1,721,040 research outputs found
Performance assessment of aided Global Navigation Satellite System for land navigation
No full textLand navigation includes the methods to determine the time varying position and velocity of a moving object on Earth surface using suitable measurements; it is typically performed in signal-degraded environments where GPS signals are blocked or degraded; hence GPS-only cannot guarantee an accurate and continuous positioning. The multi-constellation approach is a possible way to fill this gap. In this work GPS/GLONASS systems are combined and single point algorithm performance is assessed for different configurations in urban scenario. GLONASS is nearly fully operational and its inclusion guarantees satellite availability improvement, but the GPS/GLONASS multi-constellation use involves the addition, as further unknown, of the intersystem time-scale offset. The considered estimation techniques are Least Squares and Kalman filter. The first method uses only the measurement model, with the drawback of solution unavailability during GNSS outages. The last uses, in addition to a measurement model, a process model allowing the estimation of the unknowns in case of GNSS outage. To improve both methods performances aiding are considered on height and intersystem time scale offset. The main purposes of this work are the performance assessment of a multi-constellation system relative to GPS-only, adopting the aforesaid estimators, and the benefit evaluation of the aiding
Aided GPS/GLONASS navigation in urban environment
No full textIn signal-degraded environments such as urban canyons or mountainous areas many GPS signals are blocked by natural or artificial obstacles or severely degraded; hence GPS-only cannot guarantee an accurate and continuous positioning. The multi constellation approach, integrating different GNSS systems, is a possible way to fill this gap. GLONASS, the Russian navigation satellite system, is currently the main candidate as element of a multi constellation; it is nearly fully operational and its inclusion guarantees an improvement of the satellite availability. Another possible future component of integrated GNSS system is the European Galileo currently in a validation phase with only 4 satellites in orbit GIOVE A/B experimental satellites and 2 Galileo for the IOV phase.
In this work GPS/GLONASS systems are combined and relative single point algorithm performance is assessed for different configurations in signal-degraded scenario such as urban canyon. GPS/GLONASS multi-constellation use involves the addition of a further unknown to estimate, i.e. the intersystem time scale offset, which requires the “sacrifice” of one measurement.
The intersystem offset is observed to be quasi-constant, so an aiding can be introduced to account for its behavior. A similar approach can be adopted for altitude considering its typical variations in urban scenario.
The considered estimation techniques are least squares and Kalman filter, commonly adopted to calculate the navigation unknowns from pseudorange measurements. The least squares method uses a model relating measurements and state with the drawback of solution unavailability during GNSS outages (very frequent in urban areas); to improve the continuity constrained least squares adjustments are considered. Kalman filter uses, in addition to a measurement model, a process model expressing the unknown dynamics and allowing the state estimation in case of GNSS outage.
The main purpose of this work is the performance assessment of a multi-constellation system relative to GPS-only adopting least squares or Kalman filter estimators
Performance assessment of GPS/GLONASS single point positioning in an urban environment
No full textIn signal-degraded environments such as urban canyons and mountainous area, many GNSS
signals are either blocked or strongly degraded by natural and artificial obstacles. In such
scenarios standalone GPS is often unable to guarantee a continuous and accurate positioning
due to lack (or the poor quality) of signals. The combination of different GNSSs could be a
suitable approach to fill this gap, because the multi-constellation system guarantees an improved
satellite availability compared to standalone GPS, thus providing enhanced accuracy, continuity
and integrity of the positioning. The present GNSSs are GPS, GLONASS, Galileo and Beidou,
but the latter two are still in the development phase. In this work GPS/GLONASS systems are
combined for single point positioning and their performance are assessed for different
configurations. Using GPS/GLONASS multi-constellation implies the addition of an additional
unknown, i.e. the intersystem time scale offset, which requires a sacrifice of one measurement.
Since the intersystem offset is quasi-constant over a short period, a pseudo-measurement can be
introduced to compensate the sacrifice.
The benefit after adding a pseudo-measurement has been demonstrated in a vehicular test
Neustrelitz Total Electron Content Model for Galileo Performance: A Position Domain Analysis
No full textIonospheric error is one of the largest errors affecting global navigation satellite system (GNSS) users in open-sky conditions. This error can be mitigated using different approaches including dual-frequency measurements and corrections from augmentation systems. Although the adoption of multi-frequency devices has increased in recent years, most GNSS devices are still single-frequency standalone receivers. For these devices, the most used approach to correct ionospheric delays is to rely on a model. Recently, the empirical model Neustrelitz Total Electron Content Model for Galileo (NTCM-G) has been proposed as an alternative to Klobuchar and NeQuick-G (currently adopted by GPS and Galileo, respectively). While the latter outperforms the Klobuchar model, it requires a significantly higher computational load, which can limit its exploitation in some market segments. NTCM-G has a performance close to that of NeQuick-G and it shares with Klobuchar the limited computation load; the adoption of this model is emerging as a trade-off between performance and complexity. The performance of the three algorithms is assessed in the position domain using data for different geomagnetic locations and different solar activities and their execution time is also analysed. From the test results, it has emerged that in low- and medium-solar-activity conditions, NTCM-G provides slightly better performance, while NeQuick-G has better performance with intense solar activity. The NTCM-G computational load is significantly lower with respect to that of NeQuick-G and is comparable with that of Klobuchar
Algorithms for GNSS Positioning in Difficult Scenario
No full textSatellite navigation is critical in signal-degraded environments such as urban canyons and mountainous area, where many GNSS signals are blocked by natural and artificial obstacles or are strongly degraded. Hence standalone GPS is often unable to guarantee a continuous and accurate positioning. A suitable approach could be the integration of several GNSS. Multi-constellation system guarantees an improved satellite availability with respect to GPS standalone, providing a positioning enhancement in terms of accuracy, continuity and integrity. Currently the ideal candidate for supplement GPS in a multi-constellation approach is the Russian GLONASS. The main purposes of this work are the performance assessment of a GNSS multi-constellation relative to GPS stand-alone and the comparison of Least Squares and Kalman Filter
RAIM Algorithms for Aided GNSS in Urban Scenario
No full textUrban canyon is a critical scenario for satellite navigation, because many GNSS signals are blocked by artificial obstacles or severely degraded; in standalone mode GPS, currently the main GNSS, cannot guarantee an accurate and continuous positioning. A possible approach to overcome these limitations is the use of multiple GNSS systems. GLONASS, the Russian navigation satellite system, is currently fully operational and is the main candidate to support this thesis. Urban scenario is mainly affected by multipath phenomenon, yielding several blunders into the measurements and unacceptable errors in the navigation solution. The integrity concept was introduced for safety-of-life application as aviation to provide timely warnings to users when a system should not be used for navigation, and then it was expanded to not safety-of-life service as urban navigation. RAIM (Receiver Autonomous Integrity Monitoring) techniques are user-level integrity methods based on consistency check of redundant measurements. This check is crucial because only at user-level certain local errors, such as multipath and local interferences, can be detected. Multi-constellation GNSS improves navigation solution in terms of accuracy and continuity; a further enhancement is achievable even in terms of integrity owing to the gained redundancy. The multi-constellation use implies a further unknown related to the intersystem time scale offset, requiring the “sacrifice” of one measurement. This parameter is observed to be quasi-constant in the short term, so an aiding can be introduced to account for its behavior. A similar approach can be adopted for altitude considering its slow variations in urban scenario. In this work GPS/GLONASS systems are combined and the benefits of the aforesaid aids are assessed, with main focus being the improvements in terms of integrity; single point GNSS and snapshot RAIM algorithms are herein considered. PVT and RAIM algorithms are developed in MatLab® environment and belong to a tool implemented by PANG (PArthenope Navigation Group)
A Galileo IOV Assessment: Measurement and Position Domain
Full text linkThe European GNSS, Galileo, is currently in its In-Orbit Validation (IOV) phase where four satellites are finally available for computing the user position. In this phase, the analysis of the measurements and Position Velocity and Time (PVT) obtained from the IOV satellites can provide insight on the potentialities of the Galileo system. A methodology is suggested for the analysis of the Galileo IOV pseudorange and pseudorange rates collected from the E1 and E5 frequencies. Several days of data were collected and processed to determine figures of merits such as RMS and maximum errors of the Galileo observables. From the analysis, it emerges that Galileo is able to achieve better accuracy with respect to GPS. A thorough analysis of the PVT performance is also achieved using broadcast ephemerides. Galileo and GPS PVTs are compared under similar geometry conditions showing the potential of the Galileo system.JRC.G.5 - Security technology assessmen
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