Numerical calculation of channel dredging volume using 3D digital stratum model

Prediction of channel dredging volume is critical for project cost estimation. However, many proposed approximate methods are not accurate. This paper presents a novel numerical method to accurately calculate the dredg- ing volume using a 3D stratum model (DSM) and a channel surface model. First, the 3D DSM is constructed rapidly yet accurately from non-uniform rational B-splines (NURBS) surfaces through Boolean operation between a physical terrain model and a stratum surfaces model. Then, a parametric channel surface model is built from cross-section data and a channel center line using code implemented in the VC++ programming language. Finally, the volumes of different types of physical stratums can be calculated automatically and hierarchically to determine the dredging volume. Practical application shows that the DSM method is more precise and faster compared to the section method, and that the implementation of the developed software provides an interactive graphical user interface and visual presentation.     

WTO体制下的反倾销争端及我国的应对

在WTO多边贸易体制下，反倾销作为一种合法的贸易保护手段，已得到各国政府的普遍使用。随着中国加入WTO的日益临近，中国政府应对反倾销的形势也日趋严峻。国际社会反倾销立法与实践的演变，使我国应对反倾销工作更加困难。政府与企业对此应予高度重视。并积极采取措施，依法维护自身的利益，以促进国际贸易的正常发展。     

反倾销的历史演变与经济分析

反倾销是WTO框架下新贸易壁垒的主要形式之一。从WTO成立的1995年开始,中国一方面连续12年成为全球遭受反倾销指控最多的国家,另一方面运用反倾销保护国内幼稚产业又明显不足。为此,应当加强对反倾销的研究。文章对反倾销的历史演变作了粗线条的勾勒,并对反倾销的经济效应进行了分析,以期人们客观地认识反倾销的性质和作用,科学地应对这种新贸易壁垒形成的严峻挑战。     

OFDM系统改进的迭代联合信道估计与符号检测算法

在正交频分复用 (OFDM)无线通信系统中 ,系统的吞吐量和数据速率受到导频因素的制约 ,这种情况在高速移动环境下尤为明显 .本文提出了一种改进的迭代联合信道估计与符号检测算法 ,以提高系统的吞吐量和数据速率 .首先降低导频功率来提高系统的吞吐量 ,然后在一个OFDM符号内 ,通过迭代进行的信道估计与符号检测来提高系统的误码率 .每个OFDM符号的初始信道估计值取自上一个OFDM符号的信道估计 ,从而该算法能有效地跟踪衰落信道的变化 ,因此导频的数目可以大大降低 .仿真结果显示 ,与传统的迭代算法相比 ,本文提出的算法能提供更好的误码性能 .     

无线信道Jakes模型的一种改进方法

介绍和分析了传统的Jakes模型,提出了改进的Jakes模型,建立了改进的Jakes模型数学模型,并行对改进的Jakes模型进行了仿真。仿真结果表明改进的Jakes模型在计算复杂度和统计独立性方面比最初的Jakes模型更加有效。     

多天线广播系统中利用信道时间相关特性的用户选择算法

考虑无线信道的时间相关性,提出了2种多天线广播系统中降低复杂度的用户选择方案.根据信道相干时间和多普勒频率的关系,将发送信息序列划分为数据段.在每个数据段的开始时刻,利用贪婪用户选择算法做选择.在基于时间相关的用户选择算法SUSTC中,其余时隙仍然保持该段开始时刻的选择结果.而在改进的基于时间相关的用户选择算法ISUSTC中,在其余时刻,保留信道条件较好的一些用户仍被选中,然后在备选用户集合中更新其他用户.仿真结果表明,与贪婪用户选择方法相比,所提出的算法降低了用户选择复杂度而只需损失少许系统和容量.     

River morphology and river channel changes

River morphology has been a subject of great challenge to scientists and engineers who recognize that any effort with regard to river engineering must be based on a proper understanding of the morphological features involved and the responses to the imposed changes. In this paper, an overview of river morphology is presented from the geomorphic viewpoint. Included in the scope are the regime concept, river channel classification, thresholds in river morphology, and geomorphic analysis of river responses. Analytical approach to river morphology based on the physical principles for the hydraulics of flow and sediment transport processes is also presented. The application of analytical river morphology is demonstrated by an example. Modeling is the modern technique to determine both short-term and long-term river channel responses to any change in the environment. The physical foundation of fluvial process-response must be applied in formatting a mathematical model. A brief introduction of the mathematical model FLUVIAL-12 is described. CHANG Howard H, Professor Emeritus.     

一种新的OFDM系统信道盲估计的子空间算法

为提高OFDM系统的传输效率,提出了一种利用接收信号的二阶统计特性实现信道盲估计的子空间算法.首先将OFDM信号分成3部分,利用循环前缀(CP)引入的信息冗余,对OFDM系统的传输方程作矩阵变换,得到一个信道矩阵为Toeplitz矩阵的新方程.基于此方程推导出信道估计的子空间算法.Toeplitz矩阵结构使算法的推导和实际的计算大为简化.该算法不需要改变OFDM系统结构,不受信道零点位置的限制,在信道过估计的情况下也适用.实验结果验证了算法的有效性.     

Automatic generation method of geological cross-sections in dredging engineering based on 3D solid NURBS models

An automatic generation method of geological cross-sections in dredging engineering based on 3D geological solid models is presented.The 3D geological models are built applying the non-uniform rational B-splines(NURBS) technique,and a 2D profile can be calculated and generated automatically through Boolean operation to meet the demands of dredging projects.Moreover,an automatic marking method for geological attributes is put forward based on database technology,and the geological attributes include the profile name,scale,horizontal and vertical relative coordinates,geological lithology,and 2D standard lithology legend.At the same time,the automatic marking method can also provide an interactive mode for geological engineers to edit and modify the profile in the modeling system.Practical engineering applications show that the automatic generation method is a simple,flexible,fast and precise visual graphics rendering process that can create 2D standard profiles automatically and efficiently.This method also provides a convenient support tool for geological engineering digital analysis.     

试论陆水下游河段治理开发

论证了陆水河下游河段治理开发的必要性和可行性,提出了治理开发的基本构想.     

A simple channel estimator for space-time coded OFDM systems in rapid fading channels

A simple channel estimator for space-time coded orthogonal frequency division multiplexing (OFDM) systems in rapid fading channels is proposed. The channels at the training bauds are estimated using the EM (expectation-maximization) algorithm, while the channels at the data bauds are estimated based on the method for modelling the time-varying channel as the linear combination of several time-invariant "Doppler channels". Computer simulations showed that this estimator outperforms the decision-directed tracking in rapid fading channels and that the performance of this method can be improved by iteration.     

Particle filter for joint frequency offset and channel estimation in MIMO-OFDM systems

A particle filter is proposed to perform joint estimation of the carrier frequency offset (CFO) and the channel in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) wireless communication systems. It marginalizes out the channel parameters from the sampling space in sequential importance sampling (SIS), and propagates them with the Kalman filter. Then the importance weights of the CFO particles are evaluated according to the imaginary part of the error between measurement and estimation. The varieties of particles are maintained by sequential importance resampling (SIR). Simulation results demonstrate this algorithm can estimate the CFO and the channel parameters with high accuracy. At the same time, some robustness is kept when the channel model has small variations.     

基于导频和变换域的SISO/MIMO OFDM系统自适应信道估计

根据导频信号在变换域中的频响特性,将系统的变换域滤波器设计成具有更好滤波效果的"带阻滤波器";在小信噪比和大信噪比条件下,分析了变换域能量参数对系统信道估计性能的影响,推导了新的能量参数表达式,理论证明了根据接收端检测到的信噪比自适应选择能量参数可以显著改善信道估计的性能.仿真结果表明,提出的信道估计算法具有较好的性能,在一定程度上可以接近于理想信道估计的性能,适用于SISO OFDM系统和MIMO OFDM系统.     

Lagrangian time scales and its relationship to Eulerian equivalents in turbulent channel flow

Lagrangian and Eulerian time scales were obtained from the direct numerical simulation of turbulent channel flow at two Reynolds numbers based on the friction velocity and channel half-height, Rer= 80, 100. The Lagrangian integral time scales and time microscales were compared to their Eulerian equivalents. It is found that the ratio of Lagrangian to TL Eulerian integral time scales is given by TE/TiE= 1 ＋ 0.1y＋ for y＋ ≤ 10, and that the ratios between the Lagrangian to theEulerian time microscales are almost the same irrespective of the components. Those increase with y＋ are approximated by ≈ 2.75 - 1.75 exp （-v＋/a） . These results also show that these expressions are independent of the Reynolds number.     

直扩多用户超宽带系统在室内衰落信道下的BER表达式

基于室内多径衰落信道统计模型,分析并仿真了直扩二相相移键控多用户超宽带无线通信系统的比特误码率性能.通过理论分析,推导出了系统比特误码率性能的解析表达式,该表达式表示为脉冲宽度、脉冲重复周期、用户数以及脉冲波形等信道参数和系统参数的函数,从而可以方便、统一地分析这些参数对系统性能的影响.仿真结果与基于理论分析的数值计算结果相当吻合,表明直扩二相相移键控超宽带系统的多址干扰为正态分布.     

MIMO无线信道容量比较与分析

介绍了无线MIMO系统信道容量的计算方法,重点分析和比较了在瑞利衰落信道下,发射端已知或未知,但接收端完全未知的信道状态信息时的独立同分布的多入多出各态历经容量特性。并利用Matlab对其进行仿真。结果表明,在低信噪比时,采用自适应功率分配得到的信道容量特性要优于采用平均功率分配。并且信道容量随收、发天线数目的最小值呈线性增长。     

一种快衰落信道中OFDM系统的Kalman信道估计方法

针对频率选择性快衰落信道的多径干扰和较大的多普勒频率扩展,提出了一种基于导频的低维Kalman滤波算法用于正交频分复用(OFDM)系统信道估计.为了简化计算,采用一阶自回归(AR)过程对时变信道进行建模.利用复杂度大大降低的一维Kalman滤波算法进行单个子载波的并行信道估计,并采用基于导频的最小平方(LS)算法估计时变的信道衰减因子a.为了同时跟踪信道的频域相关性,采用了最小均方误差(MMSE)线性合并器对Kalman信道估计结果进行修正.在5.5 GHz频段上的仿真表明了这种基于导频的低维Kalman信道估计方法,降低了传统的Kalman滤波结构的复杂度,能够跟踪信道的时频变化,并且在一定程度上可以接近于理想信道估计的误码率性能.     

Saturation throughput analysis of RTS/CTS scheme in an error-prone WLAN channel

In this paper, a new three-dimensional Markov model is proposed for the estimation of saturation throughput of RTS/CTS （request to send/clear to send） scheme in an error-prone wireless local area network （WLAN） channel. The model takes account of the effect of bit error on all the frames, and station short and long retry limits. Saturation throughput was re-analyzed using the new Markov model and numerical results closely matched those from simulation, confirming the accuracy of the new model. Evaluation of the influence of different parameters on throughput showed that the saturation throughput is sensitive to channel bit error rates and packet length, especially in high bit error conditions.     

移动通信越区优先动态信道保留及排队算法研究

本提出了移动通信越区优先动态信道保留及排队算法(DCA-GC-QH)并加以深入研究，通过建立M／M／M／T马尔可夫链模型，以及通话阻塞率和越区通话中断率的动态建模，从而进一步优化信道分配。与固定信道策略相比，动态信道保留及排队策略的通话阻塞率和越区掉话率分别下降了约20％和30％。理论分析和仿真结果相符合。