基于精简星座鉴相的大频偏16-APSK信号载波同步

为了增大对16-APSK信号的鉴相范围,提高环路捕获带宽,提出了在环路捕获阶段使用精简星座鉴相、在捕获完成后使用混合NDA/DD鉴相的载波同步结构。这种结构在实现了环路捕获带宽增加的同时,仍然保持了混合NDA/DD法实现简单、与符号判决单元无耦合、运算速度快的优点。仿真结果验证了使用精简星座鉴相后环路捕获带宽的增加。     

Dimension splitting algorithm for a three-dimensional elliptic equation

This paper presents a finite-element dimension splitting algorithm (DSA) for a three-dimensional (3D) elliptic equation in a cubic domain. The main idea of DSA is that a 3D elliptic equation can be transformed into a series of two-dimensional (2D) elliptic equations in the X–Y plane along the Z-direction. The convergence speed of the DSA for a 3D elliptic equation depends mainly on the mesh scale of the Z-direction. P ₂ finite-element discretization in the Z-direction for DSA is adopted to accelerate the convergence speed of DSA. The error estimates are given for DSA applying P ₁ or P ₂ finite-element discretization in the Z-direction. Finally, some numerical examples are presented. We apply the parallel solving technology to our numerical examples and obtain good parallel efficiency. These numerical experiments test and verify theoretical results.     

DCT- and DST-based splitting methods for Toeplitz systems

New splitting iterative methods for Toeplitz systems are proposed by means of recently developed matrix splittings based on discrete sine and cosine transforms due to Kailath and Olshevsky [Displacement structure approach to discrete-trigonometric transform-based preconditioners of G. Strang type and of T. Chan type, SIAM J. Matrix Anal. Appl. 26 (2005), pp. 706–734]. Theoretical analysis shows that new splitting iterative methods converge to the unique solution of a symmetric Toeplitz linear system. Moreover, an upper bound of the contraction factor of our new splitting iterations is derived. Numerical examples are reported to illustrate the effectiveness of new splitting iterative methods.     

系数矩阵含参数分裂形式的SOR迭代法收敛性分析

给出预条件方后线性方程组的系数矩阵的一类含参数的分裂形式,使系数矩阵的分裂更加一般化,同时讨论在该形式下的SOR迭代法的收敛性,并与一般的预条件方法进行比较分析,说明这种方法收敛性更好,最后找到参数的最优选取.     

Delay bound analysis and splitting strategies of concurrent transmission in heterogeneous networks

We focus our attention on how to get optimal performance of concurrent transmission in heterogeneous networks. An equivalent queuing model is used to analyze the end-to-end delay performance of perfect splitting strategy with the theoretical delay bound found. Furthermore, two splitting algorithms, Minimum Queuing Delay based splitting strategy (MQD) and Unified Queuing Management Based Splitting Strategy (UQM), are presented based on the joint resources scheduled in different RATs (Radio Access Technology). In the two-RAT scenario, the two-dimensional discrete-state continuous-time Markov process is used to analyze our schemes with close-formed solutions found. Simulation results demonstrate that our proposed flow splitting strategies utilize the system resources efficiently and outperform current strategies, getting close to the theoretical delay bound especially in the heavy load region.     

一种变步长星座匹配多模算法

常数模算法(CMA)在QAM信号上的星座图匹配,存在剩余误差大、无法纠正相位偏差等问题。为此,在研究盲均衡算法的基础上,根据高阶QAM 信号的星座图特点,构造新型的均衡估值函数,并采用误差能量作为步长变化的依据,提出一种变步长星座匹配多模算法。仿真实验结果表明,该算法具有较好的收敛效果,且能改善位偏转,保持CMA算法的鲁棒性。     

基于模糊聚类的高维划分策略研究

数据集的划分策略是影响高维数据库索引性能的一个关键因素。金字塔技术是一种较好的高维索引方法，但它只对均匀分布的数据集具有良好的性能。为此，提出了一种改进的基于模糊聚类的金字塔技术，并将其用于高维划分策略，先对数据集进行模糊聚类处理，然后针对每个聚类进行金字塔划分，从而较好地实现了对非均匀分布数据的高维划分。     

计算溃坝波问题的KFVS方法

浅水波方程与可压缩无黏气体方程类似,按照这两种方程的比拟关系,作者给出了用于计算浅水波方程的动力学流矢量分裂(KFVS)方法,并应用此方法计算了两个二维溃坝波问题。计算结果与已有文献结果基本一致,证明该方法有效、稳定,能够模拟浅水长波方程中的间断解问题。     

基于快速传输协议实现卫星TCP性能的改善

在经由卫星通信系统的网络应用中， TCP的性能较低。分段连接机制作为应用最广的一种性能优化方案，可以改善TCP端对端的性能，而在此机制中，卫星链路部分采用何种传输协议直接决定性能改善的效果。XTP协议是一种应用于有线网络的高速传输协议，但经过深入研究发现：XTP协议同样也非常适用于卫星通信系统。所以建议：在分段连接机制中，采用XTP协议作为卫星链路的传输协议。性能测试结果表明采用该建议非常显著地提高了端对端TCP的性能。