Satellite Clock Bias Research Articles

Improving prediction performance of GPS satellite clock bias based on wavelet neural network

As one of the IGS ultra-rapid predicted (IGU-P) products, the orbit precision has been remarkably improved since late 2007. However, because satellite atomic clocks in space show complicated time--...

A Grey Model Based on First Differences in the Application of Satellite Clock Bias Prediction

In consideration of the characteristics of satellite clock bias (SCB), a grey GM(1,1) model based on the first difference method is proposed. The first differences between the SCB values of two adjacent epoches are firstly derived to obtain the corresponding first difference sequence. Then, a grey model is made based on the sequence to predict the first difference values for the time following. Finally, the predicted first difference sequence is recovered to be the corresponding predicted SCB. The clock bias data provided by the IGS (International GNSS Service) are used as the experimental data, and the cases with different lengths of modeling data and different prediction step lengths are compared and analyzed. The result shows that the prediction accuracy of this method is higher than that of traditional grey GM(1,1) model, especially for the PRN01 satellite clock, whose forecast effect is the best. With the first difference method, the model prediction accuracy and stability can be effectively improved and enhanced. This method is feasible and reliable for the relatively long term SCB prediction.

Improved method for estimating the inter-frequency satellite clock bias of triple-frequency GPS

Considering the contribution of the hardware biases to the estimated clock errors, an improved method for estimating the satellite inter-frequency clock bias (IFCB) is presented, i.e., the differen...

Real-Time PPP Based on the Coupling Estimation of Clock Bias and Orbit Error with Broadcast Ephemeris.

Satellite orbit error and clock bias are the keys to precise point positioning (PPP). The traditional PPP algorithm requires precise satellite products based on worldwide permanent reference stations. Such an algorithm requires considerable work and hardly achieves real-time performance. However, real-time positioning service will be the dominant mode in the future. IGS is providing such an operational service (RTS) and there are also commercial systems like Trimble RTX in operation. On the basis of the regional Continuous Operational Reference System (CORS), a real-time PPP algorithm is proposed to apply the coupling estimation of clock bias and orbit error. The projection of orbit error onto the satellite-receiver range has the same effects on positioning accuracy with clock bias. Therefore, in satellite clock estimation, part of the orbit error can be absorbed by the clock bias and the effects of residual orbit error on positioning accuracy can be weakened by the evenly distributed satellite geometry. In consideration of the simple structure of pseudorange equations and the high precision of carrier-phase equations, the clock bias estimation method coupled with orbit error is also improved. Rovers obtain PPP results by receiving broadcast ephemeris and real-time satellite clock bias coupled with orbit error. By applying the proposed algorithm, the precise orbit products provided by GNSS analysis centers are rendered no longer necessary. On the basis of previous theoretical analysis, a real-time PPP system was developed. Some experiments were then designed to verify this algorithm. Experimental results show that the newly proposed approach performs better than the traditional PPP based on International GNSS Service (IGS) real-time products. The positioning accuracies of the rovers inside and outside the network are improved by 38.8% and 36.1%, respectively. The PPP convergence speeds are improved by up to 61.4% and 65.9%. The new approach can change the traditional PPP mode because of its advantages of independence, high positioning precision, and real-time performance. It could be an alternative solution for regional positioning service before global PPP service comes into operation.

Long-term Clock Bias Prediction Based on An ARMA Model

The long-term and reliable prediction of satellite clock bias (SCB) is an important prerequisite for realizing the satellite autonomous navigation and orbit determination. Considering the shortcomings of the quadratic polynomial model (PM) and gray system model (GM) in the long-term prediction of SCB, a new prediction method of SCB based on an ARMA (Auto-Regressive Moving Average) model is proposed to represent the variation characteristics of SCB more accurately. In this paper, a careful precision analysis of the 90-day SCB prediction is made to verify the feasibility and validity of this proposed method by using the IGS (International GNSS Service) clock data. According to the variation characteristics of each satellite clock, the pattern recognition, modeling and prediction of SCB are conducted, and the detailed comparison is made with the other three models at the same time. The results show that adopting the ARMA model can effectively improve the accuracy of long-term SCB prediction.

Application of a Novel Data Mining Method Based on Wavelet Analysis and Chaotic Neural Network on Satellite Clock Bias Prediction

A novel four-stage data mining method for clock bias prediction based on wavelet analysis and chaotic neural networks is proposed. The basic ideas, prediction models and steps of clock bias prediction based on wavelet analysis and chaotic neural network are discussed respectively. And then, to validate the feasibility and validity of the proposed method, make a careful precision analysis for satellite clock bias prediction with the performance parameters of GPS satellite clock, and make comparison and analysis with Grey system model and neural network model. The results of simulation shows that the prediction precision of the novel four-stage model based on wavelet analysis and chaotic neural networks is more better, can afford high precise satellite clock bias prediction for real-time GPS precise point positioning.

Precise Point Positioning with the BeiDou Navigation Satellite System

By the end of 2012, China had launched 16 BeiDou-2 navigation satellites that include six GEOs, five IGSOs and five MEOs. This has provided initial navigation and precise pointing services ability in the Asia-Pacific regions. In order to assess the navigation and positioning performance of the BeiDou-2 system, Wuhan University has built up a network of BeiDou Experimental Tracking Stations (BETS) around the World. The Position and Navigation Data Analyst (PANDA) software was modified to determine the orbits of BeiDou satellites and provide precise orbit and satellite clock bias products from the BeiDou satellite system for user applications. This article uses the BeiDou/GPS observations of the BeiDou Experimental Tracking Stations to realize the BeiDou and BeiDou/GPS static and kinematic precise point positioning (PPP). The result indicates that the precision of BeiDou static and kinematic PPP reaches centimeter level. The precision of BeiDou/GPS kinematic PPP solutions is improved significantly compared to that of BeiDou-only or GPS-only kinematic PPP solutions. The PPP convergence time also decreases with the use of combined BeiDou/GPS systems.

Satellite clock bias estimation for iGPS

The High Integrity GPS program seeks to provide enhanced navigation performance by combining conventional GPS with a communications and ranging broadcast from the Iridium® Communications System. Through clock and message aiding, it would enable existing GPS receivers to acquire and track in more challenging environments. As is the case for standard GPS, accurate and precise timing is key to performance. An approach is presented for estimating the bias of each Iridium satellite clock using satellite-to-ground and satellite-to-satellite measurements. The satellite clock bias estimates are based on a Kalman filter that incorporates code-type observations from the measurements at 10 s intervals. Filter parameters are set based on the expected behavior of the clocks, allowing for discontinuous bias and frequency adjustments due to ground commands. Typical results show the current filter to be accurate to within 200 ns while always meeting the initial system specification of half a microsecond.

An Approach for GPS Clock Jump Detection Using Carrier Phase Measurements in Real-Time

In this study, a real-time architecture for the detection of clock jumps in the GPS clock behavior is proposed. GPS satellite atomic clocks have characteristics of a second order polynomial in the long term showing sudden jumps occasionally. As satellite clock anomalies influence on GPS measurements which could deliver wrong position information to users as a result, it is required to develop a real time technique for the detection of the clock anomalies especially on the real-time GPS applications such as aviation. The proposed strategy is based on Teager Energy operator, which can be immediately detect any changes in the satellite clock bias estimated from GPS carrier phase measurements. The verification results under numerous cases in the presence of clock jumps are demonstrated.

Optimization of Satellite Combination in Kinematic Positioning Mode with the Aid of Genetic Algorithm

Optimization of Satellite Combination in Kinematic Positioning Mode with the Aid of Genetic AlgorithmThe basis of high precision relative positioning is the use of carrier phase measurements. Data differencing techniques are one of the keys to achieving high precision positioning results as they can significantly reduce a variety of errors or biases in the observations and models. Since GPS observations are usually contaminated by many errors such as the atmospheric biases, the receiver clock bias, the satellite clock bias, and so on, it is impossible to model all systematic errors in the functional model. Although the data differencing techniques are widely used for constructing the functional model, some un-modeled systematic biases still remain in the GPS observations following such differencing. Another key to achieving high precision positioning results is to fix the initial carrier phase ambiguities to their theoretical integer values. To obtain a high percentage of successful ambiguity-fixed rates, noisy GPS satellites have to be identified and removed from the data processing step. This paper introduces a new method using genetic algorithm (GA) to optimize the best combination of GPS satellites which yields the highest number of successful ambiguity-fixed solutions in kinematic positioning mode. The results indicate that the use of GA can produce higher number of ambiguity-fixed solutions than the standard data processing technique.

GNSS signals processing via linear and extended Kalman filters

In this paper, a new linear estimator that enables solution of the user position estimation problem has been designed for the case of global navigation satellite system (GNSS) utilization. The proposed recursive linear Kalman filter (LKF) does not need any linearization for nonlinear GNSS measurements and enables accurate estimation of the user coordinates and the distance measuring errors resulting from the time differences between the user and the satellite (clock bias). Comparison of the presented linear and conventional extended Kalman filters for the stationary and moving users' position estimation via GNSS measurements is performed. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

Estimate Algorithm for Pseudo-code Phase Delay and its Uncertainty in the Assisted GPS Receiver

摘要: 快速捕获卫星信号是研制辅助型GPS (A-GPS)接收机所必须解决的一项关键技术. 针对A-GPS接收机能从辅助数据中获取有效星历的特点, 本文提出了一种伪码相位延时及其不确定度估计算法. 该算法在对建立的信号发射时刻方程泰勒展开的基础上, 利用辅助信息建立了伪码相位延时及其不确定度估计方程. 分析和仿真表明, 提出的算法能有效压缩剩余卫星伪码相位延时不确定度, 加快A-GPS接收机的捕获速度. 关键词: A-GPS / 微弱信号环境 / 伪码相位延时 / 不确定度

RTK-GPS測位における伝送遅延に関する研究

Real-time kinematic (RTK) GPS is a technique which allows a mobile user to measure its position with a cm-level precision in real-time by using carrier-phase differential corrections of reference stations. The RTK technique has found a number of industrial applications in the various areas. One of the problems of the RTK-GPS positioning is communication delay between the rover receiver and the reference station. The RTK-GPS system generally requires a continuous wireless transmission link to transmit raw observation data or correction messages from the reference station to the remote rover. Recently, the RTK-GPS has been applied to precise navigation of mobile platforms such as cars or aircrafts. One of the problems in such mobile application environment is communication delay. In this paper, we proposed new methods to correct satellite clock bias and ionospheric delay errors caused by the communication delay. In order to evaluate the proposed methods, we investigated fix rates and positioning accuracy in the existence of up to 30-second communication delay in several baseline lengths.

Stochastic Models used in Static GPS Relative Positioning

In order to achieve high-accuracy positioning results, GPS carrier phase observations have to be used in the data processing step. It is generally known that there are two important aspects to the optimal processing of GPS observations, the definitions of the so-called functional model and the corresponding stochastic model. The functional model describes the mathematical relationship between the GPS observations and the unknown parameters, while the stochastic model describes the statistics of the GPS observations. The functional model is nowadays sufficiently known, however the definition of the stochastic model still remains a challenging research topic. Data differencing techniques are extensively used for constructing the functional model as they can eliminate many of the troublesome GPS biases, such as the atmospheric bias, the receiver clock bias, the satellite clock bias, and so on. However, some unmodelled biases still remain in the GPS observations following such differencing. The challenge is to find a way to realistically incorporate information on such unmodelled biases into the stochastic model. Recently there has been interest in using three types of data, Signal-to-Noise Ratio, satellite elevation and least-squares residual, as quality indicators for a formulation of the stochastic model. In this paper, fundamental equations for processing of GPS data are explained. The three quality indicators used for a construction of the stochastic model are described. The recent development works in stochastic models for static GPS positioning are reviewed, followed by some concluding remarks and recommendations.

Hughes aircraft's architectural design of the federal aviation administration wide-area augmentation system: An international system

Hughes Aircraft is currently developing under contract with the Federal Aviation Administration (FAA) a GPS-based navigation system that is intended to become the primary navigational aid for commercial aviation during all phases of flight—from enroute through Category I precision approach. This innovative system, named the Wide-Area Augmentation System (WAAS), will make use of a network of reference stations distributed throughout the U.S. National Airspace System. These reference stations will collect GPS measurements and send them to master stations. The master stations will process the data to provide correctional information for each GPS satellite. This information will include as separate components the GPS ephemeris errors, satellite clock bias and ionospheric estimation data. The corrections will be sent to the users by means of a Geosynchronous Earth Orbit (GEO) satellite using a specific signal and data format. WAAS is first expected to provide supplemental radio navigation, and eventually to become the primary system of navigation. The system will add the following features to the current GPS system: a GEO ranging function that will improve availability and reliability; differential GPS corrections that will improve accuracy; and integrity monitoring that will provide and enhance safety. To meet the requirements associated with a primary navigation system, WAAS should be able to provide fault-free position fix with a time availability of 0.999 for Category I approaches, and 0.99999 for domestic enroute, terminal and nonprecision approach phases of flight. This paper presents the improvements that this augmentation system offers to stand-alone GPS in order to become the primary navigational system in the U.S. The paper also covers the features that make this wide-area system a naturally expandable system worldwide that will allow the integration of future local-area differential systems across the world.