基于SIC的伪卫星系统抗远近效应捕获算法研究

地基伪卫星系统中由于远近效应的影响,近场伪卫星信号可能对远场伪卫星信号形成压制干扰,导致远场伪卫星信号无法被捕获. 针对该系统中使用的跳时直接序列扩频(TH-DSSS)信号的捕获问题,引入串行干扰消除(SIC)技术,缓解伪卫星系统中的远近效应问题,通过本地重构强信号和干扰对消降低强信号对弱信号捕获的影响,并从理论和仿真两方面对其性能进行了分析. 仿真结果表明,相比传统未采用干扰消除的捕获算法而言,基于SIC的信号捕获方法在不改变伪卫星基站结构和接收机框架的基础上,可有效降低远近效应的影响,提高弱信号捕获概率,扩大系统工作范围,从而为接收机在强远近效应场景下的捕获、跟踪和定位解算提供有效保障.      

卫星导航干扰抑制与信号增强算法研究

针对功率倒置(PI)抗干扰算法只能抑制干扰而不能增强导航信号问题,采用级联空域抗干扰算法．第一级通过并行基于正交子空间投影的PI算法处理消除强干扰,然后第二级利用卫星导航信号循环平稳性对期望信号进行波束形成,增强卫星导航信号,进一步提高信干噪比．最后通过仿真验证该方法的有效性．      

基于密度聚类的北斗卫星导航弱信号自动捕获方法

在外界射频信号、导航接收机混频处理噪声的影响下，为了有效捕获北斗卫星导航弱信号信息，提出基于密度聚类的北斗导航弱信号自动捕获方法.使用密度聚类得到BDS信号来源的聚类中心，结合聚类中心设计卫星波束方向，约束卫星导航信号接收范围，抵御干扰信号的空域干扰；通过基于小波阈值方法去除波束抗干扰作用下导航信号的噪声信息；采用相关函数模值计算方法计算去噪后导航信号和已知弱信号之间相关性，相关性大于门限值时说明去噪后导航信号为弱信号.实验结果表明，在外界射频信号和混频器干扰下，此方法具备自动捕获北斗卫星导航弱信号的能力.     

改进差分相干累加算法的北斗卫星导航弱信号捕获

以提升北斗卫星导航能力为目的,设计了改进差分相干累加算法的北斗卫星导航弱信号捕获方法。该方法通过构建北斗卫星信号模型,利用该模型获得北斗卫星导航中频信号;然后以改进差分相干累加算法为基础,建立北斗卫星导航弱信号捕获模型,将北斗卫星导航中频信号作为该模型的输入,经过北斗卫星导航弱信号捕获模型对中频信号块实施累加处理和多普勒圆周位移搜索,以及快速傅里叶变换和反傅里叶变换等步骤后,通过判断北斗卫星导航弱信号捕获判决,输出北斗卫星导航弱信号捕获结果。实验结果表明：该方法在捕获北斗卫星导航弱信号时的运算量较小,可有效捕获-36 dB的北斗卫星导航弱信号,同时其捕获概率较高,应用效果较为显著。     

BOC调制信号抗干扰能力分析

抗干扰能力是卫星导航信号设计的一项重要考核要素。目前典型的方法是采用抗干扰品质因数、伪码跟踪精度下降来衡量。但是该抗干扰品质因数不能反映码速率对抗干扰能力的贡献,而伪码跟踪精度下降则不够简捷。提出了能够反映伪码速率贡献的载波跟踪抗干扰品质因数,以及能够简捷地反映伪码跟踪抗干扰能力的伪码跟踪抗干扰品质因数。采用所提出的两项指标,对二进制偏移副载波BOC(Binary Offset Carrier)调制这一新型卫星导航信号进行了抗干扰能力分析。结果表明,同码率BOC调制信号载波跟踪抗干扰能力比BPSK调制信号强,伪码跟踪抗干扰能力比BPSK调制信号弱。     

一种SINS/GPS深组合导航系统技术问题分析

为了满足高动态用户及强干扰条件下的应用需求,提出了一种基于卫星信号矢量跟踪的SINS/GPS深组合导航方法,设计了基于FPGA硬件平台的实施方案。利用组合卡尔曼滤波器反馈回路取代了传统接收机中独立、并行的跟踪环路,能够同时完成所有可视卫星信号的跟踪和导航信息处理;通过矢量跟踪算法对所有可视卫星信号进行集中处理,能够增强跟踪通道对信号载噪比变化的适应能力,从而提高接收机在强干扰或信号中断条件下的跟踪性能;根据SINS导航参数和星历信息推测GPS伪码相位和多普勒频移等参数,用以辅助卫星信号的捕获和跟踪,能够大大缩短接收机的搜索捕获时间,并增强接收机在高动态条件下的跟踪性能。基于矢量跟踪的深组合方法不仅在GPS信号短暂中断期间,能够保证系统的导航精度和可靠性,而且在强干扰环境中能够维持较好的伪码相位和载波频率跟踪性能。     

北斗地基导航信号网络测试方法研究

为尝试解决北斗卫星导航系统在特定区域因信号受遮挡而无法定位或定位精度较差的问题,引入了以伪卫星为基础构成的北斗地基导航信号网络。介绍了北斗地基导航信号网络的系统组成和关键技术,提出了一套测试评估其定位和授时效能的方法,并给出了测试评估的指标建议作为参考,为地基伪卫星增强北斗卫星导航系统的应用及推广提供了相应的评价工具。     

GPS系统及其应用 第二讲GPS系统的组成

<正> GPS系统是利用设置在地面上的专用接收机,接收卫星发射的无线电信号,来实现导航定位和时间传递的综合系统。在第一讲中已经介绍了利用CPS系统可以进行实时的三维导航、定位以及授时工作,为此需预知卫星在空间精确的坐标,卫星信号在空间的传播时间,以及地面接收机对卫星信号进行捕获跟踪的能力。为了实现上述要求,全球定位系统将由空间部份,地面控制部份和用户装置部份组成,在这讲中将介绍这三个组成部份的系统设备及其相应功能。     

北斗室内导航伪卫星信号传播效应分析

室内场所因建筑物的遮挡,卫星导航设备无法接收导航信号而失去定位能力,伪卫星可以通过发射类似导航信号的方式独立进行定位。针对伪卫星信号在室内传播面临的功率衰减、多径衰落等问题,该文在经典室内通信模型的研究基础上,分析了伪卫星信号室内传播的应用环境和约束条件,建立了伪卫星信号室内传输的信道模型,并对伪卫星信号功率以及路径损耗、多径传播模型进行了计算仿真。仿真结果表明,对数距离路径损耗模型及莱斯分布多径模型可准确描述室内伪卫星信号的传输特点。     

一种新的消除GPS互相关干扰的方法——Q路滤波法

在微弱GPS信号处理中,当接收到的信号中某颗卫星的信号能量比较强,而其他卫星信号都很微弱时,就有可能出现这颗能量比较强的卫星对其他卫星信号的捕获、跟踪产生干扰,这种干扰就是互相关干扰。通过研究现有的消除互相关干扰的方法,提出一种全新的方法——Q路滤波法,这种方法操作简单,并且可以完全消除互相关的影响。     

Modified compressive sensing approach for GNSS signal reception in the presence of interference

Pre-processing traditional navigation signals in global navigation satellite system (GNSS) receivers includes the conversion of an analog-to-digital sample and acquisition following the basic principle of Nyquist sampling theory. This condition inevitably increases the system computation time and cost of a modern wideband receiver. In recent years, the compressive sensing (CS) approach has been proven to effectively reduce the number of measurement samples required for digital signal acquisition systems. This method gives new potential to this modern design. In this study, a modified compressive sensing algorithm for the acquisition of a GNSS signal that is contaminated by an interfering signal is presented. The proposed method attempts to combine CS demodulation and the subspace projecting method to enhance GNSS signal acquisition performance with interference present. First, the received signal is sub-sampled and aliased from a compressive sampling process. This operation maintains the restricted isometry property (RIP) condition of the second sampling process using a Toeplitz-structured sensing matrix, which replaces a conventional random sensing matrix. The matrix ensures that distances between desired signals on the set of sparse space are not influenced by the sampling process. Next, the interference is eliminated through the orthogonal feature between the interference signal and the desired signal using the subspace projecting method. This also preserves the RIP of the projecting matrix to ensure that the original structure of the linear projection of the signal is preserved. After this, an iterative least-square method is utilized to recover the correlator output from the reception samples taken by the CS demodulator. In addition, the signal detection performance in the presence of co-channel interference using a CS demodulator is analyzed and evaluated. Finally, the relationships between signal detection probability, compressive factor and signal bandwidth are also illustrated. Several numerical results are presented to verify the theory.     

北斗伪卫星信号的室内多径传播特性

北斗伪卫星系统因其较强的抗干扰能力和灵活机动的组网能力可以应用于室内位置服务。多径效应是影响伪卫星定位精度的主要因素，因此，掌握北斗伪卫星室内多径传播特性是抑制多径、提高定位精度的前提。本文针对北斗伪卫星特有的信号体制，利用射线追踪法，研究了室内环境下伪卫星信号路径损耗、功率角度分布等多径特性参数，通过Wireless Insite软件，构建了大型商场的三维模型，在此基础上进行了仿真试验验证。结果表明，伪卫星多径数量在非视距条件下会急剧减少，且伪卫星多径分量以相近功率值分布在特定范围的水平方向角内；同时其衰落信道模型服从小尺度衰落，符合瑞利-对数正态分布，大尺度衰落与对数距离路径损耗模型相吻合。     

GPS/Pseudolite/INS integration: concept and first tests

This paper discusses the introduction of pseudolites (ground-based GPS-like signal transmitters) into existing integrated GPS/INS systems in order to provide higher availability, integrity, and accuracy in a local area. Even though integrated GPS/INS systems can overcome inherent drawbacks of each component system (line-of-sight requirement for GPS, and INS errors that grow with time), performance is nevertheless degraded under adverse operational circumstances. Some typical examples are when the duration of satellite signal blockage exceeds an INS bridging level, resulting in large accumulated INS errors that cannot be calibrated by GPS. Such a scenario, unfortunately, is a common occurrence for certain kinematic applications. To address such shortcomings, both pseudolite/INS and GPS/pseudolite/INS integration schemes are proposed here. Typically, the former is applicable for indoor positioning where the GPS signal is unavailable for use. The latter would be appropriate for system augmentation when the number and geometry of visible satellites is not sufficient for accurate positioning or attitude determination. In this paper, some technical issues concerned with implementing these two integration schemes are described, including the measurement model, and the appropriate integration filter for INS error estimation and correction through GPS and pseudolite (PL) carrier phase measurements. In addition, the results from the processing of simulated measurements, as well as field experiments, are presented in order to characterize the system performance. As a result, it has been established that the GPS/PL/INS and PL/INS integration schemes would make it possible to ensure centimeter-level positioning accuracy even if the number of GPS signals is insufficient, or completely unavailable. Electronic Publication     

Pseudo-Satellite Applications in Deformation Monitoring

In this article, three general classes of potential pseudolite applications for deformation monitoring are described. The first is GPS augmentation with pseudolite(s), which is suitable for circumstances such as urban canyons, or for monitoring in valleys and deep open-cut mines. The second is indoor applications of pseudolite deformation monitoring systems. Pseudolite arrays can, in principle, completely replace the GPS satellite constellation. This could extend the “satellite-based” deformation monitoring applications into tunnels or underground, where GPS satellite signals cannot be tracked. The last case is an inverted pseudolite-based deformation monitoring system, where a “constellation” of GPS receivers with precisely known “orbits” track a mobile pseudolite. The system consists of an array of GPS receivers, the base reference pseudolite, the mobile pseudolite, and a central processing system. However, in the case of such pseudolite-only or hybrid pseudolite-GPS deformation monitoring systems, some additional issues need to be addressed. These include multipath, atmospheric delay effects, and pseudolite location-dependent biases. To address deformation monitoring applications, some practical procedures to mitigate or eliminate their influence are suggested. Some experiments were carried out using NovAtel GPS receivers and IntegriNautics IN200CXL pseudolite instruments. The experimental results indicate that the accuracy of the height component can indeed be significantly improved – the RMS of the vertical component has been reduced by a factor of 4, to the same level as the horizontal components. Their performance will be demonstrated through case study example. ? 2002 Wiley Periodicals, Inc.     

GNSS接收机抗干扰自适应调零技术性能估计

GNSS抗干扰技术中常采用功率倒置算法(PI)来得到自适应波束形成的零陷。信干比为80dB时,PI算法能准确识别干扰的方向,抗干扰分辨率好,但当信干比降低到20dB左右时,在射频干扰信号方向谱周围会形成大量带状的零陷,干扰信号的分辨率恶化严重。空间谱估计中的多重信号分类(MUSIC)算法具备超分辨率特性,通过信号子空间和噪声子空间的正交功率最小化原理,采用空间二维谱峰搜索方位角和仰角,能够准确进行DOA估计,有效区分有用信号和干扰信号。在高信干比条件下,基于MUSIC算法的最小功率估计抑制深度明显好于传统的PI算法;在低信干比条件下,MUSIC-PI算法在干扰信号方向谱判别及零陷抑制方面依然有效,而传统的PI算法失效。计算机仿真结果验证了该方法在GNSS抗干扰领域的有效性和鲁棒性。     

发射信号不完善性对卫星导航系统内及系统间干扰的影响分析

研究了3种典型的卫星发射信号不完善性——载波泄漏、互调失真和杂散辐射对于卫星导航信号的接收所带来的干扰,通过信号建模以及谱分离系数、码跟踪谱灵敏度系数和等效载噪比的解析计算对干扰效果进行量化分析;针对GPS和Galileo系统L1/E1频段的信号进行了多层次的仿真计算,给出了综合考虑噪声、信号损耗、外源干扰、GNSS系统内和系统间干扰,以及3种信号不完善性单独作用、两两组合和综合作用下的结果,其中对于GPS L1C/A短码考虑了电文调制对线谱的影响。结果表明,当总的不完善干扰功率水平达到一定程度后,其对接收机信号捕获跟踪和解调的影响大于系统间干扰,不能忽略。     

一种用于BDS-3接收机工程实现的两级B1C信号捕获技术

北斗三号卫星导航系统（BDS-3）B1C信号相较北斗二号卫星导航系统卫星信号,从信号结构、编码方式再到导航电文结构都发生了改变,包括引入导频信号、二次编码、BOC调制、LDPC编码和B-CNAV1导航电文结构等.这些改变一方面提高了信号性能(如抗多路径、信号捕获和跟踪精度等);另一方面,也带来了一系列问题,对接收机的信号捕获技术提出了全新的要求，如需处理更大的数据流,解决由二次编码带来的符号翻转和BOC调制造成的捕获多峰性问题.针对BDS-3接收机的工程实现,本文提出了一种新颖有效的两级B1C信号捕获技术.其中第一阶段采用扩展并行平均相关搜获结构,用以解决符号翻转问题,同时实现高效的信号粗捕获;第二阶段在缩小的搜索范围内进行高精度搜索,此步骤可有效避免信号多峰性造成的误锁可能.除此之外,本文还介绍了单信道和多信道组合式捕获技术,用户可根据资源占用和捕获灵敏度需求选取更有效的捕获方法.实验结果表明,本文提出的方法允许使用更小更经济的快速傅里叶变换（FFT）模块,并通过大量并行处理的方法实现快速捕获.相较传统的高精度捕获技术,此方法在采样频率超过50 MHz时,能够在保证相近的捕获精度的同时减少至少61％的运算量.      

A new algorithm for fine acquisition of GPS carrier frequency

Design of a GPS signal acquisition algorithm is a trade-off between improvement of the acquisition frequency resolution and reduction in the acquisition time. A new algorithm is proposed to acquire the carrier frequency accurately by correlation of the GPS signal after completion of the coarse acquisition of the signals. The CA code in a period of 1 ms is stripped off first. Then, several local replica carriers are generated and mixed with the CA-code-stripped data. Finally, the mixed data are integrated to detect the carrier frequency accurately. By analyzing the correlated integration result, the algorithm performance is evaluated on the aspects of the computational load, the effects of the carrier-to-noise ratio, and the navigation data transition. Performance of the proposed method is verified by simulations and experiments.