On the performance of dual-frequency multiconstellation SBAS: real data results with operational state-of-the-art SBAS prototype

摘要

The analysis of the current trends observed in thenavigation community suggests that, for the comingyears, the GNSS integrity solutions may rely onSatellite Based Augmentation Systems (SBAS), GroundBased Augmentation Systems (GBAS), ReceiverAutonomous Integrity Monitoring (RAIM) or newtechniques including integration with other sensors. Inthe aviation community, SBAS already enjoyedrecognition at regulatory level and is considered as areference navigation aid. Recently, ICAO has developedthe Performance Based Navigation concept – PBN –and established an international schedule for APV at allinstrument runway ends either as the primary approachor as a back-up for precision approaches. Most countriesare producing their PBN implementation plans to meet ICAO recommendation and the use of the SBAStechnology seems to be the most adequate solution formany countries.Development and deployment of a SBAS system in anyregion of the world could be a serious technologicalchallenge. Besides, each region may have differentcharacteristics and requirements. The ionosphere behavioris, for instance, a key issue for implementation of SBASin some regions. At the current moment, WAAS in US,MSAS in Japan, and EGNOS in Europe have beendeclared operational and available for civil aviation.These systems augment the navigation service of theprimary GPS constellation but, at the same time, thedevelopment of new GNSS constellations, likeGLONASS, Galileo and COMPASS is on its way. This isan important driver for investigating the definition of newgeneration SBAS systems. The current discussions onSBAS evolution rely on enhancements towards multiconstellationand dual-frequency capabilities.As a consequence of the technological challenge, it isusual that SBAS development plans envisage thedeployment of SBAS testbeds (e.g.; WAAS NSTB,EGNOS ESTB) and pre-operational, non-certified,services at the initial stages of the operational systemdevelopment. Testbeds offer numerous advantages, inparticular provide the system developers with powerfulplatforms to early validate new concept architectures, firstdesign solutions and performance assumptions, thusgreatly mitigating design risks and helping to optimize thedesign to satisfy the requirements of the region.magicSBAS is a state-of-the-art operational SBAS testbeddeveloped by GMV to offer non-safety critical SBASaugmentation to any interested region. The algorithmsimplemented in magicSBAS have been fully developedby GMV and are the result of more than 15 years ofexperience in the development of EGNOS and otherSBAS programs. The magicSBAS algorithms, originallydesigned to mimic EGNOS performances over the ECACservice area, have been further optimized and tuned toprovide the best performances in other regions of theworld (South America, South Africa, Russian Federation,etc).Recently, magicSBAS has been upgraded with newcapabilities, as the generation of SBAS message MT28,the capability to augment several primary constellations(GPS+GLONASS) and the provision of a service to dualfrequencyusers. The paper shows first that magicSBAS isrepresentative of EGNOS performances. This is achievedby comparing EGNOS and magicSBAS performancesmaps (availability and continuity) for the same period oftime. Once the representativeness is proven, differentanalyses are run to show SBAS service improvementsusing the new magicSBAS capabilities:1. Generation of SBAS message MT28 vs. theprovision of service using MT27 message.2. Incorporation of the GLONASS constellationfor the computation of the ionospheremonitoring, which is one of the drivers forSBAS performances.3. Provision of service to dual-frequency users.Dual-frequency users are capable of getting ridof the ionosphere delay and consequently theydo not need from ionosphere corrections andintegrity parameters (GIVD and GIVE).Although a standard for these users is not yetavailable, the paper will detail the assumptionsmade for simulating these service to users.4. Service availability using a second augmentedconstellation at user level (GPS+GLONASS).One of the key advantages of magicSBAS is thecapability to process raw data in standard formats likeNTRIP, RINEX, EDAS, SPEED or EGNOS formats.There are currently hundreds of Continuous OperatingReference Stations (CORS) worldwide providing data inthese formats that can be used together withmagicSBAS to quickly evaluate the SBASperformances. This capability has been used during thestudy to show EGNOS service improvements in areaslike Africa and Eastern Europe thanks to the newmagicSBAS capabilities. It is important to remark thatall performances shown in this study have been obtainedusing real data.Thanks to all these analyses, the study provides a clearpicture of the performances that will be reached byfuture SBAS systems, once the multi-constellation andmulti-frequency capabilities are developed. Because ofthe extensive use of real data, and because of havingbased the algorithms proposed on EGNOS, the authorsare confident that the results shown in this paper arerepresentative of the ones expected in the futureoperational SBAS evolutions.