大频偏卫星扩频信号的基带处理算法的FPGA实现

多普勒频偏一直是卫星通信中不可忽视的消极因素。针对多路混叠的卫星扩频信号下变频以后所产生的大多普勒频偏,在匹配滤波结构中采取改进的部分相关算法,在基于并行导频的信道估计中根据信道状况改变估计长度,实现了大频偏下卫星扩频信号的基带处理。     

The effects of substrate bias,substrate temperature,and pulse frequency on the microstructures of chromium nitride coatings deposited by pulsed direct current reactive magnetron sputtering

Recently, great attention has been devoted to the pulsed direct current (DC) reactive magnetron sputtering technique, due to its ability to reduce arcing and target poisoning, and its capability of producing insulating thin films. In this study, chromium nitride (CrN) coatings were deposited by the bipolar symmetric pulsed DC magnetron reactive sputtering process at different pulse frequency, substrate bias voltage, and the substrate temperature. It was observed that the texture of CrN changed from (111) to (200) as substrate temperature increased to 300°C as deposited at 2 kHz without substrate bias. With increasing pulsing bias and pulse frequency of target, predominated (200) orientation of CrN film was shown due to the ion bombardment/channeling effect to preferentially sputter those unaligned planes. For the CrN coatings deposited with pulsed biasing, the grain size decreased with increasing pulse frequency and substrate bias, whereas the surface roughness showed a reverse trend. The deposition rate of the CrN films decreased with increasing pulse frequency. It was concluded that the pulse frequency, substrate bias, and substrate temperature played important role in the texture, microstructure, and surface roughness of the CrN coatings deposited by the pulsed DC magnetron sputtering process.     

天线与合路器的关系

主要探讨了在CDMA网络设计时,如何考虑空闲状态时终端的守候方式、终端业务请求时网络资源的分配方式以及跨载频硬切换的解决方案这3个方面的问题.     

一种最大长度序列四相码信号脉压性能的研究

介绍了四相编码信号产生及数字脉压实现的方法，分析了采样起始时刻和多普勒频率对脉压结果的影响，比较了两个信号部分叠加时线性脉压和硬限幅脉压的结果。     

A NOVEL INTEGER FREQUENCY OFFSET ESTIMATOR FOR OFDM

One of the principal disadvantages of Orthogonal Frequency Division Multiplexing （OFDM） is very sensitive to carrier frequency offset. The integer frequency offset has no effect on the orthogonality among the subcarriers, but it causes a circular shift and phase rotation of the received data symbols sequence, resulting in a Bit Error Rate（BER） of 0.5. In this paper, a novel integer frequency offset estimator for OFDM is derived based on maximum likelihood estimation technique and exploration of the differential relation between two consecutive OFDM data symbol sequences in frequency domain. Its performance is compared with the conventional method by computer simulations for the additive white Gaussian noise channel and a multipath fading channel. Simulation results show that the performance of the proposed estimator is better than the conventional estimator.     

基于激光信息和射频识别的运动轨迹跟踪研究

为提高运动轨迹跟踪精度,设计了基于激光信息和射频识别的运动轨迹跟踪方法,首先将射频识别阅读器与激光传感器采集数据进行速度估算处理,并利用加权因子对激光传感器估算速度进行平滑处理,然后通过相似度对比方法匹配激光传感器与射频识别阅读器获取的运动目标速度,采用粒子滤波算法融合激光传感器与射频传感器获取的运动目标速度,通过粒子滤波的预测、更新与重采样三个阶段实现准确的运动目标轨迹跟踪,最后实验结果表明,该方法对目标的运动轨迹跟踪精确度高达99%。     

2.5MW转子侧变频调速节能系统的应用研究

为了解决风机、泵类的电机耗能过多的问题,提出了一种高压转子侧变频调速的节能方法．对高压转子侧变频调速系统的主回路拓扑结构进行了研究,报告了转子侧变频调速技术的国内外研究现状,阐述了通过改变绝缘栅极双极型晶体管（Insu Iated Gate Bjpo Iar Transistor．IGBT）占空比的方法,实现转子侧的变频调速,分析了主回路主要参数的计算公式．通过举例实际数据,验证了高压转子侧变频调速节能系统的良好性能,并且此系统有效地解决了能源浪费,转子侧变频调速造价昂贵、装置体积庞大等问题。     

采用线性正则域模糊函数的QFM信号参数估计算法输出信噪比分析

采用线性正则域模糊函数的二次调频 (quadratic frequency modulated,QFM) 信号参数估计算法简单易解,估计精度较高,误差传递小,在实际应用中有较好的前景。本文对该算法的输出信噪比进行了较为深入而详细的分析,推导了输出信噪比与输入信噪比及信号采样点数之间的关系表达式;通过仿真实验比较了在同等条件下本算法和积分广义模糊函数算法(integrated generalized ambiguity function, IGAF))以及多项式相位变换(polynomial-phase transform, PPT)算法的输出信噪比大小,以及达到相同大小输出信噪比所需采样点数。发现本算法的输出信噪比要大于IGAF算法和PPT算法,且达到相同大小的输出信噪比所需采样点数分别是IGAF算法和PPT算法的1/4和1/9,即得到相同大小的输出信噪比时本算法所需的采样点数更少.      

调速传动用四象限级联中压变频器(上)

由于性能优良,H桥级联变频器在中压调速传动中得到最广泛应用。通常这类变频器H桥中的交-直变换都采用二极管整流,使之不能四象限工作。把二极管整流改为PWM整流(AFE),变频器就可以四象限工作,但需在整流输入端增加电感和电容,控制也复杂。本文建议改用I GBT整流/回馈单元,器件按同步开关模式工作,使变频器成为具有与常规H桥级联变频器同样性能的四象限变频器,且不必像AFE那样增加电感和电容,控制也特别简单。矩阵变换器MC是一类性能优良的PWM交-交直接变频器。通过三相/单相MC桥的级联可以实现四象限中压变频。文中介绍了安川公司的MC桥级联中压变频器,并把它和基于整流/回馈单元的H桥级联中压变频器进行比较。