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Todd Walter - One of the best experts on this subject based on the ideXlab platform.
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mitigation of nominal signal deformations on dual Frequency waas position errors
Proceedings of the 27th International Technical Meeting of The Satellite Division of the Institute of Navigation (ION GNSS+ 2014), 2014Co-Authors: Gabriel Wong, Todd Walter, Yuhsuan Chen, Eric R Phelts, Per EngeAbstract:Global Navigation Satellite Systems (GNSS) are used in a wide variety of applications, some critical, many essential. They are steadily being improved with the addition of new constellations, new frequencies, and new signals. Future multi-Frequency GNSS will eliminate one of the largest error sources (ionospheric delays) and promises even better performance. Unfortunately, the new frequencies and signals will have small but unavoidable biases relative to one another. These nominal satellite signal deformations – deviations of broadcast satellite signals from ideal – result in tracking errors, range biases, and position errors in GPS receivers. The impact of these biases increases as other error sources are eliminated. Left unquantified and unmitigated, future performance may be limited by these biases. Thus it is imperative to measure, characterize, and mitigate them. An effective “measure-and-verify” measurement technique for signal deformation biases was previously demonstrated by the author and collaborators for L1-Frequency signals [15]. This two-stage process produced highly-consistent measurements, thus rendering signal deformation biases observable and measurable. This measurement method is applied to obtain signal deformation bias measurements for 3 of the recent Block IIF dual-Frequency L1/L5 satellites. These dual-Frequency measurements are subsequently used to validate past projections of dual-Frequency L1/L5 biases from single-Frequency L1-only biases. In turn, this allows accurate estimations of expected and worst case 2 position errors for dual-Frequency L1/L5 positioning in the presence of unmitigated signal deformation biases. Finally, using the “measure-and-verify” technique, a proposed strategy is demonstrated to be highly effective: narrowing the space of allowed user-receiver correlator spacings. Use of this strategy mitigates the signal deformation biases and resultant position errors, allowing dual-Frequency users to reap the performance benefits of ionospheric error removal without significant limitations caused by signal deformation biases.
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future dual Frequency gps navigation system for intelligent air transportation under strong ionospheric scintillation
IEEE Transactions on Intelligent Transportation Systems, 2014Co-Authors: Todd WalterAbstract:GPS technology is essential for future intelligent air transportation systems such as the Next Generation Air Transportation System (NextGen) of the United States. However, observed deep and frequent amplitude fading of GPS signals due to ionospheric scintillation can be a major concern in expanding GPS-guided aviation to the equatorial area where strong scintillation is expected. Current civil GPS airborne avionics track signals at a single Frequency (L1 Frequency) alone because it was the only civil signal available in the Frequency band for aviation applications. The first GPS Block IIF satellite was launched in May 2010. This next-generation satellite transmits a new civil signal at the L5 Frequency, which can be used for air transportation. This paper investigates a possible improvement in the availability of GPS-based aircraft landing guidance down to 200 ft above the runway, which is also known as Localizer Performance with Vertical Guidance (LPV) 200, under strong ionospheric scintillation when dual-Frequency signals are available. Based on the availability study, this paper proposes and justifies a GPS aviation receiver performance standard mandating fast reacquisition after a very brief signal outage due to scintillation. In order to support a temporary single-Frequency operation under a single-Frequency loss due to scintillation, a new vertical protection level (VPL) equation is proposed and justified. With this new performance requirement and new VPL equation in place, 99% availability of LPV-200 would be attainable, rather than 50% at the current standards, even under the severe scintillation scenarios considered in this paper.
D A Gray - One of the best experts on this subject based on the ideXlab platform.
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weak interference direction of arrival estimation in the gps L1 Frequency band
International Conference on Acoustics Speech and Signal Processing, 2015Co-Authors: Matthew Trinkle, D A GrayAbstract:Due to its low received power, a GPS signal is vulnerable to both intentional and unintentional interferences. In this paper, the problem of estimating the direction of arrival of a weak GPS interference, which has the same power level as the GPS signals or is even weaker than them, using a GPS antenna array is considered. To achieve this, a multiple subspace projection algorithm is proposed to cancel GPS signals which are treated as relatively strong interfering sources. Comparisons with the Partitioned Subspace Projection (PSP) method are presented using simulations. Experimental results show that the DOA of an interference with an SNR of −20dB in the GPS L1 band can be accurately estimated1.
Hauschild André - One of the best experts on this subject based on the ideXlab platform.
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GNSS Yaw Attitude estimation: Results for the Japanese Quasi‐Zenith Satellite System block‐II satellites using single‐ or triple‐Frequency signals from two antennas
'Wiley', 2019Co-Authors: Hauschild AndréAbstract:The Japanese Quasi-Zenith Satellite System (QZSS) constellation has added three new Block-II satellites. Two of these satellites have been launched into inclined geosynchronous orbits and one into a geostationary orbit. All three spacecraft broadcast ranging signals on GPS L1, L2 and L5 frequencies from their main L-band antenna together with the centimeter-level augmentation service (CLAS) signal L6 (formerly LEX) on the Galileo E6 Frequency band. Like on the Block-I satellite, a sub-meter level augmentation service (SLAS) signal is transmitted from a separate antenna on the GPS L1 Frequency. A new feature is the addition of the position technology verification service (PTV) Signal on the L5 Frequency from yet another antenna. After determination of the antenna baseline vector, differential processing of measurements from different observations allows for an estimation of the satellite’s yaw attitude. The L1 SLAS and the L1 C/A-code signals have been used to estimate the yaw attitude with an accuracy of less than 1°. Differential carrier-phase center variation maps have been derived for this signal combination. Yaw estimation results are presented for periods of special interest, for example 360° yaw rotations, orbit correction maneuvers and the satellite’s eclipse period, where a special pseudo yaw steering attitude mode is applied. The second part of the paper introduces a new concept using triple-Frequency signals from two different antennas for attitude determination. This method is demonstrated with QZSS measurements, but is also applicable to other satellite navigation system, like the enhanced GLONASS-M satellites with L3 signal capabilities
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GNSS Yaw-Attitude Estimation: Results for QZSS Block-II Satellites Using Single- or Triple-Frequency Signals from two Antennas
2018Co-Authors: Hauschild AndréAbstract:The QZSS constellation has added three new Block-II satellites. Two of these satellites have been launched into inclined geosynchronous orbits and one into a geostationary orbit. All three spacecraft broadcast ranging signals on GPS L1, L2 and L5 frequencies from their main L-band antenna together with the centimeter-level Augmentation service (CLAS) signal L6 (formerly LEX) on the Galileo E6 Frequency band. Like QZS-1, a sub-meter level Augmentation service (SLAS) signal is transmitted from a separate antenna on the GPS L1 Frequency. A new feature is the addition of the position technology verification service (PTV) signal on the L5 Frequency from yet another antenna. Differential processing of measurements from different observations allow for an estimation of the satellite’s yaw attitude after determination of the antenna baseline vector. The L1 SLAS and the L1 C/A-code signals have been used to estimate the yaw attitude with an accuracy of less than 1°. Differential carrier-phase center variation maps have been derived for this signal combination. Yaw estimation results are presented for period of special interest, for example 360° yaw rotations, orbit correction maneuvers and the satellite’s eclipse period, where a special pseudo yaw steering attitude mode is applied. The second part of the paper introduces a new concept using triple-Frequency signals from two different antennas for attitude determination. This method is demonstrated with QZSS measurements, but is also applicable to other satellite navigation system, like the enhanced GLONASS-M satellites with L3 signal capabilitie
Eurico R. Paula - One of the best experts on this subject based on the ideXlab platform.
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performance analysis of κ μ distribution for global positioning system gps L1 Frequency related ionospheric fading channels
Journal of Space Weather and Space Climate, 2019Co-Authors: Alison De Oliveira Moraes, Eurico R. Paula, Jonas Sousasantos, Josue Jurgen Popov Pereira Da Cunha, Vicente Carvalho Lima Filho, Bruno Cesar VaniAbstract:The present work aims to evaluate the application of the κ -μ distribution as a representation of the fading effect caused by the phenomenon of scintillation on L -band transionospheric radio links. The ionospheric scintillation is a phenomenon defined as a rapid variation in the amplitude and phase of electromagnetic wave signals. This phenomenon starts in the first hours of the night, at latitudes near the geomagnetic equator. Scintillation occurs when radio signals cross ionospheric irregularities, also known as plasma bubbles. These plasma bubble structures are generated after the sunset due to instabilities in the F region of ionosphere. Distributions with non-single parameter usually present better results, however, this point requires further investigation by comparing different models. The goals of this study are: (1) the modeling of experimental data using the κ -μ distribution; (2) the κ -μ parameters characterization for empirical data and the evaluation of parameters estimation based in different approaches; (3) the comparison between the distribution proposed and other models adopted in the literature in order to verify the performance of two parameter models. The results of the analysis performed showed that the κ -μ distribution presents good fitting of the empirical scintillation data. These fitting results were calculated through the chi-square fit test under which the values reveal fair E [χ 2 ] for κ -μ distribution in most of the cases. The evaluation of κ -μ parameters suggests that the distribution has a more conservative outcome than in the distributions traditionally used, but being a legitimate approximation due to its adjustable features in the tail region of the distribution. Typical pairs of κ -μ coefficients are presented for theoretical works. The comparison of κ -μ distribution to Rice, Nakagami-m and α -μ models showed that κ-μ is capable of describing more severe scintillation scenarios where the tail of the distribution is more raised in comparison to the other models.
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GPS L1-Frequency Observations of Equatorial Scintillations and Irregularity Zonal Velocities
Surveys in Geophysics, 2014Co-Authors: Marcio T A H Muella, Eurico R. Paula, Olusegun F. JonahAbstract:In this work, the climatology of ionospheric scintillations at global positioning system (GPS) L-band Frequency and the zonal drift velocities of scintillation-producing irregularities were depicted for the equatorial observatory of São Luis (2.33°S; 44.21°W; dip latitude 1.3°S), Brazil. This is the first time that the hourly, monthly, and seasonal variations of scintillations and irregularity zonal drifts at São Luis were characterized during periods of different solar activity levels (from December 1998 to February 2007). The percentage occurrence of scintillations at different sectors of the sky was also investigated, and the results revealed that the scintillations are more probable to be observed in the west sector of the sky above São Luis, whereas the north–south asymmetries are possibly related to asymmetries in the plasma density distribution at off-equatorial latitudes. The scintillations on GPS signals occurred more frequently around solar maximum years, but it is also clear from the results of a strong variability in the scintillation activity in the years with moderate solar flux during the descending phase of the solar cycle. The equatorial scintillations occur predominantly during pre-midnight hours with a broad maximum near the December solstice months. In general, weak level of scintillations ( S _4 index between 0.2 and 0.4) dominated at all seasons; however, during the winter months around solar maximum years (although the scintillation occurrence is extremely low), stronger levels of scintillations ( S _4 > 0.6) may occur at comparable rate with the weak scintillations. The irregularity zonal velocities, as estimated from the GPS spaced-receiver technique, presented a different scenario for the two seasons analyzed; during the equinoxes, the magnitude of the zonal velocities appeared not to change with the solar activity, whereas during the December solstice months, the larger magnitudes were observed around solar maximum years. Other relevant aspects of the observations are highlighted and discussed.
Alison De Oliveira Moraes - One of the best experts on this subject based on the ideXlab platform.
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performance analysis of κ μ distribution for global positioning system gps L1 Frequency related ionospheric fading channels
Journal of Space Weather and Space Climate, 2019Co-Authors: Alison De Oliveira Moraes, Eurico R. Paula, Jonas Sousasantos, Josue Jurgen Popov Pereira Da Cunha, Vicente Carvalho Lima Filho, Bruno Cesar VaniAbstract:The present work aims to evaluate the application of the κ -μ distribution as a representation of the fading effect caused by the phenomenon of scintillation on L -band transionospheric radio links. The ionospheric scintillation is a phenomenon defined as a rapid variation in the amplitude and phase of electromagnetic wave signals. This phenomenon starts in the first hours of the night, at latitudes near the geomagnetic equator. Scintillation occurs when radio signals cross ionospheric irregularities, also known as plasma bubbles. These plasma bubble structures are generated after the sunset due to instabilities in the F region of ionosphere. Distributions with non-single parameter usually present better results, however, this point requires further investigation by comparing different models. The goals of this study are: (1) the modeling of experimental data using the κ -μ distribution; (2) the κ -μ parameters characterization for empirical data and the evaluation of parameters estimation based in different approaches; (3) the comparison between the distribution proposed and other models adopted in the literature in order to verify the performance of two parameter models. The results of the analysis performed showed that the κ -μ distribution presents good fitting of the empirical scintillation data. These fitting results were calculated through the chi-square fit test under which the values reveal fair E [χ 2 ] for κ -μ distribution in most of the cases. The evaluation of κ -μ parameters suggests that the distribution has a more conservative outcome than in the distributions traditionally used, but being a legitimate approximation due to its adjustable features in the tail region of the distribution. Typical pairs of κ -μ coefficients are presented for theoretical works. The comparison of κ -μ distribution to Rice, Nakagami-m and α -μ models showed that κ-μ is capable of describing more severe scintillation scenarios where the tail of the distribution is more raised in comparison to the other models.
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low latitude scintillation weakening during sudden stratospheric warming events
Journal of Geophysical Research, 2015Co-Authors: E R De Paula, O F Jonah, Alison De Oliveira Moraes, Bela G Fejer, Marcio T A H Muella, S L G Dutra, E A Kherani, Mangalathayil Ali Abdu, Inez S Batista, Roberto R. PaesAbstract:Global Positioning System (GPS) L1-Frequency (1.575 GHz) amplitude scintillations at Sao Jose dos Campos (23.1°S, 45.8°W, dip latitude 17.3°S), located under the southern crest of the equatorial ionization anomaly, are analyzed during the Northern Hemisphere winter sudden stratospheric warming (SSW) events of 2001/2002, 2002/2003, and 2012/2013. The events occurred during a period when moderate to strong scintillations are normally observed in the Brazilian longitude sector. The selected SSW events were of moderate and major categories and under low Kp conditions. The most important result of the current study is the long-lasting (many weeks) weakening of scintillation amplitudes at this low-latitude station, compared to their pre-SSW periods. Ionosonde-derived evening vertical plasma drifts and meridional neutral wind effects inferred from total electron content measurements are consistent with the observed weakening of GPS scintillations during these SSW events. This work provides strong evidence of SSW effects on ionospheric scintillations and the potential consequences of such SSW events on Global Navigation Satellite System-based applications.
