改进的TMBOC调制信号闸波相关鉴相方法

为了实现卫星导航系统中时分二进制偏移载波调制信号的无模糊抗多径跟踪问题,提出一种基于闸波相关的改进鉴相方法．首先,将时分二进制偏移载波调制信号与偏移0.5个码片的W2形闸波和偏移0.5个码片的伪随机码分别进行相关;然后,将相关结果相乘,即可获得无模糊且对称性良好的码鉴相曲线．对所提方法得到的码鉴相曲线的性质进行了分析和实验仿真,结果证明: 这种方法实现简单,且得到的鉴相曲线基本具有较好的中心对称性,具有较强的抗多径能力,能够实现无模糊跟踪．所提方法相对于已有的闸波相关方法更加适合于时分二进制偏移载波调制信号的鉴相．     

利用随机中心位置调制抑制逆变器的电磁干扰

针对电动汽车逆变器所产生的电磁干扰问题,提出了一种利用随机中心位置调制抑制逆变器的电磁干扰方法。该方法在七段对称法调制的基础上,将脉冲的中心位置在调制周期中左右移动,在一定的范围内随机地改变脉冲作用时刻,从而实现随机中心位置调制;利用Matlab/Simulink搭建了永磁同步电动机矢量控制仿真模型。仿真结果表明,与单一的七段对称法相比,随机中心位置调制可以有效地减小载波频率及载波倍次频率处的谐波幅值,从而减少逆变器对外的电磁辐射干扰。     

基于中心频率检测的应答机载波捕获技术

针对基于理想型积分环路滤波器的二阶锁相环在无信号输入时,环路中心频率会随热噪声发生漂移的问题,研究了卫星星载测控应答机的载波捕获技术.为解决无信号输入下的环路中心频率漂移问题,在基于正交欠采样技术及全数字载波恢复环的接收机结构基础上,通过一级中心频率检测器控制环路.当检测到上行信号时闭合环路,避免了接收机中心频率在无信号输入时随热噪声发生漂移.给出了中心频率检测器的设计方法,分析了检测器漏检概率和误判概率之间的关系,并在此基础上给出了检测器的具体参数选择依据.     

旋转对称能量与旋转对称性检测

为检测图像的旋转对称中心和旋转对称角,通过引入旋转对称能量的概念,提出了一种新的旋转对称性检测算法.该算法分为3个步骤:1) 对图像中任一位置,计算该位置处的旋转对称能量和旋转对称角;2) 计算各点处的旋转对称能量获取整幅图像对应的旋转对称能量图;3) 在旋转对称能量图上进行局部极大值检测获得旋转对称图形的旋转对称中心并确定旋转对称角度.实验结果表明,该算法不仅能够准确鲁棒地检测出旋转对称图形的旋转对称中心与旋转对称角,还能成功应用于图像修复.     

基于压缩感知的自适应干扰抑制算法

针对基于Nyquist采样理论的干扰抑制算法在宽频带信号接收处理中受限于信号带宽和现有器件水平的问题,提出了一种压缩域的自适应干扰抑制算法。首先利用压缩感知技术以远低于Nyquist采样率的速率获得信号的压缩测量值;然后基于最小输出能量准则,并结合空间投影技术,利用投影值完成干扰信号的检测和抑制;进一步推导并给出了算法的闭式解及LMS自适应实现过程。理论分析和仿真结果表明,该算法极大地降低了对A/D器件和后端数字处理器件的要求,且无需预知干扰信号在宽频带中的位置先验信息,并对干扰源的个数无限制,具有较强的实用性。     

根据信道特性优化OCDMA码片波形

提出一种根据信道特性优化码片波形的方法.该方法将全光信道视为滤波器,用回转椭球函数为基元函数展开表达滤波器的透过率函数,以功率谱密度(PSD)均匀为条件旨在取得最小干扰.采用Lagrange乘子法,求取用回转椭球波函数线性叠加表达的码片最优波形的解析表达.给出了系统模型及推导步骤,用K-L展开讨论其适用范围.     

一种基于多路径对消的直达波干扰抑制算法研究

在对自适应直达波抑制算法分析的基础上,给出了一种基于多路径对消的直达波抑制算法:首先,利用多路径对消器把参考通道中的多路径干扰对消掉,剩余信号作为参考直达波信号;然后,在目标通道中利用该参考信号进行自适应直达波抑制,抑制掉信号通道中的直达波干扰,提高目标回波的检测概率。该算法相对于自适应直达波干扰抑制算法,可用于参考通道中含有多路径干扰的环境,且具有较好的直达波干扰抑制效果。     

理想功率控制多用户DS-UWB信号捕获性能分析

分析了理想功率控制的多用户环境下DS-UWB系统采用串行搜索策略的捕获性能.对于多用户干扰,当干扰用户多时,根据中心极限定理,检测器输出端的多用户干扰可近似为一个高斯随机变量,推导了一定干扰用户下系统检测概率和虚警概率的闭合表达式,在给定的信噪比和一定的捕获门限下,求出捕获时间的均值和方差.数值结果表明,不同数目的多用户干扰下,系统的最佳平均捕获时间近似相同.     

Performance analysis of hybrid carrier DS CDMA communication system

A hybrid carrier (HC) DS CDMA communication system is proposed, combining 4-weighted fractional Fourier transform (4-WFRFT) with code division multiple access (CDMA) technique. The signals are modulated in a certain order fractional Fourier domain and transformed by 4-WFRFT to compose the hybrid carrier signals. In the time domain CDMA technique is adopted for multiple accesses and time diversity gain. Compared to orthogonal frequency division multiplexing (OFDM) system, in which Fourier transform is adopted, the signal energy in HC system is distributed on the time-frequency plane more evenly and symmetrically. Thus, when there is a deep fading notch or single-frequency interference in the channel, the proposed method can split the interference to a broader range in order to reduce the influence, resulting in the better system performance. Moreover, the performances of the proposed system, such as peak-to-average power rate (PAPR) and security are also discussed in the paper.     

偏置电场对THz辐射强度影响的蒙特卡罗模拟

采用系综蒙特卡罗方法对光生载流子在偏置电场作用下的输运过程进行模拟,从微观角度研究偏置电场对连续太赫兹辐射强度的影响.模拟结果表明,由于空间电荷电场屏蔽效应以及散射等因素的影响,太赫兹辐射强度先是随偏置电场的增强而上升,当达到峰值后逐渐趋于饱和.虽然降低温度使粒子发生散射的几率降低,但同时也减小粒子的初始能量,故低偏置电场时低温下连续太赫兹辐射功率比常温下小,而当偏置电场超过某一阈值时,降低温度能够提高连续太赫兹辐射功率.     

Interference analysis and novel fractional frequency reuse scheme in LTE networks

Inter-cell interference (ICI) mitigation is always a challenge issue in LTE system. In this paper, several common interference parameters are firstly analyzed for both cell edge users and center users, and then a novel fractional frequency reuse (FFR) architecture based on interference avoidance scheme coupled with power control is proposed to solve the problem of interference management in multi-cell LTE environment. The scheme divides the whole sub-carriers into three groups orthogonally. One is allocated to cell edge users, while another two are assigned to cell center users with different transmitter power. Then a parameter named interference avoidance factor (IAF) is defined to avoid ICI and adjust the number of allocated sub-carriers to match the number of users. The parameter also takes weight factor and fairness factor into consideration. The simulation results show the proposed scheme can improve the performance of cell edge users obviously.     

Rejection of Linear FM Interference in DSSS System Based on Fractional Fourier Transform

A new method for the rejection of linear frequency modulation (LFM) interference in direct sequence spread spectrum (DSSS) system based on the fractional Fourier transform is proposed, and the configuration of the receiver with an interference exciser is also presented. Based on the property that the fractional Fourier transform of a signal is equivalent to rotating the signal in the time-frequency plane, the received signal is transform into a certain fractional Fourier domain, this transform will result in the least spectrum overlap between the signal and interference. Then, a narrowband filter is exploited to extract most of the interference energy. The performance analyses show that remarkable improvements in signal-to-noise ratio (SNR) and biterror-ratio (BER) are obtained.     

临近空间高动态高速载波捕获跟踪的实现方法

为了接收临近空间高动态高信息速率用户信号,需要设计载波链路的捕获与跟踪系统.根据临近空间网络高动态高信息速率的链路特性,着重分析了HDHI(HDHI,high dynamic and high information-rate)载波链路捕获跟踪的特性及实现方案.对载波链路捕获跟踪的设计原理做了清晰的说明和推导,提出了适合HDHI载波链路捕获跟踪设计方法,并对高动态高信息环境中接收机的载波捕获与跟踪数字系统的设计做了详细的陈述.最后通过实验和对比论证了利用DQPSK方式的HDHI信号捕获跟踪设计方法是可行的.     

Research on assessment method of intrasystem and intersystem of the global navigation satellite system

The global navigation satellite system(GNSS) has become an important space infrastructure. Following GPS and GLONASS, Europe and China have been building their own global navigation satellite system, respectively, GALILEO and Compass. In order to consolidate the leadership of GPS in the globe, United States is gradually upgrading the traditional GPS. Simultaneously, Russia is also intensively restoring full performance of GLONASS. With the advancement of international satellite navigation system, satellite navigation frequency resources are already in short supply, and the design and use of the navigation signals are more sophisticated and complex due to commercial, disaster relief and other reasons. Since there may be many navigation signals in the same basic bandwidth, the coexistence of multiple systems and the combined application make intersystem mutual interference become the focus research. Under this background, the satellite navigation system mutual interference evaluation system needs to be established urgently to meet and support the compatibility and interoperability of the GNSS system. In the paper, through the performance analysis of the GNSS signal acquisition, carrier tracking, data demodulation and code tracking, the equivalent carrier to noise ratio model based on spectrum isolation coefficient is established, and the theoretical system of the GNSS signal mutual interference is proposed according to the mechanism, and the mutual interference of GPS, GALILEO and Compass system is analyzed and assessed.     

宽场光学相干层析成像系统的机电控制设计与实现

根据宽场光学相干层析成像系统的基本原理和系统硬件组成,探讨设计了宽场光学相干层析成像系统的机电控制,机电控制主要包括3个部分:宏动台与微动台的机械控制模块、图像采集模块以及宏动台和微动台与CCD相机的联动控制模块,通过精确控制宏动台和微动台的移动实现四步移相时对样品干涉信号的采集。实验测试证明,所设计的宽场OCT系统能够对较透明的样品的表面和次表面的干涉信号进行采集,所采集到的干涉信号经过图像重构基本再现了样品的结构特征。     

中心对称矿物中Cu2+六配位 的晶场势能和微扰矩阵元计算

对于离子型或以离子键为主的晶体,其光学和磁学性质可用晶体场理论解释。通过晶场微扰 矩阵元的计算,可定量地确定晶场光谱谱带位置。以往资料无矩阵元的计算过程,只是给出了部分积分 结果,这不利于在任何对称情况下晶场微扰矩阵元的计算。推导了中心对称矿物的晶场势能算符,计算 了积分值,得出了矩阵元以系数Aλx,r2和r4的表达式。并以绿松石的结构数据为基础,计算了Cu2+的 晶场微扰矩阵元表达式中的系数Aλx,从而计算了各矩阵元,通过对称矩阵的对角化,最终求得绿松石 中Cu2+d轨道能量和晶体场谱带位置计算值。与实验资料对比,符合较好。因此,用晶体场理论和实 验资料相结合可定量地阐明具离子键晶体的呈色机制。     

低信噪比条件下BOC信号的快捕算法研究

针对全球导航卫星系统中的二进制偏置载波(BOC),介绍了其生成原理,分析了其自相关函数的特点.研究了常用的BPSK-L IKE单边带和双边带捕获算法及其优缺点,结合基于快速傅立叶变换(FFT)的码并行处理结构,利用BOC信号自相关函数以及BOC信号和伪随机噪声码(PRN)序列的互相关函数两者的差值作为捕获算法的输出,给出了一种可以消除自相关函数的边峰带来的模糊性的捕获算法.仿真结果表明:该算法无能量损失,可接受的最低信噪比低于其它算法2 dB,且其复杂度低.     

基于MBOC调制的北斗导航信号的多径误差分析

为了定量地分析MBOC(Multiplexed binary offset carrier)调制的北斗导航信号的多径误差,在分析MBOC调制信号原理的基础上,建立了相应的多径信号模型,利用超前减滞后功率鉴相器和反正切函数鉴相器,推导了多径效应导致码相位跟踪误差和载波相位误差的表达式.对不同的多径直达幅度比(Multipath todirect ratio,MDR)、相关器间隔、前端带宽时MBOC调制信号的多径性能进行了仿真,并针对存在噪声干扰时的码跟踪误差进行了仿真分析.仿真结果表明,多径直达幅度比由-3 dB减小到-6 dB时,所产生的多径误差包络也相应地减小.在多径直达信号幅度比(MDR)一定时,采用窄相关技术和较宽的接收机前端带宽均能很好地抑制多径误差.存在噪声干扰时,码跟踪误差随着载噪比(Carrier to Noise Ratio,CNR)的增加逐渐减小为0.     

Design of the discriminator for tracking the loop under short-delay multipath interference

The traditional multipath eliminating methods have poor performance under short-delay multipath interference and therefore a discriminator constructing method for tracking the loop is presented. Firstly, from the analysis of the output characteristics for in-phase/quadrature-phase early, late, and prompt channels under the short-delay multipath, an improved late channel is constructed. The output of the loop discriminator is defined as the normalized function of the power difference between early and late signals. It made the error between the code phase of the direct signal and that of the local estimated signal is less than the pre-determined threshold. Theoretical analysis and simulation results show that, compared to traditional methods, the multipath mitigation technique based on the improved loop discriminator can suppress the code tracking errors produced by the multipath when the relative delay is less than 0.5 chip and effectively inhibits short-delay multipath interference, thus improving the tracking and measurement accuracy in navigation and docking systems.     

基于指纹数据库与同步参考信号灵活传输的小小区发现

针对小小区间的同频干扰与用户异频扫描的能耗问题,提出一种基于到达时间（TOA）指纹数据库与同步参考信号（PSS/SSS）灵活传输的小小区发现策略.通过减少用户大量无效异频扫描次数,以达到节能的目的.同时,网络端对小小区基站（SBSs）PSS/SSS的发送进行控制,以降低小小区间PSS/SSS的同频干扰.仿真结果表明,所提方案能有效提高小小区的检测率和用户能效.