The Effect of Aircraft Antenna Group Delay Variations on Dual Solution Ionospheric Gradient Monitoring
Anurag Raghuvanshi and Frank van Graas, Ohio University
Location: Grand Ballroom G
Date/Time: Wednesday, Jan. 31, 3:05 p.m.
The Minimum Operational Performance Standards (MOPS) for Global Positioning System Local Area Augmentation System (LAAS) Airborne Equipment was updated in 2017 . To protect against aircraft position errors due to rare ionospheric gradients, the MOPS requires a Dual Solution Ionospheric Gradient Monitoring Algorithm (DSIGMA) Range monitor, a Code Carrier Divergence (CCD) monitor, and the addition of dual-solution bias parameters to the horizontal and vertical protection levels, for Ground Based Augmentation System (GBAS) Approach Service Type D (GAST D). Both the DSIGMA Range monitor and the dual-solution bias parameters are based on differences between 100-s and 30-s carrier smoothed code measurements. A satellite will not be used for the position solution if the difference between the 100-s and 30-s smoothed corrected pseudoranges exceeds the threshold of 0.976 meters. The Airborne CDD monitor filter utilizes the rate the of change of code minus carrier(CMC) measurements for monitoring. A satellite exceeding a threshold of 0.0415 m/s will be flagged by the CCD monitor. The CMC measurement contains the combination of ionospheric errors, noise, multipath and errors due to antenna group delay variations. During the validation phase of the DSIGMA Range monitor and the CCD monitor, the data used to determine the sigma over bound and the threshold used a dual frequency antenna. Since the flight tests were performed during nominal ionospheric conditions, the difference between the 100-s and 30-s smoothed pseudorange and the CMC measurements is primarily due to noise and multipath error. Recent research has shown that it is difficult to separate multipath and antenna group delay variations for an aircraft . Thus, the DSIGMA and the airborne CCD threshold should account for the antenna group delay variations as a function of the signal arrival angle. Previous research also showed that the antenna group delay variations for a dual frequency antenna are small compared to a single frequency antenna, and thus the threshold and the sigma over bound values might increase when a single frequency antenna is used for DSIGMA and CCD. In this paper, the impact of airborne antenna group delay variations as a function of arrival angle on the DSIGMA Range monitor, the Airborne CCD monitor and the dual-solution vertical bias parameter are evaluated using computer simulations and flight test data.