A new control scheme for single-phase PWM multilevel rectifier withpower-factor correction

A new control scheme for a single-phase bridge rectifier with three-level pulsewidth modulation is proposed to achieve high power factor and low current distortion. The main circuit consists of a diode-bridge rectifier, a boost inductor, two AC power switches, and two capacitors. According to the proposed control scheme based on a voltage comparator and hysteresis current control technique, the output capacitor voltages are balanced and the line current will follow the supply current command. The supply current command is derived from a DC-link voltage regulator and an output power estimator. The major advantage of using a three-level rectifier is that the blocking voltage of each AC power device is clamping to half of the DC-link voltage and the generated harmonics of the three-level rectifier are less than those of the conventional two-level rectifier. There are five voltage levels (0, ±V_DC/2, ±V_DC) on the AC side of the diode rectifier. The high power factor and low harmonic currents at the input of the rectifier are verified by software simulations and experimental tests     

A novel instantaneous power control strategy and analytic model forintegrated rectifier/inverter systems

This paper is concerned with the design and implementation of an integrated pulse width modulation (PWM) rectifier/inverter for three-phase induction motor drives. Two identical PWM converters are used to serve as power regulator with unity power factor and servo motor drive using field-oriented control, respectively. A new input-output instantaneous power balancing approach is proposed to improve the dynamic response of input power regulation during output load change in order to minimize the DC-link capacitance. By using the synchronous rotating-frame current regulators, both the input and output currents of the integrated system are characterized with fast current response and low harmonic distortion. The effects of the dynamic response using different input power control methods are compared and the systematic design and analysis of the proposed method are also presented. Theoretical results of the analysis are verified experimentally     

Harmonics optimization of the voltage balancing control for multilevel converter/inverter systems

This paper presents a novel control method to lower the harmonic components of the conventional voltage balancing control for the multilevel converters. The harmonic components in the voltage balancing control theory are analyzed in detail. A revised control method based on the line-line voltage redundancy of the three-phase inverter is proposed to lower the harmonic components of both the converter and inverter side. The proposed method can significantly reduce the harmonic components while keeping the switching frequency nearly the same. Simulation and experimental results are provided to show the validity of the theory.     

A NOVEL CONCURRENT ERROR DETECTION/ CORRECTION SCHEME FOR FFT

By converting DFT of a data sequence into two partial transforms, a novel concurrent error detection/correction scheme for FFT networks is proposed based on coding theory. The scheme is realized in the computing procedure of FFT, which is different from the methods available, and has more error detection/correction capability than that of the known methods.     

超长距离分布式光相位传感系统定位的一种新方法

针对超长距离分布式光相位传感系统对于被探测物理量的定位问题,提出一种双Mach-Zehnder(MZ)结构和相关算法相结合的信号定位新方法.研究结果表明,该定位方案可以成功地在长距离(50 km)的范围内对信号定位.传感系统埋设于地下0.5 m处时,可以得到最小定位相对误差为0.19%.     

一种有效的基于内容的图像检索方法

本文针对基于内容的图像检索中特征和相似度问题，提出新的距离模式，并以彩色空间中扩展共发矩阵作为纹理描述，在测试系统iPhoto上，数据库为56600幅图像时，实验结果显示，本文方法优于传统方法。     

A novel call admission control scheme in cellular/WLAN integration and performance analysis

In order to achieve the Quality of Service (QoS) provisioning and efficient resource utilization in cellular network and Wireless Local Area Network (WLAN) integration, an Integrated Service-Based Call Admission Control (ISB-CAC) scheme is proposed in this paper. The integrated network is modeled by using multi-dimensional Markov chains. The numerical analysis is presented to evaluate the important performance measures such as the blocking probability of originating calls, the dropping probability, and the average transfer time, etc. The steady-state probabilities of the multi-dimensional Markov chains are obtained by using an iterative approach, and the CAC parameters are optimally designed. The analytical model is validated by the computer simulation. It is shown that compared with the conventional WLAN-First Call Admission Control (WF-CAC) scheme, the proposed ISB-CAC scheme not only provides better QoS for mobile users but also utilizes the bandwidth resources more efficiently.     

A novel watermarking scheme for H.264/AVC video authentication

As the H.264/AVC-based video products become more and more popular, issues of copyright protection and authentication that are appropriate for this standard will be very important. In this paper, a content-based authentication watermarking scheme for H.264/AVC video is proposed. Considering the new feature of H.264/AVC, the content-based authentication code for spatial tampering is firstly generated using the reliable features extracted from video frame blocks. The authentication code, which can detect malicious manipulations but allow recompression, is embedded into the DCT coefficients in diagonal positions using a novel modulation method. Spatial tampering can be located by comparing the extracted and the original feature-based watermarks. In addition, combining ECC and interleaving coding, the frame index of each video frame is used as watermark information and embedded in the residual coefficients. Temporal tampering can be detected by the mismatch between the extracted and the observed frame index. Experimental results show that the proposed scheme can discriminate the malicious tampering from the mild signal processing. The tampered location can also be approximately determined according to the glide window and the predefined threshold.     

一种基于通信时延的统一潮流控制器阻尼控制优化设计新方法

本文提出了一种以权衡时滞稳定裕度和阻尼比为目标对统一潮流控制器阻尼控制设计进行优化的技术。为解决传统设计方法中UPFC辅助阻尼控制器在通信信号传输存在时延时对区间低频振荡抑制能力不足的问题,在经典UPFC阻尼控制模型为初始模型的基础上,综合考虑广域测量系统中通信时延的时变和随机特征建立了UPFC阻尼控制时滞模型,根据Lyapunov-Krasovskii稳定性定理,得到具有极低保守性的电力系统时滞相关稳定条件,揭示了阻尼控制器参数、时滞稳定裕度、阻尼性能指标相互影响的规律,并据此实现对传统阻尼控制器的优化设计。通过仿真发现:使用该方法得到的UPFC阻尼控制器既有较好的区间低频振荡抑制能力,又能容忍一定通信时延,克服了传统阻尼控制器难以适应较长通信时延的不足。     

一种在视频图像上叠加显示时间信息的实现方案

阐述了采用TI TMS320VC5402 DSP和专用字符发生器STV5730A芯片所组成的系统及在数字视频监控图像上叠加显示时间信息的原理，说明了系统的硬件组成和软件实现方法。     

A dynamic control scheme for the IEEE 802.14 draft MAC protocolover CATV/HFC networks

We first describe the draft multiple/random access protocol for IEEE 802.14 over the cable TV/hybrid fiber coaxial (CATV/HFC) networks. To best fit this draft protocol into the target network, we propose a dynamic control scheme to adequately adjust the parameters. Simulations of the draft protocol are then presented to depict the effectiveness of the proposed scheme and further highlight the directions for the design of MAC protocols over the CATV/HFC networks     

A modulation scheme for 100 Gb/s modified minimum-shift keying format based on imbalanced bias in IQ components

We propose a modified minimum-shift keying (MSK) modulation scheme by applying the imbalanced bias on the in-phase and quadrature components of a MZM-based MSK modulator. This scheme enables constant envelope and continuous temporal phase shift of 100 Gb/s optical MSK signal by driving the MZMs with traditional sinusoidal signal instead of triangle signal. The principle of generating the optical MSK signal by this imbalanced scheme is presented. Theoretical analysis is given to modulated spectra, BER performance, residual dispersion tolerance and SPM tolerance. It is demonstrated that compared to the existing solutions the proposed scheme is able to decrease 2 dB receiver power penalty and improve SPM tolerance by 2 dB.     

A novel selective encryption scheme for H.264/AVC video with improved visual security

As cloud storage becomes more popular, concerns about data leakage have been increasing. Encryption techniques can be used to protect privacy of videos stored in the cloud. However, the recently proposed sketch attack for encrypted H.264/AVC video, which is based on the macroblock bitstream size (MBS), can generate the outline images of both intra-frames and inter-frames from a video encrypted by most existing encryption schemes; thus, the protection of the original video may be considered a failure. In this paper, a novel selective encryption scheme for H.264/AVC video with improved visual security is presented. Two different scrambling strategies that do not destroy the format compatibility are proposed to change the relative positions between macroblocks in intra-frames and inter-frames respectively, which in turn substantially distort the sketched outline images so that they do not disclose meaningful information. Moreover, the sign bits of non-zero DCT coefficients are encrypted to contribute to the visual security of our scheme, and an adaptive encryption key related to the intra prediction mode and the DCT coefficient distribution of each frame is employed to provide further security. The experimental results show that our encryption scheme can achieve a better visual scrambling effect with a small adverse impact on the video file size. Furthermore, the security analysis demonstrates that our scheme can successfully resist the MBS sketch attack compared with other related schemes. The proposed method is also proven secure against some other known attacks.     

一种考虑端口引线趋肤效应的GaAs PHEMT器件小信号模型

为了精确地表征高频GaAs赝配高电子迁移率晶体管(PHEMT)的器件特性,提出了一种考虑端口引线趋肤效应的GaAs PHEMT器件小信号模型。采用传输线理论,建立GaAs PHEMT的源-漏电压为0 V情况下沟道的T型等效网络。以量化沟道电阻为中间项,推导出含有趋肤效应模型的拓扑结构并提出参数解析提取方法。结合趋肤效应的高频响应特征,从频率高于40 GHz的测试S参数中剥离10 GHz以下的非本征参数,然后从剥离之后的网络参数中提取趋肤效应模型参数值。采用总栅宽为4×25μm GaAs PHEMT管芯用于模型和模型参数提取方法的验证。结果显示在2~110 GHz下,该模型的仿真结果与测试结果吻合较好。     

一种相干分布源中心DOA快速跟踪算法

在智能天线和无线定位等技术中,精确跟踪目标的波达方向(DOA)十分重要。大多数传统的DOA跟踪方法都将目标信号看成是点源。但在密集的移动通讯环境中,信号的多径散射将引起信号能量的扩散,采用分布式信源模型更适合。因此,研究分布源的DOA跟踪技术更有意义和价值。针对相干分布源,本文基于均匀线阵提出了一种中心DOA快速跟踪算法。该算法首先通过正交紧缩近似投影子空间跟踪(OPASTD)算法实时更新信号子空间,然后利用一种低复杂度的方法估计分布源的中心DOA。本文算法避免了对样本协方差矩阵进行重复的特征分解,计算复杂度较低。算法的跟踪性能良好,并能有效跟踪多个分布源。此外,算法不需要分布源角分布形式的先验知识,稳健性好。仿真结果证实了算法的有效性。      

一种修正的线性调频信号参数估计算法

研究了加性噪声中线性调频信号的参数估计问题。基于相位解卷和多项式拟合,考虑到初始相位可能出现模糊,提出了一种修正的线性调频信号参数的联合估计算法。仿真实验证实了所提出的修正算法的有效性。     

A small signal coupling model for predicting the coupling between LNAs

A small signal coupling model is developed to analyze the coupling between two LNAs. The mutual inductance between the adjacent on-chip inductors is considered responsible for this coupling. A set of formulas have been derived to quantitatively predict the coupling effects. Based on our analysis, a quick estimation can be made to see which pair of inductors plays a key role in evaluating the coupling between the LNAs. Source inductors of two LNAs are placed closely while the load inductors are far apart according to the analysis. To validate the proposed theory, two 2 GHz LNAs are fabricated. The LNAs have a peak gain of 18 dB and NF of 1.4 dB. The coupling between the LNAs is -30 dB.     

一种提高雷达系统输出信噪比的方法

在给定雷达的检测概率和虚警概率后,系统输出信噪比直接影响雷达的作用距离。采用距离分段加权技术,可以减小加权引起的信噪比损失,从而提高了雷达的作用距离。给出了泰勒窗函数在距离分段加权中的应用,事实已证明该方法的可行性。     

一种基于TCP／IP远程通信协议的新型远程智能电源监控切换系统

为了更好地保障铁路运输的安全和效率,确保采用双路供电的铁路系统的不间断工作,提出了一种基于TCP／IP远程通信协议的智能电源切换系统。系统由电源屏双路输入远程切换单元、控制中心的TCP／IP通信链路、用户软件控制系统组成。电源屏双路输入远程切换单元由电源信号监控、切换单元组成。TCP／IP通信链路采用嵌入式操作平台,功能包括TCP／IP链路控制;用户软件控制系统采用C＋＋编写完成,包括界面操作,授权控制等功能,能满足站点现场电源切换要求的功能。     

A New OFDM System Based on Lifting Wavelet Transform for Wireless Channel

1 Introduction The high-bit-rate and large capacity transmission be-comes more and more i mportant in future generationmobile communication systems . OFDMis an efficienttechnology for wireless datatransmission[1].It has beenadoptedinseveral wireless standards such as Digital Au-dio Broadcasting (DAB)[2], Digital Video Broadcasting(DVB-T) ,andis a potential candidatefor fourth-gener-ation (4G) mobile wireless communication systems .The advantages of OFDM[3 ~4]include robustness a-gains…