基于声光技术的扩频信号循环谱的检测

扩频信号是被伪随机码调制的周期信号,因此它应被建模为循环平稳随机信号.基于循环平稳随机信号的谱相关理论,提出了一种采用基于声光信号处理技术的扩频信号循环谱检测方法.通过研究扩频信号的循环频率、循环功率谱和基于时间积分的声光循环平稳处理模型,利用声光循环平稳时间积分相关器,在循环频率处对扩频信号的声光相关函数(循环谱)进行检测.相比于传统的能量检测方法,循环谱检测方法具有更好的检测性能;对于噪声和干扰,无论是平稳的、还是非平稳的,循环谱检测方法都具有较强的抗干扰能力,仿真结果证明了其有效性.     

临近空间高速飞行器综合信道模型研究

针对临近空间飞行器在高速飞行时所经历的高动态多普勒和等离子鞘套等恶劣通信环境以及其通信中断问题,提出了临近空间高速飞行器的综合信道模型方案,在对综合信道内电波传输信道特性分析的基础上将其建模为频率选择性快衰落信道;同时建立了等离子鞘套信道的数学模型,利用传输矩阵法和FDTD算法计算了表征大尺度衰落的电波传输透射系数,并根据散射信道建模方法给出了小尺度衰落的仿真模型并对其参数的获取进行了分析.仿真计算和定性分析表明了该综合信道模型方案的可行性.     

Longitudinal differences in the equatorial spread F characteristics between Vietnam and Brazil

We present the results of a comparative study of the equatorial spread F (ESF) and the F layer critical parameter, the base height of the F layer bottomside (h′F) over the two equatorial sites, Ho Chi Minh City – HCM (dip latitude: 2.9°N) in Vietnam and Sao Luis – SL (dip latitude: ∼2°S) in Brazil. The study utilizes simultaneous data collected by a CADI at HCM and a digisonde at SL during the year 2002 with the monthly mean solar 10.7 cm flux (F10.7) varying from ∼120 to ∼185. This study focuses on the quiet time seasonal behavior of the F layer parameters in the two widely separated longitude sectors, and addresses the question as to what can we learn from such comparative studies with respect to the ambient ionospheric and thermospheric parameters that are believed to control the ESF generation and hence its longitudinal occurrence pattern. The observed differences/similarities in the diurnal and seasonal patterns of the F Layer height vis-à-vis the ESF occurrences are evaluated in terms of the known longitudinal differences in the F layer heights, thermospheric meridional winds and the geomagnetic peculiarities of the two sites.     

基于AHP的DS/FH混合扩频测控系统抗干扰效能评价

针对DS/FH(Direct Sequence/Frequency Hopping,直扩/跳频)混合扩频测控系统抗干扰问题,提出一种效能评价方法.基于任务需求,构建系统抗干扰效能评估指标体系;将三角模糊数、指数标度和层次分析法相结合,提出一种改进的TFN-AHP(Triangular Fuzzy Number-Analytic Hierarchy Process,三角模糊数-层次分析法),提高了较小指标的区分度,剔除了极端数据,最大限度发挥专家的经验知识,实现了指标赋权的客观程度,最后通过AHP对不同设备系统关于指标体系判断矩阵的确定、一致性检验和层次总排序,实现了系统抗干扰效能的评价和选择.分析结果表明,该评价方法能够实现不同设备的抗干扰效能评估,有助于用户对设备的选择.     

FFH／DS混合扩频体制通信技术研究

简要介绍扩频通信的基本原理和不同种类扩频方式的特点,提出了一种用直扩芯片和数字频率合成器实现FFH/DS混合扩频通信系统的技术方案。     

微重力下热薄材料燃烧特性的窄通道实验研究

利用高度分别为10 mm,12 mm和14 mm的水平窄通道对微重力环境下热薄材料表面的火焰传     

Multi-station observation of ionospheric irregularities over South Africa during strong geomagnetic storms

This paper presents results pertaining to the response of the mid-latitude ionosphere to strong geomagnetic storms that occurred from 31 March to 02 April 2001 and 07–09 September 2002. The results are based on (i) Global Positioning Systems (GPSs) derived total electron content (TEC) variations accompanying the storm, (ii) ionosonde measurements of the ionospheric electrodynamic response towards the storms and (iii) effect of storm induced travelling ionospheric disturbances (TIDs) on GPS derived TEC. Ionospheric data comprising of ionospheric TEC obtained from GPS measurements, ionograms, solar wind data obtained from Advanced Composition Explorer (ACE) and magnetic data from ground based magnetometers were used in this study. Storm induced features in vertical TEC (VTEC) have been obtained and compared with the mean VTEC of quiet days. The response of the mid-latitude ionosphere during the two storm periods examined may be characterised in terms of increased or decreased level of VTEC, wave-like structures in VTEC perturbation and sudden enhancement in hmF2 and h′F. The study reveals both positive and negative ionospheric storm effects on the ionosphere over South Africa during the two strong storm conditions. These ionospheric features have been mainly attributed to the travelling ionospheric disturbances (TIDs) as the driving mechanism for the irregularities causing the perturbations observed. TEC perturbations due to the irregularities encountered by the satellites were observed on satellites with pseudo random numbers (PRNs) 15, 17, 18 and 23 between 17:00 and 23:00 UT on 07 September 2002.     

伪码扩频测距系统中多径误差的实验测量与分析

利用扩频测距发射与接收设备,设计了多径误差测量实验,获得了测距误差随多径延迟变化的实测数据,并针对实验进行理论建模与分析仿真,计算结果与实测数据基本吻合,证明了扩频测距系统中多径分析与仿真模型的正确性,确认了多径引入的扩频测距误差的影响量级。     

Thermal Stresses and Cracks During the Growth of Large-sized Sapphire with SAPMAC Method

本文利用有限元法对冷心放肩微量提拉法(SAPMAC)生长大尺寸蓝宝石单晶过程中的热应力进行了模拟计算,应用临界缺陷理论解释了裂纹的萌生与扩展机理。研究表明,晶体内的热应力主要与晶体生长速率,环境温度和结晶取向有关;较大热应力多出现在结晶界面,放肩、收尾以及直径急剧变化等位置;最大热应力总是出现在籽晶与新生晶体的界面附近。裂纹将在临界缺陷位置产生,并在应力作用下沿a或m面扩展。计算结果与实验结果基本吻合,通过晶体生长系统和生长工艺的改进,对晶体的开裂问题得到了有效的抑制。     

DS/FH混合系统多址干扰抑制

根据DS-CDMA(Direct Sequence Code Division Multi-Access)系统中多用户检测的思想,分析了并行干扰抵消PIC(Parallel Interference Cancellation)对系统性能的影响,在此基础上,提出了采用部分并行干扰抵消PPIC(Partial Parallel Interference Cancellation)技术来抑制DS/FH SSMA(Direct Sequence/Frequency Hopping Spread Spectrum Multi-Access)混合系统中的多址干扰MAI ( Multi-Access Interferences).推导了闭环形式的误码率公式,得到系统性能评估的上限表达式.仿真结果表明,采用PPIC技术可有效的提高DS/FH SSMA系统的抗多址干扰的能力,因而可以提高系统的容量.仿真是建立在AWGN信道下的,对于衰落信道和低信噪比环境下,系统的性能会有一定程度的降低.