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T. Sakai, H. Yamada, and K. Ito Electronic Navigation Research Institute, Japan

ION ITM 2012 Newport Beach, CA Jan.30 - Feb.1, 2012. Ranging Quality of QZSS L1-SAIF Signal. T. Sakai, H. Yamada, and K. Ito Electronic Navigation Research Institute, Japan. Introduction. QZSS (Quasi-Zenith Satellite System) program :

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T. Sakai, H. Yamada, and K. Ito Electronic Navigation Research Institute, Japan

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  1. ION ITM 2012 Newport Beach, CA Jan.30 - Feb.1, 2012 Ranging Quality of QZSS L1-SAIF Signal T. Sakai, H. Yamada, and K. Ito Electronic Navigation Research Institute, Japan

  2. 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; • The first QZS satellite was successfully launched on Sept. 11, 2010. • 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); • Ranging function is now available: Ephemeris information has been broadcast during the experiments conducted by ENRI since Nov. 2011; • Investigated ranging quality of L1-SAIF signal. • Expect comparable to GPS thanks to signal bandwidth of 24 MHz.

  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 135E; • Eccentricity 0.075, Inclination 43deg.

  4. 8:40 15:20 Orbital Planes of QZSS (3 SVs) Inclined Geosynchronous Orbit Apogee 40000km Perigee 32000km Ground Track • Semi-major axis (42164km) 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. 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

  6. QZSS Frequency Plan 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) Find detail in IS-QZSS document.

  7. QZSS L1-SAIF Signal • QZSS broadcasts wide-area augmentation signal: • Called L1-SAIF (Submeter-class Augmentation with Integrity Function); • 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 SBAS techniques: • 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: Large Doppler and additional messages. • Specification of L1-SAIF: See IS-QZSS document (Available at JAXA HP).

  8. Ranging Function QZS satellites GPS Constellation Error Correction Ranging Signal Integrity Function L1-SAIF Signal • 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 Receivers SAIF： Submeter-class Augmentation with Integrity Function

  9. System Horizontal Error Vertical Error Standalone GPS Standalone GPS RMS 1.45 m 2.92 m Augmented by L1-SAIF Max 6.02 m 8.45 m L1-SAIF RMS 0.29 m 0.39 m Max 1.56 m 2.57 m L1-SAIF Corrections • Example of user position error at Site 940058 (Takayama: near center of monitor station network); • Realtime operation with MSAS-like 6 monitor stations; • Period: 19-23 Jan. 2008 (5 days); • L1-SAIF provides corrections only; • No L1-SAIF ranging. No L1-SAIF Ranging Note: Results shown here were obtained with survey-grade antenna and receiver in open sky condition.

  10. Usage of L1-SAIF Ranging • Ranging function of L1-SAIF signal: • RF signal design: Identical with GPS L1 C/A modulated by PRN 183 code; • Necessary to broadcast ephemeris information in order to make ranging function available to users. • L1-SAIF extended message of Type 58 Ephemeris Information is designed for this purpose. • Completed L1-SAIF Master Station (L1SMS) upgrade: • To be capable of broadcasting MT58 Ephemeris Information during the experiments conducted by ENRI; • Using JAXA monitor stations for generation of MT58. • Investigation of ranging quality including effects of Ephemeris Information: • RF quality: Expect comparable to GPS thanks to signal bandwidth of 24MHz; • How about quality of ephemeris information on L1-SAIF ? • User receiver setup: • JAVAD ALPHA-G3T with QZSS extension; • Output pseudorange measurements are processed by ENRI; • 5 deg Elevation Mask, 100 seconds Carrier Smoothing.

  11. Preamble 8 bits Message Type 6 bits Data Field 212 bits CRC parity 24 bits 1 message = 250 bits broadcast every second Transmitted First MT Contents Interval [s] MT Contents Interval [s] 0 Test mode 6 17 GEO almanac 300 1 PRN mask 120 18 IGP mask 300 2 to 5 Fast correction & UDRE 60 24 FC & LTC 6 6 UDRE 6 25 Long-term correction 120 7 Degradation factor for FC 120 26 Ionospheric delay & GIVE 300 9 GEO ephemeris 120 27 SBAS service message 300 10 Degradation parameter 120 28 Clock-ephemeris covariance 120 12 SBAS time information 300 63 Null message — L1-SAIF Message Structure

  12. Message Type Contents Used by Status 0 Test mode SBAS and L1-SAIF Fixed 1 PRN mask Fixed SBAS and L1-SAIF 2 to 5 Fast correction & UDRE Fixed SBAS and L1-SAIF 6 UDRE Fixed SBAS and L1-SAIF 7 Degradation factor for FC SBAS and L1-SAIF Fixed 8 Reserved SBAS Fixed 9 GEO ephemeris SBAS Fixed 10 Degradation parameter SBAS and L1-SAIF Fixed 12 SBAS network time SBAS Fixed 17 GEO almanac SBAS Fixed 18 IGP mask SBAS and L1-SAIF Fixed SBAS and L1-SAIF 24 Mixed fast/long-term correction Fixed 25 Long-term correction SBAS and L1-SAIF Fixed 26 Ionospheric delay & GIVE SBAS and L1-SAIF Fixed L1-SAIF Message (1)

  13. Message Type Contents Used by Status 27 SBAS service message SBAS Fixed 28 Clock-ephemeris covariance SBAS and L1-SAIF Fixed 29 to 51 Undefined — — 52 TGP mask L1-SAIF Tentative 53 Tropospheric delay L1-SAIF Tentative 54 to 55 Advanced Ionospheric delay L1-SAIF TBD 56 Intersignal biases L1-SAIF Tentative 57 Ephemeris-related parameter L1-SAIF TBD 58 QZS ephemeris L1-SAIF Tentative 59 QZS almanac L1-SAIF TBD 60 Regional information L1-SAIF TBD 61 Reserved L1-SAIF Tentative 62 Reserved SBAS and L1-SAIF Fixed 63 Null message SBAS and L1-SAIF Fixed L1-SAIF Message (2)

  14. .. x .. y .. z L1-SAIF Ephemeris (MT58)

  15. QZS-1 L1-SAIF (PRN 183) Ephemeris in MT58 Uplink QZS-L1C/A QZS-L1C/A (PRN 193) Ephemeris in Legacy Nav JAXA MCS Decode ephemeris Format into MT58 L1-SAIF Users Compute PVA No need to receive QZS-L1-C/A (PRN 193) L1-C/A Users Ephemeris Reconstruction L1-SAIF Master Station (L1SMS) at ENRI Generation of Ephemeris • Ephemeris information is generated based on reconstruction from MCS products broadcast on QZS-L1-C/A (PRN 193): • L1SMS receives L1 C/A Nav message and extract QZS-1 PVA for generation of MT58. • Users do not need to receive any signals other than L1-SAIF (PRN 183).

  16. SV Position Error of MT58 QZS-1 Reconstructed from broadcast Nav Msg on L1C/A PRN 193 2011-08-18 00:00 to 24:00 GPST Processing by ENRI Assumed user location: @ENRI, Tokyo • Integration error in user receiver with regard to time after broadcast of MT58 with LTC (long-term correction) in MT24/25 messages; • Range error is within 0.3m for 300 seconds integration. • Note that ephemeris message of SBAS has timeout interval of 240-360s.

  17. User Receiver Setup JAVAD ALPHA-G3T with QZSS extension

  18. HPE w/L1-SAIF Ranging 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

  19. HPE w/o L1-SAIF Ranging 2011-08-18 02:18:45 to 21:16:20 L1-SAIF (PRN183) Ranging OFF 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

  20. Observed Residuals 2011-08-18 02:18:45 to 21:16:20 L1-SAIF Correction 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 • Residual error dependents upon elevation angle for GPS satellites; • L1-SAIF: Looks small dependency.

  21. Observed Residuals 2011-08-18 02:18:45 to 21:16:20 L1-SAIF Correction 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 • PRN 3 operates with Cs AFS; PRN 6 with Rb AFS; • L1-SAIF is comparable to GPS signal; A bit noisy at high elevation.

  22. Residuals on L1-SAIF 2011-08-18 02:18:45 to 21:16:20 L1-SAIF Correction 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 • Residual error within 1.8m from low to high elevation angle; 0.44m RMS; • Observed a small uncorrected bias.

  23. Residuals on GPS PRN 3 with Cs AFS PRN 6 with Rb AFS • RMS of residual error: 0.4 to 0.5m for GPS satellites; • Largely biased.

  24. Continuous Observation • ENRI has been conducting continuous observation of L1-SAIF signal for technical verification since October 2011; Also observes other supplement signals; • Observation is available on the web: URL http://www.enri.go.jp/sat/qzss_e.htm • Range measurements are converted into RINEX format and navigation message is formatted in EMS file; Both are slightly extended for QZSS; • Identifier: ‘J01’ for L1C/A and ‘S83’ for L1-SAIF. • Data files are stored on daily basis. Note - Sometimes there is missing data due to some reason such as power outage.

  25. QZSS L1-SAIF Data Source QZSS L1-SAIF General Information http://www.enri.go.jp/sat/qzss_e.htm List of RINEX Files http://www.enri.go.jp/cnspub/sat/data/rinex/ • URL http://www.enri.go.jp/sat/qzss_e.htm • General Information, RINEX observation, EMS message archive, and schedule of L1-SAIF experiments by ENRI

  26. 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. • Ranging Function of L1-SAIF: • Available as an additional ranging source with self-contained Ephemeris Information; • L1-SAIF Master Station (L1SMS) has been upgraded to broadcast Ephemeris Information and Corrections for L1-SAIF signal itself; • Tested successfully; Confirmed that residual error was comparable to GPS; • Ranging function reduces the maximum position error for both horizontal and vertical. • Ongoing work: • Experiments on mobile conditions; • Broadcasting corrections for MSAS and GLONASS satellites. • L1-SAIF observation is available at http://www.enri.go.jp/sat/qzss_e.htm • RINEX http://www.enri.go.jp/cnspub/sat/data/rinex/ • EMS http://www.enri.go.jp/cnspub/sat/data/ems/

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