Carrier Phase Tracking of Weak Signals Using Different Receiver Architectures M.G. Petovello, C. O’Driscoll and G. Lachapelle Position, Location and Navigation (PLAN) Group Department of Geomatics Engineering Schulich School of Engineering University of Calgary lock indicator values and carrier phase-based positioning quality were compared. Unexpectedly, the vector-based receiver did not perform very well and more work is needed to understand why this is the case. Of the remaining receivers, the ultra-tight receiver performed best, the estimator-based receiver performed second best and the standard receiver performed the worst. The ultra-tight receiver provided about 7 dB and 3 dB of sensitivity improvement over the standard and estimator-based receivers. INTRODUCTION High-sensitivity GNSS (HSGNSS) receivers are capable of providing satellite measurements for signals attenuated by approximately 30 dB (Fastrax 2007; SiRF 2007; ublox 2007). This capability is impressive and extends positioning applications dramatically. However, the focus of HSGNSS is generally on pseudorange measurements, thus limiting obtainable positioning accuracy to the order of tens of meters. In contrast, real-time kinematic (RTK) positioning capability (i.e., centimeter-level) in degraded environments has not received as much attention, even though many systems require – or could benefit from – such high positioning accuracy. Some potential benefits of RTK positioning include precise relative positioning of two (or more) vehicles (e.g., for autonomous vehicle operation), precise relative motion over time (e.g., for system/sensor calibration) and enhanced personal navigation/personnel tracking accuracy. Even if RTK positioning is not possible, the use of a float ambiguity solution (instead of fixed ambiguity solution with RTK) would provide tremendous improvements over pseudorange-based algorithms, primarily in terms of multipath mitigation. Unfortunately, carrier phase tracking requirements are much more stringent than those for pseudorange or carrier frequency, and loss of carrier lock is likely when the received GNSS signals are weaker than normal. As such, RTK positioning is generally
BIOGRAPHIES Dr. Mark Petovello is an Assistant Professor in the Position, Location and Navigation (PLAN) group in the Department of Geomatics Engineering at the University of Calgary. Since 1998, he has been involved in various navigation research areas including software receiver development, satellite-based navigation, inertial navigation, reliability analysis and dead-reckoning sensor integration. Dr. Cillian O’Driscoll received his Ph.D. in 2007 from the Department of Electrical and Electronic Engineering, University College Cork. His research interests are in the area of software receivers for GNSS, particularly in relation to weak signal acquisition and ultra-tight GPS/INS integration. He is currently with the Position, Location and Navigation (PLAN) group at the Department of Geomatics Engineering in the University of Calgary. Dr. Gérard Lachapelle is a Professor of Geomatics Engineering at the University of Calgary where he is responsible for teaching and research related to location, positioning, and navigation. He has been involved with GPS developments and applications since 1980. He has held a Canada Research Chair/iCORE Chair in wireless location since 2001 and heads the PLAN Group at the University of Calgary. ABSTRACT This paper investigates four receiver architectures and their ability to track the carrier phase signal under attenuated environments. The receiver architectures considered include a standard receiver, an estimator-based receiver, a vector-based receiver and an ultra-tight GPS/IMU receiver. The receiver architectures were implemented in software and tested using pedestrianbased data collected in open-sky environments but attenuated using a variable signal attenuator. To assess the performance of the different receivers, their phase...
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