NLOS GPS signal detection using a dual-polarisation antenna

The reception of indirect signals, either in the form of non-line-of-sight (NLOS) reception or multipath interference, is a major cause of GNSS position errors in urban environments. We explore the potential of using dual-polarisation antenna technology for detecting and mitigating the reception of NLOS signals and severe multipath interference. The new technique computes the value of the carrier-power-to-noise-density (C/N ₀) measurements from left-hand circular polarised outputs subtracted from the right-hand circular polarised C/N ₀ counterpart. If this quality is negative, NLOS signal reception is assumed. If the C/N ₀ difference is positive, but falls below a threshold based on its lower bound in an open-sky environment, severe multipath interference is assumed. Results from two experiments are presented. Open-field testing was first performed to characterise the antenna behaviour and determine a suitable multipath detection threshold. The techniques were then tested in a dense urban area. Using the new method, two signals in the urban data were identified as NLOS-only reception during the occupation period at one station, while the majority of the remaining signals present were subject to a mixture of NLOS reception and severe multipath interference. The point positioning results were dramatically improved by excluding the detected NLOS measurements. The new technique is suited to a wide range of static ground applications based on our results.     

基于RSI的GPS坐标时间序列瞬态地壳形变信号探测

提出了利用RSI的瞬态地壳形变信号探测方法,并将其应用于北美洲卡斯卡迪亚古陆俯冲带区域的部分GPS连续跟踪站的时间序列的瞬态形变探测中。研究结果表明：RSI方法能有效探测各序列中的瞬态形变,且能获得瞬态形变发生的开始时间、结束时间、持续时间和滑移量;与未使用偏移改正的序列相比,使用瞬态偏移改正得到的残差时间序列方差显著减小。     

GPS与Galileo共用的MBOC信号研究

介绍了GPS与Galileo共用信号的演变过程,通过BOC（1,1）在兼容性、互操作性方面的表现,以及将MBOC（6,1,1／11）与之相比较,描述了MBOC（6,1,1／11）在这两个方面的表现。可供我国卫星导航信号体制设计借鉴学习,为GPS／Galileo接收机设计提供参考。     

GPS数字中频信号仿真

GPS数字中频仿真信号可以为接收机和信号处理电路的设计测试提供信号源.基于GPS数字中频信号的数学模型,详细叙述GPS数字中频信号仿真的步骤,并利用软件接收机对仿真结果进行验证,分析采样频率和量化位数对信号信噪比的影响.     

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.     

L5载波的信号质量分析

增加第三民用频率L5载波是GPS现代化措施中的一项,目前美国已经有4颗卫星具有L5观测值。从L5的信号结构上进行分析,应用L5载波的实际观测数据,与L1载波和L2载波相比较,L5载波不但在信噪比上得到提高,而且其多路径效应的影响也比较小,具有较好的数据观测质量。     

Virtual differential GPS based on SBAS signal

In order to access the satellite-based augmentation system (SBAS) service, the end user needs access to the corresponding geostationary earth orbit (GEO) satellites that broadcast the augmentation information for the region. This is normally not a problem for aviation and maritime applications, because an open sky is typically available for such applications. However, it is difficult to access the GEO satellites directly at high latitudes for land applications because of the low elevation angles to the GEO satellites (e.g., 4–22° in Finland to the European geostationary navigation overlay services [EGNOS] GEO satellites). Results from a driving test of 6,100 km in Finland show that the EGNOS GEO satellites can be accessed in only 51.8% of the driving routes. Furthermore, it is also difficult to access the GEO satellites from city canyons, because the high buildings block the GEO signals. This article presents a solution to solve this problem by creating virtual differential GPS (DGPS) reference stations using the SBAS signal in space (SIS). The basic concept is to convert the SBAS signal to Radio Technical Commission for Maritime Services (RTCM) signals, and broadcast the converted RTCM signals over the wireless Internet using the Internet radio technology. Therefore, access to the SBAS service will not be limited by low elevation angles to the GEO satellites because the converted RTCM data streams are disseminated over the wireless Internet. Furthermore, the SBAS service can then be accessed via a legacy DGPS receiver. Two test cases have been carried out with the prototype system developed by the Finnish Geodetic Institute. The test results showed that the positioning accuracy of the virtual DGPS solution was about 1–2 m at 95%, which was similar to that of the standard WAAS/EGNOS solution. The positioning accuracy was not degraded, compared to that of the standard wide area augmentation system–European geostationary navigation overlay services (WAAS/EGNOS) solution, as long as the distance between the rover receiver and the virtual DGPS reference station was less than 150 km. A preliminary driving test of 400 km carried out in southern Finland showed that the availability of the virtual DGPS solutions was 98.6% along the driving route.     

GPS IF信号的计算机模拟和实现

A GPS IF signal computer simulation method is proposed in this article. The carrier Doppler frequency and the total propagation and delay time can be modeled or calculated with the input GPS satellite ephemeris file. The simulated GPS IF signal outputs to a text file for post-processing and analysis. The simulation signal spectrum is compared with the received real GPS IF signal spectrum, and the correctness of the simulation result is verified. Supported by the Research Fund (2008–2009) of State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, the National 863 Program of China (No.2008AA12Z308).     

GPS中频信号快速捕获技术分析

为解决GPS中频信号快速捕获问题,在介绍GPS码相位和载频信号捕获原理的基础上,重点阐述了基于FFT的并行GPS中频信号快速捕获方法,同时在非相干累加、接收信噪比、先验信息等方面分析了提高中频信号快速捕获的可能性,最后利用一组GPS实测数据对上述分析进行了的仿真计算。仿真结果表明基于FFT技术的中频信号快速捕获方法具有抗干扰、捕获速度快和检测低信噪比信号的能力,可以满足GPS软件接收机定位的要求。     

美伊冲突中的GPS信号增强分析

对2019年6月美伊冲突事件中的GPS功率增强进行了分析,具体从接收机类型、天线类型以及卫星型号三部分对GPS P(Y)码的功率增强进行了分析,分析表明,采用不同类型接收机的测站,其功率增强值明显不同,而采用不同类型天线的测站,其功率增强值相差不大;此外,在接收机或天线类型相同情况下,同组并址站的相同类型的卫星功率增强值对比结果呈一致性.      

双频接收机C／A码与P码伪距的精确比较

采用Matlab编制的精密伪距单点定位程序，利用IGS跟踪站的源数据，对P码和C／A码伪距精密定位的精度进行了比较和分析。     

双频接收机C/A码与P码伪距的精度比较

采用Matlab编制的精密伪距单点定位程序,利用IGS跟踪站的源数据,对P码和C/A码伪距精密定位的精度进行了比较和分析.     

Identification of GPS positioning solutions deteriorated by signal degradations using a fuzzy inference system

The accuracy of GPS positioning based on pseudorange measurements under signal degradation environments is limited by poor satellite geometry and signal distortions due to diffraction and multipath. As a result, the GPS position solutions could become unreliable. Those deteriorated solutions should be identified and not used for navigation. For that purpose, methods for reliable identification of deteriorated GPS positioning solutions from a navigation receiver should be developed. In this paper, a fuzzy inference system is proposed to classify the quality of GPS positioning solutions. The input for the system includes the signal quality evaluated by the difference between the measured and expected carrier-to-noise density ratio (C/N0) and the satellites geometry strength evaluated by the dilution of precision (DOP) number. The proposed fuzzy inference system is developed based on the human knowledge and understanding of the problem under consideration and is further optimized using data acquired from the field. The test results indicate that the proposed method can be used for reliable identification of deteriorated GPS position solutions affected by signal degradations.     

GPS现代化和GPS信号重构技术的进展

介绍了GPS现代化计划和GPS信号重构技术的进展。GPS信号重构的目的是确保在某些特定区域的美军能够正常使用GPS而不受影响,而在同一区域与美军对立的一方既不能使用民用GPS信号,也不能使用GPS的军码,至于在该特定区域以外的民间GPS用户,则依然能够正常使用GPS;此外还重点介绍了由美国大地测量局(NGS)主持运行的GPS陆基增强系统(CORS)。     

GPS多路径误差分析及探测方法

多路径误差严重影响动态GPS测量精度,且很难将其彻底消除.介绍多路径效应的机理及特性,利用相同环境下、连续卫星周期间数据取差以及连续历元坐标序列的移动平均方法削弱多路径误差,提高定位精度.     

自适应调零天线GPS抗干扰技术研究简析

GPS在现代高技术条件下的局部战争和人们的日常生活中的重要性日益明显，从军用和民用方面考虑均有必要研究各种有意的和无意的对GPS的干扰，以及相应的抗干扰技术。从空域处理出发给出了一种自适应天线调零干扰抑制方案，并分析了相应的技术难点和可行性，该方案可以有效地抵消干扰，同时具有很高的推广应用价值。     

GPS signal diffraction modelling: the stochastic SIGMA-δ model

The SIGMA-Δ model has been developed for stochastic modelling of global positioning system (GPS) signal diffraction errors in high precision GPS surveys. The basic information used in the SIGMA-Δ model is the measured carrier-to-noise power-density ratio (C/N0). Using the C/N0 data and a template technique, the proper variances are derived for all phase observations. Thus the quality of the measured phase is automatically assessed and if phase observations are suspected to be contaminated by diffraction effects they are weighted down in the least-squares adjustment. The ability of the SIGMA-Δ model to reduce signal diffraction effects is demonstrated on two static GPS surveys as well as on a kinematic high-precision GPS railway survey. In cases of severe signal diffraction the accuracy of the GPS positions is improved by more than 50% compared to standard GPS processing techniques. Received: 27 July 1998 / Accepted: 1 March 1999     

桥梁索塔GPS监测信号的小波分析

针对EMD分解后直接舍去高频含噪信号可能会导致有用信息的丢失,以及小波阈值去噪中采用全局阈值去噪效果不完善等问题,该文提出了一种基于SSA的改进EMD-Wavelet耦合模型运用于桥梁索塔GPS监测信号去噪。即先对原始监测信号进行奇异谱分析,提取信号的趋势项和周期项,分析不同阶段的信号特性从而对其进行合理分段。在对经过EMD分解后的高频信号进行小波去噪时,根据信号的分段结果和给定的阈值计算函数进行分段分层取阈值。结果表明,该方法能很好地对原始坐标序列进行降噪,并且各项评价指标均优于SSA重构去噪法、EMD分解去噪法和EMD-Wavelet全局阈值去噪法,去噪效果更佳,这为索塔监测数据信号提取提供了有意义的参考。     

Position and velocity reliability testing in degraded GPS signal environments

Reliability testing, namely receiver autonomous integrity monitoring (RAIM), consists of statistical testing of least-squares residuals of observations, e.g., on an epoch-by-epoch basis aiming towards reliable navigation fault detection and exclusion (FDE). In this paper, classic RAIM and FDE methods are extended with testing of range-rate residuals to find inconsistent velocity solutions in order to contribute to the reliability of the system with special focus on degraded signal environments. Reliability enhancement efforts discussed include a Backward-FDE scheme based on statistical outlier detection and an iteratively reweighted robust estimation technique, a modified Danish method. In addition, measurement weighting assigned to code and Doppler observations is assessed in the paper in order to allow fitting a priori variance models to the estimation processes. The schemes discussed are also suitable in terms of computational convenience for a combined GPS/Galileo system. The objective of this paper is to assess position and velocity reliability testing and enhancement in urban and indoor conditions and to analyze the navigation accuracy conditions with high sensitivity GPS (HSGPS) tests. The results show the necessity of weighted estimation and FDE for reliability enhancement in degraded signal-environment navigation.