Abstract
In the field of Global Navigation Satellite System (GNSS) attitude determination, the constraints usually play a critical role in resolving the unknown ambiguities quickly and correctly. Many constraints such as the baseline length, the geometry of multi-baselines and the horizontal attitude angles have been used extensively to improve the performance of ambiguity resolution. In the GNSS/Inertial Navigation System (INS) integrated attitude determination systems using low grade Inertial Measurement Unit (IMU), the initial heading parameters of the vehicle are usually worked out by the GNSS subsystem instead of by the IMU sensors independently. However, when a rotation occurs, the angle at which vehicle has turned within a short time span can be measured accurately by the IMU. This measurement will be treated as a constraint, namely the rate-gyro-integral constraint, which can aid the GNSS ambiguity resolution. We will use this constraint to filter the candidates in the ambiguity search stage. The ambiguity search space shrinks significantly with this constraint imposed during the rotation, thus it is helpful to speeding up the initialization of attitude parameters under dynamic circumstances. This paper will only study the applications of this new constraint to land vehicles. The impacts of measurement errors on the effect of this new constraint will be assessed for different grades of IMU and current average precision level of GNSS receivers. Simulations and experiments in urban areas have demonstrated the validity and efficacy of the new constraint in aiding GNSS attitude determinations.
Highlights
Ambiguity resolution is a core technique in Global Navigation Satellite System (GNSS) relative positioning and attitude determination.There is no essential difference between the two applications in terms of this technique
Four satellites with minimum Geometry Dilution of Precision (GDOP) value are selected from all visible satellites, and the satellite with the largest elevation is chosen as the “reference” satellite, the other three satellites are recognized as the “master satellites”
Contributors to the inaccuracy of testing objective involve the Inertial Measurement Unit (IMU) measurement errors, especially those associated with angle rate, GNSS carrier phase measurement errors and the actual rotational axis offsets
Summary
Ambiguity resolution is a core technique in GNSS relative positioning and attitude determination. This idea was proposed by [10] originally It utilizes both baseline length constraint and differential vector estimations for ambiguity resolution. Following this idea, [11] conducted a comprehensive research on the GNSS attitude determination technique. The platform motions were utilized to enhance the anti-cycle-slip capability of ambiguity resolution, and the methods basing on this fact were demonstrated to be especially efficient in land vehicle attitude determination [15,16]. The relative rotation angle measurements provided by IMU are used to aid ambiguity resolution As shown below, this constraint does not require high accuracies of IMU sensors, especially for the accuracy of gyroscope.
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