Abstract
Dual-frequency Global Positioning System (GPS) Real-time Kinematics (RTK) has been proven in the past few years to be a reliable and efficient technique to obtain high accuracy positioning. However, there are still challenges for GPS single-frequency RTK, such as low reliability and ambiguity resolution (AR) success rate, especially in kinematic environments. Recently, multi-Global Navigation Satellite System (multi-GNSS) has been applied to enhance the RTK performance in terms of availability and reliability of AR. In order to further enhance the multi-GNSS single-frequency RTK performance in terms of reliability, continuity and accuracy, a low-cost micro-electro-mechanical system (MEMS) inertial measurement unit (IMU) is adopted in this contribution. We tightly integrate the single-frequency GPS/BeiDou/GLONASS and MEMS-IMU through the extended Kalman filter (EKF), which directly fuses the ambiguity-fixed double-differenced (DD) carrier phase observables and IMU data. A field vehicular test was carried out to evaluate the impacts of the multi-GNSS and IMU on the AR and positioning performance in different system configurations. Test results indicate that the empirical success rate of single-epoch AR for the tightly-coupled single-frequency multi-GNSS RTK/INS integration is over 99% even at an elevation cut-off angle of 40°, and the corresponding position time series is much more stable in comparison with the GPS solution. Besides, GNSS outage simulations show that continuous positioning with certain accuracy is possible due to the INS bridging capability when GNSS positioning is not available.
Highlights
The dual-frequency Global Positioning System (GPS) real-time kinematic (RTK) technique is known to be used in many applications that require high accuracy positioning such as land surveying, precise agriculture and vehicular navigation
Sensors 2017, 17, 2462 from multiple GNSS constellations are obvious for RTK positioning capabilities, as it was shown for GPS/BeiDou navigation satellite system (BDS) [1,2,5,6,7], GPS/GLOANSS [3,8], and the four systems of GPS, Galileo, BDS and QZSS [9]
The results show that the probability of successful ambiguity resolution (AR) and positioning performance of the combined GPS/BDS/Inertial Navigation System (INS) system can be improved significantly compared with the single GNSS system
Summary
The dual-frequency GPS real-time kinematic (RTK) technique is known to be used in many applications that require high accuracy positioning such as land surveying, precise agriculture and vehicular navigation. Sensors 2017, 17, 2462 from multiple GNSS constellations are obvious for RTK positioning capabilities, as it was shown for GPS/BDS [1,2,5,6,7], GPS/GLOANSS [3,8], and the four systems of GPS, Galileo, BDS and QZSS [9] In this contribution, we will focus on the combination of three main satellite navigation systems: the U.S Global Positioning System (GPS), the Chinese BeiDou navigation satellite system (BDS) and Russia’s GLObal NAvigation Satellite System (GLONASS), and investigate the AR and positioning performance by using only single-frequency observations from multi-GNSS. One method to deal with the different wavelengths of two single-differenced ambiguities in the DD observation equation is that phase observations are expressed in the unit of cycles instead of length This strategy can recover the integer nature of the GLONASS DD ambiguities, receiver clock biases cannot be eliminated due to the different wavelengths [8,14].
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