Examination of GPS/EGNOS integrity in north‐eastern Poland
2015; Institution of Engineering and Technology; Volume: 10; Issue: 1 Linguagem: Inglês
10.1049/iet-rsn.2015.0053
ISSN1751-8792
AutoresGrzegorz Grunwald, Mieczysław Bakuła, Adam Ciećko, Rafał Kaźmierczak,
Tópico(s)Geophysics and Gravity Measurements
ResumoIET Radar, Sonar & NavigationVolume 10, Issue 1 p. 114-121 Research ArticleFree Access Examination of GPS/EGNOS integrity in north-eastern Poland Grzegorz Grunwald, Corresponding Author Grzegorz Grunwald g.grunwald@kgsin.pl Department of Satellite Geodesy and Navigation, University of Warmia and Mazury in Olsztyn, ul. Heweliusza 5, 10-724 Olsztyn, PolandSearch for more papers by this authorMieczysław Bakuła, Mieczysław Bakuła Department of Satellite Geodesy and Navigation, University of Warmia and Mazury in Olsztyn, ul. Heweliusza 5, 10-724 Olsztyn, Poland Aeronautics Faculty, Polish Air Force Academy in Dęblin, ul. Dywizjonu 303 nr 35, 08-521 Dęblin, PolandSearch for more papers by this authorAdam Ciećko, Adam Ciećko Department of Satellite Geodesy and Navigation, University of Warmia and Mazury in Olsztyn, ul. Heweliusza 5, 10-724 Olsztyn, Poland Aeronautics Faculty, Polish Air Force Academy in Dęblin, ul. Dywizjonu 303 nr 35, 08-521 Dęblin, PolandSearch for more papers by this authorRafał Kaźmierczak, Rafał Kaźmierczak Department of Satellite Geodesy and Navigation, University of Warmia and Mazury in Olsztyn, ul. Heweliusza 5, 10-724 Olsztyn, PolandSearch for more papers by this author Grzegorz Grunwald, Corresponding Author Grzegorz Grunwald g.grunwald@kgsin.pl Department of Satellite Geodesy and Navigation, University of Warmia and Mazury in Olsztyn, ul. Heweliusza 5, 10-724 Olsztyn, PolandSearch for more papers by this authorMieczysław Bakuła, Mieczysław Bakuła Department of Satellite Geodesy and Navigation, University of Warmia and Mazury in Olsztyn, ul. Heweliusza 5, 10-724 Olsztyn, Poland Aeronautics Faculty, Polish Air Force Academy in Dęblin, ul. Dywizjonu 303 nr 35, 08-521 Dęblin, PolandSearch for more papers by this authorAdam Ciećko, Adam Ciećko Department of Satellite Geodesy and Navigation, University of Warmia and Mazury in Olsztyn, ul. Heweliusza 5, 10-724 Olsztyn, Poland Aeronautics Faculty, Polish Air Force Academy in Dęblin, ul. Dywizjonu 303 nr 35, 08-521 Dęblin, PolandSearch for more papers by this authorRafał Kaźmierczak, Rafał Kaźmierczak Department of Satellite Geodesy and Navigation, University of Warmia and Mazury in Olsztyn, ul. Heweliusza 5, 10-724 Olsztyn, PolandSearch for more papers by this author First published: 01 January 2016 https://doi.org/10.1049/iet-rsn.2015.0053Citations: 11AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Integrity of positioning is one of the key aspects of satellite based augmentation systems. This paper presents a study carried out in north-eastern Poland, a region which is considered as a border of the operation of the European Geostationary Navigation Overlay Service (EGNOS) system. Detailed analyses concerning operational parameters of EGNOS were done during the 12-hour and 24-hour measurement sessions conducted at a fixed point. The study was focused on the role of ionospheric delays in the integrity model according to the Radio Technical Commission for Aeronautics guidelines. In determination of the accuracy and integrity of positioning, two variants of calculations were adopted: one based on a standard interpolation algorithm determining ionospheric delay by the EGNOS system, and the other based on the Klobuchar model. The research found that the first method is characterised by only slightly better accuracy results, while significant differences were obtained by examining the integrity of positioning. For both variants of the calculation design, the values of protection levels determined for the fixed point are much higher than the positioning accuracy, which meets the integrity requirements of the navigation system. 1 Introduction Satellite based augmentation systems (SBAS) systems transmit additional data to the users of Global Navigation Satellite Systems via geostationary satellites. Their task is to enhance accuracy and integrity of Global Navigation Satellite Systems (GNSS) positioning in air navigation, maritime, rail, road and agriculture [1]. Similar systems (meeting requirements of the same standards) are being developed by the US (Wide Area Augmentation System - WASS), Europe (European Geostationary Navigation Overlay Service – EGNOS), Japan (MTSAT Satellite based Augmentation System – MSAS), India (GAGAN) and Russia (System of Differential Correction and Monitoring). EGNOS was designed and built to support the operation of the GNSS by improving the positioning accuracy, delivering information on integrity of the data transmitted to the user and providing synchronisation of EGNOS network time with UTC time [2]. The purpose of the system is the transmission of differential corrections and information about failures of the GPS system via satellites located in geostationary orbits. The EGNOS consists of three segments [2]: space (three geostationary satellites which are in orbit 35,786 km above the Earth's surface, sending data to users in the European service area, of which two are operational satellites and one serves as a test satellite), ground segment (about 40 Ranging and Integrity Monitoring Stations – RIMS mainly located in Europe, used for continuous measurement and observation of GPS and EGNOS satellites, Mission Control Centres and Navigation Land Earth Stations) and the users’ segment. The EGNOS positioning accuracy is provided by the Open Service (OS) of the system, while integrity is provided by Safety-of-Life (SoL) service [2]. The motivation for the paper was the examination of EGNOS performance on the edge of the coverage of EGNOS services. Previous studies and analyses on the performance of the EGNOS in eastern Poland were characterised by unsatisfactory performance of the system [3]. Especially availability of EGNOS APV-I (aviation procedure with vertical guidance) was poor, mainly due to the lack of RIMS stations east from the WRS station operating in Warsaw (Polish central area). Today the ionosphere is the main source of errors in GNSS positioning. Due to the different local and temporal conditions it is difficult to predict the state of the ionosphere (especially for SBAS) for the whole Europe [4]. Its impact on positioning can be estimated using a number of models and calculation methods [5, 6]. To estimate ionospheric error on GPS/EGNOS positioning, the receiver should define the ionospheric pierce point (IPP). IPP is the intersection between the ionosphere layer located at an altitude of 350 km and the line between the receiver position and the satellite [2]. Calculated ionospheric corrections are transmitted for each point located on virtual grid at the altitude of 350 km. The receiver is able to calculate a correction for the IPP on the basis of interpolation algorithm made for delays given for ionospheric grid points. As a result precise ionospheric correction is included in GPS/EGNOS positioning algorithm. Insufficient determination of the ionospheric delay for the Polish territory can cause significant errors in GPS/EGNOS positioning, especially during increased ionospheric disturbance [7]. Not stable performance of EGNOS was very often the reason not to utilise the system for practical scientific studies carried out in eastern Poland [8, 9], during which DGPS service was used instead. However, since 2014 according to the new [1] OS Definition Document, EGNOS should be available to the entire territory of Poland (Fig. 1). Performance of EGNOS and influence of ionosphere on quality of SBAS systems have already been the subject of scientific research carried out, for example by [10-15]. Fig. 1Open in figure viewerPowerPoint Availability of EGNOS signal [1] 2 Integrity of GPS/EGNOS positioning Integrity can be thought of as a probability measure, which can be attributed to the correctness of information provided by the navigation system [16]. The provision of information allowing the determination of the integrity of GPS/EGNOS positioning in real time is achieved with the use of protection levels to be monitored during operation of the system [17]. If the values do not exceed those prescribed for a given phase of flight alarm limits (AL), integrity is assured [18]. For aviation applications, a mathematical model was developed which shows the integrity of positioning using horizontal protection level (HPL) and vertical protection level (VPL). HPL is defined by the radius of the circle in the horizontal plane (with the centre on the real position), which describes the zone guaranteed to contain the horizontal position calculated (Fig. 2), while the VPL means the length of half of the cylinder's axis (with the centre on the real position), corresponding to the zone guaranteed to contain the vertical position calculated (Fig. 2) [19]. Fig. 2Open in figure viewerPowerPoint HPL and VPL According to Radio Technical Committee for Aeronautics [19] positioning using SBAS can be done by two operating modes: a less demanding en-route and a precision approach – which is characterised by much greater demands on the integrity of positioning and shorter maximum age of the data used for generation of pseudorange corrections [20]. The values of protection levels are calculated on the basis of following formulae [2, 18, 21, 22] (1) (2) where, KH – a factor bounding user's horizontal position with a probability of 10−9 (for en-route navigation KH = 6.18 and for precision approach KH = 6.0), KV – a factor bounding the user's vertical position with a probability of 0.5 × 10−7 (KV = 5.33) (3) (4) (5) where, S – design matrix, , – variances of the East, North and Up (vertical) component of the position solution expressed in topocentric system, dEN – covariance between East and North axis, SE,i – the partial derivative of position error in the east direction with respect to the pseudorange error on the ith satellite, SN,i – the partial derivative of position error in the north direction with respect to the pseudorange error on the ith satellite, SU,i – the partial derivative of position error in the up (vertical) direction with respect to the pseudorange error on the ith satellite, (6) – full variance of the pseudorange measurement, – variance of the residual error after application of fast and slow corrections, – variance of the residual error after application of ionospheric correction, – variance of the contribution of the receiver to the residual error, – variance of the residual error after application of tropospheric correction. The availability of a navigation system is the ability of the system to provide the required function and performance at the initiation of the intended operation [19]. Signal availability is the percentage of time that navigational signals transmitted from external sources are available for use. The availability of the SBAS service is defined as the ratio of the number of samples that are available for a given operation to the total number of valid samples and it can be calculated on the basis of formula: (7) where, SAV – service availability, – number of samples that are available for an operation (valid samples for which the PL < AL), – all valid samples. Availability is a function of both the physical characteristics of the environment and the technical capabilities of the transmitter facilities. Position domain safety index (SI) is defined as the ratio between the true navigation system error and the corresponding protection level [23]: (8) where, xSI – horizontal or vertical SI, xPE – horizontal or vertical position error, xPL – HPL or VPL. There is potential misleading information (MI) situation if SI is bigger than 0.75. There is real MI every time when the instantaneous SI exceeds 1. Effect of the ionosphere is the main factor influencing parameters characterising the availability of SBAS services [11]. Therefore, the study focuses on the designations of ionospheric delays and errors associated with them in accordance with the formula described in [19]. Delay values for the grid points, for which the calculations are carried out on the basis of data collected by the RIMS stations, are transmitted by geostationary satellites. However, the variance of the residual error after the application of ionospheric correction is determined on the basis of formulae [19]: (9) (10) (11) where, FPP – obliquity factor (transforms vertical delay to slant), Wn – weighting function, – grid ionospheric vertical error bound with degradation over time, xPP, yPP – coordinates of interpolation grid points, – grid ionospheric vertical error bound, – degradation of ionospheric correction information. During the phases of the flight other than precise approach, instead of the ionosphere model based on EGNOS interpolation algorithm, we can use a standard model of the ionosphere based on the Klobuchar algorithm. The error of the delay determination is then calculated based on the maximum value taken from the set of two elements described in the formula [20]: (12) where, c – speed of light, Tiono – ionospheric corrections of Klobuchar error model, The τvert is dependent on the geomagnetic latitude of IPP calculated on the basis of Klobuchar algorithm: (13) where, Φm – geomagnetic latitude (in degrees) of IPP. The Klobuchar model, widely used in the code measurements, is characterised by its simple structure and convenient calculation process [24]. It is based on determination of the total electron content coefficient between the satellite and the receiver, eliminating the ionospheric delay by 50–60%, depending on solar activity and the location of the user [24]. The exact computation process based on this model can be found in [25]. Table 1 contains performance requirements for navigation using EGNOS. Table 1. EGNOS performance requirements in aviation [26] Typical operation Accuracy Integrity Continuity Availability Horizontal (95%) Vertical (95%) Horizontal alarm limit (HAL) Vertical alarm limit (VAL) En-route (oceanic/continental low density) 3.7 km N/A 7.4 km N/A 1–1 × 10 −4/h to 1–1 × 10 −8/h 0.99 to 0.99999 En-route (continental) 3.7 km N/A En-route, Terminal 0.74 km N/A 1.85 km N/A 1–1 × 10 −4 /h to 1–1 × 10 −8 /h 0.99 to 0.99999 Initial approach, Intermediate approach, Non-precision approach (NPA), Departure 220 m N/A 556 m N/A 1–1 × 10 −4 /h to 1–1 × 10 −8 /h 0.99 to 0.99999 Approach operations with vertical guidance (APV-I) 16 m 20 m 40 m 50 m 1–8 × 10 −6 /15s 0.99 to 0.99999 3 Practical study To analyse the parameters characterising the integrity of GPS/EGNOS positioning, on November 4–6, 2012 (the ionosphere during that period was stable), three daily measurement sessions were conducted at fixed location close to the city of Olsztyn. A Septentrio AsteRx2 receiver was used for data collection. The receiver's antenna was mounted on the roof of a building (no obstructions or infrastructure components were present in the surrounding terrain which could potentially interfere with the satellite signal). Each measurement session began at 0:00:00 and ended at 23:59:59 on the same day. For each analysed epoch (every single second) the position was determined in real time using GPS/EGNOS positioning, using the EGNOS ionosphere's interpolation algorithm based on data transmitted by a geostationary satellites – PRN 126 (November 4–5) and PRN 120 (November 6). For further studies, Septentrio Post Processing SDK software and a self-created application, a PP_SBAS_Analyser (which allows calculation of ionospheric delay determined by the Klobuchar model and the error of those designations) were used. Based on the raw measurement data and the data transmitted through the EGNOS satellite, the GPS/EGNOS positions were determined in the following configurations: Ionospheric delay applied: EGNOS ionosphere interpolation model. Ionospheric delay applied: Klobuchar ionosphere model. For all configurations, a navigation ‘en-route’ mode was adopted, the elevation mask was set to 10 degrees and the pseudoranges to EGNOS geostationary satellites were excluded from the algorithm (Fig. 3). Fig. 3Open in figure viewerPowerPoint Location of the test point and measurement equipment To check the availability of EGNOS data transmitted by satellites PRN 120 and PRN 126, the EGNOS User Support portal was used. The portal is operated under the supervision of the European Satellite Services Provider. As shown in Table 2 on 11/06/2012 in hours 6:41:56 to 8:02:55 there were a few breaks in the signal transmission via EGNOS PRN 126 satellite. Because of the problems with satellite PRN 126 on 11/06/2012, satellite PRN 120 was used instead on that day. Table 2. Gaps in operation of EGNOS PRN 126 satellite [27] PRN DATE GAP START GAP END GAP LENGTH, s PRN 126 11/06/2012 06:41:56 07:51:20 4165 PRN 126 11/06/2012 07:53:59 07:54:56 58 PRN 126 11/06/2012 07:58:49 07:59:33 45 PRN 126 11/06/2012 08:01:59 08:02:55 57 Figs. 4-9 present the horizontal and vertical position error (HPE and VPE), HPL or VPL, the number of GPS satellites used to determine the position (NSV) using EGNOS PRN 126 satellite (for days: November 4–5) and PRN 120 (for day: November 6). Figs. 4, 6, 8 present values calculated on the basis of original EGNOS ionospheric correction, while Figs. 5, 7, 9 are based on solution using Klobuchar model. Reference position (for the designated accuracy), was calculated with centimeter accuracy using the network of Polish reference stations working in the EUPOS system. Fig. 4Open in figure viewerPowerPoint Positioning accuracy, protection levels and the number of satellites used for GPS/EGNOS positioning (EGNOS ionospheric correction) for EGNOS PRN 126 satellite on 11/04/2012 Fig. 5Open in figure viewerPowerPoint Positioning accuracy, protection levels and the number of satellites used for GPS/EGNOS positioning (Klobuchar ionospheric correction) for EGNOS PRN 126 satellite on 11/04/2012 Fig. 6Open in figure viewerPowerPoint Positioning accuracy, protection levels and the number of satellites used for GPS/EGNOS positioning (EGNOS ionospheric correction) for EGNOS PRN 126 satellite on 11/05/2012 Fig. 7Open in figure viewerPowerPoint Positioning accuracy, protection levels and the number of satellites used for GPS/EGNOS positioning (Klobuchar ionospheric correction) for EGNOS PRN 126 satellite on 11/05/2012 Fig. 8Open in figure viewerPowerPoint Positioning accuracy, protection levels and the number of satellites used for GPS/EGNOS positioning (EGNOS ionospheric correction) for EGNOS PRN 120 satellite on 11/06/2012 Fig. 9Open in figure viewerPowerPoint Positioning accuracy, protection levels and the number of satellites used for GPS/EGNOS positioning (Klobuchar ionospheric correction) for EGNOS PRN 120 satellite on 11/06/2012 Based on the presented analyses, it can be concluded that the use of the Klobuchar model instead of the EGNOS ionospheric algorithm gives comparable accuracy results in the horizontal plane (maximum difference about 0.5 m), while significant differences for vertical accuracy were observed (maximum difference about 2.5 m during the third measurement day). The number of satellites used for positioning stood at 5 to 12 and was the same in both versions adopted for the calculation. The results of achieved values of protection levels in two calculation variants clearly show greater confidence of the system to the variant based on EGNOS interpolation algorithm (HPL value of about 10 to 60 m and VPL from about 10 to 70 m). In the case of the Klobuchar model, the HPL is at the level of about 30 to 95 m, while the VPL from about 30 to 115 m. The poorest performance of Klobuchar model for both horizontal and vertical positioning was observed every day between 6–8 AM. On the third day, the EGNOS algorithm achieved the worst horizontal and vertical accuracy of approximately 3.5 m, while the Klobuchar model achieved a horizontal accuracy of about 2.5 m, and a vertical accuracy of about 5 m. The largest fluctuations of protection levels values for EGNOS corrections were observed on the third day in the early morning (3:00–4:00 AM). The ionosphere is one of the main factors affecting the accuracy of GNSS positioning. Therefore, further detailed analyses of slant ionospheric delays for EGNOS model and Klobuchar model were performed, which have a direct impact on the accuracy of the values obtained in Figs. 4-9. The analysis concerned slant ionospheric delays (two variants of calculation) and their standard deviations, which were implemented to the positioning algorithm. Figs. 10-12 represent ionospheric data values for the selected satellites, which have been applied to both: the GPS/EGNOS positioning using the algorithm based on EGNOS corrections, as well as GPS/EGNOS positioning using the Klobuchar model. All data analysis was adopted for the measurement sessions conducted in the hours 6:00–18:00 on each of the three days of measurements. Fig. 10Open in figure viewerPowerPoint EGNOS and Klobuchar ionospheric delay for the selected satellites on 11/04/2012 Fig. 11Open in figure viewerPowerPoint EGNOS and Klobuchar ionospheric delay for the selected satellites on 11/05/2012 Fig. 12Open in figure viewerPowerPoint EGNOS and Klobuchar ionospheric delay for the selected satellites on 11/06/2012 The comparison of ionospheric delay values calculated for the two presented concepts is characterised by the maximum differences at the level of 3 m (the delay values calculated with the Klobuchar model are always greater than the values determined with the traditional EGNOS model). It should be noted that differences in both ionospheric delays and standard deviations take their maximum values at the low elevation angles of the satellites. High values of standard deviation of ionospheric delay achieved for Klobuchar model directly affect the values of protection levels presented in Figs. 4-9. The last step of the integrity examination with the use of EGNOS is the analysis of SI. Tables 3 and 4 present the mean and the maximum values of horizontal and vertical SI. Table 3. Horizontal SI analyses Date 11/04/2012 11/05/2012 11/06/2012 HSI mean value HSI maximum value HSI mean value HSI maximum value HSI mean value HSI maximum value EGNOS ionospheric model 0.08 0.41 0.03 0.40 0.09 0.32 Klobuchar ionospheric model 0.03 0.09 0.03 0.08 0.03 0.07 Table 4. Vertical SI analyses Date 11/04/2012 11/05/2012 11/06/2012 VSI mean value VSI maximum value VSI mean value VSI maximum value VSI mean value VSI maximum value EGNOS ionospheric model 0.04 0.26 0.04 0.30 0.04 0.23 Klobuchar ionospheric model 0.02 0.08 0.02 0.09 0.02 0.09 The results of HSI and VSI analyses clearly indicate a lack of non-integrity situations throughout the examined period. The maximum SI values reaching about 0.4 obtained for the EGNOS model are much smaller than the values indicating possible MI and loss of integrity. They also show 100% availability of EGNOS during the whole tested period. 4 Conclusions The subject of this paper was to study the use of original EGNOS ionospheric correction as well as alternative correction and their influence on GPS/EGNOS positioning in north-eastern Poland. Several analyses of the system were conducted, based on the values of protection levels. The effect of ionospheric delay on integrity was also examined. The presented results show that the protection levels obtained for a fixed point of the test are much larger than the positioning accuracy, which meets the requirements of integrity of the system. The results of this study show significant differences in determining protection levels calculated with the formula commonly used by EGNOS and for the model based on Klobuchar. The EGNOS version presents much better performance due to significantly lower values of the standard deviation of ionospheric delays determined in comparison with the Klobuchar algorithm. These studies, however, do not translate directly into the results of positioning accuracy. The use of the Klobuchar model in GPS/EGNOS positioning did not show much worse accuracy results than the standard EGNOS model (especially in the horizontal plane) and could be used as a substitution for the original EGNOS ionospheric delays. The great advantage of Klobuchar solution is its high accuracy. What's more, achieved during the tests average values of accuracy, could be expected in the places not covered by RIMS stations (e.g. Africa). The HPE and HPL values determined during the experiment with the use of both EGNOS and Klobuchar ionospheric model did not exceed values, which in practice guarantees accuracy, integrity and availability for NPA and en-route operations (Table 1). However it should be emphasised that tests were performed during three days of stable ionosphere and presented analyses should be considered as preliminary ones. Significant differences of EGNOS and Klobuchar solutions are expected during ionosphere disturbances. This will be the subject of future studies of the authors of this paper. 5 References 1 European Commission, Directorate-General for Enterprise and Industry: ‘ EGNOS open service definition document’, 2014, v 2.1 2Allien, A., Taillander, C., Capo, C. et al: ‘ User guide for EGNOS application development’ ( ESA, 2009) 3Felski, A., Nowak, A., Woźniak, T.: ‘Accuracy and availability of EGNOS – results of observations’, Artif. Satell., 2011, 46, pp. 111– 118 (doi: https://doi.org/10.2478/v10018-012-0003-0) 4Sanz, J., Juan, J.M., Hernandez-Pejares, M. et al: ‘ Definition of an SBAS ionospheric activity indicator and its assessment over Europe and Africa during the last solar cycle’. The Int. Beacon Satellite Symp. BSS2013, Bath, 2013 5Jensen, A.B., Mitchell, C.: ‘GNSS and the ionosphere’, GPS World, 2011, 22, (2), pp. 40– 42 6Allain, D.J., Mitchell, C.N.: ‘Ionospheric delay corrections for single-frequency GPS receivers over Europe using tomographic mapping’, GPS Solut., 2009, 13, (2), pp. 141– 151 (doi: https://doi.org/10.1007/s10291-008-0107-y) 7Grzegorzewski, M., Świątek, A., Oszczak, S., Ciećko, A., Ćwiklak, J.: ‘Study of EGNOS safety of life service during the period of solar maximum activity’, Artif. Satell., 2012, 47, pp. 137– 145 (doi: https://doi.org/10.2478/v10018-012-0019-5) 8Bakuła, M.: ‘Network code DGPS positioning and reliable estimation of position accuracy’, Surv. Rev., 2010, 42, pp. 82– 91 (doi: https://doi.org/10.1179/003962610X12572516251448) 9Popielarczyk, D., Templin, T.: ‘Application of integrated GNSS/hydroacoustic measurements and GIS geodatabase models for bottom analysis of Lake Hancza: the deepest inland reservoir in Poland’, Pure Appl. Geophys., 2013, doi: https://doi.org/10.1007/s00024-013-0683-9 10Aquino, M., Moore, T., Dodson, A., Waugh, S., Souter, J.: ‘Implications of ionospheric scintillation for GNSS users in northern Europe’, J. Navig., 2005, 58, pp. 241– 256 (doi: https://doi.org/10.1017/S0373463305003218) 11Jan, S.-S., Chan, W., Walter, T., Enge, P.: ‘ MATLAB simulation toolset for SBAS availability analysis’. Proc. of ION GPS, Salt Lake City, UT, 2001, pp. 2366– 2375 12Jan, S.-S., Walter, T., Enge, P.: ‘ Techniques for graceful reversion from dual to single frequency WAAS’. Proc. of ION GPS, Salt Lake City, 2003 13Sakai, T., Matsunaga, K., Hoshinoo, K.: ‘ Improving availability of ionospheric corrections in the low magnetic latitude region’. Proc. of the 2005 National Technical Meeting of The Institute of Navigation, San Diego, CA, 2005, pp. 569– 579 14Sakai, T., Matsunaga, K., Hoshinoo, K., Walter, T.: ‘ Prototype of satellite-based augmentation system and evaluation of the ionospheric correction algorithms’. Proc. of the 2006 National Technical Meeting of The Institute of Navigation, Monterey, CA, 2006, pp. 368– 379 15Grzegorzewski, M., Ciećko, A., Oszczak, S., Popielarczyk, D.: ‘ Autonomous and EGNOS positioning accuracy determination of cessna aircraft on the edge of EGNOS coverage’. Proc. of the 2008 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2008, pp. 407– 410 16 Department of Defense, Department of Homeland Security, and Department of Transportation: ‘ 2010 Federal Radionavigation Plan’, 2010, Springfield, Virginia 17Azaola-Saenz, M., Cosmen-Shortmann, J.: ‘Autonomous integrity’, Inside GNSS, 2009, 4, pp. 28– 36 18Oliveira, J., Tiberius, C.: ‘Quality control in SBAS: Protection levels and reliability levels’, J. Navig., 2009, 62, pp. 509– 522 (doi: https://doi.org/10.1017/S0373463309005311) 19 Radio Technical Committee for Aeronautics: ‘ Minimum operational performance standards for airborne equipment using global positioning system/wide area augmentation system’, 2006, DOC. DO-229D 20Perrin, O., Scaramuzza, M., Buchanan, T.: ‘Flying EGNOS Approaches in the Swiss Alps’, J. Navig., 2006, 59, pp. 177– 185 (doi: https://doi.org/10.1017/S0373463306003754) 21Tiberius, C., Odijk, D.: ‘ Does the HPL bound the HPE?’. NAVITEC, Proc. of NaviTec'08 Workshop, ESA-Estec, Noordwijk, The Netherlands, 2008 22Walter, T., Blanch, J., Enge, P.: ‘ L5 satellite based augmentation systems protection level equations’. Proc. of the 2007 Int. Symp. on GPS/GNSS, Sydney, Australia, 2007 23Vassiley, B., Vassileva, B.: ‘EGNOS performance before and after applying an error extraction methodology’, Annu. Navig., 2012, 19, (2), pp. 121– 130 24Yuan, Y., Huo, X., Ou, J. et al: ‘Klobuchar ionospheric coefficients based on GPS observations’, IEEE Trans. Aerosp. Electron. Syst., 2008, AES-44, pp. 1498– 1510 (doi: https://doi.org/10.1109/TAES.2008.4667725) 25Klobuchar, J.A.: ‘Ionospheric time-delay algorithm for single-frequency GPS users’, IEEE Trans. Aeros. Electron. Syst., 1987, AES-23, pp. 325– 331 (doi: https://doi.org/10.1109/TAES.1987.310829) 26 International Civil Aviation Organization: ‘ ICAO standards and recommended practices (SARPS), Annex10 volume I (Radio navigation aids)’, 2006 27‘ European satellite services provider, EGNOS user support’, http://egnos-user-support.essp-sas.eu/egnos_ops/data_gaps?sid=26438, accessed February 2013 Citing Literature Volume10, Issue1January 2016Pages 114-121 FiguresReferencesRelatedInformation
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