# t. sakai, k. matsunaga, k. hoshinoo, k. ito, enri t. walter, stanford university t. sakai, k....

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- T. Sakai, K. Matsunaga, K. Hoshinoo, K. Ito, ENRI T. Walter, Stanford University T. Sakai, K. Matsunaga, K. Hoshinoo, K. Ito, ENRI T. Walter, Stanford University Mitigating Ionospheric Threat Using a Dense Monitoring Network Mitigating Ionospheric Threat Using a Dense Monitoring Network ION GNSS 2007 Fort Worth, TX Sept. 25-28, 2007
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 1 The ionospheric effect is a major error source for SBAS:The ionospheric effect is a major error source for SBAS: The ionospheric term is dominant factor of protection levels; Necessary to reduce GIVE values not only in the storm condition but also in the nominal condition to improve availability of vertical guidance. The problem is caused by less density of IPP samples:The problem is caused by less density of IPP samples: The current planar fit algorithm needs inflation factor (Rirreg) and undersampled threat model to ensure overbounding residual error; Solution: integrating the external network such as GEONET and CORS; Developed a GIVE algorithm suitable to such a situation. Evaluated a new GIVE algorithm with GEONET:Evaluated a new GIVE algorithm with GEONET: 100% availability of APV-II (VAL=20m) at most of Japanese Airports; Still protects users; No HMI condition found. Introduction
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 2 MSAS Status Launch of MTSAT-1R (Photo: RSC) All facilities installed:All facilities installed: 2 GEOs: MTSAT-1R (PRN 129) and MTSAT-2 (PRN 137) on orbit; 4 GMSs and 2 RMSs connected with 2 MCSs; IOC WAAS software with localization. Successfully certified for aviation use:Successfully certified for aviation use: Broadcast test signal since summer 2005 with Message Type 0; Certification activities: Fall 2006 to Spring 2007. Began IOC service on Sept. 27 JST (15:00 Sept. 26 UTC).Began IOC service on Sept. 27 JST (15:00 Sept. 26 UTC).
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 3 Position Accuracy Horizontal RMS 0.50m MAX 4.87m Vertical RMS 0.73m MAX 3.70m GPS MSAS GPS MSAS @Takayama (940058) 05/11/14 to 16 PRN129 @Takayama (940058) 05/11/14 to 16 PRN129
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 4 The current MSAS is built on the IOC WAAS:The current MSAS is built on the IOC WAAS: As the first satellite navigation system developed by Japan, the design tends to be conservative; The primary purpose is providing horizontal navigation means to aviation users; Ionopsheric corrections may not be used; Achieves 100% availability of Enroute to NPA flight modes. Concerns for MSAS The major concern for vertical guidance is ionosphere:The major concern for vertical guidance is ionosphere: The ionospheric term is dominant factor of protection levels; Necessary to reduce GIVE to provide vertical guidance with reasonable availability.
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 5 APV-I Availability of IOC MSAS MSAS Broadcast 06/10/17 00:00-24:00 PRN129 (MTSAT-1R) Test Signal Contour plot for: APV-I Availability HAL = 40m VAL = 50m Note: 100% availability of Enroute through NPA flight modes.
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 6 Components of VPL The ionospheric term is dominant component of Vertical Protection Level.The ionospheric term is dominant component of Vertical Protection Level. VPL Clock & Orbit (5.33 flt ) Ionosphere (5.33 UIRE ) MSAS Broadcast 06/10/17 00:00-12:00 3011 Tokyo PRN129 (MTSAT-1R) Test Signal
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 7 Problem: Less Density of IPP Ionospheric component: GIVE:Ionospheric component: GIVE: Uncertainty of estimated vertical ionospheric delay; Broadcast as 4-bit GIVEI index. Current algorithm: Planar Fit:Current algorithm: Planar Fit: Vertical delay is estimated as parameters of planar ionosphere model; GIVE is computed based on the formal variance of the estimation. The formal variance is inflated by:The formal variance is inflated by: Rirreg: Inflation factor based on chi-square statistics handling the worst case that the distribution of true residual errors is not well-sampled; a function of the number of IPPs; Rirreg = 2.38 for 30 IPPs; Undersampled threat model: Margin for threat that the significant structure of ionosphere is not captured by IPP samples; a function of spatial distribution (weighted centroid) of available IPPs.
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 8 Using External Network Integrating the external network to the SBAS:Integrating the external network to the SBAS: Increase the number of monitor stations and IPP observations dramatically at very low cost; Just for ionospheric correction; Clock and orbit corrections are still generated by internal monitor stations because the current configuration is enough for these corrections; Input raw observations OR computed ionospheric delay and GIVE from the external network; loosely-coupled systems. Necessary modifications:Necessary modifications: A new algorithm to compute vertical ionospheric delay and/or GIVE is necessary because of a great number of observations; Safety switch to the current planar fit with internal monitor stations when the external network is not available.
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 9 Available Network: GEONET GEONET (GPS Earth Observation Network):GEONET (GPS Earth Observation Network): Operated by Geographical Survey Institute of Japan; Near 1200 stations all over Japan; 20-30 km separation on average. Open to public:Open to public: 30-second sampled archive is available as RINEX files. Realtime connection:Realtime connection: All stations have realtime datalink to GSI; Realtime raw data stream is available via some data providers. GEONET station MSAS station
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 10 Sample IPP Distribution A snap shot of all IPPs observed at all GEONET stations at an epoch;A snap shot of all IPPs observed at all GEONET stations at an epoch; GEONET offers a great density of IPP observations;GEONET offers a great density of IPP observations; There are some Japan- shape IPP clusters; each cluster is corresponding to the associated satellite.There are some Japan- shape IPP clusters; each cluster is corresponding to the associated satellite.
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 11 New Algorithms (1) Residual Bounding: An algorithm to compute GIVE for given vertical delays at IGPs; Vertical delays are given; For example, generated by planar fit; Determine GIVE based on observed residuals at IPPs located within 5 degrees from the IGP; Not on the formal variance of estimation; Improves availability of the system. (2) Residual Optimization: An algorithm to optimize vertical delays at IGPs; Here Optimum means the condition that sum square of residuals is minimized; GIVE values are generated by residual bounding; Improves accuracy of the system.
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 12 Residual Bounding (1) An algorithm to compute GIVE for given vertical delays at IGPs:An algorithm to compute GIVE for given vertical delays at IGPs: The MCS knows ionospheric correction function (bilinear interpolation) used in user receivers, I v,broadcast (, ), for given vertical delays at IGPs broadcast by the MCS itself; Residual error between the function and each observed delay at IPP, I v,IPPi, can be computed; Determine GIVE based on the maximum of residuals at IPPs located within 5 degrees from the IGP. Vertical delay for user Observed delay at IPP
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 13 Residual Bounding (2) Interpolated plane for users Largest residual Confidence bound Overbounding largest residual IGP iIGP i+1 Vertical Delay Location IPP measurements Determine GIVE based on the maximum of residuals at IPPs located within 5 degrees from the IGP.Determine GIVE based on the maximum of residuals at IPPs located within 5 degrees from the IGP.
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 14 Residual Optimization An algorithm to optimize vertical delays at IGPs:An algorithm to optimize vertical delays at IGPs: Vertical delays at IGPs can also be computed based on IPP observations as well as GIVE values; Again, define residual error between the user interpolation function and each observed delay at IPP, I v,IPPi ; The optimum set of vertical delays minimizes the sum square of residuals; GIVE values are minimized simultaneously; The optimization can be achieved by minimizing the energy function (often called as cost function) following over IGP delays (See paper): Function of IGP delays
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 15 Number of Available IPPs The histogram of the number of IPPs available at each IGP (located within 5 deg from the IGP);The histogram of the number of IPPs available at each IGP (located within 5 deg from the IGP); For 68% cases, 100 or more IPPs are available;For 68% cases, 100 or more IPPs are available; Exceeds 1000 for 27% cases.Exceeds 1000 for 27% cases.
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- ION GNSS 25-28 Sept. 2007 - ENRI S LIDE 16 GIVE by Residual Bounding (1) Histogram of computed GIVE values in typical ionospheric condition for two algorithms;Histogram of computed GIVE values in typical ionospheric condition for two algorithms; Residual bounding with GEONET offers significantly reduced GIVE values;Residual bounding with GEONET offers significantly reduced GIVE values; Blue lines indicate quantization steps for GIVEI.Blue lines indicate quantization steps for GIVEI. Plan

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