Outlier Accommodation for GNSS Precise Point Positioning using Risk-Averse State Estimation

Reliable and precise absolute positioning is necessary in the realm of Connected Automated Vehicles (CAV). Global Navigation Satellite Systems (GNSS) provides the foundation for absolute positioning. Recently enhanced Precise Point Positioning (PPP) technology now offers corrections for GNSS on a global scale, with the potential to achieve accuracy suitable for real-time CAV applications. However, in obstructed sky conditions, GNSS signals are often affected by outliers; therefore, addressing outliers is crucial. In GNSS applications, there are many more measurements available than are required to meet the specification. Therefore, measurement selection is important to avoid outlier measurements is of interest. The recently developed Risk-Averse Performance-Specified (RAPS) state estimation optimally selects measurements to minimize outlier risk while meeting a positive semi-definite constraint on performance; at present, the existing solution methods are not suitable for real-time computation and have not been demonstrated using challenging real-world data or in Real-time PPP (RT-PPP) applications. This article makes contributions in a few directions. First, it uses a diagonal performance specification, which reduces computational costs relative to the positive semi-definite constraint. Second, this article considers GNSS RT-PPP applications. Third, the experiments use real-world GNSS data collected in challenging environments. The RT-PPP experimental results show that among the compared methods: all achieve comparable performance in open-sky conditions, and all exceed the Society of Automotive Engineers (SAE) specification; however, in challenging environments, the diagonal RAPS approach shows improvement of 6-19% over traditional methods. Throughout, RAPS achieves the lowest estimation risk.

I. Introduction

Reliable and accurate real-time positioning is crucial for CAV within the framework of intelligent transportation systems [1], [2]. The widespread adoption of CAV holds promise to alleviate congestion, decrease both the frequency and severity of accidents, reduce emissions, enhance system resilience by addressing bottlenecks, and offer numerous other benefits [3]. Precise and dependable localization and positioning are fundamental requirements for CAV applications [1], [4]. Accurate absolute positioning is facilitated by GNSS. For CAV applications, the SAE J2945 specification defines the requirement for horizontal and vertical position errors to be less than 1.5 m and 3.0 m, respectively, with a probability of 68% [5]. However, standalone GNSS receivers, when not supplemented with external corrections, usually achieve positioning accuracy around 10 meters [6]. This limitation is caused by common-mode errors (CME) in GNSS measurements [7], [8].