REGULARIZATION APPROACH FOR FAST INTEGER AMBIGUITY RESOLUTION OF MEDIUM-LONG BASELINE GPS NETWORK RTK

An improved method based on the Tikhonov regularization principle and the precisely known reference station coordinate is proposed to design the regularized matrix. The ill-conditioning of the normal matrix can be improved by the regularized matrix. The relative floating ambiguity can be computed only by using the data of several epochs. Combined with the LAMBDA method, the new approach can correctly and quickly fix the integer ambiguity and the success rate is 100% in experiments. Through using measured data sets from four mediumlong baselines, the new method can obtain exact ambiguities only by the Ll-frequency data of three epochs. Compared with the existing methods, the improved method can solve the ambiguities of the medium-long baseline GPS network RTK only using L1-frequency GPS data.

ALGORITHM FOR AMBIGUITY RESOLUTION IN RANGE AND VELOCITY

For enhancing performances and increasing functions of PD radar, High PRF, medium PRF and low PRF are commonly applied into system ambiguity appeared in range and velocity in some PRF. Based on clustering, a sliding window correlator algorithm for resolving the radar object ambiguity in range and velocity is described. Slide window algorithm is a searching algorithm. The probability of ambiguity resolution for targets and the computational efficiency are discussed. The relations between the probability of ambiguity resolution of this algorithm and PRF, the range of interest, and the width of sliding window are analyzed. Simulational results are also given.

Improvement of GPS ambiguity resolution using prior height information. Part Ⅰ: The method by using height validation

It is an attractive method to combine GPS observations with the information from other surveying system to improve the ambiguity resolution. This research is conducted to investigate how to obtain the prior height information in bathymetric surveying by GPS positioning and how to use the prior height information and to obtain a robust result. The authors deal with the collection and the description of the prior height and the method using height validation to improve the ambiguity resolution. The principle of the method, the relationships between the height threshold and the ambiguity search space are presented. A method to determine the threshold for the height validation is suggested. The field tests are carried out to show the feasibility of the proposed methods.

Ambiguity Resolution in Direction of Arrival Estimation with Linear Antenna Arrays Using Differential Geometry

Linear antenna arrays(LAs)can be used to accurately predict the direction of arrival(DOAs)of various targets of interest in a given area.However,under certain conditions,LA suffers from the problem of ambiguities among the angles of targets,which may result inmisinterpretation of such targets.In order to cope up with such ambiguities,various techniques have been proposed.Unfortunately,none of them fully resolved such a problem because of rank deficiency and high computational cost.We aimed to resolve such a problem by proposing an algorithm using differential geometry.The proposed algorithm uses a specially designed doublet antenna array,which is made up of two individual linear arrays.Two angle observation models,ambiguous observation model(AOM)and estimated observation model(EOM),are derived for each individual array.The ambiguous set of angles is contained in the AOM,which is obtained from the corresponding array elements using differential geometry.The EOM for each array,on the other hand,contains estimated angles of all sources impinging signals on each array,as calculated by a direction-finding algorithm such as the genetic algorithm.The algorithm then contrasts the EOM of each array with its AOM,selecting the output of that array whose EOM has the minimum correlation with its corresponding AOM.In comparison to existing techniques,the proposed algorithm improves estimation accuracy and has greater precision in antenna aperture selection,resulting in improved resolution capabilities and the potential to be used more widely in practical scenarios.The simulation results using MATLAB authenticates the effectiveness of the proposed algorithm.

ALGORITHM FOR THE NOMINAL RESOLUTION IN RECTANGULAR PULSE SIGNAL USING THE AMBIGUITY MATRIX

It is a main form using the main beamwidth of the ambiguity function to judge the signal resolution, in which the range or Doppler resolution of the signals are investigated for the targets close to each other. However, for the pulse signal with rectangular envelope, if the nominal range resolution is calculated from the classic definition, there exists the problem of infinite integral for the high power terms of sine function, and a definite result could not be obtained. Though a definite solution of the nominal velocity resolution can be calculated from the definition, the calculation for the signal consisting of multiple-pulse, especially several periods, is very complex. The paper begins with the physical meaning of nominal resolution rather than from the definition formula to solve the problem using the ambiguity matrix, and make the calculation simplified greatly.

Ambiguity Resolution in English Language Processing

Language ambiguity resolution has been widely studied by psycholinguists.Studies of lexical ambiguity resolution,syntactic ambiguity resolution and anaphoric ambiguity resolution have showed different results.One account assumes that ambiguity resolution involves"competition"of analysis which causes processing difficulties.The other account claims that an initial analysis is adopt and"reanalysis"occurs when the initial analysis turns out to be implausible.

Analysis of Resolution of Bistatic SAR

In this paper, the spatial resolutions at different directions of bistatic synthetic aperture radar （BiSAR） have been derived from the ambiguity function. Compared with monostatic signal to noise ratio, BiSAR＇s resolutions of a fixed point target are varying with slow time since BiSAR system is space-variant. Constraints for the assumption of space-invariant bistatic topology are proposed in the paper. Moreover, under the assumption of invariance, the change of resolutions at different point in the image scene is taken into account, and we have specified two key parameters that affect resolutions directly and analyzed the way how they influence on the resolutions.

Multi-dimensional ambiguity function for subarray-based space-time coding radar

Space-time coding radar has been recently proposed and investigated.It is a radar framework which can perform transmit beamforming at the receiver.However,the range resolution decreases when the number of the transmit element increases.A subarray-based space-time coding(sub-STC)radar is explored to alleviate the range resolution reduction.For the proposed radar configuration,an identical waveform is transmitted and it introduces a small time offset in different subarrays.The multidimensional ambiguity function of sub-STC radar is defined by considering resolutions in multiple domains including the range,Doppler,angle and probing direction.Analyses on properties of the multi-dimensional ambiguity function of the sub-STC radar with regard to the spatial coverage,resolution performance and low sidelobes are also given.Results reveal that the range resolution and low sidelobes performance are improved with the proposed approach.

Precise orbit determination of Haiyang‑2D using onboard BDS‑3 B1C/B2a observations with ambiguity resolution

The Haiyang-2D altimetry mission of China is one of the first Low Earth Orbit(LEO)satellites that can receive new B1C/B2a signals from the BeiDou-3 Navigation Satellite System(BDS-3)for Precise Orbit Determination(POD).In this work,the achievable accuracy of the single-receiver ambiguity resolution for onboard LEO satellites is studied based on the real measurements of new BDS-3 frequencies.Under normal conditions,six BDS-3 satellites on average are visible.However,the multipath of the B1C/B2a code observations presents some patchy patterns that cause near-field variations with an amplitude of approximately 40 cm and deteriorate the ambiguity-fixed rate.By modeling those errors,for the B2a code,a remarkable reduction of 53%in the Root Mean Square(RMS)is achieved at high elevations,along with an increase of 8%in the ambiguity-fixed rates.Additionally,an analysis of the onboard antenna’s phase center offsets reveals that when compared to the solutions with float ambiguities,the estimated values in the antenna’s Z direction in the solutions with fixed ambiguities are notably smaller.The independent validation of the resulting POD using satellite laser ranging at 16 selected high-performance stations shows that the residuals are reduced by a minimum of 15.4%for ambiguity-fixed solutions with an RMS consistency of approximately 2.2 cm.Furthermore,when compared to the DORIS-derived orbits,a 4.3 cm 3D RMS consistency is achieved for the BDS-3-derived orbits,and the along-track bias is reduced from 2.9 to 0.4 cm using ambiguity fixing.

ACCELERATION AMBIGUITY FUNCTION OF RADAR SIGNALS AND ITS APPLICATION

High acceleration of radar targets is analyzed using Acceleration Ambiguity Function (AAF). The acceleration resolution based on AAF is defined. The AAF and acceleration resolution of rectangle pulse signal are derivated and the conclusion that its acceleration resolution is in inverse proportion with the square of its duration is drawn. In the end, these conclusions are applied to the parameter designing and performance evaluation for a certain type of pulse Doppler radar.

基于韵律的英语介词短语挂靠歧义消解研究

在言语交际过程中,说话人口语表达的韵律线索对交际双方的语言理解发挥着重要作用。为了深入了解中国英语学习者英语口语产出的韵律线索与预期表达含义之间的相关性,本文以中国大学英语学习者为研究对象,采用基于情境的半开放式口语产出任务,考察在特定的情境化实验条件下,被试对英语介词短语挂靠造成的歧义句的朗读任务完成情况。研究结果表明:中国大学英语学习者具有对口语韵律特征与句法结构之间关系的潜在敏感性,能够通过口语的韵律停顿和音高重音实现对英语介词短语动、名词挂靠引起的歧义的消解。本研究结果进一步证实了英语口语韵律特征与预期含义之间的相互关系,凸显了韵律训练在大学英语课堂教学中的重要性,为高校英语听说及阅读教学实践的开展提供了参考建议。

嵌套阵的疏密子阵融合波达方向估计方法

为有效利用嵌套阵包含疏密子阵的几何结构以提高估计性能,本文提出一种在2子阵上分别测向再融合的波达方向估计方法。通过理论分析和实际案例阐明融合嵌套阵的两子阵测向结果可以消除信源角度估计模糊,且不会出现互质阵解模糊时伴随的匹配错误。利用无需谱峰搜索的求根多重信号分类方法在嵌套阵2子阵上求解测向结果,若稀疏子阵间距为N倍半波长,推导出对其复根开N次方可获含模糊角的高精度估计,再结合最小方差准则与精度较低但无模糊的密集子阵测向结果进行融合,最终得到高精度的波达方向估计。与嵌套阵已有算法相比,该算法提高了波达方向估计精度和分辨率,由于无需2子阵协方差降低了计算量,且能够支持嵌套阵的分布式配置。仿真结果验证了所提算法的有效性。

基于Hatch滤波的改进矩阵变换法在BDS多频模糊度解算中的应用

长基线条件下,空间相关性弱,电离层延迟残差和噪声影响变大,致使矩阵变换法模糊度解算过程中,窄巷组合受噪声影响大,单历元模糊度解算成功率低。因此,削弱电离层残差及噪声影响可以一定程度提高模糊度解算成功率。本文在分析矩阵变换算法基础上,利用Hatch滤波有效抑制伪距测量噪声和多径效应特点,结合弱电离层、低噪声的载波组合,通过相位平滑伪距代替组合伪距值参与解算,从而削弱电离层残差及观测噪声影响。通过实测数据分析,本文算法可有效提高矩阵变换法模糊度解算成功率。

一种针对机动目标的解速度模糊新算法

解速度模糊是脉冲多普勒雷达中需要解决的重要问题,通常的解速度模糊算法皆未考虑加速度信息,当雷达跟踪火箭弹等长助推段目标时存在速度解算误差大或无法解算、不能有效预测目标速度信息等问题。针对上述情况,提出一种面向加速度目标的解速度模糊算法。计算机仿真及雷达模拟数据表明,该方法对长助推段目标速度、加速度解算准确度高,对传统目标兼容性良好。该文还给出了新算法的工程实现方法。

基于不同模糊度固定产品的PPP-AR定位性能评估

基于CODE、GFZ、CNES、武汉大学PRIDE实验室和内部估计的模糊度固定产品,从收敛时间、首次固定时间及定位精度等方面进行PPP-AR固定性能的研究。实验选用2022年40个IGS测站7 d的观测数据和各模糊度固定产品配套使用的精密产品,结果表明,在置信度为95%的静态解算模式下,5种产品在解算时间为1 h时固定解较浮点解定位精度提升最明显,分别提升46.58%(3.4 cm)、41.10%(3.0 cm)、45.21%(3.3 cm)、34.25%(2.5 cm)和41.10%(3.0 cm)。仿动态解算模式下,5种产品E、N方向的定位精度都能达到mm级,U方向较浮点解精度提升较小,其中使用GBM产品的精度提升最小,E、N、U方向分别提高72.73%(2.4 cm)、47.37%(0.9 cm)、5.41%(0.2 cm);提升效果较好的是WUM和COM产品,分别为81.82%(2.7 cm)、63.16%(1.2 cm)、24.32%(1.1 cm)和81.82%(2.7 cm)、63.16%(1.2 cm)、15.58%(0.8 cm)。

多系统PPP天顶对流层延迟时空序列精度评估及分析

利用2021-09全球80个MGEX测站进行PPP实验,以国际GNSS服务组织(IGS)发布的ZTD产品为参考进行比较分析。结果表明,多系统联合估计ZTD在精度上具有较大优势,GPS+BDS双系统比单GPS系统平均RMSE精度提高约0.6 mm, GPS+BDS+GLONASS+Galileo四系统比双系统精度提高约0.9 mm,单系统条件下GPS的ZTD估计精度高于BDS。在精度空间分布上,随着纬度升高ZTD估计精度提升较为明显,当纬度大于50°时,四系统PPP估计的ZTD精度优于5 mm。在纬度基本不变的情况下,观测站海拔升高可提升ZTD估计精度。在模糊度固定的情况下,ZTD估计精度明显提升,单GPS系统估计ZTD的平均绝对误差(MAE)和均方根误差(RMSE)分别为7.6 mm和8.4 mm,相比于浮点解分别提高约11%和12%,平均收敛时间加快20 min。

BDS-3 PPP模糊度固定实现及精度评估

精密单点定位(PPP)模糊度固定(AR)能够显著提升精密定位的收敛速度和精度。通过在BDS-2和BDS-3之间添加系统间偏差的方法实现BDS-3的模糊度固定,并基于全球MGEX测站静态、仿动态数据和车载实验数据全面评估了BDS-3模糊度固定的效果。结果表明,相对于浮点解,BDS-3 PPP模糊度固定能够显著提升PPP的精度,在东北天3个方向上静态解算精度提升依次为37.4%、26.2%和20.1%;仿动态解算精度提升依次为38.3%、27.2%和11.1%;车载动态实验BDS-3模糊度固定精度在三维方向上综合提升为40.4%。此外,模糊度固定后,以浮点解稳定后的两倍定位精度为基准,在东北天方向上,静态定位时间提升程度依次为63.5%、64.0%和40.3%;仿动态定位时间提升程度依次为58.7%、56.8%和25.4%;车载实验在三维方向的收敛时间为30.0 min。以上结果证明了所提方法的有效性及BDS-3模糊度固定的性能提升。

北斗四频中长基线模糊度解算研究

随着北斗三号卫星导航系统完成全球组网并正式开通,中国已成为世界上第3个独立拥有全球卫星导航系统的国家.目前BDS-3卫星可播发5个频点的观测信号,研究BDS-3多频组合对于实现模糊度快速固定、提高定位精度具有重要意义.针对中长基线解算,本文充分利用BDS-3四频中存在电离层延迟极小且具有整数特性的组合,同时考虑对流层延迟的影响,建立了基于弱电离层组合的中长基线解算模型.实验结果表明,相比于传统双频无电离层模型,该模型的模糊度固定速度提高10%以上,N、E、U 3个方向定位精度相比最优双频无电离层组合分别提高了7.7%、7.9%、8.2%.

Galileo三频非组合PPP相位小数偏差估计与模糊度解算

欧洲的Galileo目前已经有28颗在轨可用卫星,具备全球精密定位能力,并且所有卫星均能够播发多频信号,多频信号融合有望进一步改善精密单点定位(precise point positioning,PPP)模糊度固定解性能.本文研究了Galileo三频非组合PPP相位小数偏差(fractional cycle bias,FCB)估计与模糊度解算(ambiguity resolution,AR)方法,并将其结果同双频非组合PPP模糊度固定解与浮点解结果进行了对比分析.结果表明:利用155个全球分布的地面跟踪站数据进行FCB估计,单个频率上的FCB估值序列标准差(standard deviation,STD)优于0.04周;双频PPP浮点解在E、N、U方向收敛时间分别为32.0 min、10.0 min、43.5 min,双频PPP固定解收敛时间分别减少到30.5 min、8.5 min、32.0 min,三频PPP固定解收敛时间分别进一步缩短到16.5 min、8.0 min、32.0 min.

分步北斗三频部分模糊度解算方法

针对动态环境下半周模糊度导致全集模糊度难以固定的问题,提出了一种分步北斗三频部分模糊度解算方法。该方法首先基于半周模糊度特性,设计了一种连续观测历元部分模糊度解算(COE-PAR)方法,初步筛选出质量较优的模糊度子集,减少了后续部分模糊度解算的计算量。进一步设计了一种逐级部分模糊度解算(CPAR)方法,通过多种基于观测质量的模糊度筛选方法对超宽巷、宽巷和窄巷模糊度进行逐级部分固定,获得了不含半周模糊度的部分模糊度固定解。最后通过动态车载实验验证了方法的有效性。实验结果表明,分步北斗三频部分模糊度解算方法可有效提高动对动相对定位的模糊度固定率。城市动态环境下,与传统全集模糊度解算方法相比,Ratio检验后的模糊度固定率从91%提高至100%,相对定位误差降低了18%~79%;同时,COE-PAR方法减少了CPAR方法中模糊度剔除时最小二乘模糊度降相关平差(LAMBDA)算法约55%的执行次数。