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Sensors 2018, 18(9), 3052; https://doi.org/10.3390/s18093052

Benefits of Multi-Constellation/Multi-Frequency GNSS in a Tightly Coupled GNSS/IMU/Odometry Integration Algorithm

Department of Physical and Satellite Geodesy, Technische Universität Darmstadt, Franziska-Braun-Straße 7, 64287 Darmstadt, Germany
Parts of this paper have been published as Performance Evaluation of a Tightly Coupled GNSS/IMU Integration Algorithm with Multi-Constellation/Multi-Frequency GNSS, in: Proceedings of the European Navigation Conference (ENC), Gothenburg, Sweden, 14–17 May 2018.
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Received: 14 June 2018 / Revised: 6 September 2018 / Accepted: 7 September 2018 / Published: 12 September 2018
(This article belongs to the Special Issue GNSS and Fusion with Other Sensors)
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Abstract

Localization algorithms based on global navigation satellite systems (GNSS) play an important role in automotive positioning. Due to the advent of autonomously driving cars, their importance is expected to grow even further in the next years. Simultaneously, the performance requirements for these localization algorithms will increase because they are no longer used exclusively for navigation, but also for control of the vehicle’s movement. These requirements cannot be met with GNSS alone. Instead, algorithms for sensor data fusion are needed. While the combination of GNSS receivers with inertial measurements units (IMUs) is a common approach, it is traditionally executed in a single-frequency/single-constellation architecture, usually with the Global Positioning System’s (GPS) L1 C/A signal. With the advent of new GNSS constellations and civil signals on multiple frequencies, GNSS/IMU integration algorithm performance can be improved by utilizing these new data sources. To achieve this, we upgraded a tightly coupled GNSS/IMU integration algorithm to process measurements from GPS (L1 C/A, L2C, L5) and Galileo (E1, E5a, E5b). After investigating various combination strategies, we chose to preferably work with ionosphere-free combinations of L5-L1 C/A and E5a-E1 pseudo-ranges. L2C-L1 C/A and E5b-E1 combinations as well as single-frequency pseudo-ranges on L1 and E1 serve as backup when no L5/E5a measurements are available. To be able to process these six types of pseudo-range observations simultaneously, the differential code biases (DCBs) of the employed receiver need to be calibrated. Time-differenced carrier-phase measurements on L1 and E1 provide the algorithm with pseudo-range-rate observations. To provide additional aiding, information about the vehicle’s velocity obtained by an odometry model fed with angular velocities from all four wheels as well as the steering wheel angle is incorporated into the algorithm. To evaluate the performance improvement provided by these new data sources, two sets of measurement data are collected and the resulting navigation solutions are compared to a higher-grade reference system, consisting of a geodetic GNSS receiver for real-time kinematic positioning (RTK) and a navigation grade IMU. The multi-frequency/multi-constellation algorithm with odometry aiding achieves a 3-D root mean square (RMS) position error of 3.6 m / 2.1 m in these data sets, compared to 5.2 m / 2.9 m for the single-frequency GPS algorithm without odometry aiding. Odometry is most beneficial to positioning accuracy when GNSS measurement quality is poor. This is demonstrated in data set 1, resulting in a reduction of the horizontal position error’s 95% quantile from 6.2 m without odometry aiding to 4.2 m with odometry aiding. View Full-Text
Keywords: global navigation satellite systems; GNSS; inertial measurement unit; IMU; odometry; tightly coupled; multi-frequency; multi-constellation global navigation satellite systems; GNSS; inertial measurement unit; IMU; odometry; tightly coupled; multi-frequency; multi-constellation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Reuper, B.; Becker, M.; Leinen, S. Benefits of Multi-Constellation/Multi-Frequency GNSS in a Tightly Coupled GNSS/IMU/Odometry Integration Algorithm. Sensors 2018, 18, 3052.

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