Global positioning system accuracy under varying ionospheric conditions for surface Automatic Dependent Surveillance-Broadcast applications

Abstract

New flight deck-based applications of Automatic Dependent Surveillance-Broadcast (ADS-B) offer the potential to meet improved critical safety and economic targets for airport surface operations. Specifically, standards for ADS-B applications have been developed [1] to reduce and prevent runway collisions between aircraft on the airport surface using flight deck equipment. Such applications require surveillance information with position accuracy ranging between 10 to 30 meters 95 percent of the time. Global Positioning System (GPS) information without Wide Area Augmentation System (WAAS) provides sufficient position accuracy under most conditions; however, significant solar flare activities can change the ionization characteristics of the upper layers of the atmosphere which alters GPS signal propagation resulting in decreased position accuracy, potentially making the information unusable for ADS-B surface applications. This paper describes the results of an analysis of the impact of ionospheric disturbances on the position accuracy of a single frequency GPS receiver under a range of assumed operational conditions. The results are expected to be useful for an assessment of single frequency GPS technology for ADS-B surface applications and to help identify mitigations. The analysis assumes a nominal GPS constellation as defined in the GPS Standard Positioning Service (SPS) Performance Standards (PS) and a set of GPS receiver errors models. These include tropospheric, multi-path, and receiver noise error models, which are either adopted by the GPS WAAS aviation receiver performance standard or shown in open literature as representative of actual GPS receiver errors. Interference errors are assumed to be zero and interference risks are assumed to have been mitigated by airport operation authorities. The ionospheric errors are modeled based on the errors in actual GPS Navigation Message broadcast values under minimum, maximum, and average solar cycle activity conditions. Results show the impact of these activities on various position accuracy parameters and horizontal position, and include worst case conditions. Given the assumed models, the accuracy requirements for ADS-B surface applications were always exceeded for modern GPS receivers operating in all-in-view mode, suggesting feasibility of non-WAAS, single frequency GPS for ADS-B surface applications. The paper concludes with an outline of research needs and proposed next steps.