Showing papers by "Patrick Henkel published in 2009"

Multifrequency, Multisatellite Vector Phase-Locked Loop for Robust Carrier Tracking

Abstract: A new vector phase-locked loop (PLL) for joint tracking of carrier phase from all satellites on multiple frequencies is presented. It increases the robustness to ionospheric scintillations, carrier phase multipath and interference from jammer. The tracking error is split into a position error, a clock offset, ionospheric, and tropospheric errors which are filtered individually. The filter coefficients are optimized with orthogonal projections of the tracking error that eliminate the nuisance parameters. The tracking performance is determined recursively, and a significant reduction of the tracking error is observed during strong ionospheric scintillations with deep amplitude fades.

Modified LAMBDA for Absolute Carrier Phase Positioning in the Presence of Biases

Abstract: The least-squares integer ambiguity decorrelation adjustment (LAMBDA) method is adapted for absolute positioning with satellite-satellite single difference measurements. The integer decorrelation transformation of LAMBDA takes only the covariance matrix of float ambiguities into account which results in a substantial amplification of biases due to orbital errors, satellite clock offsets and multipath. Therefore, a partial integer decorrelation is suggested to achieve the optimum trade-off between variance reduction and bias amplification. The reliability of ambiguity resolution is further improved by using two geometrypreserving, ionosphere-free multi-frequency linear combinations: a code-carrier combination of maximum discrimination and a code-only combination of minimum noise. The optimized widelane and narrowlane linear combinations are presented for two, three and four Galileo frequencies. The achievable probabilities of wrong fixing have been computed for an exponential bias profile and are several orders of magnitude lower than in the case of complete integer decorrelation. Moreover, a partial fixing scheme is proposed for severe carrier phase multipath. The method bounds the biases by an exponential profile and determines the optimum fixing order by a sequential search with an azimuthal separation constraint between the satellites of two consecutive ambiguity fixings.

Method for a global satellite navigation system

Abstract: A method for estimating satellite-satellite single difference biases is described. The method uses an ionosphere-free mixed code-carrier combination of maximum ambiguities discrimination defined at the ration between wavelength and noise standard deviation. The accuracy of the biases estimation is further improved by an additional ionosphere-free mixed code-carrier combination of time-difference measurement that is uncorrelated with the first combination. Finally, an alternative method is based on a combination of carrier signals in a common frequency band which allows estimating the biases individually.

Method for vector phase tracking a plurality of global positioning satellite carrier signals

Abstract: A method for vector phase tracking a plurality of global positioning satellite carrier signals is disclosed, in which for a tracked satellite a discriminator (25) is generating phase tracking error signals at different frequencies associated with the various carrier signals of the tracked satellite and in which a multi-frequency estimation of the disturbances is performed based the phase tracking error signal supplied by the discriminator unit (28). In the method the ionospheric error is taken into account for determining output phase error signals.

Estimation of phase and code biases on multiple frequencies with a Kalman filter

Abstract: Method for Determining Biases of Satellite Signals a new method for bias estimation on multiple frequencies with a Kalman filter is proposed. It consists of four steps: First, a least-squares estimation of ranges, ionospheric delays, ambiguities, receiver phase biases and satellite phase biases is performed. The code biases are absorbed in the ranges and ionospheric delays, and a subset of ambiguities is mapped to the phase biases to remove linear dependencies between the unknown parameters. In a second step, the accuracy of the bias estimates is efficiently improved by a Kalman filter. The real-valued a posteriori ambiguity estimates are decorrelated by an integer ambiguity transformation to reduce the time of ambiguity resolution. Once the float ambiguities have sufficiently converged, they are fixed sequentially in a third step. Finally, a second Kalman filter is used to separate the receiver and satellite code biases and the tropospheric delays from the ranges.

Partial ambiguity fixing for multi-frequency ionospheric delay estimation

Abstract: A method is suggested for robust estimation of a subset of carrier phase integer ambiguities for precise ionospheric delay estimation. The advantages of this method are the precise estimation of receiver and satellite biases, an increase in the number of reliably fixable ambiguities, and an improved accuracy for the ionospheric delay estimation.