A Kalman filter clock ensemble algorithm that admits measurement noise

Greenhall, C. A.

doi:10.1088/0026-1394/43/4/s19

Cited by 36 publications

(47 citation statements)

References 11 publications

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“…Each satellite can thus compute a composite time associated with all time offsets measured in the system. Corresponding algorithms were developed by Brown [10] and Greenhall [11]. Due to the lack of long term stability of the CSL, a time scale based on CSL alone would successively drift.…”

Section: Synchronization and Kepler Time Scalementioning

confidence: 99%

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Kepler � Satellite Navigation without Clocks and Ground Infrastructure

Günther¹

2018

Proceedings of the 31st International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GNSS+ 201

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Global Navigation Satellite Systems receivers use pseudorange measurements for positioning and time determination. The control system uses the same measurements for estimating the satellite orbits, clock offsets and signal biases in a complex estimation process, which additionally involves the determination of atmospheric delays. In current systems, the separation of these different parameters imposes strong requirements on the stability of the satellite clocks and on the ground infrastructure. Several hundred ground monitoring stations are additionally used in high accuracy applications. The Kepler proposal follows a different approach. It re-uses the Galileo constellation of Medium Earth Orbiting (MEO) satellites, as well as its signals but complements them by a small constellation of Low Earth Orbiting (LEO) satellites and by selected optical Inter-Satellite Links (ISL). The LEO satellites are used to observe the signals transmitted by the MEO satellites from outside the atmosphere. The optical ISL connect all satellites in a multi-hop fashion. This enables a direct synchronization of the satellites at a level not achievable today and additionally does not require that the MEO satellites are equipped with clocks. The optical ISL furthermore provide ranges rather than pseudoranges for orbit determination as well as a broadband intra-system communication network. Terrestrial infrastructures become mostly obsolete with the Kepler approach. A single monitoring and control station remains necessary to maintain the alignment with earth-rotation, the synchronization to Universal Time Coordinate (UTC), and the capability of controlling the system.

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Section: Synchronization and Kepler Time Scalementioning

confidence: 99%

“…The blending of CSL and H-masers leads to an ensemble of clocks with widely varying properties. Greenhall's algorithm [11] is best suited for handling such situations. The resulting Implicit Ensemble Mean (IEM) essentially follows the most stable source at all values of τ , i.e.…”

Section: Synchronization and Kepler Time Scalementioning

confidence: 99%

Kepler � Satellite Navigation without Clocks and Ground Infrastructure

Günther¹

2018

Proceedings of the 31st International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GNSS+ 201

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“…The discrete solution of the SDE, with τ equal to 15 min, is used to simulate the clock types [6][7][8]. Following the assumptions of the Kalman Filter, it can be shown that the process noise matrix () Q  is a simple function of the q's and the filter time spacing  : 3 5 2 4 3 1 2 3 2 3 3 2 4 3 2 2 3 2 3 3 3 2 3 3 3 1 1 1 1 1 3 20 2 8 6 1 1 1 1 () 2 8 3 2 1 1 6 2…”

Section: Simulation Of Three Improved Monitor Station Clocks and Satementioning

confidence: 99%

“…Two composite clock algorithms [7,8] are applied to process the time offset measurements between the control stations and the satellite clocks and to estimate the three states of the satellite and control station clocks with respect to its implicitly defined time scales. Since N clocks involve maximal N-1 linearly independent measurements, each composite clock algorithm includes a method to prevent the formal covariance of the solution parameters from growing without bound.…”

Section: Composite Clock Algorithms -Brown and Greenhallmentioning

confidence: 99%

Simulating Future GPS Clock Scenarios with Two Composite Clock Algorithms

Suess

Matsakis

Greenhall

2010

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Using the GPS Toolkit, the GPS constellation is simulated using 31 satellites (SV) and a ground network of 17 monitor stations (MS). At every 15-minute measurement epoch, the monitor stations measure the time signals of all satellites above a parameterized elevation angle. Once a day, the satellite clock estimates are uploaded to the satellites. Two composite clock algorithms are applied to estimate the station and satellite clocks. The first composite clock (B) is based on the Brown algorithm [1], and is now used by GPS. The second one (G) is based on the Greenhall algorithm [2]. The composite clock of G and B performances are investigated using three ground-clock models. Model C simulates the current GPS configuration, in which all stations are equipped with cesium clocks, except for masers at USNO and Alternate Master Clock (AMC) sites. Model M is an improved situation in which every station is equipped with active hydrogen masers. Finally, Models F and O are future scenarios in which the USNO and AMC stations are equipped with fountain clocks instead of masers. Model F is a rubidium fountain, while Model O is a more precise but futuristic Optical Fountain. Each model is evaluated using three performance metrics. The timing-related user range error having all satellites available is the first performance index (PI1). The second performance index (PI2) relates to the stability of the broadcast GPS system time itself. The third performance index (PI3) evaluates the stability of the time scales computed by the two composite clocks. A distinction is made between the "Signal-in-Space" accuracy and that available through a GNSS receiver.

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“…[9]. For metrology purposes, several algorithms, [10], [11], [8], have been developed to characterize atomic standards and to weight clocks to profitably offset them before combining, in order to have an optimum clock ensemble, [13].…”

Section: Optimum Clock Predictionmentioning

confidence: 99%

Phase error reduction method for free-run QZSS clock

Dempster

Iwata

2007

2007 IEEE International Frequency Control Symposium Joint With the 21st European Frequency and Time Forum

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A method for limiting the phase error of the remote time keeping system, RTKS, clock for the Japanese QuasiZenith Satellite System (QZSS), is presented. To provide a proper positioning signal, QZSS satellites need stable on-board time references. Instead of using atomic references, the recently proposed RTKS employs a remote synchronization scheme that provides an opportune synchronization/correction signal able to keep a master time reference, located on the ground, and the QZSS satellite on-board time reference constantly in lock step. One of the critic issues regarding this architecture is the loss of synchronization due to satellite communication interruption. The proposed method consists of a learning algorithm that monitors the on-board clock behavior during its regular functioning. Consequently, when synchronization becomes unavailable the QZSS onboard clock phase/frequency drift is kept contained by using a consecutive estimation of the clock phase error. The proposed system is particularly suitable for the RTKS for QZSS and is characterized by a low hardware requirement profile, particularly suitable for the RTKS satellite payload.

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A Kalman filter clock ensemble algorithm that admits measurement noise

Cited by 36 publications

References 11 publications

Kepler � Satellite Navigation without Clocks and Ground Infrastructure

Kepler � Satellite Navigation without Clocks and Ground Infrastructure

Simulating Future GPS Clock Scenarios with Two Composite Clock Algorithms

Phase error reduction method for free-run QZSS clock

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