GNSS载波相位多天线实时测姿系统的设计与实现

载体姿态的精确测量是航空和航天、航海的关键技术之一,在军事和民用等方面的作用日益重要。基于GNSS的姿态测量系统具有体积小、成本低以及误差不累积等诸多优点,对于轮船等大型低速度运动载体的姿态确定具有很好的应用价值。本文基于GNSS载波相位观测量,以Turbo C++为平台设计了实时测姿系统,并编写了实时测姿软件。最后将该测姿系统应用于某型测量船上,利用船上记录的原始接收机二进制记录文件,模拟实时进行处理;并与船上惯导输出值相比对验证了测姿系统的有效性及精度。针对船上多路径大的特点,给出了一些数据处理经验。试验结果表明,设计实现的GNSS测姿系统,其航向测姿精度为40″;纵摇及横摇测姿精度分别为130″和100″。     

BDS三频双差载波相位组合平滑伪距算法

针对现有的载波相位平滑伪距算法多基于GNSS双频观测值且在伪距平滑过程中易受电离层延迟累积干扰的问题,提出一种基于北斗三频观测值的载波相位平滑伪距算法。首先通过构建北斗三频优选线性组合,进一步削弱双差载波相位观测值的电离层延迟以及观测噪声;接着通过经典Hatch滤波平滑器,用优选三频双差载波相位观测值代替原始载波相位观测值对组合伪距观测值进行平滑,得到最终伪距平滑解用于伪距定位。最后采用0.004、14.4、61.7和131.6 km这4组不同基线长度的北斗三频实测数据对算法进行验证,给出了平滑前后伪距历元差对比图及算法对4组基线观测值的平滑率。结果表明,所提算法对短基线和中长基线三频观测值的平滑率均能达到90%以上。通过对4组基线条件下平滑效果进行比较分析,验证了本文中的理论推导及算法的有效性。     

基于快速傅立叶变换的干涉SAR基线估计

首先论述干涉SAR初始基线估计的基本原理；接着对用2维快速傅立叶变换（FFT）功率谱进行干涉SAR初始基线估计的具体算法进行了详细阐述；最后，基于1994年10月9日和10日的SIR－C L波段单视复雷达数据，用该算法进行了干涉SAR初始基线的垂直分量估计，并结合用航天飞机轨道数据得到的初始基线平行分量估计值进行去平地相位的试验。将结果与只用航天飞机轨道数据得到的初始基线进行去平地相位的结果及本区域的地形图进行比较分析。     

载噪比加权的GPS单频单历元定姿算法

针对GPS定姿系统中,传统的利用高度角的加权不能有效反映遮挡情况的问题,从接收机的卫星载噪比出发,对载波相位精度进行分析,提出新的权重矩阵W,对观测模型进行加权。加权后模型根据最小二乘得到整周模糊度和基线矢量的浮点解。加权方法能够降低弱信号卫星的载波相位观测值对姿态测量成功率的影响。通过对比试验验证了加权算法的合理性和有效性。部分试验结果表明,相比于未加权算法,载噪比加权算法可以使单历元定姿成功率提高5个百分点;相比于高度角加权算法,载噪比加权可以使成功率提高1~2个百分点。     

陆地导航中GNSS/陀螺仪组合实时测姿方法

在陆地导航系统中使用GNSS/INS组合导航会增加系统成本,多天线GNSS测姿精度受基线长度影响,且存在的模糊度固定问题。本文提出仅利用一个陀螺仪和单天线GNSS组合来进行实时测姿。先由单天线GNSS计算姿态角3参数,航向角为陆地导航的关键参数,为此将陀螺信息与GNSS导出的航向角进行融合。分析了单天线测姿在载体静止或低速运动时精度很差的原因,提出了在组合滤波中进行解决的方案。推导了GNSS和陀螺信息融合的滤波模型,将陀螺仪信息作为状态模型的控制输入,以GNSS航向为滤波观测值。实验结果表明,GNSS/陀螺仪组合计算的航向角精度和可靠性相对GNSS测姿结果均有很大提升。     

运行中解算GPS相位模糊值

运行中解算相位模糊值，即接收机运行时载波相位观测值中的初始模值的求解，是ＧＰＳ数据处理技术方面的新进展。本文阐述了运行中相位模糊值求解法的基本概念。并介绍作者为提高整周模值求争度和可靠性而开发的计算程序。     

GPS相位测量轨道改进基线定位

利用GPS载波相位观测值进行基线测定具有重要意义。本文讨论了基线测定中卫星星历误差对定位结果的影响,提出了基线上轨道改进的定位方法,编制了基线测定的定位软件,并使用高精度基线上的实际观测资料进行了计算。计算结果表明在基线上用轨道改进定位方法是可行的,可以提高定位精度。     

GPS姿态测量中模糊度搜索方法的确定与比较

GPS载波相位观测值作为高精度观测量在姿态测量中得到广泛应用。姿态测量系统中,基线长度可以通过提前量测精确求得。作为约束条件,可以用于模糊度搜索,提高模糊度搜索效率和准确度。本文介绍了传统的LAMBDA方法,且在此基础上提出了附有基线长度约束的LAMBDA搜索方法,并比较了两者的搜索效率。     

顾及模糊度函数及残差的GPS快速定向算法

GPS除了能进行定位、测速和授时外，还可以进行方位的测量。对基于两片GPS OEM板同步载波相位观测量来测定载体的精确方位进行了算法研究。应用GPS的相位双差观测方程和两个天线间已知的准确距离，对方位角和俯仰角进行两维的搜索，搜索中采用了模糊度函数作为初始判断依据，然后再依据一定历元数据的残差进行分析得到比较准确的方位角。从而再反求出相位的模糊度，最后采用最小二乘原理计算出基线矢量，从而最终得到精确的方位和俯仰角。经过试验表明，该算法是切实可行，在5m基线下，方位精度能达到0．08度，而且定向时间一般只需40秒钟左右。     

GPS载波相位平滑伪距精度分析与应用探讨

分析了载波相位平滑伪距在动态短基线解算、精密单点定位、动态长基线解算的精度,提出了载波相位平滑伪距在多种高精度定位中的应用。     

New method for single epoch, single frequency land vehicle attitude determination using low-end GPS receiver

Stand-alone, unaided, single frequency, single epoch attitude determination is the most challenging case of GNSS compass processing. For land vehicle applications, the baseline approximately lies in the plane of the local geodetic horizon. This provides an important constraint that can be exploited to directly aid the ambiguity resolution process. We fully integrate the constraint into the observation equations, which are transformed orthogonally. Our method can acquire the high-quality float solution by means of a heading search strategy. The fixed solution is obtained by weighted constrained integer least squares for each possible heading. The correct solution is identified by three consecutive steps: Kolmogorov?CSmirnov test, heading verification, and global minimizer of the fixed ambiguity objective function. The analysis focuses on single frequency, single epoch land vehicle attitude determination using low-end GPS receivers with very low precision of carrier phase and code measurements. The error analysis is given for choosing a proper baseline length in practical application. Experimental results demonstrate that this scheme can improve the ambiguity success rate for very short baseline.     

基于载噪比加权的GPS单频单历元定姿算法

针对GPS定姿系统中,传统的利用高度角的加权不能有效反映遮挡情况的问题,从接收机的卫星载噪比出发,对载波相位精度进行分析,提出新的权重矩阵?,对观测模型进行加权。     

Integrity monitoring of high-accuracy GNSS-based attitude determination

Global navigation satellite system (GNSS)-based attitude determination has been widely used in the navigation fields. The reliability of attitude determination is indispensable for safety-critical applications. Since the multi-antenna-based attitude determination uses ultra-short baseline carrier phase double differential processing, the incorrect ambiguity resolution and the excessive measurement error are two main factors affecting the reliability of attitude determination. Since the ambiguity correctness validation cannot guarantee the reliability of the attitude solution, therefore an integrity monitoring method is proposed for the attitude determination in the measurement domain. The proposed integrity monitoring method constructs double test statistics to satisfy the requirements of integrity risk and continuity risk, simultaneously. Furthermore, the attitude alarm limit has been derived from the required navigation performance as the threshold to test the availability of attitude determination. The performance of the proposed method is tested by conducting the static and kinematic experiments, respectively. The static results have shown that the proposed integrity monitoring method is able to monitor the ambiguity fault and the excessive measurement noise. The real-world kinematic data have indicated that the proposed method can reduce the maximum attitude error by about 2.3°, when compared with the standalone ratio-test method.     

Smoothing GPS carrier phase double differences using inertial measurements for high performance applications

This paper will describe an enhancement to the GPS double difference carrier phase measurements on a single airborne platform by smoothing them with inertial measurements while preserving the dynamic bandwidth. This enhancement will reduce the impact of carrier phase multipath and carrier phase noise on baseline determination between multiple antennas on an aircraft when in flight. This type of measurement system has numerous applications where platform pointing and relative body motion must be determined at the mm-level for applications such as sensor stabilization, Synthetic Aperture Radar, long range RADAR (i.e. angle-of-arrival measurements). Lower noise levels (mm-level and below) enable more performance to the stabilized system such as increased aperture for longer range, operation at higher frequencies, and more image resolution. The focus of this paper will be on a technique to provide this enhanced performance for these various applications using the available navigation systems. Additionally, this type of smoothing can effectively remove the additional noise induced by carrier phase measurement differencing. The noise level of a double or triple difference can be reduced below that of the raw measurement. A complimentary synthesized double difference quantity with ultra-low-noise characteristics will be used to smooth the GPS carrier phase double difference measurements without losing dynamic bandwidth since it follows the airborne dynamics. Flight test data will be presented to demonstrate the performance improvement in the midst of aircraft dynamics. Results will show that the noise reduction follows the theoretical prediction.     

组合码和相位观测值在线解双差模糊度的算法

如何在线精确地求解整周模糊度,是ＧＰＳ高精度动态相对定位的关键问题。在线解算取决于很多因素：基线长度、数据处理方法、接收机的性能（如双频还是单频）以及抗ＡＳ和ＳＡ的能力等。现代双频ＧＰＳ接收机能获得载波相位和Ｌ１、Ｌ２频道上的精度伪距观测值,组合这４个观测值可进行单历元整周模糊度解算。文中对组合码和相位观测值在线解整周度的算法进行了试验和分析,得出了很有实用意义的结合。     

Integer least-squares theory for the GNSS compass

Global navigation satellite system (GNSS) carrier phase integer ambiguity resolution is the key to high-precision positioning and attitude determination. In this contribution, we develop new integer least-squares (ILS) theory for the GNSS compass model, together with efficient integer search strategies. It extends current unconstrained ILS theory to the nonlinearly constrained case, an extension that is particularly suited for precise attitude determination. As opposed to current practice, our method does proper justice to the a priori given information. The nonlinear baseline constraint is fully integrated into the ambiguity objective function, thereby receiving a proper weighting in its minimization and providing guidance for the integer search. Different search strategies are developed to compute exact and approximate solutions of the nonlinear constrained ILS problem. Their applicability depends on the strength of the GNSS model and on the length of the baseline. Two of the presented search strategies, a global and a local one, are based on the use of an ellipsoidal search space. This has the advantage that standard methods can be applied. The global ellipsoidal search strategy is applicable to GNSS models of sufficient strength, while the local ellipsoidal search strategy is applicable to models for which the baseline lengths are not too small. We also develop search strategies for the most challenging case, namely when the curvature of the non-ellipsoidal ambiguity search space needs to be taken into account. Two such strategies are presented, an approximate one and a rigorous, somewhat more complex, one. The approximate one is applicable when the fixed baseline variance matrix is close to diagonal. Both methods make use of a search and shrink strategy. The rigorous solution is efficiently obtained by means of a search and shrink strategy that uses non-quadratic, but easy-to-evaluate, bounding functions of the ambiguity objective function. The theory presented is generally valid and it is not restricted to any particular GNSS or combination of GNSSs. Its general applicability also applies to the measurement scenarios (e.g. single-epoch vs. multi-epoch, or single-frequency vs. multi-frequency). In particular it is applicable to the most challenging case of unaided, single frequency, single epoch GNSS attitude determination. The success rate performance of the different methods is also illustrated.     

Initial assessment of the COMPASS/BeiDou-2 regional navigation satellite system

An initial characterization and performance assessment of the COMPASS/BeiDou-2 regional navigation system is presented. Code and carrier phase measurements on up to three frequencies have been collected in March 2012 with a small regional network of monitoring stations. The signal and measurement quality are analyzed and compared with the Japanese Quasi Zenith Satellite System. A high level of stability is demonstrated for the inter-frequency carrier phase biases, which will facilitate the application of triple-frequency undifferenced ambiguity resolution techniques in future precise point positioning applications. The performance of the onboard Rubidium frequency standards is evaluated in comparison to ground-based hydrogen masers and shown to be well competitive with other GNSS satellite clocks. Precise orbit and clock solutions obtained in post-processing are used to study the presently achievable point positioning accuracy in COMPASS/BeiDou-2-only navigation. Finally, the benefit of triple-frequency measurements and extra-wide-lane ambiguity resolution is illustrated for relative positioning on a short baseline.     

Single-Epoch Ambiguity Resolution for Real-Time GPS Attitude Determination with the Aid of One-Dimensional Optical Fiber Gyro

High-accuracy real-time GPS-based attitude determination requires that integer ambiguities be resolved very quickly so that the attitude angles can be output with minimum delay. This article describes an attitude determination algorithm that can resolve integer ambiguities instantaneously, relative to one antenna of a multi-antenna array configuration. The carrier phase and pseudorange observations are used with fixed baseline length constraints and fiberoptic gyro data. Real-time stochastic model improvement using empirical elevation-dependent standard deviation function and an estimated scale factor are a feature of this algorithm. Integer ambiguity search using the LAMBDA method, sophisticated validation criteria, and an adaptive procedure has also been implemented within the software. An experiment was carried out using four Leica dual-frequency GPS receivers (but only the L1 carrier phase and pseudorange data were used) and a low-cost fiberoptic on a car. The results indicate that integer ambiguities can be resolved on a single-epoch basis with a 98.9% success rate. ? 1999 John Wiley & Sons, Inc.     

On-the-fly GPS-based attitude determination using single- and double-differenced carrier phase measurements

Carrier phase measurements are primary observations for GPS attitude determination. Although the satellite-related errors can be virtually eliminated by forming single differences, the baseline-related errors such as line biases are still present in the single-differenced carrier phase measurements. It is, therefore, difficult to resolve the single-differenced integer ambiguities due to the line biases. By forming double differences, the line biases of the single-differenced carrier phase measurements can be effectively removed. However, the main disadvantages of this method lie in the fact that the double-differenced measurements are mathematically correlated and consequently the attitude obtained from the double differences is noisy. This paper presents a new algorithm through which both single and double differences are used simultaneously to resolve these problems in real-time. The solution of the integer ambiguities can be obtained by searching for the most likely grid point in the attitude domain that is independent of the correlation with the double differences. Next, the line biases and corresponding single difference integer ambiguities can be resolved on the fly by using the noisy attitude solution obtained from the previous double difference procedure. In addition, the relationship between the physical signal path difference and the line bias is formed. A new method is also applied to derive the attitude angles through finding the optimal solution of the attitude matrix element. The proposed new procedure is validated using ground and flight tests. Results have demonstrated that the new algorithm is effective and can satisfy the requirement of real-time applications.