Carrier Phase Relative RAIM Algorithms and Protection Level Derivation

Abstract

The concept of Relative Receiver Autonomous Integrity Monitoring (RRAIM) using time differential carrier phase measurements is investigated in this paper. The precision of carrier phase measurements allows for mitigation of integrity hazards by implementing RRAIM monitors with tight thresholds without significantly affecting continuity. In order to avoid the need for cycle ambiguity resolution, time differences in carrier phase measurements are used as the basis for detection. In this work, we examine RRAIM within the context of the GNSS Evolutionary Architecture Study (GEAS), which explores potential architectures for aircraft navigation utilizing the satellite signals available in the mid-term future with GPS III. The objectives of the GEAS are focused on system implementations providing worldwide coverage to satisfy LPV-200 operations, and potentially beyond. In this work, we study two different GEAS implementations of RRAIM. General formulas are derived for positioning, fault detection, and protection level generation to meet a given set of integrity and continuity requirements.2. GEAS. 3. GPS III. I N T R O D U C T I O N. Carrier phase differential RAIM implementations have been investigated in prior work to help detect specific navigation threats, including ephemeris broadcast anomalies [1] and ionospheric storm fronts [2]. The great precision of carrier phase measurements allowed for tight detection thresholds without significantly affecting continuity. It also provided the sensitivity to detect a much larger range of failure magnitudes than was possible using traditional code-based RAIM. The need for cycle ambiguity estimation was eliminated by differencing measurements in time, creating spatial baselines associated with the user's translation over the time-difference interval. We refer globally to these time-differenced carrier phase RAIM implementations as Relative RAIM (RRAIM) functions. The results in [1,2] showed that many troublesome ionospheric and ephemeris threats could be detected with carrier phase RRAIM implementations, even for applications where positioning was based on code phase [2]. The current process of modernization of Global Navigation Satellite Systems (GNSS) will improve navigation user capabilities in many ways. There will be

GNSS Carrier Phase Anomaly Detection and Validation for Precise Land Vehicle Positioning

“…The residuals in (14) are applied to the error propagation law [9], [10], [17] to estimate the potential position errors in the position domain (δx). The results are multiplied by a scale factor (k) that is suitable for the user system to calculate the protection level (PL) [20].…”

“…The threshold for determining an anomaly in (13) was 1.5 cycles (1-cycle uncertainty plus three-sigma variation). The threshold for position error in (17) was 1 m, considering the width of the road lane (3 m) and the uncertainty of the map (0.5 m) [14], [15].…”

“…Gratton et al [17] used carrier phase variations in the position and measurement domains to detect code-based pseudorange anomalies with relative RAIM to meet the localizer performance with vertical guidance (LPV)-200 in wide area augmentation system. This paper focused on detecting pseudorange anomalies in a dynamic environment.…”

A-RAIM and R-RAIM Performance using the Classic and MHSS Methods

“…The comparison of the range domain and position domain R-RAIM with the Classic RAIM method was conducted in Gratton et al (2010). With very similar precision from these two positioning methods, the difference in the integrity results is caused by different error propagation methods.…”

Relative RAIM Based on IMM

“…Positioning and protection level calculation primarily bases ''current'' measurement and uses the least square method to get the result. Fault detection is a ''hard decision'', which means for a certain measurement, there is only fault or fault-free condition could be determined [5]. This kind of fault detection simplifies the fault state, and cannot specify the fault condition for users.…”