多天线干涉阵的时间同步技术北大核心CSCD

多天线干涉阵利用多个远端天线同时接收信号以提升探测灵敏度和角分辨率,其多路信号干涉合成的特性要求不同路之间高精度的时间同步。本文提出一种复用型分布式多路时间同步方法,利用单个数字延迟脉冲发生器对时间信号进行再生和分配,并设计了相应测量及控制算法,在精确测量多路光纤传输延时的同时,向多个远端天线分配稳定的时间信号。实验结果表明,系统在25km传输链路下具有ps级传输延时测量精度和优于20ps的时间信号分配精度。方案可同时支持本地回传信号数字化和远端数字化两种信号接收汇聚方案,在保证时间同步精度的同时有效降低了分布式同步系统的成本。     

利用时空混沌同步进行数字加密通信

提出一种利用时空混沌同步的计算机网络数字加密通信方案,并用软件实现了语音双工实时密码通信.在该方案中,收、发端两个单向耦合映射格点(OCOML)系统被同一混沌信号所驱动而达到同步,其时空混沌输出信号分别用作加密和解密的密钥序列,OCOML的耦合参数为系统的主密钥.系统的主要优点是传输效率高,便于用软件实现实时通信,且通信的安全性获得了改善. 关键词： 时空混沌同步 密码系统 传输效率     

磁共振信号并行高速接收系统设计

针对低场磁共振成像系统,该文设计了一种紧凑灵活的信号接收方案,实现对多通道磁共振信号的高速采样与直接数字解调. 系统采用高速模数转换器(A/D)对磁共振信号直接采样;以单片数字下变频器(DDC)--AD6636, 完成4路采样信号的数字解调;以数字信号处理器（DSP）作为控制器,实现对AD6636的配置以及I/Q数据的读取. 信号采样频率可达100 MSPS,适用于1 T以下的系统. 实验证明该设计具有结构紧凑,采样速率高,配置方便快速,滤波器设计丰富灵活等特点,为磁共振成像谱仪的研制提供了一种高性能的信号接收方案.     

采用可编程I/O接口的多路串行通讯模拟器设计

某航天器闭式贮箱增压控制系统的测试中,需要设计具有多路串行通讯接口的模拟器,用于模拟数字式压力传感器的输出信号。对于72路串行发送和10路串行接收功能,若采用传统商用的标准串行通讯接口板,则整个模拟器需要十多套板卡,系统复杂,体积大,且多个通道之间难以实现同步与实时控制。为此提出了一种采用多路可编程I/O接口板实现485通讯功能的方案,借助于LabVIEW软件开发平台,由FPGA编程实现通讯协议;并配置信号调理板以实现信号的隔离传输和驱动。最终仅用一台小型便携式设备和三块板卡就实现了模拟器的所有功能,可以灵活地根据系统设置的工作模式模拟传感器的输出,在增压系统的测试中表现优异。试验结果表明,此种设计方案具有较强的通用性和适应性,可以广泛推广到多种通讯应用场合。     

数字相位测距仪信号源的研究与设计

在相位激光测距仪中,信号初始相位的相对稳定性对测距仪的测量精度非常重要.对于如何得到全同步的主振信号、本振信号、差频参考信号以及填充脉冲,给出了采用单片机控制频率合成器(DDS)直接数字频率合成芯片,直接滤波以及FPGA软件模拟DDS原理三种不同的方案,最后对这三种方案进行了比较.直接滤波法实现起来简单且成本较低,适合测量精度不是很高的系统.另外两种方案可用于测量精度较高的系统,但是成本较高.     

高精度多路脉冲延时技术

针对全固态直线变压器驱动源(LTD)中大规模开关同步触发的需求,设计了一款基于ZYNQ-7000 SoC平台的全数字多路脉冲延时系统。介绍了该系统各功能模块,并重点从时间数字转换器(TDC)、多路脉冲输出及ARM核控制三个模块进行分析设计。详细阐述了TDC模块抽头延时法原理及高精度进位链的构造;采用粗延时和细延时结合设计多路脉冲输出模块,有效提高信号的延时精度和范围,且模块化设计提高了通道数目的可扩展性;阐述ARM核控制流程,实现了响应快、稳定性高的控制。最后对系统进行了仿真验证,固化后在器件上进行了实测。实验结果表明,系统能够对外部触发信号实现多路延时输出,信号脉冲宽度1200 ns,幅值1.8 V,延时步进1 ns,延时调节范围0～4.29 s,输出误差低于1 ns。     

基于外触发和软件控制的多摄像机同步采集处理系统

从硬件和软件两方面对摄像机同步的原理和方法进行了研究,设计并实现了基于外触发和软件控制的多摄像机同步采集和处理系统.提出了通过编程控制将一种通用的数字输出模块作为同步触发信号发生器,并利用Visual C++平台开发了控制程序,能够通过触发信号的周期和波形来调整图像采集频率和摄像机触发电平.设计了软件同步策略,保证多台摄像机之间的图像同步曝光之后能够同步处理.经过验证,所设计的同步采集系统同步精度较高,同步误差小于10 μs,具有设备简单、使用方便、成本低等优点,并且能够消除丢帧、错帧等现象,提供了一种通用的多摄像机同步解决方案.     

基于现场可编程门阵列技术的混沌数字通信系统——设计与实现

提出了基于IEEE-754标准和现场可编程门阵列(FPGA)技术的混沌数字通信系统的通用设计与硬件实现的一种新方法,实现了混沌加密体制与传统密码体制的结合.根据Euler算法,对连续混沌系统作离散化处理,通过FPGA硬件设计混沌离散系统,使其产生作为密钥的混沌数字序列,其中加密算法采用置乱扩展技术,并对算法进行了分析.设计驱动响应式同步保密通信系统,构建包含信号在内的闭环,实现发送端与接收端离散混沌系统的同步.以网格蔡氏混沌系统为例,对该保密通信系统进行了FPGA硬件实验,给出了技术实现过程、算法流程、硬 关键词： 网格多涡卷蔡氏电路 置乱扩展矩阵 现场可编程门阵列技术 混沌数字通信系统     

模块化多路同步快脉冲触发源设计

基于超快速高压大功率半导体开关、脉冲形成电路以及同心等间距传输的关键技术,提出一种模块化多路同步快脉冲触发源技术方案。设计出在负载阻抗为50Ω时,可同步输出两种快脉冲触发信号:一种幅度大于20V(4路)、脉冲前沿小于820ps、脉冲宽度大于100ns;另一种则是幅度大于100V(4路)、前沿小于1.4ns、脉宽大于100ns;在外触发作用下,触发源系统抖动和脉冲输出同步分散性分别达到2ns和36.6ps。电路结构上充分利用等间距电信号传输的原理,实现了快脉冲触发源模块化的设计。通过实验结果验证了所采用的设计原理及方法的可行性,给出了在外触发脉冲单次和重频(5kHz)作用下该同步快脉冲触发源输出的实验结果。     

光通信数字接收中位同步信号的智能提取

在光通信数字接收机中,为了达到系统的位同步,结合数字锁相环的基本原理,采用现场可编程技术,设计了位同步信号的时序逻辑电路,并用FPGA芯片实现了整个位同步电路.通过单片机实时控制FPGA,进行频带宽度和中心频率的实时调节,实现了位同步信号的智能提取.仿真分析和实际测试表明,该系统具有实时跟踪,提取快速且稳定,抗干扰能力强,升级方便等特点.     

New analog electronics for the new challenges in the synthesis of superheavy elements

A new series of experiments aimed at the synthesis and study of decay properties of the most neutron-deficient isotopes of element Fl (Z = 114) and of the heaviest isotopes of 118 element is planned at the DGFRS (FLNR JINR). An appropriate registering system is to be implemented to transfer spectrometric data from double-sided silicon strip detector (DSSD). New analog modules were designed that allow to simplify existing multi-channel measurement system and to improve the real-time method of “active correlations” in search for the rare events of SHE formation and decay. The main features of the new modules the 16-channel charge-sensitive preamplifier, the 16-channel analog multiplexer and the 1.25 MSPS 12-bit Parallel ADC are presented.     

实际大气中无线光通信的系统差错性能

无线光通信(FSO)系统的性能受大气湍流影响会产生剧烈波动。根据系统和大气参数评估系统差错性能的研究具有现实意义。以大气湍流信道和光电探测模型为基础,使用拟合概率分布替换常用的对数正态分布,建立了FSO系统差错性能的数学仿真模型,改进了湍流条件下系统误码率计算公式,并且进行全天的验证实验。实验结果显示,光强概率分布对系统性能有显著的影响,原有公式在某些情况下的计算结果有较大偏差,而改进公式的计算结果具有更好的适应性和准确性。该改进公式可有效评估湍流条件下FSO系统性能,并为相关理论研究提供参考。     

Quasi-monochromatic bound on ultrashort light-pulse transmission through fog

The use of ultrashort (femtosecond duration) light pulses for line-of-sight free-space optical (FSO) communication through fog is receiving increasing attention. Assuming that the transmitter power is low enough to preclude nonlinear interactions, and that scattering-induced multipath spread is less than the reciprocal of the scattering-induced Doppler spread, it is shown that the average transmitter-to-receiver fractional energy transfer of an ultrafast FSO system cannot exceed that of a quasimonochromatic (nanosecond pulse duration) system operating at the optimum wavelength within the ultrafast system's spectrum. Thus, an ultrashort-pulse system is not a solution for high-data-rate FSO communication through fog, because, at best, it will reproduce on average the energy-transfer performance of a wavelength-optimized quasimonochromatic system.     

光纤接口模块自动测试系统的研究与应用

雷达系统内部含有多种带有光纤接口的数字电路模块,对于这类电路板的测试问题,文中提出了一种构建自动测试系统的通用方法。基于CPCI总线的多功能光纤测试模块作为该测试系统的核心测试部件,对外提供10个可收发的光纤接口,光纤接口数据传输速率可在一定范围内设定,以匹配被测模块的光口速率要求,协议数据包可按用户自定义方式发送和录取,解决了被测模块的多光口测试,光口数据传输速率不统一,数据包格式各不相同的等问题。整个测试过程可由软件控制自动完成。该测试系统能够实现对标准总线和非标准总线的光纤接口雷达数字模块的自动测试,经过实际测试验证表明,该系统运行稳定可靠,提高了武器装备的综合保障能力。     

湍流大气光通信系统误码率分析与实验研究

自由空间光通信(FSO)系统的性能由于受大气湍流影响会产生剧烈波动。根据系统和大气参数评估系统差错性能的研究具有现实意义。以大气湍流信道和光电探测两个模型为基础,建立了FSO系统差错性能的数学仿真模型,提出了湍流条件下系统误码率计算公式。对仿真结果与弱湍流条件下获得的实验数据进行了比较,并依据此模型对光强起伏和背景噪声等因素的影响进行仿真。仿真结果表明,基于该模型的仿真结果与实验数据一致,光强起伏是引起系统性能波动的主要因素,最优判决阈值需根据实际大气条件进行调整。该模型可有效评估湍流条件下FSO系统性能,并为相关理论研究提供参考。     

A cost effective 100 Gbps hybrid MDM–OCDMA–FSO transmission system under atmospheric turbulences

FSO or free space optics is a familiar name used in a wide array of applications in the area of telecommunications. Due to its features of low maintenance cost and deployment time, most of the applications consider FSO as the alternative solution for appropriately replacing fiber optics. In this work, we have designed 100 Gbps FSO system by combining mode division multiplexing (MDM) and optical code multiple access scheme (OCDMA). Ten channels, each carrying 10 Gbps data, are transported over 8 km FSO link by using MDM of two Laguerre Gaussian modes and random diagonal codes. Moreover, the performance of proposed MDM–OCDMA–FSO system is also investigated under atmospheric turbulences.     

Performance comparison of various modulation schemes over free space optical (FSO) link employing Gamma–Gamma fading model

Free Space Optics (FSO) is an emerging line-of-sight technology intending to provide last-mile solution to the network problem where fiber technology is not feasible. The use of Wavelength Division Multiplexing (WDM) technology for FSO is inspired due to the demand for broadband communication. This technique has brought a revolution because the system data capacity is enhanced by simply adding more number of channels and reducing the channel spacing without having the need of more than one FSO link. By reducing the channel spacing to an appropriate level, Dense Wavelength Division Multiplexing (DWDM) based FSO systems are also be attained and are reported by various research works. FSO finds applications in vast areas like backhaul networks for cellular communication, disaster recovery, LAN–LAN connectivity, high-definition TV, MAN-extension, video transmission, medicine industry and surveillance. However, its usage is limited due to the serious challenges of link vulnerability to weather and atmospheric turbulence-induced fading. This paper is based on a WDM-FSO system. An 8-channel WDM based FSO system is proposed and performance is evaluated on widely accepted modulation schemes under weak, moderate and strong turbulence conditions. Gamma–Gamma fading model is employed for atmospheric turbulence modelling. The system is simulated on OptiSystem 14.0.     

Enhancement of free space optical link in heavy rain attenuation using multiple beam concept

Free space optics (FSO) has attracted a lot of attention for a variety of applications in telecommunications area, and it is dream of every researcher and telecommunication society to make it a real alternative solution for the last mile problem, to replace fiber optics. FSO is much preferred because of its low maintenance cost and deployment time. FSO with single-beam system is vulnerable to atmospheric attenuation, so to overcome this, a multiple-beam FSO transceiver system has become prominent and is usually used. In this paper, average rain attenuation is evaluated from the collected rain intensity data which are collected for a period of seven months, and implemented in the study concerning results relating link distance, and received optical power of using multiple-beam FSO system in tropical rainy weather. Comparison is made in terms of received optical power, geometrical losses, atmospheric losses, and bit error rate (BER) on using different number of optical beams, based on simulation at data rate of 1 Gb/s. From the results it is clear that the quality of received power is improved by using up to four beams, along with link distance up to 1141.2 m as compared to one-beam, two-beam, and three-beam, with link distances 833.3 m, 991.0 m, 1075.4 m, respectively.     

Realization of free space optics with OFDM under atmospheric turbulence

Free space optics (FSO) technology provides a promising solution for future broadband networks, offering high data transmission compared to RF technology. This work is focused on investigating the performance of an FSO system with OFDM and QAM. A 10 Gbps data stream is transmitted using a 4-level QAM sequence through the FSO system under different atmospheric conditions. Results indicate that the integration of SOA prolongs the maximum achievable distance with acceptable SNR to 185 km under clear weather conditions whereas under atmospheric fog, the maximum distance is extended to 2.5 km.     

ER-200D-SRC型EPR谱仪微机系统的改造

详细叙述了德国BRUKER分析仪器公司ER-200D-SRC型EPR谱仪与IBM PC/386微机联机的软硬件系统,该系统综合了仪器的自动磁场扫描控制,数据采集累加和数据分析处理及数据绘图、打印等各项功能。其硬件由IBMPC/386微机及二大接口模块组成。一块为商品化的12位A/D、D/A接口卡,另一块为自行设计的以INTEL-8255可编程通用接口电路为主体的数字量输入输出控制接口卡,可分别独立地插入PC机的扩展槽中,其软件采用C语言编写,具有菜单式、结构化、模块化、汉字工作提示、实验数据实时屏幕绘图、实验参数实时显示等特点,用户界面良好,该系统恢复并提高了原谱仪的整体性能,具有一定的推广价值。