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4 th AOR W/S on GNSS Kuala Lumpur, Malaysia Dec. 8-10, 2012 Multi-GNSS Augmentation by L1-SAIF Signal: Preliminary Results Multi-GNSS Augmentation by L1-SAIF.

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Presentation on theme: "4 th AOR W/S on GNSS Kuala Lumpur, Malaysia Dec. 8-10, 2012 Multi-GNSS Augmentation by L1-SAIF Signal: Preliminary Results Multi-GNSS Augmentation by L1-SAIF."— Presentation transcript:

1 4 th AOR W/S on GNSS Kuala Lumpur, Malaysia Dec. 8-10, 2012 Multi-GNSS Augmentation by L1-SAIF Signal: Preliminary Results Multi-GNSS Augmentation by L1-SAIF Signal: Preliminary Results Takeyasu Sakai Electronic Navigation Research Institute Takeyasu Sakai Electronic Navigation Research Institute

2 AOR W/S Dec Slide 1 Introduction QZSS (Quasi-Zenith Satellite System) program:QZSS (Quasi-Zenith Satellite System) program: –Regional navigation service broadcast from high-elevation angle by a combination of three satellites on the inclined geosynchronous (quasi-zenith) orbit; –Broadcast GPS-like supplemental signals on three frequencies and two augmentation signals, L1-SAIF and LEX. L1-SAIF (Submeter-class Augmentation with Integrity Function) signal offers:L1-SAIF (Submeter-class Augmentation with Integrity Function) signal offers: –Submeter accuracy wide-area differential correction service; –Integrity function for safety of mobile users; and –Ranging function for improving position availability; all on L1 single frequency. ENRI has been developing L1-SAIF signal and experimental facility:ENRI has been developing L1-SAIF signal and experimental facility: –Signal design: SBAS-like message stream on L1 C/A code (PRN 183); –Possibility of Multi-GNSS augmentation: combined use of GPS and other constellations would improve the availability of position solutions.  Especially where visibility is limited.  Upgraded L1-SAIF experimental facility and conducted a Multi-GNSS trial.

3 AOR W/S Dec Slide 2 QZSS Concept Broadcast signal from high elevation angle;Broadcast signal from high elevation angle; Applicable to navigation services for mountain area and urban canyon;Applicable to navigation services for mountain area and urban canyon; Augmentation signal from the zenith could help users to acquire other GPS satellites at any time.Augmentation signal from the zenith could help users to acquire other GPS satellites at any time. Footprint of QZSS orbit;Footprint of QZSS orbit; Centered at 135E;Centered at 135E; Eccentricity 0.075, Inclination 43deg.Eccentricity 0.075, Inclination 43deg. QZS GPS/GEO

4 AOR W/S Dec Slide 3 QZSS L1-SAIF Signal QZSS broadcasts wide-area augmentation signal:QZSS broadcasts wide-area augmentation signal: –Called L1-SAIF (Submeter-class Augmentation with Integrity Function); –Augmentation signal for mobile users designed and developed by ENRI. L1-SAIF signal offers:L1-SAIF signal offers: –Wide-area differential correction service for improving position accuracy; Target accuracy: 1 meter for horizontal; –Integrity function for safety of mobile users; and –Ranging function for improving position availability. Augmentation to GPS L1C/A based on the SBAS specifications:Augmentation to GPS L1C/A based on the SBAS specifications: –Broadcast on L1 freq. with RHCP; Common antenna and RF front-end;  Modulated by BPSK with C/A code (PRN 183);  250 bps data rate with 1/2 FEC; Message structure is identical with SBAS;  Differences from SBAS: PRN, large Doppler, and some additional messages. –Developed easily if one has the experience to develop SBAS-capable receiver; –Specification of L1-SAIF: See IS-QZSS document (Available at JAXA HP).

5 AOR W/S Dec Slide 4 L1-SAIF Signal Functions User GPS/L1-SAIF Receivers Three functions by a single signal: ranging, error correction (Target accuracy: 1m), and integrity;Three functions by a single signal: ranging, error correction (Target accuracy: 1m), and integrity; User receivers can receive both GPS and L1-SAIF signals with a single antenna and RF front-end;User receivers can receive both GPS and L1-SAIF signals with a single antenna and RF front-end; Message-oriented information transmission: Flexible contents.Message-oriented information transmission: Flexible contents. SAIF : Submeter-class Augmentation with Integrity Function RangingFunction ErrorCorrection IntegrityFunction QZS satellites GPS Constellation Ranging Signal 3 Functions by L1-SAIF

6 AOR W/S Dec Slide 5 ENRI L1-SAIF Master Station L1-SAIF Master Station (L1SMS):L1-SAIF Master Station (L1SMS): –Generates L1-SAIF message stream in realtime and transmits it to QZSS MCS developed by and installed at JAXA; –Installed at ENRI, Tokyo; 90km from JAXA Tsukuba Space Center; –Dual frequency GPS measurements at some locations in Japan necessary to generate L1-SAIF messages are sent from GEONET in realtime. L1SMSGEONET QZS QZSS MCS GPSSatellites Measure-mentsL1-SAIFMessage GSI Server (Tokyo)ENRI(Tokyo) JAXA TKSC (Tsukuba) L1-SAIF Signal Ranging Signal K-band Uplink

7 AOR W/S Dec Slide 6 L1-SAIF Correction: GPS only Example of user position error at Site (Takayama);Example of user position error at Site (Takayama); Realtime operation with MSAS-like 6 reference stations in Japan;Realtime operation with MSAS-like 6 reference stations in Japan; Period: Jan (5 days).Period: Jan (5 days). HorizontalErrorVerticalError 1.45 m 2.92 m 6.02 m 8.45 m System StandaloneGPS 0.29 m 0.39 m 1.56 m 2.57 m w/ L1-SAIF RMS Max RMS Max Note: Results shown here were obtained with geodetic- grade antenna and receivers at open sky condition. User location for this test 6 reference stations L1-SAIF expe- rimental area Standalone GPS L1-SAIF Augmentation GPS Only Result

8 AOR W/S Dec Slide 7 Adding GLONASS: Motivation Increase of augmented satellites improves availability of position solution;Increase of augmented satellites improves availability of position solution; Also possibly reduce protection levels; Improve availability of navigation;Also possibly reduce protection levels; Improve availability of navigation; Chance of robust position information at mountainous areas and urban canyons.Chance of robust position information at mountainous areas and urban canyons. QZS GPS constellation Additional Constellation = GLONASS Augmentation Users

9 AOR W/S Dec Slide 8 GLONASS: Differences from GPS FDMA signals:FDMA signals: –Change carrier frequency settings with regard to ranging sources. Reference time and coordinates:Reference time and coordinates: –Time: broadcast time offset information by an L1-SAIF message; Avoids increase of unknowns in user receivers; –Coordinates: convert PZ to WGS-84. PRN numbers and insufficient capacity of mask pattern:PRN numbers and insufficient capacity of mask pattern: –Assign PRN numbers of 38 to 61 as GLONASS slot numbers of 1 to 24; –Introduce dynamic PRN mask solution to broadcast augmentation information supporting more than 51 ranging sources, reflecting the actual visibility. Missing IOD (Issue of Data):Missing IOD (Issue of Data): –IOD is used to identify ephemeris information in order to match ephemerides between L1-SAIF Master Station and users; Currently using IODE for GPS; –Identify ephemeris information based on the time of broadcast. Satellite position computation: based on PVA as described in GLONASS ICD.Satellite position computation: based on PVA as described in GLONASS ICD.

10 AOR W/S Dec Slide 9 Software Implementation ENRI’s L1-SAIF Master Station (L1SMS) Software:ENRI’s L1-SAIF Master Station (L1SMS) Software: –Generates L1-SAIF message stream: one message per second; –Run modes:  Offline operation mode: for preliminary investigation using RINEX files;  Realtime operation mode: verification of actual performance with realtime raw data. –Needs user-domain receiver software to evaluate performance. Upgrade of L1SMS for supporting GLONASS and QZSS:Upgrade of L1SMS for supporting GLONASS and QZSS: –Input module: RINEX observation and navigation files containing GLONASS; –Implemented GLONASS extension as explained before, for offline mode of L1SMS; –User-domain receiver software is also upgraded to be GLONASS-capable; –QZSS is also supported as it is taken into account like GPS. L1-SAIF Master Station (L1SMS) Software User-Domain Receiver Software Network GPS Observables(RINEX) Position Error SBAS Message Stream Position Output User-side observations Reference station observations Upgrade for GLONASS

11 AOR W/S Dec Slide 10 Experiment: Monitor Stations Recently Japanese GEONET began to provide GLONASS and QZSS observables in addition to GPS;Recently Japanese GEONET began to provide GLONASS and QZSS observables in addition to GPS; Currently more than 150 stations are GLONASS/QZSS-capable;Currently more than 150 stations are GLONASS/QZSS-capable; Data format: RINEX 2.12 observation and navigation files.Data format: RINEX 2.12 observation and navigation files. For our experiment:For our experiment:  8 sites for reference stations; Reference Station (1) to (8)  3 sites for evaluation. User Station (a) to (c) Period: 12/7/18 – 12/7/20 (3 days).Period: 12/7/18 – 12/7/20 (3 days).

12 AOR W/S Dec Slide 11 PRN Mask Transition Showing satellite PRN identifier being augmented at each epoch;Showing satellite PRN identifier being augmented at each epoch; Reflecting our implementation, PRN mask is updated periodically at every 30 minutes;Reflecting our implementation, PRN mask is updated periodically at every 30 minutes; Semi-dynamic PRN mask: GPS and QZSS satellites are always ON in the masks;Semi-dynamic PRN mask: GPS and QZSS satellites are always ON in the masks; PRN masks for GLONASS satellites are set ON if the satellite are visible and augmented.PRN masks for GLONASS satellites are set ON if the satellite are visible and augmented. IODP (issue of Data, PRN Mask) indicates change of PRN mask.IODP (issue of Data, PRN Mask) indicates change of PRN mask. GPS GLONASS QZSS

13 AOR W/S Dec Slide 12 Elevation Angle Rising satellites appear at 5-12 deg above the horizon; Latency due to periodical update of PRN mask;Rising satellites appear at 5-12 deg above the horizon; Latency due to periodical update of PRN mask; However, GPS satellites also have similar latency; Not a major problem because low elevation satellites contribute a little to improve position accuracy.However, GPS satellites also have similar latency; Not a major problem because low elevation satellites contribute a little to improve position accuracy. GPS GLONASS QZSS PRN Mask Transition 5 Tokyo

14 AOR W/S Dec Slide 13 # of Satellites vs. Mask Angle Introducing GLONASS satellites increases the number of satellites in roughly 75%;Introducing GLONASS satellites increases the number of satellites in roughly 75%; QZSS increases a satellite almost all day by only a satellite on the orbit, QZS-1 "Michibiki"QZSS increases a satellite almost all day by only a satellite on the orbit, QZS-1 "Michibiki" Multi-constellation with QZSS offers 17 satellites at 5 deg and 9.8 satellites even at 30 deg.Multi-constellation with QZSS offers 17 satellites at 5 deg and 9.8 satellites even at 30 deg. 9.8 SVs 17 SVs 7.4 User (b)

15 AOR W/S Dec Slide 14 DOP vs. Mask Angle GLONASS-only users suffer poor geometries;GLONASS-only users suffer poor geometries; Multi-constellation with QZSS offers HDOP of 2.3 even for 40 deg mask.Multi-constellation with QZSS offers HDOP of 2.3 even for 40 deg User (b) HDOP = 2.3

16 AOR W/S Dec Slide 15 User Position Error: Mask 5deg GPS+GLO+QZS: 0.310m RMS of horizontal error at user location (b);GPS+GLO+QZS: 0.310m RMS of horizontal error at user location (b); Looks some improvement by using multi-constellation.Looks some improvement by using multi-constellation.

17 AOR W/S Dec Slide 16 User Position Error: Mask 30deg GPS+GLO+QZS: 0.372m RMS of horizontal error at user location (b);GPS+GLO+QZS: 0.372m RMS of horizontal error at user location (b); Multi-constellation offers a good availability even for 30 deg mask.Multi-constellation offers a good availability even for 30 deg mask.

18 AOR W/S Dec Slide 17 RMS Error vs. Mask: User (a) Northernmost user location;Northernmost user location; Multi-constellation provides robust position information through mask angle of 5 to 40 deg.Multi-constellation provides robust position information through mask angle of 5 to 40 User (a) 0.528m

19 AOR W/S Dec Slide 18 RMS Error vs. Mask: User (b) User location near the centroid of reference station network;User location near the centroid of reference station network; For vertical direction, 10 deg mask shows the best accuracy except GLONASS only case.For vertical direction, 10 deg mask shows the best accuracy except GLONASS only User (b) 0.602m

20 AOR W/S Dec Slide 19 RMS Error vs. Mask: User (c) Southernmost user location;Southernmost user location; There is little dependency upon user location; possibly because ionosphere condition is quiet for the period of this experiment.There is little dependency upon user location; possibly because ionosphere condition is quiet for the period of this User (c) 0.588m

21 AOR W/S Dec Slide 20 Availability vs. Mask Angle The number of epochs with valid position solution decreases with regard to increase of mask angle;The number of epochs with valid position solution decreases with regard to increase of mask angle; Multi-constellation with QZSS achieves 100% availability even for 40 deg mask.Multi-constellation with QZSS achieves 100% availability even for 40 deg mask. 100% User (b)

22 AOR W/S Dec Slide 21 Conclusion Combined use of GPS and GLONASS with L1-SAIF:Combined use of GPS and GLONASS with L1-SAIF: –Potential problems and solutions on realizing a Multi-GNSS L1-SAIF, capable of augmenting GPS, GLONASS, and QZSS simultaneously were investigated; –L1-SAIF Master Station is upgraded for supporting Multi-GNSS augmentation and tested successfully; Currently only for offline mode using RINEX files; –It is confirmed that the performance of L1-SAIF augmentation is certainly improved by adding GLONASS and QZSS, especially when satellite visibility is limited. Ongoing and future works:Ongoing and future works: –Support of realtime operation mode; –Broadcast of augmentation information for both GPS and GLONASS on QZS-1 real signal; Plan from the second half of this month; –Use of GLONASS/QZSS observables in generation of ionospheric correction; –Further extension to support Galileo. For further information, contact to


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