Showing papers by "Patrick Henkel published in 2014"

Tightly coupled position and attitude determination with two low-cost GNSS receivers

Abstract: A precise position and attitude information is essential for autonomous driving of any vehicle. Low-cost GNSS receivers and antennas can provide a precise attitude and drift-free position information. However, severe code multipath, frequent half cycle slips and losses of lock might temporarily reduce the accuracy. Inertial sensors are robust to GNSS signal interruption and very precise over short time frames, which enables a reliable cycle slip correction. However, low-cost inertial sensors suffer from a substantial drift. In this paper, we propose a tightly coupled position and attitude determination method for two low-cost GNSS receivers, a gyroscope and an accelerometer. It improves classical tightly coupled solutions by including a synchronization correction, by the estimation of the code multipath for each satellite and receiver, and by the additional determination of satellite-satellite single difference ambiguities. The proposed method was verified in a test drive. We obtained a heading with an accuracy of 0.25°/baseline length [m] and an absolute position with an accuracy of 1 m.

Sequential Best Integer-Equivariant Estimation for GNSS

Abstract: The key to high precision parameter estimation in global navigation satellite system (GNSS) applications is to properly deal with the integer valued carrier-phase ambiguities. The class of integer estimators fixes all ambiguities to integer values. This can also decrease the precision of the estimates of the non-ambiguity parameters, if the fixing is incorrect. The best integer-equivariant (BIE) estimator is optimal in the sense of minimizing the mean-squared error (MSE) of both the ambiguities and the real valued parameters, regardless of the precision of the float solution. However, the BIE estimator comprises a search in the integer space of ambiguities, whose complexity grows exponentially with the number of ambiguities. This search is not feasible for large-scale network solutions. To overcome this problem, a sequential BIE (SBIE) algorithm is proposed, which shows close to optimal performance with only linearly increasing complexity. Numerical simulations are used to verify the performance of the SBIE algorithm.

Calibration of magnetic field sensors with two mass-market GNSS receivers

Abstract: Global Navigation Satellite System (GNSS) signals, inertial measurements (angular rates, accelerations) and magnetometer measurements complement each other for position determination: GNSS provides a precise and drift-free position solution but is susceptible to signal outages. Inertial measurements are continuously available and of higher rate but suffer from integration drifts. Magnetic field measurements provide an instantaneous orientation in static conditions but are affected by both static and dynamic disturbances. In this paper, we provide a calibration method for magnetometers, which determines the biases and misalignment errors of the magnetometer as well as the magnetic flux including static disturbances. The method uses the iterative Gauss-Newton method and precise attitude information (heading, pitch) obtained from two low-cost GPS receivers. The attitude determination requires a tree search of the carrier phase integer ambiguities using a priori information on the distance between both GPS receivers. We also verified the proposed method with kinematic measurements from the CMPS10 sensor. We observe an accuracy of a few degrees for the unfiltered heading and a heading offset of less than 10° in 99.5% of all measurement epochs.

Cost-effective Cooperative RTK Positioning of Rowing Boats

Abstract: Low-cost single-frequency GNSS receivers with patch antennas can track carrier phase measurements with millimeter- to centimeter level and can therefore provide position information comparable to geodetic grade receivers. However, in order to use carrier phase measurements for positioning, one has to first resolve the integer ambiguities, which is challenging in the case of low-cost receivers because code multipath errors can be tens of meters. A new Kalman filter is proposed in this paper for determining jointly the cooperative RTK float solution of multiple rover receivers with respect to a fix base station. The measurement model as well as the state space model used in the Kalman filter are carefully designed for simultaneous tracking of multiple rowing boats. The measurement model exploits the correlation between measurements and the state parameters are chosen without redundancy (i.e. common states are only estimated once). The characteristic periodic movement of a racing rowing boat is also exploited in this paper to correct for carrier phase measurement outliers, i.e. cycle slip. Extensive tests were conducted with low-cost single-frequency GPS receivers. Static and kinematic test results show that with the new cooperative RTK Kalman filter, float ambiguities converge much faster and integer ambiguities can be correctly fixed in less than a minute. With the movement model, cycle slips are reliably corrected during the precise tracking of the boats after ambiguity resolution.

Reliable Integer Ambiguity Resolution

Abstract: In this paper, a maximum a posteriori probability estimation of baselines and ambiguities is proposed for RTK and attitude determination. The estimator uses statistical a priori information about the baseline length, pitch and heading, and thereby improves the accuracy of the float solution. It is more robust than traditional attitude determination techniques with deterministic baseline constraints. The inertia of the receivers are considered in a movement model, which is integrated into an extended Kalman filter. Moreover, a new set of multi-frequency code carrier linear combinations is derived, which enables an arbitrary scaling of the geometry, an arbitrary scaling of the ionospheric delay, and any preferred wavelength.

Method for determining a baseline between two receivers

Abstract: In the method for determining a baseline (8) between two receivers (6, 7) of a satellite navigation system (1), the receivers (6, 7) perform measurements on signals emitted by satellites (2) of the satellite navigation system (1). The baseline (8) is then determined by an evaluation unit (11) connected to the receivers (6, 7). The evaluation unit (11) first estimates the individual clock offsets of the receivers (6, 7). A clock offset difference is calculated from the individual clock offsets. The clock offset difference is used for calculating a satellite motion correction for the motion of the satellites (2) during the clock offset difference. For determining the position and orientation of the baseline (8), the evaluation unit (11) uses double-differences of the measurements, wherein the satellite motion correction is used for correcting the double-differences of the measurement resulting in corrected double differences of the measurements. The baseline (8) is finally determined based on the corrected double differences of the measurements. Using this method allows to determine the baseline (8) between two receivers (6, 7) with high precision even if low cost receivers (6, 7) are used that are provided with imprecise receiver clocks.