基于AD9911频率源的设计与实现

设计了一种由单片机PIC18LF4520控制DDS芯片AD9911的频率源电路。阐述了单片机控制DDS的软硬件实现方法,以及AD9911内部寄存器的配置要点。系统设计外围电路简单,可方便地实现对频率源电路输出频率、相位和工作模式的控制,输出信号频率范围为25~75 MHz。实验结果表明,该频率源具有输出频率精确、频率分辨率高和相位噪声低等特点,符合通信系统对频率源的设计要求。     

基于Modbus RTU协议的FX3U PLC与变频器的通信设计

本文在阐述Modbus通讯协议的基础上,构建了基于Modbus RTU通讯协议的变频调速控制系统。该系统采用三菱可编程控制器中的小型至尊产品FX3U-32MR作为主站,支持Modbus RTu通讯协议的三菱变频器FR-A740-3.7K-CHT为从站,通过FX3U-485-BD扩展板进行连接,基于Modbus RTU协议通讯规格编写PLC主站通信程序,实现PLC与变频器之间的通信控制。     

射频CO2激光器电源激励功率与频率关系的研究

以气体放电理论为基础,利用简化模型推导出射频激励CO2激光器气体放电击穿电压的数学关系式,指出影响激光气体放电击穿的几个物理参量。并通过实验测定了引起气体击穿时所需的注入功率与频率之间的关系。理论结果与相关试验测试结果符合一致。     

Improving PAPR performance of filtered OFDM for 5G communications using PTS

The filtered orthogonal frequency division multiplexing (F-OFDM) system has been recommended as a waveform candidate for fifth-generation (5G) communications. The suppression of out-of-band emission (OOBE) and asynchronous transmission are the distinctive features of the filtering-based waveform frameworks. Meanwhile, the high peak-to-average power ratio (PAPR) is still a challenge for the new waveform candidates. Partial transmit sequence (PTS) is an effective technique for mitigating the trend of high PAPR in multicarrier systems. In this study, the PTS technique is employed to reduce the high PAPR value of an F-OFDM system. Then, this system is compared with the OFDM system. In addition, the other related parameters such as frequency localization, bit error rate (BER), and computational complexity are evaluated and analyzed for both systems with and without PTS. The simulation results indicate that the F-OFDM based on PTS achieves higher levels of PAPR, BER, and OOBE performances compared with OFDM. Moreover, the BER performance of F-OFDM is uninfluenced by the use of the PTS technique.     

Approximation of the Posterior Distribution in a Change-Point Problem

We consider a family of models that arise in connection with sharp change in hazard rate corresponding to high initial hazard rate dropping to a more stable or slowly changing rate at an unknown change-point . Although the Bayes estimates are well behaved and are asymptotically efficient, it is difficult to compute them as the posterior distributions are generally very complicated. We obtain a simple first order asymptotic approximation to the posterior distribution of . The accuracy of the approximation is judged through simulation. The approximation performs quite well. Our method is also applied to analyze a real data set.     

Effective protein conformational sampling based on predicted torsion angles

Protein structure prediction is a long‐standing problem in molecular biology. Due to lack of an accurate energy function, it is often difficult to know whether the sampling algorithm or the energy function is the most important factor for failure of locating near‐native conformations of proteins. This article examines the size dependence of sampling effectiveness by using a perfect “energy function”: the root‐mean‐squared distance from the target native structure. Using protein targets up to 460 residues from critical assessment of structure prediction techniques (CASP11, 2014), we show that the accuracy of near native structures sampled is relatively independent of protein sizes but strongly depends on the errors of predicted torsion angles. Even with 40% out‐of‐range angle prediction, 2 Å or less near‐native conformation can be sampled. The result supports that the poor energy function is one of the bottlenecks of structure prediction and predicted torsion angles are useful for overcoming the bottleneck by restricting the sampling space in the absence of a perfect energy function. © 2015 Wiley Periodicals, Inc.     

移动卫星通信信道多普勒频移特性研究

在分析移动卫星通信信道特性的基础上，研究增加直射分量的多普勒实时频移和多径信号入射角范围及其变化对移动卫星通信信道多普勒频移特性的影响，推导了其不对称多普勒功率谱形式，对其进行了理论分析并给出了仿真结果。     

20GHz镜频抑制谐波混频器

镜频抑制混频器能有效地抑制镜像频率,提高雷达和通信系统的抗干扰能力。介绍了一个20 GHz二次谐波镜频抑制混频器的设计与制作,该镜频抑制混频器采用两个相同的二次谐波混频器做为两路混频单元,两路射频输入和中频输出分别用90°的功分器/合路器与两路混频器相连,本征用威尔金森功分器等幅同相输入两路混频。借助于90°的功分器,两路混频器的镜频产物在中频90°合路器的输出端口反相抵消,有用中频在90°合路器的输出端口同相叠加。利用ADS和HFSS对该混频器进行了仿真设计,并对实际电路进行了加工测试。经测试,当中频固定在400 MHz时,射频在20～21 GHz内变频损耗小于10 dB,镜频抑制大于20 dB。     

基于Multisim8的电压串联负反馈放大器仿真

采用Multisim8软件创建负反馈放大电路,利用其虚拟仪表和仿真分析了功能测试和仿真分析负反馈对放大电路的影响,通过对串联负反馈放大电路的理论研究和利用Multisim8仿真软件对电路实际工作情况进行模拟,根据二者结果的对比,研究并提出了串联负反馈放大电路的Multisim电路仿真研究的方法。Multisim8仿真分析中图像清晰、现象直观、结果精确,是一种有效的辅助实验手段。     

高斯噪声下跳频信号的提取与噪声抑制

本文提出了一种在高斯白噪声环境下提取跳频信号的算法,将广义S变换(GST)和短时傅立叶变换(STFT)相结合,引入形态学图像处理技术,分别对其时频谱图进行平滑和锐化,结果进行乘积合并后,设计一种针对跳频信号的时频滤波算子进一步抑制噪声,提升跳频信号,得到高分辨率稳健的时频图案。仿真实验证明该算法得到的时频图案信噪比有明显提高,时频分辨率也有很大改善。