Attitude Determination Methods Used in the PolaRx2@ Multi-antenna GPS Receiver

Leen Vander Kuylen, Frank Boon and Andrew Simsky

Abstract:	Septentrio has designed a lightweight single-board position/attitude determination system based on its unique multi-antenna dual-frequency GNSS receiver, PolaRx2@, which receives and provides measurements from 3 antennas. One of the antennas serves as a main antenna and its output is used to compute position. Two additional antennas provide measurements for attitude determination. The tracking channels are configurable, and consequently, the same receiver can be used with one, 2, or 3 antennas. Currently, the main antenna can be dual frequency, while the auxiliary antennas are single frequency only. Attitude determination in the PolaRx2@ is therefore based only on L1 code/phase measurements. This paper focuses on two methods that can be used for attitude determination based on GPS measurements only. The first method uses a Kalman filter in which double differenced phase and pseudo range measurements are used to determine the positions of the auxiliary antennas relative to the main antenna in the local-level navigation frame. The attitude angles are computed based on these relative positions. This method is known as Direct Computation Method (DCM) and is currently implemented in the PolaRx2@. The second method uses a Kalman filter in which double differenced phase and pseudo range measurements are used to directly determine attitude angles expressed as quaternion. This method requires a priori knowledge of the antenna positions in the vehicle frame, which are determined using a calibration procedure. This method is currently under development and is referred to as the quaternion-based Kalman filter. In this paper, both attitude determination methods are described, and their performance is compared using simulated error-free measurements. Static tests are used to obtain the Time-To-First-Fixed Attitude (TTFFA) statistics for the DCM. The flight tests have demonstrated high robustness of the PolaRx2@ in real-life high dynamic environment. The test with a car and a trailer shows how the DCM algorithm can be used to obtain information on the deformations of flexible vehicles.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	125 - 135
Cite this article:	Kuylen, Leen Vander, Boon, Frank, Simsky, Andrew, "Attitude Determination Methods Used in the PolaRx2@ Multi-antenna GPS Receiver," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 125-135.
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