一种新型矩阵式高频链逆变器控制方法

基于拓扑解耦思想提出了一种针对矩阵式高频链逆变器的新型控制策略。根据高频逆变桥生成的高频环的极性,将矩阵变换器的拓扑解耦成两个常规的三相电压源型逆变器,从而就可将常规电压源逆变器的控制方法引入到对矩阵变换器控制当中,简化了对矩阵变换器的分析。进行了实验研究,结果表明该控制方法具有较好的控制效果。     

一种基于长码扩频技术的无人机遥控链路实现

为了满足无人机遥控链路远距离、高动态、强抗干扰能力的军事通信需求,设计了基于长码直接序列扩频技术的FPGA实现方案.该方案采用了一种基于FFT算法的快速伪码捕获方法,将传统的伪码相位与多普勒频移二维搜索过程简化为两者同时捕获的一维搜索过程.经过硬件实现与测试,该方案可有效减少硬件资源消耗,同时缩短捕获时间.     

An energy‐efficient link quality monitoring scheme for wireless networks

Link quality is one of the most important factors that affect the performance of wireless networks. In a densely deployed wireless network, continuous link quality monitoring consumes significant amount of energy and bandwidth at each node. In this paper, we propose a sensitivity model and a spatial correlation model that can be used to derive a set of deputy links to monitor, instead of monitoring all of the links in the network. The proposed scheme can improve energy efficiency of the link quality monitoring process. A greedy algorithm is presented to derive the deputy links set based on three different optimization objective functions. Performance of the proposed method is studied extensively and it is shown that the proposed method can save almost 90% energy in typical simulation scenarios than the method of monitoring all links. We also demonstrate that the energy consumption of the greedy deputy set‐based method is upper‐bounded. Copyright © 2010 John Wiley & Sons, Ltd.     

On the quality of VoIP with DCCP for satellite communications

We present experimental results for the performance of selected voice codecs using Datagram Congestion Control Protocol (DCCP) with CCID4 congestion control over a satellite link. We evaluate the performance of both constant and variable data rate speech codecs for a number of simultaneous calls using the ITU E‐model. We analyse the sources of packet losses and additionally analyse the effect of jitter, which is one of the crucial parameters contributing to Voice over IP (VoIP) quality and has, to the best of our knowledge, not been considered previously in the published DCCP performance results. We propose modifications to the CCID4 algorithm and demonstrate how these improve the VoIP performance, without the need for additional link information other than what is already monitored by CCID4. We also demonstrate the fairness of the proposed modifications to other flows. Although the recently adopted changes to TCP‐Friendly Rate Control specification alleviate some of the performance issues for VoIP on satellite links, we argue that the characteristics of commercial satellite links necessitate consideration of further improvements. We identify the additional benefit of DCCP when used in VoIP admission control mechanisms and draw conclusions about the advantages and disadvantages of the proposed DCCP/CCID4 congestion control mechanism for use with VoIP applications. Copyright © 2012 John Wiley & Sons, Ltd.     

TD-LTE室内分布系统规划与组网方案

本文系统分析了频率应用和规划策略、单双路分布系统建设策略、分布系统共用策略、与其他系统干扰规避等TD-LTE室内覆盖组网方案所涉及的核心技术问题,随后基于组网方案研究阐述了TD-LTE室内分布系统的规划方法及规划原则,最后提出了现阶段TD-LTE室内分布系统建设策略.     

高误码率星地链路上DWT类压缩图像的传输策略

星上图像压缩的方法越来越广泛地被数据量巨大的卫星型号所采用,而DWT类图像压缩方法以其更高的压缩比、独特的码流结构及良好的抗误码性能成为星上图像压缩的主要方法。针对高误码率星地链路上DWT类压缩图像的误码扩散问题,提出了一种截断压缩码流并对保留码流加强信道编码保护的策略。分析和仿真结果表明,该策略重建图像的效果相比现有的传输模式有大幅提高,甚至能够优于直接下传模式。     

基于DSP组合式变频器的设计

介绍了基于DSP的三相航空变频电源的设计原理和方法。采用电压型PWM整流器、高频链逆变器和周波变流器级联组合,使整机开关最大程度地实现了软开关,可靠解决了周波变流器的换流问题。实验结果表明,该变换器设计合理,具有较高的功率因数和可靠性。     

高强钢组合K形偏心支撑框架抗震性能对比分析

为研究不同强度组合的高强钢组合K形偏心支撑框架结构的抗震性能,设计了一组不同强度(Q345、Q460、Q690钢材)组合的5层K形偏心支撑框架结构算例Q345-5、Q460-5和算例Q690-5,选取10条地震动记录对其进行动力时程分析,得到各算例在不同水准地震作用下的耗能梁段转角和层间位移角。研究表明：8度罕遇地震作用下,高强钢组合K形偏心支撑框架的层间位移角比传统K形偏心支撑钢框架大,各算例耗能梁段全部进入塑性变形阶段;塑性层间位移角到达规范限值时,算例Q460-5框架梁开始进入塑性变形阶段,算例Q690-5框架柱、框架梁和支撑均处于弹性变形阶段,还可以承受更大的地震作用;达到定义的极限状态时,与传统偏心支撑钢框架相比,算例Q460-5能够承受的地震作用和耗能梁段转角更小;算例Q690-5承受的地震作用和耗能梁段转角更大。     

试探影响工程造价的主要因素与控制

在众多内外因素的影响下,工程造价和工程建设的规划与实际管理有很大的波动性和不可控性,因此要确保工程造价的良好管理和调控,需要从现实问题出发,具体问题具体分析,采取科学合理的调控措施。本文从影响工程造价的主要因素出发,分析这些因素对于工程建设的正面与负面作用,针对性地为工程造价的有效控制提出建议和措施。     

Seismic performance of Y‐type eccentrically braced frames combined with high‐strength steel based on performance‐based seismic design

In the Y‐type eccentrically braced frame structures, the links as fuses are generally located outside the beams; the links can be easily repairable or replaceable after earthquake without obvious damage in the slab and beam. The non‐dissipative member (beams, braces, and columns) in the Y‐type eccentrically braced frames are overestimated designed to ensure adequate plastic deformation of links with dissipating sufficient energy. However, the traditionally code design not only wastes steel but also limits the application of eccentrically braced frames. In this paper, Y‐type eccentrically braced steel frames with high‐strength steel is proposed; links and braces are fabricated with Q345 steel (the nominal yield stress is 345 MPa); the beams and columns are fabricated with high‐strength steel. The usage of high‐strength steel effectively decreases the cross sections of structural members as well as reduces the construction cost. The performance‐based seismic design of eccentrically braced frames was proposed to achieve the ideal failure mode and the same objective. Based on this method, four groups Y‐type eccentrically braced frames of 5‐story, 10‐story, 15‐story, and 20‐story models with ideal failure modes were designed, and each group includes Y‐type eccentrically braced frames with ordinary steel and Y‐type eccentrically braced frames with high‐strength steel. Nonlinear pushover and nonlinear dynamic analyses were performed on all prototypes, and the near‐fault and far‐fault ground motions are considered. The bearing capacity, lateral stiffness, story drift, link rotations, and failure modes were compared. The results indicated that Y‐type eccentrically braced frames with high‐strength steel have a similar bearing capacity to ordinary steel; however, the lateral stiffness of Y‐type eccentrically braced frames with high‐strength steel is smaller. Similar failure modes and story drift distribution of the prototype structures designed using the performance‐based seismic design method are performed under rare earthquake conditions.