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

Ambiguity Function Method Scheme for Aircraft Attitude Sensor Utilising GPS/GLONASS Carrier Phase Measurement

When the receivers of GPS, GLONASS, COMPASS and other such systems are equipped with multiple antennas, they can give attitude information. Based on the difference carrier phase equations established in local level frame (LLF), a new algorithm is presented to resolve aircraft attitude determination problems in real-time. Presuming that the cycle integer ambiguity is known, the measurement equations have attitude analytical resolutions using single difference (SD) equations of two navigation satellites in-view. Similar with SD process, the doubledifference (DD) measurements are established and analysed. In addition, the SD and DD algorithms are capable of reducing the integer search space into some discrete point space and then the ambiguity function method (AFM) resolves the ambiguity function within the point solutions space. Therefore the procedures have very low computation, thus saving time. The hardware architecture has been realised using multiple  GPS/GLONASS OEMs. The experimental results have demonstrated that the proposed approach is effective and can satisfy the requirement of real-time application in cases of GPS, and combined GPS, and GLONASS.Defence Science Journal, 2009, 59(5), pp.466-470, DOI:http://dx.doi.org/10.14429/dsj.59.154

Attitude determination of GPS satellite vehicles

There is an increasing demand for navigation systems that has led to rapid development of Global Positioning System (GPS) across industries. Apart from position and speed, precise attitude measurements are needed for many GPS applications. This thesis presents techniques for attitude determination of satellite vehicles in both real-time and stand-alone positioning applications. The GPS system used is a differential GPS system that estimates the body frame baselines using at least four receivers. The attitude information is obtained using these baselines and projecting them onto a local level frame. Integer ambiguity is a major constraint in attitude determination. Least Squares Ambiguity Deco-relation method is implemented to fix the ambiguities prior to baseline estimation. Estimation techniques such as Least Squares and Kalman Filter are implemented for deriving baseline components. Finally, this system will compute body frame coordinates and attitude components in reference to the desired coordinate frames.Engineering Technology, Department o

GNSS-Based Attitude Determination Techniques - A Comprehensive Literature Survey

GNSS-based Attitude Determination (AD) of a mobile object using the readings of the Global Navigation Satellite Systems (GNSS) is an active area of research. Numerous attitude determination methods have been developed lately by making use of various sensors. However, the last two decades have witnessed an accelerated growth in research related to GNSS-based navigational equipment as a reliable and competitive device for determining the attitude of any outdoor moving object using data demodulated from GNSS signals. Because of constantly increasing number of GNSS-based AD methods, algorithms, and techniques, introduced in scientific papers worldwide, the problem of choosing an appropriate approach, that is optimal for the given application, operational environment, and limited financial funding becomes quite a challenging task. The work presents an extensive literature survey of the methods mentioned above which are classified in many different categories. The main aim of this survey is to help researchers and developers in the field of GNSS applications to understand pros and cons of the current state of the art methods and their computational efficiency, the scope of use and accuracy of the angular determination.https://doi.org/10.1109/ACCESS.2020.297008

Improved Knight method based on narrowed search space for instantaneous GPS attitude determination

The Knight algorithm can instantaneously resolve integer ambiguities and significantly improve search speed by skipping over most less-likely integer ambiguity candidates. However, its reliability depends on the volume ofthe integer ambiguity search space. Using coarse attitude knowledge can reduce the size of the search space. This paper proposes a new method for narrowing the search space by taking into account a geometric constraint of visible satellites. The constraint is formulated as a recursive procedure and is thus very suitable for incorporation into the search loop of the Knight method. Experimental results demonstrate that the proposed method can improve the search efficiency and reliability of the Knight method

Testing a new multivariate GNSS carrier phase attitude determination method for remote sensing platforms

GNSS (Global Navigation Satellite Systems)-based attitude determination is an important field of study, since it is a valuable technique for the orientation estimation of remote sensing platforms. To achieve highly accurate angular estimates, the precise GNSS carrier phase observables must be employed. However, in order to take full advantage of the high precision, the unknown integer ambiguities of the carrier phase observables need to be resolved. This contribution presents a GNSS carrier phase-based attitude determination method that determines the integer ambiguities and attitude in an integral manner, thereby fully exploiting the known body geometry of the multi-antennae configuration. It is shown that this integral approach aids the ambiguity resolution process tremendously and strongly improves the capacity of fixing the correct set of integer ambiguities.In this contribution, the challenging scenario of single-epoch, single-frequency attitude determination is addressed. This guarantees a total independence from carrier phase slips and losses of lock, and it also does not require any a priori motion model for the platform. The method presented is a multivariate constrained version of the popular LAMBDA method and it is tested on data collected during an airborne remote sensing campaign

Implementation of Moving-Base-GNSS en NAVKA Multisensor GNSS / MEMS /optics navigation algorithms and systems

[EN] Implementation of Moving-Base-GNSS in NAVKA Multisensor GNSS / MEMS / Optics Navigation Algorithms and Systems. Development and implementation of an ambiguity resolution algorithm related to the Moving-Base-GNSS situation. Algorithm implementation in the RTKLIB open source library (C / C ++). Development of software that allows to calculate the position of a rover from the coordinates of a master receiver (DGNSS / PPP) and from the baselines calculated with the algorithm in question.[ES] Implementation of Moving-Base-GNSS in NAVKA Multisensor GNSS/MEMS/Optics Navigation Algorithms and Systems. Desarrollo e implementación de un algoritmo de resolución de ambigüedades relacionado con la situación Moving-Base-GNSS. Implementación del algoritmo en la librería de código abierto RTKLIB (C/C++). Desarrollo de un software que permite calcular la posición de un rover a partir de las coordenadas de un receptor máster (DGNSS/PPP) y de las líneas base calculadas con el algoritmo en cuestión.Hernández Olcina, J. (2019). Implementation of Moving-Base-GNSS en NAVKA Multisensor GNSS / MEMS /optics navigation algorithms and systems. http://hdl.handle.net/10251/139434TFG

Low-Complexity Instantaneous Ambiguity Resolution with the Affine-Constrained GNSS Attitude Model

In this contribution a new approach to ambiguity resolution for Global Navigation Satellite System (GNSS)-based attitude estimation applications is discussed and tested. This approach enhances the observation model by means of additional linear constraints. These constraints are implicitly derived by applying an affine transformation to the unknown real-valued parameters, and largely aid the integer ambiguity estimation through an improved float estimation. The new method is characterized by a lower computational complexity than a rigorous nonlinearly-constrained GNSS attitude model, and at the same time it guarantees higher performance than unconstrained, and therefore weaker, models. The ambiguity resolution performance of the affine-constrained approach is tested through a series of simulated as well as actual data sets, demonstrating the validity and usefulness of the proposed approach for multi-antenna GNSS-based attitude determination applications

Instantaneous GPS-Galileo attitude determination: single-frequency performance

New and modernized global navigation satellite systems (GNSSs) are paving the way for an increasing number of applications in positioning, navigation, and timing (PNT). A combined GNSS constellation will significantly increase the number of visible satellites and, thus, will improve the geometry of observed satellites, enabling improvements in navigation solution availability, reliability, and accuracy. In this paper, a global positioning system (GPS) +Galileo robustness analysis is carried out for instantaneous single-frequency GNSS attitude determination. Precise attitude determination using multiple GNSS antennas mounted on a platform relies on successful resolution of the integer carrier-phase ambiguities. The multivariate-constrained least squares ambiguity decorrelation adjustment (MC-LAMBDA) method has been developed to resolve the integer ambiguities of the nonlinearly constrained GNSS attitude model that incorporates the known antenna geometry. In this paper, the method is used to analyze the attitude determination performance of a combined GPS +Galileo system. Special attention is thereby given to the GPS and Galileo intersystem biases (ISBs).The attitude determination performance is evaluated using GPS/Galileo data sets from a hardware-in-the-loop experiment and two real-data campaigns. In the hardware-in-the-loop experiment, a full GPS/Galileo constellation is simulated, and performance analyses are carried out under various satellite-deprived environments, such as urban canyons, open pits, and other satellite outages. In the first real-data experiment, single-frequency GPS data, combined with the data of Galileo in-orbit validation element (GIOVE) satellites GIOVE-A/GIOVE-B (the two experimental Galileo satellites), are used to analyze the two constellation attitude solutions. In the second real-data experiment, we present the results based on single-frequency data from one of the Galileo IOV satellites, combined with the data of GIOVE-A and GPS. We d- monstrate and quantify the improved availability, reliability, and accuracy of attitude determination using the combined constellation