Global Positioning System Pseudorange Measurements Research Articles

Study of the GPS inter-frequency calibration of timing receivers

When calibrating Global Positioning System (GPS) stations dedicated to timing, the hardware delays of P1 and P2, the P(Y)-codes on frequencies L1 and L2, are determined separately. In the international atomic time (TAI) network the GPS stations of the time laboratories are calibrated relatively against reference stations. This paper aims at determining the consistency between the P1 and P2 hardware delays (called dP1 and dP2) of these reference stations, and to look at the stability of the inter-signal hardware delays dP1–dP2 of all the stations in the network. The method consists of determining the dP1–dP2 directly from the GPS pseudorange measurements corrected for the frequency-dependent antenna phase center and the frequency-dependent ionosphere corrections, and then to compare these computed dP1–dP2 to the calibrated values.Our results show that the differences between the computed and calibrated dP1–dP2 are well inside the expected combined uncertainty of the two quantities. Furthermore, the consistency between the calibrated time transfer solution obtained from either single-frequency P1 or dual-frequency P3 for reference laboratories is shown to be about 1.0 ns, well inside the 2.1 ns uB uncertainty of a time transfer link based on GPS P3 or Precise Point Positioning. This demonstrates the good consistency between the P1 and P2 hardware delays of the reference stations used for calibration in the TAI network.The long-term stability of the inter-signal hardware delays is also analysed from the computed dP1–dP2. It is shown that only variations larger than 2 ns can be detected for a particular station, while variations of 200 ps can be detected when differentiating the results between two stations. Finally, we also show that in the differential calibration process as used in the TAI network, using the same antenna phase center or using different positions for L1 and L2 signals gives maximum differences of 200 ps on the hardware delays of the separate codes P1 and P2; however, the final impact on the P3 combination is less than 10 ps.

A Novel Approach for Improved Vehicular Positioning Using Cooperative Map Matching and Dynamic Base Station DGPS Concept

In this paper, a novel approach for improving vehicular positioning is presented. This method is based on the cooperation of the vehicles by communicating their measured information about their position. This method consists of two steps. In the first step, we introduce our cooperative map matching method. This map matching method uses the V2V communication in a vehicular ad hoc network (VANET) to exchange global positioning system (GPS) information between vehicles. Having a precise road map, vehicles can apply the road constraints of other vehicles in their own map matching process and acquire a significant improvement in their positioning. After that, we have proposed the concept of a dynamic base station DGPS (DDGPS), which is used by vehicles in the second step to generate and broadcast the GPS pseudorange corrections that can be used by newly arrived vehicles to improve their positioning. The DDGPS is a decentralized cooperative method that aims to improve the GPS positioning by estimating and compensating the common error in GPS pseudorange measurements. It can be seen as an extension of DGPS where the base stations are not necessarily static with an exact known position. In the DDGPS method, the pseudorange corrections are estimated based on the receiver's belief on its positioning and its uncertainty and then broadcasted to other GPS receivers. The performance of the proposed algorithm has been verified with simulations in several realistic scenarios.

Laser-based Relative Navigation Using GPS Measurements for Spacecraft Formation Flying

This study presents a precise relative navigation algorithm using both laser and Global Positioning System (GPS) measurements in real time. The measurement model of the navigation algorithm between two spacecraft is comprised of relative distances measured by laser instruments and single differences of GPS pseudo-range measurements in spherical coordinates. Based on the measurement model, the Extended Kalman Filter (EKF) is applied to smooth the pseudo-range measurements and to obtain the relative navigation solution. While the navigation algorithm using only laser measurements might become inaccurate because of the limited accuracy of spacecraft attitude estimation when the distance between spacecraft is rather large, the proposed approach is able to provide an accurate solution even in such cases by employing the smoothed GPS pseudo-range measurements. Numerical simulations demonstrate that the errors of the proposed algorithm are reduced by more than about 12% compared to those of an algorithm using only laser measurements, as the accuracy of angular measurements is greater than 0.001° at relative distances greater than 30 km.

Performance analysis of federated filter for SAR/TRN/GPS/INS integration

Decentralized integration of global positioning system (GPS), synthetic aperture radar (SAR), and terrain referenced navigation (TRN) system into an inertial navigation system (INS) is analysed in comparison to the centralized integration method in this paper. Many publications have shown different decentralized integration methods. The main advantage of the decentralized filter architecture is flexibility and modularity. Especially the federated no-reset filter has received considerable attention in literature because of improved fault detection and isolation (FDI) capability, which is an important feature in multi-sensor navigation systems. Fault detection capability of the federated no-reset filter is well-established. However, this filter type combines sensor data in a suboptimal way and a loss of accuracy compared to the centralized Kalman filter is generally observed. Other publications mentioned this loss of accuracy, but did not give the amount of accuracy loss for SAR/TRN/GPS/INS systems. In this paper additionally a slight modification of the federated filter is presented. Typically a GPS/INS filter tends to be overoptimistic due to long-term timecorrelated atmospheric errors of the GPS pseudo-range measurements. A rather simple modification of the federated filter is given to take into account this overoptimistic behaviour. A covariance correction yields a more reasonable covariance of the GPS/INS local filter and an improved overall position estimation of the federated filter.

Efeitos de segunda e terceira ordem da ionosfera no posicionamento GNSS no Brasil

O Sistema de Posicionamento Global (GPS) transmite seus sinais em duas freqüências, o que permite eliminar matematicamente os efeitos de primeira ordem da ionosfera através da combinação linear ionosphere free. Porém, restam os efeitos de segunda e terceira ordem, os quais podem provocar erros da ordem de centímetros nas medidas GPS. Esses efeitos, geralmente, são negligenciados no processamento dos dados GPS. Os efeitos ionosféricos de primeira, segunda e terceira ordem são diretamente proporcionais ao TEC presente na ionosfera, porém, no caso dos efeitos de segunda e terceira ordem, comparecem também o campo magnético da Terra e a máxima densidade de elétrons, respectivamente. Nesse artigo, os efeitos de segunda e terceira ordem da ionosfera são investigados, sendo que foram levados em consideração no processamento de dados GPS na região brasileira para fins de posicionamento. Serão apresentados os modelos matemáticos associados a esses efeitos, as transformações envolvendo o campo magnético da Terra e a utilização do TEC advindo dos Mapas Globais da Ionosfera ou calculados a partir das observações GPS de pseudodistância. O processamento dos dados GPS foi realizado considerando o método relativo estático e cinemático e o posicionamento por ponto preciso (PPP). Os efeitos de segunda e terceira ordem foram analisados considerando períodos de alta e baixa atividade ionosférica. Os resultados mostraram que a não consideração desses efeitos no posicionamento por ponto preciso e no posicionamento relativo para linhas de base longas pode introduzir variações da ordem de poucos milímetros nas coordenadas das estações, além de variações diurnas em altitude da ordem de centímetros.

A New GPS Data Processing Algorithm for the Positioning of Oceanographic Experiments

Abstract In this paper, the authors present a Global Positioning System (GPS) algorithm for medium accuracy (1-m rms) positioning of ocean buoys. The application addressed in this paper is that of the Fast Pegasus experiments that require the positioning of surface buoys used in collecting subsurface acoustic data for ocean current profiling. The current GPS system designed for the Fast Pegasus experiments requires a land-based single-frequency GPS receiver for differential GPS positioning. In contrast, the technique presented here is designed for the point positioning of a stand-alone single-frequency GPS receiver (which is in motion) and does not require the use of a land-based reference receiver. The precise point positioning algorithm developed here uses postprocessed GPS satellite ephemerides and clock corrections to compute the position of a single GPS receiver. A square root information filter/smoother uses the GPS pseudorange and carrier phase measurements to estimate the position and clock offset...

Accuracy assessment of GPS satellite orbits

Global Positioning System (GPS) orbit determination using data collected by the civilian tracking network CIGNET have been used in a variety of experiments, along with data collected from special campaigns to augment the global tracking data. These experiments have been used to investigate the fidelity of the satellite force and kinematic models with the goal of improving the GPS ephemeris accuracy. Software has been developed for the preprocessing of GPS pseudo-range and phase measurements, including procedures for cycle slip correction. A multi-satellite orbit determination program, MSODP, allows for satellite-dependent force models, including high-low satellite constellations. Assessments of orbit accuracies derived from measurements collected in campaigns with nearly global networks have been performed with a variety of techniques, including determination of baselines known from SLR or VLBI, the computation of long, multi-week arcs and the comparison of predicted ephemerides with determined ephemerides. These results have provided indications of inadequacies in the force models, especially with the nongravitational forces, particularly those aspects associated with eclipsing.