GPS/GLONASS/QZSS Multi-GNSS Augmentation Trial by L1-SAIF Signal 5th AOR W/S on GNSS Hanoi, Vietnam Dec. 1-3, 2013 GPS/GLONASS/QZSS Multi-GNSS Augmentation Trial by L1-SAIF Signal Takeyasu Sakai Electronic Navigation Research Institute

Introduction QZSS (Quasi-Zenith Satellite System) program: 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, L1-SAIF and LEX. 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: 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.

QZSS Concept Broadcast signal from high elevation angle; AOR W/S Dec. 2013 - Slide 2 QZSS Concept QZS GPS/GEO 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. Footprint of QZSS orbit; Centered at 135E; Eccentricity 0.075, Inclination 43deg.

QZSS L1-SAIF Signal QZSS broadcasts wide-area augmentation signal: AOR W/S Dec. 2013 - Slide 3 QZSS L1-SAIF 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: 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: 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).

L1-SAIF Signal Functions AOR W/S Dec. 2013 - Slide 4 L1-SAIF Signal Functions Ranging Function Error Correction Integrity QZS satellites GPS Constellation Ranging Signal 3 Functions by L1-SAIF 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; Message-oriented information transmission: Flexible contents. User GPS/L1-SAIF Receivers SAIF： Submeter-class Augmentation with Integrity Function

ENRI L1-SAIF Master Station AOR W/S Dec. 2013 - Slide 5 ENRI L1-SAIF Master Station 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. L1SMS GEONET QZS QZSS MCS GPS Satellites Measure- ments L1-SAIF Message GSI Server (Tokyo) ENRI JAXA TKSC (Tsukuba) L1-SAIF Signal Ranging Signal K-band Uplink

L1-SAIF Correction: GPS only AOR W/S Dec. 2013 - Slide 6 L1-SAIF Correction: GPS only Standalone GPS L1-SAIF Augmentation GPS Only Result 6 reference stations User location for this test L1-SAIF expe- rimental area Horizontal Error Vertical 1.45 m 2.92 m 6.02 m 8.45 m System Standalone GPS 0.29 m 0.39 m 1.56 m 2.57 m w/ L1-SAIF RMS Max 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). Note: Results shown here were obtained with geodetic-grade antenna and receivers at open sky condition.

Adding GLONASS: Motivation AOR W/S Dec. 2013 - Slide 7 Adding GLONASS: Motivation QZS GPS constellation Additional Constellation = GLONASS Augmentation Users 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.

GLONASS: Differences from GPS 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 L1-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 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.

Upgrade of L1SMS L1-SAIF Master Station (L1SMS): AOR W/S Dec. 2013 - Slide 9 Upgrade of L1SMS L1-SAIF Master Station (L1SMS): Generates the L1-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. L1SMS GEONET QZS QZSS MCS GPS Measure- ments L1-SAIF Message GSI ENRI JAXA L1-SAIF Signal L1C/A L2P K-band GLONASS L1SA Upgrade

Configuration of Experiment 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 L1SMS generates L1-SAIF message in realtime and broadcast it via QZS-1. For our experiment: 6 sites for reference stations; Reference Station (a) to (f) 11 sites for evaluation. User Station (1) to (11) Period: 2013/1/6 01:00 to 2013/1/9 23:00 (94 hours).

PRN Mask Transition QZSS GLONASS GPS AOR W/S Dec. 2013 - Slide 11 PRN Mask Transition GPS GLONASS QZSS 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.

Elevation Angle GPS GLONASS QZSS PRN Mask Transition 5 deg @ User (7) AOR W/S Dec. 2013 - Slide 12 Elevation Angle GPS GLONASS QZSS PRN Mask Transition 5 deg @ 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.

# of Satellites vs. Mask Angle 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.

User Position Error: Mask 5deg AOR W/S Dec. 2013 - Slide 14 User Position Error: Mask 5deg GPS+GLO+QZS: 0.310m RMS of horizontal error at user location (7); Looks some limited improvement by using multi-constellation.

User Position Error: Mask 30deg AOR W/S Dec. 2013 - Slide 15 User Position Error: Mask 30deg GPS+GLO+QZS: 0.335m RMS of horizontal error at user location (7); Multi-constellation offers a good availability even for 30 deg mask.

Error vs. User Location: 5 deg AOR W/S Dec. 2013 - Slide 16 Error vs. User Location: 5 deg North South 0.421m 0.283m Expect horizontal accuracy of 0.3 to 0.5m with L1-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.

Error vs. User Location: 30 deg AOR W/S Dec. 2013 - Slide 17 Error vs. User Location: 30 deg North South 0.425m The horizontal accuracy is still within a range between 0.3 and 0.5m for the multi-constellation configuration; The accuracy degrades to 1 or 2.5m for GPS-only single-constellation configuration.

Conclusion ENRI has been developing L1-SAIF signal: AOR W/S Dec. 2013 - Slide 18 Conclusion ENRI has been developing L1-SAIF signal: Signal design: GPS/SBAS-like L1 C/A code (PRN 183); Planned as an augmentation to mobile users. GPS/GLONASS/QZSS multi-constellation support: L1-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 L1-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: sakai@enri.go.jp