Iterative receiver for OFDM systems based on semi-blind channel estimation

In this paper we propose two iterative algorithms of joint channel estimation and symbol detection for Orthogonal Frequency Division Multiplexing （OFDM） systems. In which, superimposed pilot scheme is adopted and an initial Channel State Information （CSI） is obtained by employing a first-order statistic. In each subsequent iteration, we propose two algorithms to update the CSI. The Mean Square Error （MSE） of channel estimation and Bit Error Rate （BER） performance are given and simulation results demonstrate that the iterative algorithm using method B has good performance approaching the ideal condition.     

Carrier Frequency Offset estimation for interleaved OFDMA uplink based on subspace processing

This paper investigates Carrier Frequency Offset （CFO）, estimation in the uplink of the Orthogonal Frequency-Division Multiple Access （OFDMA） systems with the interleaved subcarrier assignment. CFOs between the transmitters and the uplink receiver will destroy orthogonality among different subcarriers, hence resulting in inter-carrier interference and multiuser interference. A two-stage frequency offset estimation algorithm based on subspace processing is proposed. The main advantage of the proposed method is that it can obtain the CFOs of all users simultaneously using only one OFDMA block. Compared with the previously known methods, it not only has a relatively low implementation complexity but is also suitable for random subchannel assignment.     

The theoretical BER performance analysis of a cooperative diversity scheme in frequency selective fading channel

A novel cooperative diversity scheme based on Distributed Space-Time Block Coding and Multi-Carrier Code Division Multiple Access (DSTBC-MC-CDMA) is proposed which works well in frequency selective fading channels with multiple single-antenna users. And an analytical error model is established to describe the symbol decoding errors between interusers, based on which a close form expression for theoretical Bit Error Rate (BER) performance of the scheme is derived to analyze the influence of the interuser decoding errors on the BER performance of the scheme. Then simulation is complimented to verify the analytic result above, which also shows that the BER performance of DSTBC-MC-CDMA outgoes that of non-cooperative MC-CDMA with considerable gains. Further- more, the simulations coincide with the theoretical results well.     

基于CDCM7005的时钟设计及其在数字中频系统中的应用

高速ADC、DAC对时钟质量的要求越来越高.对此介绍了一种基于时钟同步器与抖动清除器CDCM7005的低抖动时钟设计.并分析了时钟抖动对信噪比的影响及抖动的计算,介绍了在WCDMA数字中频系统中CDCM7005的具体设计应用,引入了SignalTap这种新的测试方法,最后测试了时钟性能,计算了时钟相位噪声、抖动值和ADC的信噪比,整体指标达到设计要求.     

LECO CS-600高频红外碳硫仪故障分析与排除

简单介绍了Leco公司CS-600高频红外碳硫仪的一些典型故障的处理过程,总结了维修的思路和方法.     

近红外传感器在无线遥控计数系统中的应用

利用反射式近红外传感器、无线电收/发模块及四合一功能组合计数集成电路等器件,研究了无线遥控红外线计数器。当有产品通过红外线检测区域时,就会有一部分红外光信号经产品反射回来,被与红外线发射管同排安装的光敏接收管收到并转换成同频率的电信号,再经红外传感器模块内电路进行放大、比较处理,输出高电平信号,启动发射机工作。接收机收到发射机发来的无线遥控编码信号后,再经解调、解码电路处理,输出编码脉冲,对此脉冲信号进行计数,就实现了对产品的统计。整个系统为模块化结构,具有安装容易、抗震能力强、传输距离远、工作稳定、计数准确、高亮度数字显示等特点。可用于重工业、轻纺工业、食品工业、农牧业一些设备或流水线上对产量或流量进行遥控计数。     

卫星通信终端通用测试平台高速接口设计

卫星通信系统向多频段多体制发展的趋势对卫星通信终端测试平台的通用性提出了更高的要求,基于通用处理器的软件无线电(GPP-SDR)技术可用于解决该问题。但目前GPP-SDR处理器和射频前端之间的高速数据传输仍是主要的技术瓶颈。本文针对卫星通信终端通用测试平台需求,提出了基于中断机制的PCI-e高速传输方法和流程设计,并通过移植Xenomai操作系统对高速接口传输的实时性进行优化;设计了一系列的测试实验对所设计接口的实际传输速率和中断丢失概率等指标进行测试。实验结果验证了所提方案具备高速率和低时延的传输特性,能够很好地满足当前卫星通信终端通用测试需求。     

窗口傅里叶变换的三维面形测量

由于窗口傅里叶变换具布局部分析特性,且局部谱比全局的谱更简单、更不容易频谱混叠。本文提出在基于频谱分析的三维面形测量中,用窗口傅里叶变换（WFT）代替传统的快速傅里叶变换（FFT）去获取三维物体面形分布。理论分析和实验结果表明：窗口傅里叶变换不但可以减小频谱混叠对测量精度的影响,并且若在窗口傅里叶变换的处理过程中,设置合理的“门限”,还能够有效的抑制噪声。从而在一定程度上保证了基于频谱分析的三维面形测量的精度。     

真三维立体显示静态成像技术研究

简述了二维立体显示的现状,分析了真三维立体显示静态成像技术的基本原理和成像空间材料选取的依据,给出了真三维立体显示系统的控制模型,最后以人体心脏为例实现了真三维立体显示静态成像的模拟,并列举了它在各领域中的应用。