面向低成本GNSS接收机终端的周跳修复策略

载波相位周跳是影响低成本GNSS接收机观测质量的主要因素之一.提出了一种面向低成本GNSS接收机终端的周跳修复策略,通过两种不同观测结果的联合检测以避免时钟和星历突变导致的误修复,并利用载噪比和多项式拟合误差检测载波观测中的无效观测,旨在提升低成本接收机在多径等复杂场景下载波相位观测的可用性.该策略仅使用了单频载波相位和载噪比信息,适用于各类低成本的接收设备.分别在开阔场景和多径场景下使用小米8手机和F9P接收机进行观测试验,结果表明,所有的有效载波相位观测得到了正确修复,仅约0.7％的无效观测被误修复,验证了所提策略的有效性.     

优选小波神经网络在周跳探测与修复中的应用

北斗导航定位过程中,传统的周跳探测与修复方法缺乏检验环节,无法保证修复结果的可靠性。为此,提出了一种级联式小波变换结合NARX神经网络多步循环预测修复的方法处理周跳问题。该方法通过构造载波相位双差模型检验量,探测周跳发生历元,采用NARX神经网络预测方法修复周跳,利用优选小波基函数进行周跳修复效果检验。实验证明,相较于经验模态分解和变分模态分解等模态分解法,优选小波神经网络周跳探测与修复方法可用于小周跳探测并判断出周跳正负性;构造的NARX神经网络周跳修复模型,解决了普通神经网络模型和传统多项式拟合法容易造成的二次奇异值问题。相较于长短期记忆(LSTM)和门控循环单元(GRU)深度学习神经网络模型,周跳预测精度分别提高了45.2%和55.9%。     

北斗三频周跳探测与修复算法研究

载波相位观测值已越来越多地应用到增强系统中,由于观测环境影响,载波相位测量不可避免地会产生周跳,周跳的成功探测与修复是提高导航定位精度的一个重要因素。针对北斗卫星导航系统三频观测数据,分析其不同线性组合观测值的特性,选取合适的组合系数,形成一个伪距相位组合和两个无几何相位组合,采用历元间差分的方法探测和修复组合观测值的周跳,然后还原求解出原始信号的周跳,最后通过实验验证了该方法的可行性。     

《飞行器测控学报》2006年第25卷第1～6期（总第99～104期）总目录

测控总体卫星导航定位方程的病态条件……………………………………………………………………………………帅平曲广吉(一)1~5基于小波变换的GPS载波相位周跳检测与修复……………………………………………………………………………赵军祥(一)6~9飞船自主应急返回控制参数确定方     

Blewitt周跳探测方法的改进

在精密单点定位中,能否准确可靠地探测载波相位观测量中出现的周跳,直接影响到定位的精度及可靠性。本文概述了Blewitt周跳探测方法的基础原理,并对周跳的探测算法进行了改进,将电离层残差组合观测量一次差的变化是否超限作为周跳存在与否的判断依据。最后利用一段人为加入了几个典型周跳组合的双频观测数据进行验证,结果表明,改进后的算法能准确探测出两个载波上大于1周的任意周跳,提高了周跳探测的准确性。     

智能手机广域精密定位研究

智能手机作为位置服务的重要载体，由于其天线结构等因素，导致利用手机原始观测值进行定位不能满足高精度定位的需求。针对这一问题，提出了利用广域增强技术，提高手机单频原始观测值实时定位精度的方法。首先，针对手机观测值周跳较为严重的问题，对单频载波相位观测值进行了周跳探测。然后，利用手机观测值获取的伪距、载波相位以及IGS站播发的轨道和钟差改正实现增强定位。实验结果表明，定位精度收敛到1m约需要20min，收敛后水平方向和垂直方向精度分别提高了66.7%和28.9%，平面精度达到1.5m。     

星载双频GPS相位历元差缩减动力学定轨(英文)

研究了星载双频GPS相位历元差缩减动力学定轨方法,该方法既克服了相位历元差运动学方法在观测几何较差或数据不足情况下无法应用的缺点,又避免了相位非差动力学方法易受周跳和模糊度影响的缺点。历元差方法对相位周跳的影响不敏感,因此能够降低相位数据预处理中周跳探测的难度。在模型求解过程中,解决了高维矩阵的计算问题,将长弧段观测数据分成若干短弧段,相邻两个短弧段的连接处不做差分,仅在每个短弧段内部进行历元间差分处理。通过对GRACE卫星进行试算,并与GFZ事后科学轨道进行比较,结果表明相位历元差缩减动力学定轨精度在径向、沿迹方向和轨道法向分别可达1.92cm、3.83cm和3.80cm,三维位置精度可达5.76cm,该方法与相位非差缩减动力学定轨精度相当。     

载波相位平滑伪距在GPS/SINS紧组合导航系统中的应用

针对GPS/SINS紧组合导航系统中伪距噪声大从而引起组合导航系统精度低的问题,提出了将载波相位平滑伪距方法引入到组合导航系统中,利用具有较高精度的载波相位对低精度伪距进行平滑滤波,在建立观测方程的同时,为了减小Kalman滤波器计算量,选用最佳4颗卫星的伪距与伪距率作为观测值,并提出了一种四面体选星法,该方法不需要进行矩阵求逆运算,减小了运算量。利用光纤陀螺捷联惯导系统与GPS接收机搭建了实验验证系统,通过车载实验对所提出的方法进行了验证,实验结果表明,经过载波相位平滑后的伪距噪声得到了降低,从而能够进一步提高GPS/SINS组合导航系统的定位精度,其位置误差均方根值相比无载波相位平滑减小近40%。     

利用旋转双天线载波相位双差的欺骗干扰检测技术

有效的欺骗干扰检测是防止卫星导航接收机被欺骗干扰攻击的前提。提出了一种基于旋转双天线载波相位双差的卫星导航接收机欺骗干扰检测技术,在对接收机双天线匀速旋转时输出载波相位测量值进行载波相位双差处理后,利用广义似然比检验实现了对单一发射天线输出欺骗干扰信号的检测。进一步分析了旋转半径和数据长度对检测性能的影响,并与旋转单天线和天线阵载波相位双差欺骗干扰检测方法的性能进行了对比。最后,通过蒙特卡罗方法进行了仿真验证,结果表明了该检测方法和检测性能分析的正确性。     

GPS 双基线载体姿态测量研究

研究了采用双基线方案测量载体的姿态,利用GPS双差相位测量基线矢量,双差伪距观测值辅助解相位整周模糊,双频时引入空间变换缩小置信空间搜索次数,通过实例分析得出了正确解算相位模糊与观测次数、伪距测量精度的关系,并利用误差传播定律对姿态测量精度进行分析,结合卫星星历数据计算表明,在卫星运行周期内航向角和俯仰角平均测量精度在一定条件下优于2mrad.     

Cycle-slip Detection of GPS Carrier Phase with Methodology of SA4 Multi-wavelet Transform

That cycle-slips remain undetected will significantly degrade the accuracy of the navigation solution when using carrier phase measurements in global positioning system (GPS). In this paper, an algorithm based on length-4 symmetric/anti-symmetric (SA4) orthogonal multi-wavelet is presented to detect and identify cycle-slips in the context of the feature of the GPS zero-differential carrier phase measurements. Associated with the local singularity detection principle, cycle-slips can be detected and located precisely through the modulus maxima of the coefficients achieved by the multi-wavelet transform. Firstly, studies are focused on the feasibility of the algorithm employing the orthogonal multi-wavelet system such as Geronimo-Hardin-Massopust (GHM), Chui-Lian (CL) and SA4. Moreover, the mathematical characterization of singularities with Lipschitz exponents is explained, the modulus maxima from wavelet to multi-wavelet domain is extended and a localization formula is provided from the modulus maxima of the coefficients to the original observation. Finally, field experiments with real receiver are presented to demonstrate the effectiveness of the proposed algorithm. Because SA4 possesses the specific nature of good multi-filter properties (GMPs), it is superior to scalar wavelet and other orthogonal multi-wavelet candidates distinctly, and for the half-cycle slip, it also remains better detection, location ability and the equal complexity of wavelet transform.     

GPS多径信号的自适应滤波估计方法

 研究全球定位系统(GPS)多径信号估计的问题。通过分析自适应滤波器的原理,建立了数字中频信号处理的数学模型,提出一种用自适应滤波实现GPS多径幅度、码相位和载波相位估计的方法。该方法采用不同延迟的伪随机序列对信号进行解扩、解调和累加,得到了作为期望信号的系列自适应滤波相关值。对该方法与其他3种方法进行了理论上的分析比较,得出本方法具有信噪比高、自适应滤波性能好、带有码相位信息和不存在载波模糊度问题等优点。根据各种滤波器算法的特点和本应用的需求,给出了选用递归最小二乘算法实现的方法。通过计算机仿真,验证了提出的方法能够在14 dB的信噪比下,以1个采样间隔的时间延迟分辨率和0.005周的载波相位估计精度估计出GPS L1的多径信号。     

Instantaneous GPS attitude determination

A procedure for instantaneous GPS (Global Positioning Satellite) attitude determination, i.e., a solution for the GPS integrated carrier Doppler wavelength ambiguities using only measurements at a single epoch, is described. Most previous techniques to solve the phase ambiguity problem have required some form of time history processing relying on GPS satellite and/or user motion to provide enough geometry change to eliminate false solutions. The algorithm described assumes three noncollinear antennas and integrated carrier Doppler measurements from four or more satellites. Double-difference processing provides at least three independent observables for the two antenna separation vectors to compute the three attitude Euler angles     

Phase Residual Estimations for PCVs of Spaceborne GPS Receiver Antenna and Their Impacts on Precise Orbit Determination of GRACE Satellites

In-flight phase center systematic errors of global positioning system(GPS) receiver antenna are the main restriction for improving the precision of precise orbit determination using dual-frequency GPS.Residual approach is one of the valid methods for in-flight calibration of GPS receiver antenna phase center variations(PCVs) from ground calibration.In this paper,followed by the correction model of spaceborne GPS receiver antenna phase center,ionosphere-free PCVs can be directly estimated by ionosphere-free carrier phase post-fit residuals of reduced dynamic orbit determination.By the data processing of gravity recovery and climate experiment(GRACE) satellites,the following conclusions are drawn.Firstly,the distributions of ionosphere-free carrier phase post-fit residuals from different periods have the similar systematic characteristics.Secondly,simulations show that the influence of phase residual estimations for ionosphere-free PCVs on orbit determination can reach the centimeter level.Finally,it is shown by in-flight data processing that phase residual estimations of current period could not only be used for the calibration for GPS receiver antenna phase center of foretime and current period,but also be used for the forecast of ionosphere-free PCVs in future period,and the accuracy of orbit determination can be well improved.     

SNR-based multipath error correction for GPS differential phase

Carrier phase multipath is currently the limiting error source for high precision Global Positioning System (GPS) applications such as attitude determination and short baseline surveying. Multipath is the corruption of the direct GPS signal by one or more signals reflected from the local surroundings. Multipath reflections affect both the carrier phase measured by the receiver and signal-to-noise ratio (SNR). A technique is described which uses the SNR information to correct multipath errors in differential phase observations. The potential of the technique to reduce multipath to almost the level of receiver noise was demonstrated in simulations. The effectiveness on real data was demonstrated with controlled static experiments. Small errors remained, predominantly from high frequency multipath. The low frequency multipath was virtually eliminated. The remaining high frequency receiver noise can be easily removed by smoothing or Kalman filtering     

多径效应对GPS载波相位观测量的影响

推导了ＧＰＳ接收机中多径效应引入的最大载波相位跟踪误差的闭合形式。得到以下结论：当直达信号跟踪误差不超过１码片时,最大载波测相多径误差为１／４周,该值出现在测码伪距多径误差最小的情况下;当直达信号跟踪误差超过或等于１码片时,接收机跟踪多径信号,信号误检发生。     

A novel multistage estimation of signal parameters

A multistage estimation scheme is presented for estimating the parameters of a received carrier signal possibly phase-modulated by unknown data and experiencing very high Doppler, Doppler rate, etc. Such a situation arises, for example, in the case of the Global Positioning Systems (GPS). In the proposed scheme, the first-stage estimator operates as a coarse estimator of the frequency and its derivatives, resulting in higher RMS estimation errors but with a relatively small probability of the frequency estimation error exceeding one-half of the sampling frequency (an event termed cycle slip). The second stage of the estimator operates on the error signal available from the first stage, refining the overall estimates, and in the process also reduces the number of cycle slips. The first-stage algorithm is a modified least-squares algorithm operating on the differential signal model and referred to as differential least squares (DLS). The second-stage algorithm is an extended Kalman filter, which yields the estimate of the phase as well as refining the frequency estimate. A major advantage of the proposed algorithm is a reduction in the threshold for the received carrier power-to-noise power spectral density ratio (CNR) as compared with the threshold achievable by either of the algorithms alone     

Carrier phase navigation architecture for shipboard relative GPS

Carrier phase differential GPS (DGPS) navigation architectures and algorithms for automatic shipboard landing of aircraft are described. Processing methodologies are defined to provide high integrity carrier phase cycle estimation and positioning by optimally exploiting the complementary benefits of measurement filtering and satellite geometric redundancy for the terminal navigation problem. Navigation performance sensitivity to the standard deviations of raw carrier and code phase measurement errors, measurement error correlation times, and the filtering duration is quantified. Necessary conditions to ensure acceptable terminal navigation availability are specifically defined.     

基于混沌和LWT-SVD的盲信息隐藏算法

为了提高秘密信息的安全性和鲁棒性,将混沌、提升小波变换（LWT）和奇异值分解（SVD）结合,提出一种盲信息隐藏算法。首先将要隐藏的秘密图像用混沌序列进行加密;然后对载体图像进行提升小波变换,并对低频子带进行分块奇异值分解;最后根据最大奇异值最高位的奇偶性将已加密的秘密图像进行隐藏。提取秘密图像时,不需要载体图像。仿真实验表明,该算法隐蔽性好,对加噪、滤波、旋转、剪切、缩放和JPEG压缩等攻击具有良好的鲁棒性。