GPS接收机伪距测量方法研究

介绍了一种高精度伪距测量方法。该方法通过位同步、帧同步、码捕获、码跟踪算法以及载波辅助技术等方法来获取高精度伪距测量值。重点研究了秒模糊度、毫秒模糊度和毫秒内的精度测量方法,得到了通过设置码跟踪环的相关间隔来设置其测量精度的方法。实验结果验证了算法的可行性。     

基于FPGA的高动态P码直捕算法设计与实现

长周期精密测距码（P码）的直接捕获技术对提高导航接收机的性能十分关键,为了设计出高动态、低信噪比环境下的P码快速直接捕获接收机,采用部分匹配滤波器组实现伪码时域并行搜索,结合小点数的快速傅里叶变换（FFT）,将匹配滤波器输出的部分相关值进行功率谱分析,完成多普勒频率偏移的并行搜索。硬件实现时结合FPGA的特殊结构,提高资源利用率,同时采用并行流水机制处理ADC的采样信号,对于每一个采样点,均可以在下一个采样点到达之前完成该点的码相位和频率的二维搜索。对比国内外P码接收机的研究成果,算法在捕获时间上有很大改进。在信号功率为-165 dBW,伪码相位±1 s的时间不确定度,以及多普勒频率偏移±16 kHz的条件下,捕获时间小于10 s,完全适用于高动态环境下的P码快速直接捕获。     

基于DSP辅助的伪随机码快速捕获实验分析

提出了利用DSP进行辅助捕获的PN码快捕实现新方法。利用DSP强大的数据处理能力，通过软件算法估计出接收信号和本地产生PN码信号的相对时延，指导串行搜索系统从接收信号最可能的相位位置附近开始搜索，从而达到快捕的目的。实验结果表明：通过DSP器件进行辅助捕获，不仅能在很短的时间内完成PN码的捕获；同时，通过对“超前码片数”置不同的值，可以很方便地控制串行捕获电路从开始捕获到完成捕获所需的捕获时间。     

微弱信号下基于模糊度搜索的辅助式GPS定位算法研究

针对微弱信号下GPS接收机无法测量得到完整信号发射时刻的问题,提出了一种基于模糊度搜索的辅助式GPS定位算法。基于该算法接收机不需要位同步、帧同步和解调导航电文,仅对GPS信号进行伪码相位测量,在获取卫星星历、卫星钟差参数等辅助信息的基础上完成定位解算。论文从数学上严格推导了消除信号发射时刻模糊度的条件,并对五颗以上的观测卫星建立了定位解算方程,给出了算法流程。利用实测数据仿真验证了该算法的有效性。比较表明,该算法的定位精度与常规GPS定位算法(信号发射时刻不存在模糊度)相当。     

载波/多普勒平滑伪距在Android手机中的定位实现

针对Android手机GNSS伪距定位精度较低的问题，利用手机端观测信息，通过载波相位/多普勒平滑伪距改善手机端伪距观测值的质量，从而达到提高定位精度的效果。首先给出了Android手机GNSS原始观测量的获取方法，然后推导了载波相位平滑伪距和多普勒平滑伪距算法模型，并设计合理有效的试验对算法的精度进行评定。试验结果表明：在手机端静态定位中载波相位和多普勒平滑算法均可提高原始伪距的定位精度，且多普勒平滑算法表现更优；在手机端动态定位中多普勒平滑算法可获得比原始伪距更优的定位精度，但是载波相位平滑算法较原始伪距更差；由于硬件的制约手机端周跳和信号失锁严重，占比超过50%，载波相位在手机端的可用性较低；多普勒平滑算法的最优平滑时间常数小于等于10 s，具有实时动态定位的巨大潜力。     

GPS单频载波相位相对定位的OTF算法及实现

利用单频接收机的C/A码伪距和LI载波相位观测值,采用星间和站间双差数学模删,消除卫星相关误差、接收机相关误差,削弱信号传播误差,利用LAMBDA算法高效快速地固定整周模糊度,从而实现高精度载波实时相对定位,对于短基线,可以获得厘米级的定位精度.     

中频数据卫星捕获算法研究

软件无线电技术在卫星导航接收机中的应用在很大程度上改变了基带信号的处理方法.本文详细论述了基于FFT的频域快速捕获技术,通过对实测中频数据实验分析,指出仅利用门限方法无法准确在频域判决可视卫星,必须依靠其他信息进行辅助判决.在分析通过实测数据获得的可视卫星在连续扩频码周期内多普勒和伪码相位变化规律的基础上,给出了采用多...     

相位平滑P1码伪距及其单点定位精度分析

针对C/A码、P1码、P2码伪距的精度问题,利用郑州J3JG站实测数据进行计算,结果表明:该站接收机产生3种伪距的精度从高到低依次为P1码、C/A码、P2码.在此基础上,利用相位观测值对精度最高的P1码伪距进行平滑,采用自编程序,对相位平滑Pl码伪距的单点定位精度进行研究.实验结果表明:相位平滑P1码伪距的单点定位结果较P1码伪距的定位结果更稳定,X、Y、Z方向的平均误差和RMS值也较P1码伪距有明显提高.     

智能手机虚拟格网伪距差分定位方法研究

针对智能手机全球卫星导航定位系统(GNSS)观测数据质量差、定位精度低的问题,该文提出了基于多普勒平滑的格网伪距差分算法.首先对观测数据进行分析、粗差剔除,再利用多普勒观测值对伪距进行平滑,最后利用虚拟格网伪距观测值改正相关误差进行定位.结果 表明:经过手机观测值质量控制,利用多普勒观测值平滑伪距后进行虚拟格网伪距差分,可以得到平面优于1.5m,垂直优于3 m的定位结果.     

两种不同方式智能手机伪距平滑分析

针对智能手机受导航芯片和天线接收器限制、伪距观测值精度不高、粗差较多等问题,本文提出利用各观测量进行历元间求双差,以探测观测值中的粗差并予以剔除,再结合多普勒观测值和载波相位观测值平滑伪距,从数据质量和伪距平滑两方面分析影响智能手机定位精度的原因,说明智能手机载波相位观测值和多普勒观测值平滑伪距的可用性。试验结果表明：智能手机载波相位平滑伪距可有效提高定位精度;多普勒观测值平滑伪距定位精度与导航芯片获取的多普勒观测值有关,小米MI8多普勒观测值精度优于华为P30。     

A scheme for weak GPS signal acquisition aided by SINS information

In order to enhance the acquisition performance of global positioning system (GPS) receivers in weak signal conditions, a high-sensitivity acquisition scheme aided by strapdown inertial navigation system (SINS) information is proposed. The carrier Doppler shift and Doppler rate are pre-estimated with SINS aiding and GPS ephemeris, so that the frequency search space is reduced, and the dynamic effect on the acquisition sensitivity is mitigated effectively. Meanwhile, to eliminate the signal-to-noise ratio gain attenuation caused by data bit transitions, an optimal estimation of the unknown data bits is implemented with the Viterbi algorithm. A differential correction method is then utilized to improve the acquisition accuracy of Doppler shift and therefore to meet the requirement of carrier-tracking loop initialization. Finally, the reacquisition experiments of weak GPS signals are implemented in short signal blockage situations. The simulation results show that the proposed scheme can significantly improve the acquisition accuracy and sensitivity and shorten the reacquisition time.     

RETRACTED ARTICLE: Likelihood-based GNSS positioning using LOS/NLOS predictions from 3D mapping and pseudoranges

The accuracy of conventional global navigation satellite systems (GNSS) positioning in dense urban areas is severely degraded due to blockage and reflection of the signals by the surrounding buildings. By using 3D mapping of the buildings to aid GNSS positioning, the accuracy can be substantially improved. However, positioning performance must be balanced against computational load. Here, a likelihood-based 3D-mapping-aided (3DMA) GNSS ranging algorithm is demonstrated that enables signals predicted to be non-line-of-sight (NLOS) to contribute to the position solution without explicitly computing the additional path delay due to NLOS reception, which is computationally expensive. Likelihoods for an array of candidate positions are computed based on the difference between the measured and predicted pseudoranges. However, a skewed distribution is assumed for those signals predicted to be NLOS on the basis that the ensuing ranging errors are always positive. An overall position solution is then extracted from the likelihood surface. GNSS measurement data have been collected at several locations in both traditional and modern dense urban environments. Horizontal root-mean-square single-epoch position accuracies of 4.7, 5.6 and 6.5 m are obtained using, respectively, a Leica Viva geodetic receiver, a u-blox EVK M8T consumer-grade receiver and a Nexus 9 tablet incorporating a smartphone GNSS antenna and a GNSS chipset that outputs pseudoranges. The corresponding accuracies using single-epoch conventional GNSS positioning are 20.5, 23.0 and 28.4 m, about a factor of four larger. The 3DMA GNSS algorithms have also been implemented in real time on a Raspberry Pi 3 at a 1-Hz update rate.

     

基于铱星突发信号的导航定位技术研究

全球导航卫星系统(GNSS)存在落地信号弱、易受干扰等问题,而低轨卫星系统因其较高的信号落地功率、较低的信号空间损耗以及较好的多普勒特性逐渐成为导航领域的研究热点. 铱星星座是目前唯一已实现全球覆盖的低轨卫星系统,其提供的授时与定位(STL)能力主要服务于美国军方,具体信号体制及接收处理技术均未公开发布. 通过对铱星STL突发信号体制开展深入研究及解析,提出利用STL突发信号实现非合作导航定位,并通过实收信号完成了定位解算算法验证,实收试验结果表明所提算法能够实现精度优于100 m的定位. 研究成果能够为我国低轨导航系统建设提供理论基础,有效推进下一代卫星导航系统持续发展.      

<Emphasis Type="Italic">sub</Emphasis>ATTO indoor GPS – pitfalls,solutions and performance using a conventional correlator

A key requirement for emergency call location (e.g. E911), for robust operation of location-based m-commerce systems and for telematics systems is that the location technology be able to operate in urban canyons and inside buildings. We start from a definition of the target environments, which includes multi-level parking garages, office buildings and homes, but not underground parking garages or tunnels. Based on experience in these target environments and understanding of typical applications we derive specific requirements for sensitivity and acquisition speed. The primary problems associated with weak signal operation are as follows. (1) In conventional GPS receivers sampling at the correlator output typically occurs at a sampling interval of the order of 1 ms. With weak signals, however, the signal-to-noise ratio of these samples is too low to support lock-in of a phase-locked or frequency-locked loop. (2) With weak signals, the signal-to-noise ratio is too low to support the extraction of the 50BPS navigation message from the signal. Therefore, aiding data is required from an external source. (3) Because the data cannot be extracted, it is not possible for the receiver to synchronize to the incoming bits, words or subframes. Therefore, it is not possible to construct pseudoranges without prior information. (4) The paper describes Sigtec Navigation's subATTO technology. This technology provides sensitivity down to –185 dBW (19 dBHz assuming NF of 1.5 dB and no other implementation loss). This is 5 dB below an attoWatt (10^–18 W) and has been shown to provide reliable positioning inside buildings, multi-level parking garages and in urban canyons without any aiding at all. The paper describes the patented signal processing scheme, how ambiguity resolution and time synchronization are achieved, the wireless assistance technique, the acquisition strategy and the use of scanning channels. Results are presented from trials in a multi-level parking garage. The results obtained in most parking garages are similar to these in terms of availability of fixes, signal strengths received and location accuracy achieved. The performance achieved in multi-level parking garages is rarely worse than this. One of the major impediments to practical application of weak signal-processing schemes is the limited dynamic range imposed by the GPS C/A code signal structure. This problem is discussed along with the problems of multipath distortion in the context of telematics operation in urban canyons. A realistic urban accuracy goal of 20 m for 95% of fixes is proposed based on experience with GPS and dead reckoning. Enhancements under development will provide sensitivity of –188 dBW, which will provide continuous availability within a broader range of indoor environments. For practical applications, this will require the use of modern 'search engine' hardware for acceptable acquisition speed. As the paper shows, this sensitivity is near the practical limit of sensitivity with acceptable acquisition times and dynamic capability. Electronic Publication     

煤矿井下基于Attention机制的LSTM地磁定位算法

针对利用无线射频信号对井下人员定位受环境影响大的问题,本文提出了基于Attention机制的LSTM地磁定位算法。利用矿用智能手机以路径连续采集方式获取井下地磁数据,通过分析井下巷道地磁信号变化的空间差异性和时间稳定性,建立面向井下拓扑结构的地磁指纹数据库;在LSTM模型中引入Attention机制,使其能够根据地磁序列与位置的相关性进行训练且给予不同的权重;将井下实时采集的地磁数据输入模型后进行位置估计。试验结果表明,通过神经网络LSTM学习地磁序列与相应位置的映射关系,可有效提高定位精度。     

Secure User Plane Location: concept and performance

Assisted GPS (A-GPS) has received much attention from both academic and industry because of its two major advantages, faster positioning and greater sensitivity. Secure User Plane Location (SUPL) is an emerging standard for A-GPS produced by the Open Mobile Alliance. This article briefly reviews A-GPS, then introduces the SUPL architecture and explains how SUPL works. An intensive SUPL A-GPS survey under different environments is reported in detail, while a standalone GPS test was utilized for comparison. The survey was carried out in 24 locations over the University of New South Wales campus representing 5 types of terrain: Urban, Suburban, Rural, Indoor, and Open sky with a wide range of acquisition difficulty levels. The results show SUPL can bring a great benefit in fast positioning—much shorter Time-To-First-Fix and high sensitivity—and a much lower failure rate.     

视觉辅助下的室内惯导位姿修正

惯性导航系统可以短期内提供连续的高精度信息，但是误差会随时间增大，不能长期独立工作。而在大型仓库、地下停车场等室内卫星信号薄弱的场景中，传统的惯导+卫星组合方法也不再适用。针对该问题，本文提出了一种视觉与惯导组合定位的方法。本文研究的惯导+视觉组合的定位方法中，采用基于合作目标的单目视觉定位方法对惯导误差进行修正。对于惯导误差的修正方法，本文利用视觉定位的位姿信息建立量测方程，进行卡尔曼滤波，并选取合适的试验设备，通过实际试验对比验证了该算法对惯导系统误差的修正具有良好的效果。     

GPS卫星信号Doppler频移的计算与分析

在GPS导航定位系统中，多普勒频率偏移直接影响接收机性能。为了克服多普勒频率偏移的影响，提高接收机的GPS信号捕获速度，对多普勒频移估计算法进行研究。通过分析可视卫星的判定、Doppler频移计算方法，基于NewStar150GPS原理实验平台，使用C＋＋语言编程，开发Doppler频移计算程序。实验结果表明，Doppler频移的大小与a有关。当a〈90°时，多普勒频移为正，用户接收机收到的频率比卫星发射的频率要低。当a〉90°时，多普勒频移为负；当a=90°时，多普勒频移为0。