DVB-S载波恢复技术实现

对DVB-S载波恢复给出较为详细的实现方案,通过仿真验证性能,得出该结果可以扩展到其他单载波系统接收机中。     

浅析宽带多制式无线通信信号解调测试算法

文章从宽带无线通信的发展现状出发,针对当前宽带无线通信信号解调测试算法中存在的问题,结合宽带无线通信的实时多域分析架构,提出了一种新的解调测试算法,对I／O信号的解调预处理载波频偏进行补偿和粗估计,确定采样率与码率的倍数关系,以实现载波相位的同步跟踪和符号的同步定位,提高测试的精度,为铁路通信工程施工提供相关借鉴。     

同步误差对OFDM系统的影响

OFDM系统相对于单载波系统来说,同步技术尤为关键。由于OFDM系统各个子载波间的正交性,使得OFDM系统对频率偏移非常敏感,为了保证系统性能的良好,我们要保证频率的稳定性。本文分析了同步误差对OFDM系统性能的影响,给出了一种新算法,仿真表明OFDM系统频率同步误差比时间同步误差对系统性能的影响要严重得多,只有当OFDM系统频偏小于0.02个子载波间隔时,系统才是处于稳定性能的,这时它所产生的ICI对系统的影响可以忽略不计。     

频偏对分布式MIMO-OFDM系统性能影响分析

本文从理论上分析了频偏对采用迫零检测的分布式多入多出(MIMO)正交频分复用(OFDM)系统性能的影响.推导了由频偏导致的载波间干扰(ICI)功率,进而得到系统信干噪比(SINR)的表达式.通过分析迫零检测的特性,指出传统SINR计算方法不准确的原因并给出了新的更为准确的SINR计算方法.分析结果表明,传统方法所得SINR结果偏小而本文所提方法所得结果更为准确.     

浅析4G移动通信系统的核心技术——OFDM-CDMA

文章简述了4G移动通信系统中使用的两类核心技术CDMA多址通信和OFDM多载波调制技术,并对各自的工作原理和特点进行了归纳总结,在此基础上,探讨了三种基于OFDM的多载波CDMA系统方案,即MC-CDMA、MC-DS-CDMA和MT-CDMA,研究三种方案的基本原理并对各自优缺点进行探讨。     

OFDM系统中符号同步与频率同步最大似然检测器的改进方案

本文提出只用输出的符号比特来估计帧偏移和频偏,并且提出了两种不同的方法来降低硬件复杂度和电路功耗。仿真结果显示,在AWGN信道和多径衰落信道的传播环境下都能正常工作,并且降低了硬件复杂度和电路的功耗。     

一种适用于任意码率的OQPSK载波频偏恢复方案

文章基于软件无线电算法通用性的构想,提出了一种方案,即在AFC环前面加上一级采样率转化环节,将AFC环的输入信号中每个码元的采样点数调整为所期望的整数值,然后再让AFC环进行载波频率跟踪。文章通过计算机仿真,验证了上述方案的可行性。     

一种适用于任意码率的OQPSK载波频偏恢复方案

文章基于软件无线电算法通用性的构想,提出了一种方案,即在AFC环前面加上一级采样率转化环节,将AFC环的输入信号中每个码元的采样点数调整为所期望的整数值,然后再让AFC环进行载波频率跟踪。文章通过计算机仿真,验证了上述方案的可行性。     

基于Cordic算法的MPSK信号载波恢复设计

本文阐述了一种实现MPSK信号载波恢复的设计方案。整个设计可通过设置参数来实现不同载波频率以及不同符号率的MPSK信号的载波恢复,具有很强的通用性。在实际应用中,只要参数设计适当,就可以达到较快的载波跟踪速度和较小的相位误差方差抖动。     

计算机与多台单片机的串行通信方案实现

为了提高靶场测试系统的运行效率,提出了一种计算机与多台单片机通过串行口进行数据传输的方法。引入RS485总线,使用一台计算机通过不同的地址命令控制分布在不同位置的测试系统中的单片机,令单片机将采集到的数据发送给计算机,形成分布式测试系统。本文研究的多机串行通信方案具有一定的先进性,其性能经过试验现场验证工作稳定、可靠。     

量化误差对信道估计的影响

针对提高无线信道的传输性能,提出了改进的基于叠加训练序列的MIMO信道估计算法。利用训练序列与信息序列的不相关,在没有带宽损失的情况下初步估计出信道参数;然后利用加权因子对信道参数在相邻信号段之间进行加权平均,得到最终的信道参数。与以往的叠加训练序列估计方法比较,利用算法具有更低的估计均方误差,且适用于时变信道。通过计算机仿真结果表明,估计方法提高了信道传输精度和性能。     

用改进的蒙特卡罗模拟估计我国商业银行操作风险

运用蒙特卡罗模拟方法估计银行业操作风险时,对于事件发生频率,一般不考虑预测模型参数的时变性,致使预测结果存在较大偏差。针对这一不足,建立了灰色动态残差GM(1,1)模型来估计与预测损失事件的发生频率,并通过对起始时点的比较选择和残差的修正,进一步改进了预测模型。再用蒙特卡罗方法对操作风险的损失金额进行模拟,配合使用所建立的损失事件发生频率预测模型,得到商业银行操作风险的损失值,并据以确定监管资本和减少商业银行操作风险的对策。     

The interchangeability of safety stocks and safety lead time

Due to the uncertainty in estimating both the demand for end products and the supply of components from lower levels, buffering techniques should be included before the loading of a material requirement planning (MRP) system. Safety stocks and safety lead time are two techniques of providing buffering for loading. There have been many studies made concerning the determination of the amount of safety stocks and safety lead time. Some guidelines for choosing between safety stocks and safety lead time for dealing with uncertainty in both demand and supply also have been established. Although these two different methods have been used successfully, it has not been documented that using these two methods in a given situation will yield essentially the same results; that is, the interchangeability of these two buffering techniques has not been explored quantitatively.Since the net influence of safety stocks and safety lead time and their quantitative interchangeability are of major interest, an analytical model is proposed for this study. The lead-time offset procedure for components loading are represented by a matrix model that is based on a lot-for-lot lot-sizing technique. This lead-time offset matrix model is the product of the precedence matrix and the fixed-duration matrix. The precedence matrix is formed according to the total requirement factor matrix and the duration matrix is formed by each component process time. Thus, the lead-time offset matrix will generate the starting period of each component.When the lead-time offset procedure is modeled, the net influence of buffering quantity can be analyzed. The planned safety stock that is normally used to accommodate unexpected demand, shortage in supply, and defects from the operation at each process can be combined with demand to form the master production schedule. The revised lead time due to the integration of the safety stocks can be calculated through the lead-time offset model. The safety lead time may extend the component process time as well as overall production lead time if the designated safety lead time is longer than the available slack time in a fixed lead-time loading system.When the proposed lead-time offset model is further examined, it is found that planned safety stocks at the higher level can buffer the fluctuations of lower level components quantity as well as the fluctuations of same level components quantity. Safety stocks can also buffer shortages that are caused by the delay of raw material and manufacturing processes. Thus, safety stocks can be used to buffer unexpected delay time up to certain limits. A planned safety lead time at higher level component process can buffer the fluctuations of lower level components process time, as well as the same level component process time. The safety lead time can be used to produce additional products to meet unexpected excessive demand up to certain limits under the following conditions: 1. The excessive demand is known before the actual processing of the components in the lowest level. 2. The raw material at the lowest level is available.Although safety stocks and safety lead time are interchangeable in terms of the ability to buffer variations in quantity, the conditions for safety lead time are seldom met in actual practices. Thus, the slack time in a fixed lead-time loading system cannot be considered as an effective measure to substitute safety stocks. However, all or part of the delay in manufacturing processes or the supply from the lower level components can be buffered by the safety stock and the MPS will still be met. From this study, it is obvious that the slack time can be reduced when safety stocks are planned for an MRP system. The reduction of fixed lead-time duration will be beneficial to the overall planning and scheduling in MRP systems.     

基于Labview的油膜涡动和油膜振荡诊断系统的研究

传统的信号处理方法对于非平稳故障信号处理有所欠缺,Hilbert-Huang变换(HHT)能求得的瞬时频率可用于复杂的非平稳信号的分析,得到振幅瞬时频率-时间的分布,准确反映系统的固有特性。本文利用LabVIEW编程平台开发转子振动数据采集分析系统,该系统中的HHT模块能在油膜涡动和油膜振荡故障发生的早期作出准确诊断。     

Forecast combinations under structural break uncertainty

This paper proposes two new weighting schemes that average forecasts based on different estimation windows in order to account for possible structural change. The first scheme weights the forecasts according to the values of reversed ordered CUSUM (ROC) test statistics, while the second weighting method simply assigns heavier weights to forecasts that use more recent information. Simulation results show that, when structural breaks are present, forecasts based on the first weighting scheme outperform those based on a procedure that simply uses ROC tests to choose and forecast from a single post-break estimation window. Combination forecasts based on our second weighting scheme outperform equally weighted combination forecasts. An empirical application based on a NAIRU Phillips curve model for the G7 countries illustrates these findings, and also shows that combination forecasts can outperform the random walk forecasting model.     

Siting noxious facilities: A siting lottery with victim compensation

This paper proposes a scheme to facilitate the siting of noxious facilities. A regional government announces that it will (a) use a lottery to choose a site for a noxious facility and (b) transfer income from tenants to host-city landowners to at least partly offset the effects of the noxious facility on local property values. The government will hold the lottery only if all citizens agree, in advance, to abide by the resulting siting decision. The lottery approach is superior to the conventional approach to siting (advance notification) in the sense that the lottery approach achieves unanimous support for the siting decision with less compensation. The compensation scheme can be financed with a regionwide tenant tax or a tax on residents in the nonhost city. For “small” compensation programs, the nonhost tax is superior to the regional tax.     

一种适用于高铁沿线的多台站快速地震预警方法

对于地震预警技术来说,根据参与监测预警的台站数量不同,可以将高速铁路地震监测预警系统分为单台站地震P波预警技术和多台站地震P波预警技术。单台站P波预警由于信息量较少以及噪声影响,在定位方面存在较大误差。多台站P波预警技术是在单台站P波预警的基础之上,综合多个单台站信息进行综合震源参数估算并发出地震预警信息的预警方式。通过应用多台站P波预警定位技术,能够在震源估算方面得到更准确的结果。     

东江铁路大桥桥墩偏移整治工程施工监控

文章介绍了广州东江铁路大桥桥墩偏移整治工程的施工监控方案和实施方法。结果表明,监控方案有效可行,可为类似的整治工程施工监控提供参考。     

基于zigbee的物联网实训平台的硬件设计

本文提出了基于zigbee的物联网综合教学实训平台的硬件设计方案,该方案采用Jennic公司的一款集收发器和微控制器于一体的zigbee基带和射频芯片JN5121为控制核心,外加多个从节点和一个RFID读写模块。对于高职院校来说,此综合实训平台能够很好地解决物联网专业实训对象少的问题,同时能够弥补相关操作,以及仪器设备的空缺。