- Slides: 19
5 th AOR W/S on GNSS Hanoi, Vietnam Dec. 1 -3, 2013 GPS/GLONASS/QZSS Multi-GNSS Augmentation Trial by L 1 -SAIF Signal Takeyasu Sakai Electronic Navigation Research Institute
AOR W/S Dec. 2013 - Slide 1 Introduction • 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, L 1 -SAIF and LEX. • L 1 -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 L 1 single frequency. • ENRI has been developing L 1 -SAIF signal and experimental facility: – Signal design: SBAS-like message stream on L 1 C/A code (PRN 183); – Possibility of Multi-GNSS augmentation: combined use of GPS and other constellations would improve the availability of position solutions. w Especially where visibility is limited. w Upgraded L 1 -SAIF experimental facility and conducted a Multi-GNSS trial.
AOR W/S Dec. 2013 - Slide 2 QZSS Concept GPS/GEO • • • Footprint of QZSS orbit; Centered at 135 E; Eccentricity 0. 075, Inclination 43 deg. QZS • Broadcast signal from high elevation angle; • 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.
AOR W/S Dec. 2013 - Slide 3 QZSS L 1 -SAIF Signal • QZSS broadcasts wide-area augmentation signal: – Called L 1 -SAIF (Submeter-class Augmentation with Integrity Function); – Augmentation signal for mobile users designed and developed by ENRI. • L 1 -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 L 1 C/A based on the SBAS specifications: – Broadcast on L 1 freq. with RHCP; Common antenna and RF front-end; w w w 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 L 1 -SAIF: See IS-QZSS document (Available at JAXA HP).
AOR W/S Dec. 2013 - Slide 4 L 1 -SAIF Signal Functions 3 Functions by L 1 -SAIF QZS satellites Ranging Function GPS Constellation Error Correction Integrity Function • Three functions by a single signal: ranging, error correction (Target accuracy: 1 m), and integrity; • User receivers can receive both GPS and L 1 -SAIF signals with a single antenna and RF front-end; • Message-oriented information transmission: Flexible contents. SAIF： Submeter-class Augmentation with Integrity Function Ranging Signal User GPS/L 1 -SAIF Receivers
AOR W/S Dec. 2013 - Slide 5 ENRI L 1 -SAIF Master Station • L 1 -SAIF Master Station (L 1 SMS): – Generates L 1 -SAIF message stream in realtime and transmits it to QZSS MCS developed by and installed at JAXA; – Installed at ENRI, Tokyo; 90 km from JAXA Tsukuba Space Center; – Dual frequency GPS measurements at some locations in Japan necessary to generate L 1 -SAIF messages are sent from GEONET in realtime. GPS Satellites Measurements IF A -S 1 L L 1 SMS al n g Si k lin Up GEONET Ra ng in g Si gn al nd ba K- g in g n Ra al n g Si QZS L 1 -SAIF Message QZSS MCS GSI Server ENRI JAXA TKSC (Tokyo) (Tsukuba)
AOR W/S Dec. 2013 - Slide 6 L 1 -SAIF Correction: GPS only GPS Only Result 6 reference stations User location for this test Standalone GPS L 1 -SAIF Augmentation L 1 -SAIF experimental area Horizontal Error 1. 45 m Standalone RMS GPS Max 6. 02 m RMS 0. 29 m w/ L 1 -SAIF Max 1. 56 m System • Example of user position error at Site 940058 (Takayama); • Realtime operation with MSAS-like 6 reference stations in Japan; • Period: 19 -23 Jan. 2008 (5 days). Vertical Error 2. 92 m 8. 45 m 0. 39 m 2. 57 m Note: Results shown here were obtained with geodeticgrade antenna and receivers at open sky condition.
AOR W/S Dec. 2013 - Slide 7 Adding GLONASS: Motivation QZS Augmentation GPS constellation Users Additional Constellation = GLONASS • Increase of augmented satellites improves availability of position solution; • Also possibly reduce protection levels; Improve availability of navigation; • Chance of robust position information at mountainous areas and urban canyons.
AOR W/S Dec. 2013 - Slide 8 GLONASS: Differences from GPS • FDMA signals: – Change carrier frequency settings with regard to ranging sources. • Reference time and coordinates: – Time: broadcast time offset information by an L 1 -SAIF message; Avoids increase of unknowns in user receivers; – Coordinates: convert PZ-90. 02 to WGS-84. • 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): – IOD is used to identify ephemeris information in order to match ephemerides between L 1 -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.
AOR W/S Dec. 2013 - Slide 9 Upgrade of L 1 SMS • L 1 -SAIF Master Station (L 1 SMS): – Generates the L 1 -SAIF message stream and transmits it to JAXA MCS. • Upgrade for supporting GLONASS and QZSS: Input module: Supports BINEX observables and navigation message records; Implemented GLONASS extension based on SBAS standards; User-domain receiver software (MCRX) is also upgraded to be GLONASS-capable; QZSS is also supported as it is taken into account like GPS. QZS GPS GLONASS L 1 SA Upgrade GEONET GSI Measurements C/A 1 L IF A -S L 1 SMS ENRI al n g Si L 1 -SAIF Message nd ba K- L 1 L 2 C/A P L 1 C/A L 2 P – – QZSS MCS JAXA
AOR W/S Dec. 2013 - Slide 10 Configuration of Experiment • Japanese GEONET is already providing GLONASS and QZSS observables in addition to GPS; • Currently about 1, 200 stations are GLONASS/QZSS-capable; • Data format: BINEX • L 1 SMS generates L 1 -SAIF message in realtime and broadcast it via QZS-1. • For our experiment: w 6 sites for reference stations; Reference Station (a) to (f) w 11 sites for evaluation. User Station (1) to (11) • Period: 2013/1/6 01: 00 to 2013/1/9 23: 00 (94 hours).
AOR W/S Dec. 2013 - Slide 11 PRN Mask Transition QZSS GLONASS GPS • PRN Mask indicates which satellites are currently augmented; • 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; • Reflecting our implementation, PRN mask is updated periodically at every 30 minutes. • IODP (issue of Data, PRN Mask) indicates change of PRN mask.
AOR W/S Dec. 2013 - Slide 12 Elevation Angle GPS GLONASS QZSS 5 deg PRN Mask Transition @ User (7) • 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.
AOR W/S Dec. 2013 - Slide 13 # of Satellites vs. Mask Angle 16 SVs 9. 8 SVs 7. 3 SVs @ User (7) • 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" • Multi-constellation with QZSS offers 16 satellites at 5 deg and 7. 3 satellites even at 40 deg.
AOR W/S Dec. 2013 - Slide 14 User Position Error: Mask 5 deg • GPS+GLO+QZS: 0. 310 m RMS of horizontal error at user location (7); • Looks some limited improvement by using multi-constellation.
AOR W/S Dec. 2013 - Slide 15 User Position Error: Mask 30 deg • GPS+GLO+QZS: 0. 335 m RMS of horizontal error at user location (7); • Multi-constellation offers a good availability even for 30 deg mask.
AOR W/S Dec. 2013 - Slide 16 Error vs. User Location: 5 deg 0. 421 m 0. 283 m North South • Expect horizontal accuracy of 0. 3 to 0. 5 m with L 1 -SAIF augmentation, regardless GLONASS is used or not; • There is a little dependency upon the latitude of user location possibly due to an effect of ionosphere activities.
AOR W/S Dec. 2013 - Slide 17 Error vs. User Location: 30 deg 0. 425 m North South • The horizontal accuracy is still within a range between 0. 3 and 0. 5 m for the multi-constellation configuration; • The accuracy degrades to 1 or 2. 5 m for GPS-only single-constellation configuration.
AOR W/S Dec. 2013 - Slide 18 Conclusion • ENRI has been developing L 1 -SAIF signal: – Signal design: GPS/SBAS-like L 1 C/A code (PRN 183); – Planned as an augmentation to mobile users. • GPS/GLONASS/QZSS multi-constellation support: – L 1 -SAIF Master Station was upgraded to support GLONASS and QZSS in addition to GPS based on the existing SBAS specifications; – Conducted an experiment with broadcast of L 1 -SAIF signal containing augmentation information of GPS, GLONASS, and QZSS; – Using multi-constellation it can be expected to maintain a good position accuracy even in higher mask angle conditions representing limited visibility conditions. • Further Investigations will include: – – Dynamic PRN mask driven by almanac information; Use of GLONASS observables in generation of ionospheric corrections; Considerations of different types of receiver for reference/user stations; and Extension to Galileo. For further information, contact to: [email protected] go. jp