调制和编码对超宽带接收机性能改善的比较

1 INTRODUCTION Ultra- wideband (UWB) technology can achieve 100Mbps high- speed wireless communications by use of GHz bandwidth short pulses. Because it has some merits such as very low radio power, difficult to be detected, good penetration and centimeter level location ability, it can be used in secret communications, target detection, personnel search and so on military applications. Since the large bandwidth of UWB signal cause the channel to be extreme frequency selectivity, a con…     

接收分集OFDM系统的信道估计研究

研究了天线分集OFDM系统的高速无线数据传输特点,通过计算信道冲击响应与参考信号的相关函数,提出了一种增强型的信道估计方法。理论分析与计算机仿真表明,该方法能够有效地降低加性噪声对信道估计的影响,提高信道估计精度。在采用QPSK调制的一发四收的接收分集OFDM系统中,该增强型的信道估计方法的性能明显好于最小二乘信道估计和基于DFT的信道估计。     

一种基于Kalman滤波的盲多用户检测RAKE接收机

提出了一种基于Kalman滤波的盲多用户检测RAKE接收机(RakeKAL)模型。给出的接收机具有RAKE接收机的结构，它的每条支路可视为一个利用线性限制最小方差(LCMV)准则设计的多用户线性滤波器，用于抑制多址干扰(MAI)；后接一个用于消除多径畸变(MPD)的多径结合器。利用Kalman滤波算法和自适应向量跟踪算法实现盲多用户检测和多径接收信号的最佳结合。该模型与传统多用户检测器比较具有所需参数少，不需要训练序列的优点。研究结果表明，在多径衰落信道下，接收机具有较强的抑制多址干扰和多径畸变的能力，并且能快速收敛。     

光纤连接在高压变频器中的应用研究

为解决单元串联多电平高压变频器中主控系统与功率单元之间存在的强弱电隔离及功率单元与功率单元之间的电磁干扰问题,提出了采用光纤连接方法实现功率驱动PWM信号的远距离传送。设计了由HFBR-1524发送器和HFBR-2524接收器组成的光纤连接电路。实验结果表明,该方法能够实现PWM信号的精确传送。该电路已经在高压变频器的开发中得到应用。     

一款盲用邮件接收器的设计与实现

盲用邮件接收器是帮助视力障碍者阅读邮件而设计的。盲人借助语音导航,通过上下左右键就能阅读邮箱中的邮件内容。该文主要介绍了运用pop3协议对邮件进行接收,形成相应邮件树型列表,并调用文本朗读(tts)进行语音导航和邮件阅读的实现步骤。     

Thermal analysis and design of a volumetric solar absorber depending on the porosity

The thermal evaluation of different absorber configurations for a volumetric solar receiver designed for a solar furnace has been carried out by means of commercial Computational Fluid Dynamics (CFD) software in a 2D numerical model. Simulation results for proposed configurations depending on the porosity are discussed and compared to find the optimum configuration for which flow instabilities and thermal stresses are minimized and higher efficiencies are reached. The results obtained from the comparison of air velocity and thermal profiles at the absorber outlet propose a gradual-porosity configuration as an alternative to a previous design of a porous silicon-carbide honeycomb structure in order to heat an air stream up to temperatures suited for several high-temperature industrial processes.     

Mantle dynamics of the reactivating North China Craton:Constraints from the topographies of the 410-km and 660-km discontinuities

The topographies of the 410-km and 660-km discontinuities have important implications for mantle dynamics.Here we present high-resolution seismic imaging of the 410-km and 660-km discontinuities beneath the North China Craton (NCC) employing the receiver function method.Depth anomalies (deeper or shallower than the global average depths) at both discontinuities were detected by introducing a three-dimensional regional velocity model.The depressions of the 410-km discontinuity are mostly located in the easte...     

A unified heat transfer model in a pressurized volumetric solar receivers

In the present work, we developed an overall mathematical model adequately describing the main heat transfer processes in a pressurized volumetric receiver. The key components, a windowed cavity, incorporating with the irradiated surface of the absorber, were theoretically modeled as a closed diffuse-gray surfaces system. Accordingly, a boundary condition for the absorber concerning its porous structure surface was developed using net radiation method (NRM) under local thermal non-equilibrium (LTNE) condition. The same method is also applied to the back cavity. Then a modified P1 approximation with collimated irradiation was introduced to incorporate the radiation transfer penetrating in the absorber. The major characteristic of the heat transfer behavior combining radiation, thermal conduction, and convection in the windowed cavity, absorber and the back cavity, are detailedly presented. Also, the key design parameters, such as those relating to pore structure (φ and d_p), the volumetric heat transfer coefficient h_v, the emissivity ε for window and absorber, and their thickness L_a and L_g were systematically analyzed. Optimization design can be carried out for both of the solar thermal system and the receiver itself in the future work based on our model.     

DAM自动测试系统的研制

数字阵列雷达是近几年发展迅速的一种新型相控阵雷达,其中,数字阵列模块是数字阵列雷达的关键核心部件之一。针对数字阵列模块的大批量生产以及测试难点,需要专门研究数字阵列模块自动测试技术。详细介绍了 DAM 自动测试系统的功能组成、系统硬件及测试软件设计,尤其是 DAM 通道数字化接收性能指标的数据分析处理方法。目前系统已经成功应用,具有测试效率高、测量结果准确、操作简易等特点,有效地解决了 DAM 批量生产测试需求,具有较大的社会效益和经济效益。     

GNSS信号接收机的构件初识──GNSS导航信号的收发问题之十

GNSS信号接收机是GNSS导航卫星的用户设备,是实现GNSS卫星导航定位的终端仪器。它是一种能够接收、跟踪、变换和测量GNSS卫星导航定位信号的无线电接收设备,既具有常用无线电接收设备的共性,又具有捕获、跟踪和处理弱达3.5E-16W~2.5E-17W卫星微弱信号的特性。为此,GNSS信号接收机的构件必须满足这种捕获、跟踪和测量GNSS信号的需求。