuate rapidly over time, in the sense that the complex gain, the arrival time, and the Dopplers of each arrival all change dynamically. A sparse channel estimation technique is developed based on the delay-Doppler-spread function representation of the channel. The delay-Doppler-spread function may be considered as a first-order approximation to the rapidly time-varying channel in which each channel component is associated with Doppler shifts that are assumed constant over an averaging interval. The sparse structure of the delay-Doppler-spread function is then exploited by sequentially choosing the dominant components that minimize a least squares error. The advantage of this approach is that it captures both the channel structure as well as its dynamics without the need of explicit dynamic channel modeling. As the symbols are populated with the sample Dopplers, the increase in complexity depends on the channel Doppler spread and can be significant for a severely Doppler-spread channel. Comparison is made between nonsparse recursive least squares (RLS) channel estimation, sparse channel impulse response estimation, and estimation using the proposed approach. The results are demonstrated using experimental data. In training mode, the proposed approach shows a 3-dB reduction in signal prediction error. In decision-directed mode, it improves significantly the robustness of the performance of the channel-estimate-based equalizer against rapid channel fluctuations. 相似文献
112.
The aim of this paper is to investigate the shape and tension distribution of fishing nets in current. A numerical model is developed, based on lumped mass method to simplify the net. The motion equation is set up for each lumped mass. The Runge–Kutta–Verner fifth-order and sixth-order method is used to solve these simultaneous equations, and then the displacement and tension of each lumped mass are obtained. In order to verify the validity of the numerical method, model tests have been carried out. The results by the numerical simulation agree well with the experimental data. 相似文献
113.
Horiguchi T Li Z Uno S Shimizu M Shiraishi H Morita M Thompson JA Levings CD 《Marine environmental research》2004,57(1-2):75-88
Gastropods and bivalves were collected at 15 sites at Vancouver and Victoria, Canada between 24 May and 7 June, 1999, to establish tissue concentrations of butyltin and phenyltin compounds, to record imposex symptoms in gastropods, and to assess the present status of organotin contamination around Vancouver. No neogastropods (such as Nucella lima) were found around Vancouver. Neogastropod populations could have been extirpated by severe TBT contamination in Vancouver, as relatively high concentrations of TBT were detected in tissues of Mytilus trossulus from Vancouver, and the neogastropods distributed in Vancouver might be sensitive to TBT. Recovery from imposex, however, was observed in neogastropod populations from three sites at Victoria and Mission Point. TBT contamination has continued around Vancouver, arising from continuous use of TBT in antifouling paints for vessels larger than 25 m in length; however, TBT has decreased around Victoria and Mission Point. Different patterns of TBT accumulation in tissue were observed among the bivalve species from Vancouver. The highest TBT concentration detected in Tresus capax suggested some possible adverse effects. TBT was the most predominant butyltin component in almost all bivalve specimens surveyed, suggesting a low rate of TBT metabolism. Phenyltin compounds were not detected in any molluscan specimens in this study. 相似文献
114.
115.
-Based on the feasibility study of developing the navigation resources of the Guanhe River and the model test results of the mouth bar regulation, this paper presents some basic principles for the regulation of the channel on the mouth bar, for instance, the direction of navigation channel should be identical with that of the ebb tide current and the main waves, and perpendicular to the bathymetric contours. The principles for regulating mouth bars are also discussed in this paper. 相似文献
116.
根据香港附近海区1985,1986年两次台风大浪的实测资料,以有效波高为相应水平,对波群作统计分析,得出可供海洋工程参考的波群连长、波群重复长度、波群出现频率以及波群中最大波高与有效波高的关系等。并将统计值与理论值作比较,结果表明:统计值大于“连”的理论值,而与包线理论中采用合田修正公式的汁算值相近。 相似文献
117.
热带气旋活动对中国夏季雨带类型与ENSO的响应关系 总被引:2,自引:0,他引:2
本文分析研究了热带气旋1)活动与中国夏季2)3组(包括8种)主要多雨带类型的响应关系。同时对热带气旋活动与夏季大陆气温和ENSO事件的始终时间的响应关系,也进行了探讨。分析表明,夏季中国的雨带分布特征对热带气旋活动有着十分重要的指示意义。热带气旋活动与中国大陆气温有着正相关关系,与ENSO事件的发生有着反相关关系 相似文献
118.
Discussion on Coastal Erosion Near Xizhuang, Penglai, China 总被引:1,自引:0,他引:1
Wu Guiqiu Li Wei Professor First Institute of Oceanography State Oceanic Administration Qingdao Associate Researcher 《中国海洋工程》1994,(2)
-In this work, on the basis of the characteristics of coastal erosion near Xizhuang (Penglai, Shandong, China) and the in-situ measured data and theoretical calculation, the causes of coastal erosion there are obtained: (1) natural erosion, (2) beach sand borrowing, and (3) sand borrowing at the Dengzhou shoal near Xizhuang, which results in the loss of the function of the wave force resistance of the shoal. Since the wave energy is increased, the longshore sediment transport rate is increased. Coastal erosions are more and more serious. A scientific basis to reduced the calamity of coastal erosion in local area is presented. Some experiences are accumulated for studying coastal erosion. 相似文献
119.
根据湄州湾表层沉积物70个样品18个化学成分的分析结果,得出:本海区沉积物属于海相陆源物,其中细颗粒主要来自台湾海峡,粗颗粒来自当地陆域;化学成分含量按聚类分析,可归为三组:粘土矿物组、碳酸盐组和分散组,微量元素Zn,Cr,Be,Cu和Sr的含量与地壳及台湾海峡相似,但低于胶州湾,说明该海区污染很少。 相似文献
120.