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ION GNSS 2012 Nashville, TN Sept. 17-21, 2012

ION GNSS 2012 Nashville, TN Sept. 17-21, 2012. The L1-SAIF Signal How was it designed to be used?. Takeyasu Sakai Electronic Navigation Research Institute. Introduction. QZSS (Quasi-Zenith Satellite System) program :

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ION GNSS 2012 Nashville, TN Sept. 17-21, 2012

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  1. ION GNSS 2012 Nashville, TN Sept. 17-21, 2012 The L1-SAIF Signal How was it designed to be used? Takeyasu Sakai Electronic Navigation Research Institute

  2. Introduction • QZSS (Quasi-Zenith Satellite System) program: • Regional navigation service broadcast from high-elevation angle by a combination of three or more satellites on the inclined geosynchronous (quasi-zenith) orbit; • Broadcast GPS-like supplemental signals on three frequencies and Two Augmentation Signals, L1-SAIF and LEX; • The first QZS satellite was successfully launched on Sept. 11, 2010. • L1-SAIF (Submeter-class Augmentation with Integrity Function) signal: • Augmentation service on L1 single frequency designed for mobile users; • Signal design: SBAS-like message stream on L1 C/A code (PRN 183). • ENRI has been developing L1-SAIF signal and conducting experiments: • L1-SAIF Master Station (L1SMS) experimental facility installed at ENRI; • IS-QZSS contains specification of L1-SAIF signal as well as other signals.

  3. GPS/GEO QZS QZSS Concept • 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 longitude of 135E; • Eccentricity 0.075, Inclination 43deg.

  4. 8:40 15:20 Orbital Planes of QZSS (3 SVs) Inclined Geosynchronous Orbit Apogee 40,000km Perigee 32,000km Ground Track • Semi-major axis (42,164km) is equal to GEO orbit: synchronous with rotation of the earth; • Inclined obit makes ground track ‘8’-figure; Called IGSO or Quasi-Zenith Orbit; • With three or more satellites on the same ground track, navigation service can be provided from the zenith to regional users at any time.

  5. 80.3 deg 75.9 deg 3 satellites constellation @Tokyo 4 satellites constellation @Tokyo Broadcast from the Zenith • The constellation of 3 or more QZS satellites is capable of broadcasting signals from near the zenith to regional users at any time; • This property is attractive for augmentation channel; Users can expect to receive the augmentation signal anytime anywhere.

  6. 25.3m Radiation Cooled TWT TWSTFT Antenna Successfully launched on Sept. 11, 2010 and settled on Quasi-Zenith Orbit (IGSO). Nickname: “Michibiki” C-band TTC Antenna Laser Reflector L1-SAIF Antenna L-band Helical Array Antenna Space Segment: QZS-1

  7. Signal Channel Frequency Bandwidth Min. Rx Power Interoperability 1575.42 MHz GPS-like supplemental signals with minimum modifications from GPS signals QZS-L1C L1CD 24 MHz –163.0 dBW L1CP 24 MHz – 158.25 dBW QZS-L1-C/A 24 MHz – 158.5 dBW QZS-L2C 1227.6 MHz 24 MHz – 160.0 dBW QZS-L5 L5I 1176.45 MHz 25 MHz – 157.9 dBW L5Q 25 MHz – 157.9 dBW QZS-L1-SAIF 1575.42 MHz 24 MHz – 161.0 dBW SBAS-like augmentation signal (250bps) QZS-LEX 1278.75 MHz 42 MHz – 155.7 dBW QZSS-specific augmenta-tion signal (2kbps) Frequency Plan Find detail in IS-QZSS document.

  8. 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).

  9. Ranging Function QZS satellites GPS Constellation Error Correction Ranging Signal Integrity Function L1-SAIF Signal Functions 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

  10. Clock Correction • Same contribution to any user location; • Not a function of location; • Needs fast correction. Ionospheric Correction • Function of user location; • Up to 100 meters; • Vertical structure may be described as a thin shell. Orbit Correction • Different contribution to different user location; • Not a function of user location; but a function of line-of-sight direction; • Long-term correction. Ionosphere Tropospheric Correction • Function of user location, especially height of user; • Up to 20 meters; • Can be corrected enough by a fixed model. Troposphere • Broadcast separate corrections to each error factor to enlarge the service area; • User receivers reconstruct pseudorange corrections with regard to its location. WADGPS Concept

  11. Preamble 8 bits Message Type 6 bits Data Field 212 bits CRC parity 24 bits Transmitted first Sync to GPS epoch L1-SAIF Message Structure 250 bits per second Note: Message Types 29 to 61 have no definitions in the current specification of SBAS. • Message structure is identical with SBAS; • Basic function is supported by only SBAS-compatible messages; Easy to develop!

  12. GPS Satellites QZS Ranging Signal L1-SAIF Signal K-band Uplink Ranging Signal Measure- ments L1-SAIF Message GEONET L1SMS QZSS MCS GSI Server (Tokyo) ENRI (Tokyo) JAXA TKSC (Tsukuba) 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.

  13. Message Generator Ionosphere Processor I/F Storage Storage Storage Router to GEONET/JAXA GEONET Server UPS UPS L1SMS at ENRI

  14. System Horizontal Error Vertical Error Standalone GPS L1-SAIF Augmentation Standalone GPS RMS 1.45 m 2.92 m Max 6.02 m 8.45 m L1-SAIF RMS 0.29 m 0.39 m Max 1.56 m 2.57 m Preliminary Result 6 reference stations User location for this test L1-SAIF expe- rimental area • 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.

  15. Realtime Operation using GEO GPS Satellites ETS-VIII Satellite L1-SAIF L1SMS in Tokyo GPS/L1-SAIF Rx in Sendai Airport 350 km Separation • ENRI joined communication experiment of ETS-VIII geostationary satellite; • L1SMS transmitted L1-SAIF message to ETS-VIII; Received L1-SAIF message was input to the GPS/L1-SAIF receiver and processed in realtime; No ranging function; • Successfully completed in Feb. 2009.

  16. Resulted Position via GEO 2009/2/17 01:21:39 to 07:23:14 (6 hours) Standalone GPS L1-SAIF Augmentation H Error RMS = 1.221m V Error RMS = 4.043m H Error RMS = 0.412m V Error RMS = 0.464m

  17. Experiment by Car GPS+IMU • L1-SAIF technical verification experiment: • L1-SAIF is originally planned as an augmentation for mobile users; • Conducted experiment with a car; • Location: urban/suburban environment, freeway; • Experiment period: Dec. 2010 to March 2011. • Experiment setup: • Reference: GPS+IMU sensor; • Post-processing with GEONET stations (20- 30 km separation) for accurate reference; • GPS/L1-SAIF receiver and PC in cabin; • Receives L1-SAIF signal on PRN 183; • Applies L1-SAIF corrections in realtime and outputs position fix. GPS/L1-SAIF Receiver

  18. GEONET Ichinomiya 2 km GEONET Nakamichi On the Freeway Plan View of the Route Typical Situation • On Dec. 14, 2010; QZS near the Zenith; • About 10 km drive at the Kofu Basin on Chuo Freeway going westward from Tokyo; • Plain ground with less bridges across the Freeway.

  19. Freeway: No Augmentation Chuo Freeway: GPS without Augmentation Horizontal Position Error, m 1.2m UTC Time 1:22:08 to 1:37:08 15min

  20. Freeway: L1-SAIF Augmented Chuo Freeway: L1-SAIF Augmentation Horizontal Position Error, m 0.5m UTC Time 1:22:08 to 1:37:08 15min

  21. GEONET Tsukuba 1 1 km In the City Plan View of the Route Typical Situation • On Dec. 16, 2010; QZS near the Zenith; • About 6 km drive in West part of Tsukuba City in Ibaraki Pref.; • Road on the ground level with less tall buildings around.

  22. City: No Augmentation Tsukuba: GPS without Augmentation Horizontal Position Error, m 2.0m UTC Time 5:30:01 to 5:45:01 15min

  23. City: L1-SAIF Augmented Tsukuba: L1-SAIF Augmentation Horizontal Position Error, m 0.6m UTC Time 5:30:01 to 5:45:01 15min

  24. Ranging by L1-SAIF 2011-08-18 02:18:45 to 21:16:20 L1-SAIF (PRN183) Ranging ON L1SMS Configuration: 6 DF GPS GMS (GEONET) 4 SF GPS/QZS GMS (JAXA) User location: @ENRI, Tokyo Receiver: JAVAD ALPHA-G3T Processing by ENRI Mask 5deg, Smoothing 100s

  25. Conclusion • ENRI has developed L1-SAIF augmentation signal: • Planned as an augmentation for mobile users; • Signal design: SBAS-like message stream on L1 C/A code (PRN 183); • The first QZSS satellite “Michibiki” has been broadcasting L1-SAIF signal. • Experiments for L1-SAIF: • ENRI has implemented L1-SAIF Master Station (L1SMS) which generates augmentation message stream in realtime and transmit it to QZSS MCS; • Preliminary tests have shown promising performance; • Technical verification experiments confirmed the performance for mobile users. • Ongoing work: • Continue experiments regularly (two weeks per month); • Define messages to be used to broadcast regional information; • Support augmentation to GLONASS satellites for further improvement of availability; • Support dual frequency operations. • Information available at: http://www.enri.go.jp/sat/qzss_e.htm

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