Modeling GPS multipath effect based on spherical cap harmonic analysis

Most GPS positioning errors can be eliminated or removed by the differential technique or the modeling method,but the multipath effect is a special kind of system or gross error,so it is difficult to be simulated or eliminated.In order to improve the accuracy of GPS positioning,the single-epoch pseudorange multipath effects at GPS station were calculated,and firstly modeled based on the spherical cap harmonic（SCH）,which is the function of satellite longitude and latitude with the robust method.The accuracy of the kinematic point positioning technique was improved by correcting pseudorange observations with the multipath effect calculated by the SCH model,especially in the elevation direction.The spherical cap harmonic can be used to model the pseudorange multipath effect.

Characteristics of Multipath Effects in GPS Dynamic Deformation Monitoring

ABSTRACT The multipath has long been considered a major error source in GPS applications .The characteristics 0f the GPS signal multipath effects are analyzed. based on which an experiment that considers the characteristics of dynamic deformation monitoring has been carried out. The solution results of observation data in two successive days are processed by a method,which combines the wavelet filtering and the differential correction betweentwo successive days. The research demonstrates that the multipath errors have stronger repeatability on successive days;after significantly mitigating the influence of multipath effects,the accuracy of three-dimensional positioning for GPS dynamic deformation monitoring can attain the mm level,an obvious accuracy improving particularly invertical component.The characteristics of GPS signal multipath,th eexperimental scheme and the qualitative and quantitative analysis of results are detailed.

Analysis and Solution of Multipath Effect on Wireless Communications of Launch Vehicle

The electrical system in a launch vehicle contains multiple wireless communications systems. A large number of prelaunch tests are needed to verify the correctness and reliability of electric systems at the launch site. The complex electromagnetic environment at a launch site will inevitably cause multipath effect which interfere with prelaunch tests. Theory analysis and simulation of multipath effect, combined with engineering practice, can effective identify and quickly correct abnormal situations, and identify methods and measures to eliminate the influence of multipath interference.

Impact of multipath effects on theoretical accuracy of TOA-based indoor VLC positioning system

This paper discusses the time-of-arrival(TOA) based indoor visible light communication(VLC) positioning system in a non-line-of-sight environment. The propagation delay is assumed to be gamma distributed. The generalized Cramer–Rao lower bound for multipath propagation is derived as the theoretical accuracy limitation. The performance of the positioning system is affected by the shape parameter and the scale parameter of gamma distribution.The influences on positioning accuracy of multipath effects are analyzed through discussing the physical meaning of the gamma distribution parameters. It is concluded that the lower bound of positioning accuracy is attained when variance of the non-line-of-sight propagation-induced path lengths is zero. The simulation result provesthat the theoretical positioning accuracy is in the order of centimeters with the given scenario.

Analysis of Multipath and CW Interference Effects on GNSS Receivers with EMLP Discriminator

Multipath and continuous wave (CW) interference may cause severe performance degradation of global navigation satellite system (GNSS) receivers. This paper analyzes the code tracking performance of early-minus-late power (EMLP) discriminator of GNSS receivers in the presence of multipath and CW interference. An analytical expression of the code tracking error is suggested for EMLP discriminator, and it can be used to assess the effect of multipath and CW interference. The derived expression shows that the combined effects include three components: multipath component;CW interference component and the combined component of multipath and CW interference. The effect of these components depends on some factors which can be classified into two categories: the receiving environment and the receiver parameters. Numerical results show how these factors affect the tracking performances. It is shown that the proper receiver parameters can suppress the combined effects of multipath and CW interference.

基于低空目标检测的分布式多输入多输出雷达功率分配合作博弈算法

为提升低空突防作战场景下分布式多输入多输出(Multiple Input and Multiple Output,MIMO)雷达系统的目标检测效能,提出一种合作博弈功率分配(Cooperative Game Power Allocation,CGPA)算法。基于带误差的支援信息建立了低空多径环境下的分布式MIMO雷达信号模型,并推导了基于奈曼皮尔逊准则的检测模型。结合Max-Min准则以信干噪比(Signal to Interference plus Noise Ratio,SINR)为优化模型的效用函数。在此基础上,利用加权方法简化了联盟利益Shapley值的计算,得到满足帕累托最优性和公平性的合作资源分配方案。通过对发射功率资源的细致化管理,有效减小多径效应引起接收信号幅度的参差与衰落。在改善接收信号的稳定性的同时,挖掘并利用多径环境下丰富的散射特性,有效提升了雷达系统的探测效能。仿真实验验证了分布式MIMO雷达系统低空多径目标检测的出色性能,所提功率分配算法能够有效提升系统检测性能,并具有较好的实时性。

Temporal Spreading Effect of Oceanic Lidar System

In this paper, multipath temporal spreading distributions of laser pulses are calculated when they travel through the seawater. Individual photon is followed in Monte Carlo calculation A modified Henyey-Greenstein （HG） function is applied to represent the scattering phase function of seawater. This paper proposes a new scaling method, which uses the effective scattering thickness τd to replace the optical thickness used in the traditional scaling technique. This paper compares the temporal spreading distributions of photons on conditions of different attenuation coefficients and target depths. The experiments reveal that these mutual deviations are changing in the range from 0.5% to 5%, so long as the corresponding effective scattering thicknesses τd remains the same. Therefore, a conclusion can be obtained, that the temporal spreading distribution is only dependent on the effective diffusion thickness τd .

基于ADMM的SAR成像多径效应抑制方法

针对合成孔径雷达(SAR)成像发生多径效应时产生目标虚假影像的问题,提出了一种基于交替方向乘子法(ADMM)的多径效应抑制方法.首先推导了多径条件下SAR成像的多径回波信号模型,对多径效应造成SAR图像上出现目标伪像的原因进行了理论分析;然后建立了基于压缩感知(CS)理论的多径回波观测模型,并将多径抑制问题转化为对成像区域的稀疏重构问题;最后利用基于ADMM在稀疏先验约束条件下求解目标区域各个位置处的真实散射系数,从而重构出无多径干扰的观测场景SAR图像.仿真结果表明,相比传统距离-多普勒(RD)成像算法和基于粒子群优化(PSO)算法的多径效应抑制方法,本文所提方法获得了更小的距离向和方位向旁瓣,可以有效抑制SAR图像中多径效应造成的目标虚假影像.

基于原子范数的波达方向与时延联合估计方法

为了解决水声通信环境下自主式水下机器人定位难的问题,提出了一种基于原子范数的波达方向(DOA)与时延联合估计方法。首先,基于水声多径多普勒效应的特点建立信道冲激响应公式,将接收信号用矩阵形式表示并对参数进行归一化处理。然后,针对水听器阵列的几何结构和多普勒效应带来的相位误差建立一个新的原子集合,考虑到水声信号在空间域的稀疏性,利用原子范数最小化求解相应的原子。最后,针对由任意线阵带来半正定矩阵中的子矩阵为非Toeplitz矩阵结构而无法进行Vandermonde分解的问题,定义了一个有关水听器几何结构的Hermitian集合,利用长椭球波函数进行半正定规划求解,获得DOA和时延的联合估计。实验结果表明,所提方法在信噪比为20 dB时,DOA估计的均方根误差低至0.2°,在DOA间隔低至3°时仍有77.98%的估计成功概率,估计时延与实际时延的误差可以达到微秒级。

基于文氏谱海浪的无人机海面多径信号传播特性研究

针对无人机海上通信场景,对其海面多径信号传播特性进行了重点研究分析。完成了基于文氏谱的海浪模型建模;分析了海浪对多径信号传播的影响,建立了适用于不同海况下的无人机海面多径信号传播模型;仿真得到在不同海况下多径信号有效反射点数目与多径信号衰减幅度,并给出无人机通信链路误码率曲线;分析结果表明,海况恶劣程度决定海面多径信号传播情况,进而对无人机通信系统效能造成干扰,该研究为海上无人机通信系统设计具有重要意义。

GPS/QZSS在亚太地区实时相对定位性能分析

利用BNC(BKG NTRIP client)传输的实时观测数据,从可见卫星数、位置精度因子(position dilution of precision, PDOP)、多路径效应、信噪比和实时相对定位精度等方面对GPS和QZSS在亚太地区的定位性能进行评估和分析。结果表明,QZSS与GPS组合后,可见卫星数增加,卫星几何构型更好,可提高定位精度的可用性和可靠性;QZSS卫星多路径效应的变化规律与GPS卫星一致,且QZSS卫星各频点的多路径误差大多小于GPS卫星;GPS和QZSS卫星各频点的信噪比随高度角变化趋势基本相同;在N、E、U方向上,GPS/QZSS组合的实时相对定位精度比GPS有所提升。

远海环境低成本RTK接收机多路径效应与平滑伪距单点定位性能

低成本RTK接收机抗多路径性能较弱,导致远海环境中的单点定位性能显著下降。综合分析远海环境中载波相位平滑抑径算法对低成本RTK接收机单点定位性能的影响。结果表明,远海环境中RTK接收机的多路径效应为陆地环境的2~3倍,E5频点的抗多路径性能最强;平滑抑径效果与伪距多路径效应大小有关,采用平滑抑径算法后,RTK接收机SPP定位精度在远海环境提升62%,在陆地环境提升24%;平滑抑径后GPS/Galileo/BDS-3多系统SPP定位精度优于1 m,可满足海上较精细作业的需求。

基于CEEMDAN-WP-SSA的GPS/BDS-RTK多路径噪声抑制方法

针对GNSS-RTK技术在复杂环境下的多路径效应误差和随机噪声难以消除的问题,提出一种自适应完备集合经验模态分解(CEEMDAN)、小波包(WP)去噪和奇异谱分析(SSA)结合的联合去噪方法,来消除基线坐标序列的噪声影响,在此基础上构建适用于GPS/BDS组合的恒星日滤波模型。首先采用CEEMDAN方法将原始信号分解成若干个特征模态函数(IMF),使用排列熵区分高频和低频分量,然后分别利用WP和SSA对高频信号和低频信号进行去噪,最后重构去噪后信号并通过恒星日滤波削弱后续坐标序列里的多路径误差。实验结果表明,基于CEEMDAN-WP-SSA构建的恒星日滤波模型能够很好的去除随机噪声以及削弱多路径误差影响,与CEEMDAN和CEEMDAN-WP方法相比,文中方法东(E)、北(N)、高程(U)3个方向的定位精度分别提升约17%、23.6%、13.6%和17%、19.8%、10%。

削弱大型水闸BDS监测多路径效应的MHM方法

大型水闸变形监测复杂环境中存在的多路径效应限制了全球导航卫星系统(global navigation satellite system,GNSS)精密定位的精度。对此,提出一种顾及北斗导航卫星系统(Beidou navigation satellite system,BDS)不同星座类型多路径效应的半天球图(multipath hemispherical map,MHM)方法。该方法建立以监测站为球心的半天球进行格网点划分,通过格网点内参数化实现多路径误差建模,适用于BDS多星座以及大型水闸复杂的监测环境。采用曹娥江大型水闸监测案例,对多路径改正前后的单差残差及变形监测坐标序列进行分析,XYZ方向精度较多路径误差改正前提升63.06%、54.17%、57.84%,表明采用该方法可以有效削弱多路径效应,提高变形监测精度。

基于可视化近超声的狭长管道人员定位系统

针对工业系统室内管道空间所具有的狭长和弯折等复杂特征,以及现有室内定位技术精度不够、实用性不强的问题,提出一种基于可视化近超声的狭长管道人员定位系统。采用逐帧归一化互相关方法和联合小波导数寻峰的方法确定到达时间。将改进变异率和选择策略的差分进化算法(EA)与极大似然的TDOA算法结合进一步增强定位准确度,将MDS分解与基站定位融合实现基站自标定功能。仿真和实验结果表明,该方法可以很好克服狭长弯折空间以及环境噪声干扰带来的影响,满足狭长管道空间人员定位系统的高精度定位需要。

多径信道下基于恒模算法的遥测信号盲均衡

运载火箭在塔架静态测试时易受多径衰落影响,导致遥测信号产生码间干扰。本文对PCM-FM体制遥测信号的多径信道使用恒模算法(CMA)进行盲均衡研究,针对遥测信道中的码间干扰展开理论分析和Matlab仿真,并搭建盲均衡功能测试平台开展实验验证。结果表明:CMA收敛速度高、误码率低,对多径干扰具有较好的鲁棒性和实用性。

北斗卫星导航系统桥梁变形监测的影响因素分析

基于北斗卫星导航系统的桥梁变形监测,以天津市永和大桥为例,分析星历、解算时间、测站距离、多路径效应等对变形监测效果的影响。结果表明:星历采用多卫星解算时,变形监测精度更高;解算时间越长,变形监测越高;测站距离对变形监测的精度影响较小;多路径效应对变形监测的精度有一定影响,建议通过优化算法来弱化多路径效应。

VDE-SAT下行链路信道建模方法

海面的散射特性导致VDES海上通信信道模型复杂多变,在VDE-SAT下行链路中,低仰角通信导致海浪反射带来的多径效应更加严重。针对此问题,提出一种基于球坐标系的VDE-SAT下行链路信道建模方法,根据不同海情级分析海浪反射对于信号接收特性的影响。首先,将海面散射特性的统计结果参数化,结合地球曲率的影响,建立基于球坐标系的星船通信几何模型,基于此,得到海面有效漫反射区。其次,建立星船通信链路的信号多径传播模型,基于G1139协议,根据各个路径的信道参数分析接收信号的功率分布,以及不同海情级下信号的接收特性。仿真结果表明:在海况较好时,该多径信道以镜面反射为主;海况较差时,以漫反射为主。相比于卷积码,Turbo码的抗多径性能更优。

双基地米波MIMO雷达低空目标俯仰维DOD和DOA联合估计方法

对于双基地米波多输入多输出(MIMO)雷达低空目标俯仰维测向场景,受多径效应影响,发射接收导向矢量因存在耦合现象而与噪声子空间失去正交性,导致以多重信号分类(MUSIC)为主的子空间类算法在该场景下不可用,而基于空间平滑预处理的子空间类算法由于阵列孔径损失存在角度估计精度不高的问题。为解决上述难题,建立了双基地米波MIMO雷达单目标和非相干多目标镜面反射信号模型,在信号模型数学变换和分析的基础上发现了一种仍旧与噪声子空间正交的导向矢量矩阵,然后利用新的导向矢量矩阵结合广义MUSIC和最大似然算法提出了双基地米波MIMO雷达低空目标俯仰维波离方向和波达方向联合估计方法,最后通过仿真验证了所提方法的有效性和俯仰维测向性能的优越性。

适用雷达外场测量的近地多路径效应抑制方法

针对雷达在外场低空测量目标过程中受到的多路径效应问题,提出基于吸收阵元装置对多路径效应进行抑制的方法。对雷达工作时的电磁波发射和接收过程进行分析,引入3具有较高吸波效率的吸收阵元装置,并合理设计装置参数。结合飞行目标理论方程,建立吸收阵元布设模型,形成能够覆盖低空飞行目标全弹道的连续抑制区域。试验表明该方法可改善外场测量设备的使用环境,有效抑制雷达在静态校准与低空动态目标测量中的多路径效应。