卫星导航抗干扰技术应用

卫星导航定位系统提供精确的位置、时间和速度的同时,存在着信号微弱,易受干扰的天然弱点。在定位导航过程中,导航接收机的抗干扰能力是决定导航定位服务可用性的关键因素,伴随着卫星导航的推广应用和深入研究,抗干扰技术不断迭代更新。文章对卫星导航系统的抗干扰接收技术进行分析。     

GPS卫星信号的捕获算法

GPS接收机运行中,卫星信号高效捕获是准确定位的前提和基础,捕获算法决定捕获效果,对于接收机性能具有重要影响。算法不同,捕获质量也有所差别。文章从GPS信号结构入手,从不同方面探讨GPS卫星信号捕获算法,并借助仿真结果验证捕获方案准确性。     

新体制信号频域窄带抗干扰算法研究

本文主要研究频域窄带抗干扰算法在北斗三代新体制信号中的应用。通过选择合理的窗函数及 FFT 变换点数,通过自适应门限检测及频域过门限置零,可以较好的对干扰信号进行抑制。通过对单干扰、三干扰抑制的仿真,验证了算法在新体制信号抗窄带干扰中的性能。     

伽利略卫星导航系统E1信号的捕获算法分析

对伽利略卫星系统中E1信号的四种捕获算法:自相关旁瓣消除方法(ASPecT)、filtered相关法、类二进制相移键控法(BPSK-Like)和偏移正交BOC互相关法(OQCC)进行了详细理论分析。采集了真实的伽利略卫星E1信号进行捕获算法的仿真分析,并从基本捕获结果、计算复杂度、相关主峰均值比和检测性能等方面进行了对比分析。仿真结果表明OQCC相关法和其他算法相比,性能更优异,能更有效地提高主峰值与去除副峰。所以OQCC相关法更适合推广,具有更高的实用价值。     

多卫星导航信号联合捕获算法的检测性能分析

针对多卫星联合捕获算法缺乏检测性能分析与评估的问题,该文采用处理增益来衡量联合捕获相对于传统捕获的灵敏度提高程度。分别给出了处理增益在匹配接收和不完全匹配接收条件下的表达式,详细推导了多卫星信号的时延和多普勒误差引起的检测损耗,比较了联合捕获与传统捕获在时延和多普勒误差下的检测损耗。采用数值仿真方法验证了理论分析的正确性,仿真结果表明联合捕获的检测损耗总体上小于传统捕获的检测损耗。     

GPS频域相关捕获算法的Matlab/C实现

为研究频域相关捕获算法及其在嵌入武GPS软件接收机中的实现,采用两步捕获法的算法模型,用Matlab进行了仿真,证明了算法的正确性和优越性;并将该算法用C语言实现,在基于ARCA 3嵌入式微处理器的GT3000A平台上运行,成功实现了对真实GPS信号的捕获,为嵌入武软件接收机的研究提供了一定的依据.     

弱导航信号捕获技术仿真分析

本文介绍了导航信号的特点及低信噪比条件下的捕获思想和方法,分析了相干积分、非相干积分及二者相结合的原理。对于GNSS信号的搜索捕获采用长时间相干积分算法,会导致频率的搜索范围增加;采用非相干积分算法将增加平方损失：采用相干积分与非相干积分结合的方法提高整体信号强度,避免多普勒现象产生的影响,实现对弱信号的捕获。仿真结果表明,采用20ms的相干积分时间和5次非相干积分,在没有互相关干扰的情况下,可以接收信噪比为一35dB的弱信号。     

我国未来卫星导航信号的优先选择——BOC调制信号

对BOC调制信号的产生、谱特性、自相关、码跟踪和接收处理方法进行了分析。结果表明,与BPSK信号相比,该信号可以实现频段共用,同时实现频谱分离,具有较强的抗干扰能力;在相同码速率条件下,其相关函数曲线更陡峭,具有更高的码跟踪精度和更好的多径分辨能力;采取有效处理方法可以消除BOC信号相关函数中多峰造成的模糊问题。鉴于BOC信号的优点,建议我国未来卫星导航信号优先选用该信号。     

卫星接收信号的干扰和抗干扰

利用通信卫星或广播电视直播卫星传输广播电视信号已经被广泛使用。然而,在卫星地面接收信号时会遇到各种形式的干扰,本文就接收信号的干扰和抗干扰作一分析,并指出解决干扰的措施。     

非完备空际间叠干扰下星基导航信号捕获性能分析

该文针对星基定位接收机导航信号捕获的干扰问题,提出一种非完备空际间叠干扰信号模型。首先对提出的干扰模型以及非完备空际间叠引起的干扰裂变效应进行了阐述分析与推究证明,而后推导计算出了星基定位接收机输出信干噪比(SINR)与空际间叠长度的函数式,论证了两者函数单调性关系。仿真实验表明星基定位接收机输出信干噪比为空际间叠长度的单调增函数,短空际间叠长度干扰可抑制3维频码域相关峰突起,降消星基定位接收机捕获性能。

     

一种GNSS信号捕获中的比特压缩与重构方法

在全球导航卫星系统(GNSS)双模接收机的信号捕获过程中,采用"多段匹配滤波器(MMF)+快速傅里叶变换(FFT)"的方式实现信号的时频二维搜索,采用非相干累加算法以提高捕获灵敏度,这2种算法在硬件实现中需要占用大量的存储资源。由于现场可编程门阵列(FPGA)芯片的存储资源有限,本文提出了一种比特压缩方法,极大地降低了非相关累加后的随机存取存储器(RAM)资源,比特重构方法对压缩数据做还原处理,保证了数据的精确度。该方法只对强信号的非相干累加结果做压缩,对弱信号结果不做压缩处理。仿真结果表明,该算法在满足0.9的检测概率,0.01的虚警概率下,节省了0.64 Mbit的RAM资源。     

Code tracking performance analysis of GNSS signal in the presence of CW interference

Continuous wave (CW) interference can cause severe performance degradation of global navigation satellite system (GNSS) receiver. In analysing the code tracking performance of pilot channel under CW interference, the signal spectrum consists of discrete spectral lines and the interference term of the correlator output shows the characteristics of direct current or sine. Thus the traditional assumptions that the interference obeys the Gaussian distribution and that the spectrum of the signal is continuous no longer hold. Considering this fact, this paper presents the analytic expressions of the code tracking error bound for the early-minus-late power (EMLP) discriminator and the dot-product (DP) discriminator. The derived expressions can be used to assess the susceptibility of code tracking performance under CW interference for the pilot channel of GNSS signals. Then the GPS L5 signal is taken as an example of the application of the derived mathematic expressions. The effects of finite front-end bandwidth, correlator spacing, and discrete spectrum of pseudo-random noise (PRN) code on performance are discussed. It is shown that the code tracking performance can be improved by choosing proper receiver parameters and some of the L5 codes are more vulnerable to the interference compared with the average level.     

宽带跳频信号捕获分析方法研究

跳频通信系统在军事、雷达通信等领域应用广泛。在电子对抗战中,跳频通信技术可用于保障通信的稳定。在民用通信领域中,如家庭射频、无线个人局域网中,利用跳频通信技术能够实现可靠的抗干扰数据传输。快速、准确地实现跳频同步是跳频通信系统正常运行的基础。跳频同步又分为同步捕获和同步跟踪两个阶段。文章主要对宽带跳频信号捕获分析方法进行研究。     

GPS接收机信号捕获方法的改进与实现

在GPS卫星定位中,由于卫星和接收机之间的相对运动产生高达10kHz的多普勒频移,同时大多数情况下卫星信号容易被遮挡,接收到的信号都比较弱,需要有一种有效的捕获方法实现GPS信号的捕获。分析了已有捕获方法的特点和缺陷,提出了一种改进的基于循环相关的捕获方法,并进行验证,表明该方法能实现相对弱信号的快速捕获。     

Transfer function modeling and dynamic performance analysis of single-axis acoustic-levitation systems

The development of contactless acoustic-levitation technology has grown rapidly in recent years, and the acoustic-levitation system is an electromechanical system with complex dynamics. However, the traditional differential equation model, used as the core basement for the system, is ineffective at describing the effects of structural changes or parameter adjustments on system performance, which is vital for the design and analysis of the system. This paper proposes a transfer function model to solve this issue. The model can characterize the dynamic performance of the system. Meanwhile, it is competent to describe the effects of structural changes or parameter adjustments on system performance because it can directly derive the relationship between the system performance index and the system parameter variation. It simplifies system design and analysis. In the proposed model, the displacement of the acoustic trap and that of the object are considered as the input and output, respectively, clearly demonstrating the relationship between the acoustic-trap movement and the object motion. Based on the model, the time-domain dynamic performance and the frequency-domain characteristics of the system are systematically described. Furthermore, the model describes the effects of the parameters (the stiffness coefficient, levitated objects, and media) adjustments on the time-domain dynamic performance (damped oscillation frequency, rise time, and peak time) and the frequency-domain characteristics (resonance frequency and bandwidth frequency) of the system. The damping oscillation frequency, resonance frequency, and bandwidth frequency are positively correlated with the stiffness coefficient, while the rise time and peak time are negatively correlated with the stiffness coefficient. These results are verified by numerical simulations and physical experiments. These works will support the design of the acoustic-levitation controller, serve the analysis of the whole system performance, and guide the parameter adjustment during the debugging process. The findings of this paper will lay the foundation for precision motion control of levitated objects, promoting the development of acoustic-levitation technology.     

Auto-correlation function analysis of amorphous interlayers in Ti/Si systems

High-resolution transmission electron microscopy (HRTEM) in conjunction with auto-correlation function (ACF) analysis was utilized to determine the structure of the amorphous TiSi_x layer formed in the initial stage prior to the formation of crystalline silicides. Enhanced formation of C54-TiSi₂ on (0 0 1) Si by tensile stress and/or high-temperature sputtering was found. The present work strongly suggested that the presence of a high density of silicide crystallites in the amorphous TiSi_x layer leads to the favorable TiSi₂ formation.     

GNSS空间覆盖性仿真分析

全球导航卫星系统（GNSS）对空间用户的应用价值在于GNSS信号对空间的覆盖性能,这不仅取决于星载信号发射器的信号辐射角范围,而且取决于用户自身的最小观测角。针对该问题,对GNSS空间覆盖性原理进行了分析,给出了判别依据,然后对GPS、GLONASS、GALILEO系统、北斗区域服务系统、“北斗”全球导航系统及“北斗”与其他GNSS组合共8种仿真方案,不同轨道高度用户的空间覆盖性进行了仿真。在实际应用中,可以根据仿真结果针对不同的应用任务选取不同的卫星星座或选取多星座互操作,以保证最大同时可见卫星数,从而更好地提升GNSS卫星星座的应用价值。     

一种快速的DS/FH混合扩频信号捕获方案及其性能分析

为了提高DS/FH混合扩频信号的捕获速度,提出了一种将DS/FH信号中三维搜索转化为二维搜索的快速捕获方案。通过对搜索过程的详细分析,推导出在单、双驻留条件下的平均捕获时间数学表达式以及高斯信道下系统的检测性能计算公式。理论推导与仿真结果表明:相对于传统的捕获方式,该方案有效地缩短了系统的平均捕获时间,具有更强的抗噪性能,适用于存在较强噪声的复杂通信环境。     

一种实时雷达脉冲信号检测算法及其性能分析

提出了一种新的实时雷达脉冲信号检测算法,该算法首先将数据分为两路,对一路进行单点滑动、取共轭,然后与另一路信号相乘,再累加、取模,最后与门限比较,得到检测结果。算法具有递推和流水结构,硬件实现时只需一个复数乘法器、一个复数加法器、一个复数减法器和一个复数取模运算器。在此采用一阶扰动分析,推导了算法起始点检测误差的解析式,给出了算法性能边界,仿真结果验证了理论推导的正确性。与其他信号检测算法相比,该算法结构规整,易于硬件应用,可实现实时检测。     

On the performance of wide-bandwidth signal acquisition in dense multipath channels

This paper investigates important properties of acquisition receivers that employ commonly used serial-search strategies. In particular, we focus on the properties of the mean acquisition time (MAT) for wide bandwidth signals in dense multipath channels. We show that a lower bound of the MAT over all possible search strategies is the solution to an integer programming problem with a convex objective function. We also give an upper bound expression for the MAT over all possible search strategies. We demonstrate that the MAT of the fixed-step serial search (FSSS) does not depend on the timing delay of the first resolvable path, thereby simplifying the evaluation of the MAT of the FSSS. The results in this paper can be applied to design and analysis of fast acquisition systems in various wideband scenarios.